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Most of the neutron stars we know of have a mass between 1.4 and 2.0 Suns. The upper limit makes sense, since, beyond about two solar masses, a neutron star would collapse to become a black hole. The lower limit also makes sense given the mass of white dwarfs. While neutron stars defy gravitational collapse thanks to the pressure between neutrons, white dwarfs defy gravity thanks to electron pressure. As first discovered by Subrahmanyan Chandrasekhar in 1930, white dwarfs can only support themselves up to what is now known as the Chandrasekhar Limit, or 1.4 solar masses. So it’s easy to assume that a neutron star must have at least that much mass. Otherwise, collapse would stop at a white dwarf. But that isn’t necessarily true.

It is true that under simple hydrostatic collapse, anything under 1.4 solar masses would remain a white dwarf. But larger stars don’t simply run out of fuel and collapse. They undergo cataclysmic explosions as a supernova. If such an explosion were to squeeze the central core rapidly, you might have a core of neutron matter with less than 1.4 solar masses. The question is whether it could be stable as a small neutron star. That depends on how neutron matter holds together, which is described by its equation of state.

Neutron star matter is governed by the Tolman–Oppenheimer–Volkoff, which is a complex relativistic equation based on certain assumed parameters. Using the best data we currently have, the TOV equation of state puts an upper mass limit for a neutron star at 2.17 solar masses and a lower mass limit around 1.1 solar masses. If you tweak the parameters to the most extreme values allowed by observation, the lower limit can drop to 0.4 solar masses. If we can observe low-mass neutron stars, it would further constrain the TOV parameters and improve our understanding of neutron stars. This is the focus of a new study on the arXiv.

Previous searches for low-mass neutron stars. Credit: Kacanja & Nitz

The study looks at data from the third observing run of the Virgo and Advanced LIGO gravitational wave observatories. While most of the observed events are the mergers of stellar-mass black holes, the observatories can also capture mergers between two neutron stars or a neutron star and a black hole companion. The signal strength of these smaller mergers is so close to the noise level of the gravitational wave detectors that you need to have an idea of the type of signal you’re looking for to find it. For neutron star mergers, this is complicated by the fact that neutron stars are sensitive to tidal deformations. These deformations would shift the “chirp” of the merger signal, and the smaller the neutron star, the greater the deformation.

So the team simulated how sub-white-dwarf mass neutron stars would tidally deform as they merge, then calculated how that would affect the observed gravitational chirp. They then looked for these kinds of chirps in the data of the third observation run. While the team found no evidence for small-mass neutron stars, they were able to place an upper limit on the hypothetical rate of such mergers. Essentially, they found that there can be no more than 2,000 observable mergers involving a neutron star up to 70% of the Sun’s mass. While that might not seem like much of a limit, it’s important to remember that we are still in the early stages of gravitational wave astronomy. In the coming decades, we will have more sensitive gravitational telescopes, which will either discover small neutron stars or prove that they can’t exist.

Reference: Kacanja, Keisi, and Alexander H. Nitz. “A Search for Low-Mass Neutron Stars in the Third Observing Run of Advanced LIGO and Virgo.” arXiv preprint arXiv:2412.05369 (2024).

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The James Webb Space Telescope (JWST) was specifically intended to address some of the greatest unresolved questions in cosmology. These include all of the major questions scientists have been pondering since the Hubble Space Telescope (HST) took its deepest views of the Universe: the Hubble Tension, how the first stars and galaxies came together, how planetary systems formed, and when the first black holes appeared. In particular, Hubble spotted something very interesting in 2003 when observing a star almost as old as the Universe itself.

Orbiting this ancient star was a massive planet whose very existence contradicted accepted models of planet formation since stars in the early Universe did not have time to produce enough heavy elements for planets to form. Thanks to recent observations by the JWST, an international team of scientists announced that they may have solved this conundrum. By observing stars in the Small Magellanic Cloud (LMC), which lacks large amounts of heavy elements, they found stars with planet-forming disks that are longer-lived than those seen around young stars in our Milky Way galaxy.

The study was led by Guido De Marchi, an astronomer at the European Space Research and Technology Centre (ESTEC) in Noordwijk, Netherlands. He was joined by researchers from the INAF Osservatorio Astronomico di Roma, the Space Telescope Science Institute (STScI), Gemini Observatory/NSF NOIRLab, the UK Astronomy Technology Centre (UK ATC), the Institute for Astronomy at the University of Edinburgh, the Leiden Observatory, the European Space Agency (ESA), NASA’s Ames Research Center, and NASA’s Jet Propulsion Laboratory. The paper detailing their findings appeared on December 16th in The Astrophysical Journal.

James Webb Space Telescope image of NGC 346, a massive star cluster in the Small Magellanic Cloud. Credit: NASA/ESA/CSA/STScI/Olivia C. Jones (UK ATC)/Guido De Marchi (ESTEC)/Margaret Meixner (USRA)

According to accepted cosmological models, the first stars in the Universe (Population III stars) formed 13.7 billion years ago, just a few hundred million years after the Big Bang. These stars were very hot, bright, massive, short-lived, and composed of hydrogen and helium, with very little in the way of heavy elements. These elements were gradually forged in the interiors of Population III stars, which distributed them throughout the Universe once they exploded in a supernova and blew off their outer layers to form star-forming nebulae.

These nebulae and their traces of heavier elements would form the next generation of stars (Population II). After these stars formed from gas and dust in the nebula that underwent gravitational collapse, the remaining material fell around the new stars to form protoplanetary disks. As a result, subsequent populations of stars contained higher concentrations of metals (aka. metallicity). The presence of these heavy elements, ranging from carbon and oxygen to silica and iron, led to the formation of the first planets.

As such, Hubble‘s discovery of a massive planet (2.5 times the mass of Jupiter) around a star that existed just 1 billion years after the Big Bang baffled scientists since early stars contained only tiny amounts of heavier elements. This implied that planet formation began when the Universe was very young, and some planets had time to become particularly massive. Elena Sabbi, the chief scientist for the Gemini Observatory at the National Science Foundation’s NOIRLab, explained in a NASA press release:

“Current models predict that with so few heavier elements, the disks around stars have a short lifetime, so short in fact that planets cannot grow big. But Hubble did see those planets, so what if the models were not correct and disks could live longer?”

James Webb Space Telescope image of NGC 346, a massive star cluster in the Small Magellanic Cloud. Credit: NASA/ESA/CSA/STScI/Olivia C. Jones (UK ATC)/Guido De Marchi (ESTEC)/Margaret Meixner (USRA)

To test this theory, the team used Webb to observe the massive, star-forming cluster NGC 346 in the Small Magellanic Cloud, a dwarf galaxy and one of the Milky Way’s closest neighbors. This star cluster is also known to have relatively low amounts of heavier elements and served as a nearby proxy for stellar environments during the early Universe. Earlier observations of NGC 346 by Hubble revealed that many young stars in the cluster (~20 to 30 million years old) appeared to still have protoplanetary disks around them. This was also surprising since such disks were believed to dissipate after 2 to 3 million years.

Thanks to Webb’s high-resolution and sophisticated spectrometers, scientists now have the first-ever spectra of young Sun-like stars and their environments in a nearby galaxy. As study leader Guido De Marchi of the European Space Research and Technology Centre in Noordwijk put it:

“The Hubble findings were controversial, going against not only empirical evidence in our galaxy but also against the current models. This was intriguing, but without a way to obtain spectra of those stars, we could not really establish whether we were witnessing genuine accretion and the presence of disks, or just some artificial effects.”

“We see that these stars are indeed surrounded by disks and are still in the process of gobbling material, even at the relatively old age of 20 or 30 million years. This also implies that planets have more time to form and grow around these stars than in nearby star-forming regions in our own galaxy.”

Side-by-side comparison shows a Hubble image of the massive star cluster NGC 346 (left) versus a Webb image of the same cluster (right). Credit: NASA/ESA/CSA/STScI/Olivia C. Jones (UK ATC)/Guido De Marchi (ESTEC)/Margaret Meixner (USRA)/Antonella Nota (ESA)

These findings naturally raise the question of how disks with few heavy elements (the very building blocks of planets) could endure for so long. The researchers suggested two distinct mechanisms that could explain these observations, alone or in combination. One possibility is that a star’s radiation pressure may only be effective if elements heavier than hydrogen and helium are present in sufficient quantities in the disk. However, the NGC 346 cluster only has about ten percent of the heavier elements in our Sun, so it may take longer for a star in this cluster to disperse its disk.

The second possibility is that where heavier elements are scarce, a Sun-like star would need to form from a larger cloud of gas. This would also produce a larger and more massive protoplanetary disk, which would take longer for stellar radiation to blow away. Said Sabbi:

“With more matter around the stars, the accretion lasts for a longer time. The disks take ten times longer to disappear. This has implications for how you form a planet, and the type of system architecture that you can have in these different environments. This is so exciting.”

“With Webb, we have a really strong confirmation of what we saw with Hubble, and we must rethink how we model planet formation and early evolution in the young universe,” added Marchi.

Like many of Webb’s observations, these findings are a fitting reminder of what the next-generation space telescope was designed to do. In addition to confirming the Hubble Tension, the JWST observed more galaxies (and bigger ones!) in the early Universe than models predicted. It also observed that the seeds of Supermassive Black Holes (SMBH) were more massive than expected. In this respect, the JWST is doing its job by causing astronomers to rethink theories that have been accepted for decades. From this, new theories and discoveries will follow that could upend what we think we know about the cosmos.

Further Reading: NASA, The Astrophysical Journal

The post Webb Observes Protoplanetary Disks that Contradict Models of Planet Formation appeared first on Universe Today.

The James Webb Space Telescope was designed and built to study the early universe, and hopefully revolutionary our understanding of cosmology. Two years after its launch, it’s doing just that.

One of the first things that astronomers noticed with the James Webb was galaxies that were brighter and larger than our models of galaxy formation suggested they should be. They were like seeing teenagers in a kindergarten classroom, challenging our assumptions of cosmology. But while there were some breathless claims that the Big Bang was broken, those statements were a little overblown.

But still, big, bright, mature galaxies in the early universe are forcing us to reconsider how galaxy formation is supposed to proceed. Whatever nature is telling us through the James Webb, it seems to be that galaxies form far faster than we thought before.

Related to that, for several years cosmologists have recognized a certain tension in their measurements of the present-day expansion rate of the universe, called the Hubble rate. Appropriately called the Hubble tension, the difference comes when comparing measurements of the distant, early universe with measurements of the later, nearby universe.

There’s definitely something funky going on here, but cosmologists can’t figure out exactly what. It might have something to do with our measurements of the deep universe, or it might be because of our lack of understanding of dark matter and dark energy. Either way, the James Webb didn’t help anything by confirming that the tension is very, very real.

No matter what comes out of the Hubble tension problem, the James Webb is delivering spectacular results in other areas. One of its primary missions was to find evidence for Population III stars, the first generation of stars to appear in the universe. There are no such stars left in the modern-day cosmos, as they all apparently died off billions of years ago. So our only hope to detect them is to use super-telescopes like the James Webb.

This year a team reported the first tentative detections of a galaxy in the young universe that just might contain Population III stars. The detection is not confirmed, but hopefully upcoming observation campaigns will tell us if we’re on the right track.

No matter what, we know we have a lot left to learn about the universe, and that the James Webb will continue delivering results – and hopefully a few surprises – for years to come.

The post James Webb’s Big Year for Cosmology appeared first on Universe Today.

Titan is one of the solar system’s most fascinating worlds for several reasons. It has something akin to a hydrological cycle, though powered by methane. It is the solar system’s second-largest moonMooner our own. It is the only other body with liquid lakes on its surface. That’s part of the reason it has attracted so much attention, including an upcoming mission known as Dragonfly that hopes to use its thick atmosphere to power a small helicopter. But some of the most interesting features on Titan are its lakes, and Dragonfly, given its means of locomotion, can’t do much with those other than look at them from afar. So another mission, initially conceived by James McKevitt, then an undergraduate at Loughborough University but now a PhD student at University College London would take a look at both their surface and underneath.

The mission, which has undergone several iterations, was initially designed to mimic the hunting motion of a gannet. This seabird famously dives under the water to search for fish and then floats back up to the top before setting off again. In the original paper describing the mission concept, Mr. McKevitt focused on the hydrodynamics of how such a mission would be possible on Titan, including the physics of diving into a lake of liquid methane without breaking the probe.

Luckily, the most fascinating lakes on Titan are all clustered around the north pole, so it would be theoretically possible to hop between one lake and another, given there was enough thrust/power. However, as time went on, the original mission concept seemed less and less feasible – especially given the most required to both take off from a resting position on top of a lake and dive down deeply enough into the next lake to make a meaningful difference in the environment.

Fraser discusses the importance of a mission to Titan.

Of particular concern was the power system – RTGs, the only current system that would feasibly power such a probe on Titan’s fully enveloped surface, would be too heavy for such a mission architecture. So, Mr. McKevitt changed tact and created something entirely different.

During COVID-19, he created an organization known as Conex Research to explore complex missions in a collaborative think-tank format. He then adapted Astraeus, as the mission was known, to a more achievable format, which was then described on Conex’s website. In a press release from August of 2022, the mission had morphed into a four-part system.

First is a “Main Orbital Spacecraft,” which would orbit the Moon Moondeploy two smaller vehicles – Mayfly and Manta. As their names suggest, Mayfly would flit about as an aerial observation platform, while Manta would dive into the lakes that were so intriguing in the original mission architecture. A series of 2U Cubesats, called “Mites,” would also join them and measure different parts of Titan’s atmosphere during a slow descent period after being released from the MOS.

Fraser discusses the Dragonfly mission planned to visit Titan’s surface.

That sounds like a pretty hefty lift, especially for a group of volunteer contributors, even if there are almost 30 of them. Lately, the group hasn’t had much of an update since they presented the mission format at the International Astronautical Conference in 2022. But if they are still making progress on the mission, there is a chance it might one day make it all the way to the bottom of one of Titan’s lakes.

Learn More:
James McKevitt – ASTrAEUS: An Aerial-Aquatic Titan Mission Profile
Conex Research – The Astraeus Mission to Titan
UT – Scientists Construct a Global Map of Titan’s Geology
UT – Titan May Have a Methane Crust 10 Km Thick

Lead Image:
Surface of Titan (left) with modeling mockups of the Mayfly (middle) and Manta (right).
Credit – Conex Research

The post A Mission to Dive Titan’s Lakes – and Soar Between Them appeared first on Universe Today.

Catching the best sky watching events for the coming year 2025.

Comet C/2023 A3 Tsuchinshan-ATLAS captured over the McMath-Pierce Solar Telescope at Kitt Peak National Observatory, Arizona. Credit: Robert Sparks

How about that eclipse in 2024? Certainly, the Great North American Eclipse of April 8th 2024 was one for the ages, instilling the eclipse-chasing bug in many a new skywatching fan. Now, for the bad news: 2025 is a rare, totality free year, featuring only a pair of remote partial solar eclipses. The good news is, there’s lots more in store to see in the sky in 2025, with a pair of fine total lunar eclipses, Mars at its best, and lunar occultations galore. And hey, the Sun is still mighty active, and the cosmos does still owe us another fine comet.

2024: The Year in Brief

To be sure, the April eclipse was spectacular… but 2024 was almost more notable for the unpredictable. First, the Sun unleashed two epic solar storms, sending amazing aurora displays southward towards latitudes and populations of skywatchers that rarely see them. Then, Comet C/2023 A3 Tsuchinshan-ATLAS survived perihelion in late September, and went on to put on a fine show for northern hemisphere watchers at dusk in October. All of this transpired against a record number of rocket launches worldwide, as SpaceX and its competitors race to fill the sky with Starlink and its ilk.

Will artificial stars outnumber real ones in the coming generation? We’re differently witness to an evolving sky, as the clockwork gears unfold in the drama of the heavens above us.

The Rules

First up, some ground rules. We think of this list as a ‘best of the best’ for the year, distilled down to top events, with a little strangeness thrown in to make things unique. Think conjunctions closer than a degree, comets brighter than +6th magnitude, etc. as a sort of ‘101 Top Astronomy Events for the Year.’

The Top 12 Events for 2025

Such is astronomy and skywatching in 2025. First, here’s a quick subjective rundown of the dozen very best skywatching events to look forward to in the coming year:

-The peak for Solar Cycle 25 continues

-Mars at opposition in January

-Venus rules the dusk sky at the start of the year, and transitions to the dawn sky

-A once a generation Major Lunar Standstill sees the Moon swinging wide north-to-south

-Saturn’s rings are edge on as seen from our Earthly vantage point

-Comet G3 ATLAS ‘may’ break negative magnitudes in January

-Two total lunar eclipses for the year worldwide

-Lunar occultations worldwide for the stars Spica, Regulus and Antares

-A rare ‘triple year’ for lunar-stellar occultations

-The Moon meets up with Saturn and Mars multiple times in 2025

-A rare, ‘smiling emoticon’ triple conjunction involving the Moon, Regulus and Venus on September 19th

-The Moon occults sections of Messier 45 (The Pleiades) on every pass for 2025

Aurorae light up the sky over Ottawa, Canada. Credit: Andrew Symes The Sun, the Seasons and the Solar Cycle in 2025

We’re just coming off of the historic solar maximum in 2024 for Solar Cycle Number 25, and the wild ride is far from over. On an 11-year period from one maxima to the next, the Sun doubtless has more in store for 2025 in terms of space weather and aurora. We’re now on a long, slow downslide towards solar minimum in 2029-2030.

Earth reaches perihelion on January 4th at 0.98333 AU in 2025, and aphelion on July 3rd at 1.01664 AU from the Sun.

Seasons in 2025 start on:

March 20th (northward equinox)

June 20th (northward solstice)

September 22nd (southward equinox)

December 21st (southward solstice)

The Moon in 2025

2025 is a ‘hilly’ year for the path of the Moon, as we cross what’s known as a Major Lunar Standstill. The actual node crossing for the event occurs on January 29th. The Moon’s orbit is inclined a little over five degrees relative to the ecliptic plane. The entire orbit of our Moon is also dragged (mainly by the Sun) one revolution every 18.6-years, in what’s known as lunar nodal precession. All this means that once every 18.6 years, the Moon ‘swings wide’ in the sky, as the tilt of its orbit is applied to the Earth’s versus the ecliptic plane.

A rare ‘Lunar Standstill’, seen down the Sistine Axis in Rome, Italy in late 2024. Credit: Gianluca Masi. A ‘Hilly Year’

We just had the northernmost Full Moon the decade on December 15th, 2024, and we’re due for the southernmost Full Moon on June 11th.

Major and Minor Lunar Standstills for the first half of the 21st century. Credit: Dave Dickinson

The year is also rare in that a Black Moon (in the old-timey sense as the third New Moon in an astronomical season with four) occurs on August 23rd, and the Harvest Moon nearest to the September Equinox occurs in October, on the 7th.

Moon Phases for 2025 (in Universal Time)Closest Perigee–May 26 1:53 UT (357,309 km)Most Distant Apogee-Oct 24 15:31 UT (405,614 km)New MoonBrown LunationFull MoonNotesDec 30 – 22:28 UT (2024)1262Jan 13 – 22:28 UT1st Full Moon of 2025Jan 29 – 12:37 UT1263Feb 12 – 13:54 UT
Feb 28 – 00:47 UT1264Mar 14 – 6:56 UTTotal Lunar Eclipse (Mar14)Mar 29 – 11:00 UT1265Apr 13– 00:24 UTPartial Solar Eclipse (March 29)Apr 27 – 19:33 UT1266May 12 – 16:58 UT
May 27 – 3:04 UT1267Jun 11 – 7:46 UTClosest Full Moon of the year, Southernmost Full Moon of 2025Jun 25 – 10:34 UT1268Jul 10 – 20:39 UT
Jul 24 – 19:12 UT1269Aug 9 – 7:57 UT
Aug 23 – 6:07 UT1271Sep 7 – 18:11 UTTotal Lunar Eclipse (Sep 7) 3rd New (Black) Moon in SeasonSep 21 -19:55 UT1272Oct 7 – 3:49 UTOctober Harvest Moon Partial Solar Eclipse (Sep 21)Oct 21 – 12:26 UT1273Nov 5 -13:20 UT
Nov 20 – 6:48 UT1274Dec 4 – 23:15 UTLong Night’s Full Moon Most distant Moon of the yearDec 20 – 1:44 UT1275Jan 3 – 10:04 UT1st Full Moon of 2026 Eclipses in 2025 Totality! As seen on May 16th, 2022. Credit: Andrew Symes.

As mentioned previous, 2025 features 4 eclipses—the minimum number than can occur in a calendar year. These are 2 total lunar and 2 partial solar eclipses, bookending two eclipse seasons in 2025:

Circumstances for the total lunar eclipse on the night of March 13-14th. Credit: Fred Espenak/GSFC/NASA

-A total lunar eclipse on the night of March 13-14th for the Americas;

-A partial solar eclipse for March 29th spanning the North Atlantic;

-A total lunar eclipse on the night of September 7-8th centered on Central Asia;

-A partial solar eclipse on September 21st for New Zealand and the South Pacific.

An animation of the March 29th partial solar eclipse. Note that the umbral shadow of the Moon juuuust misses the Earth (!) Credit: NASA/GSFC/A.T. Sinclair. The Inner Planets in 2025

Fleeting Mercury reaches greatest elongation six times in 2025 (3 in the dawn and 3 in the dusk) marking the best time to spy the elusive world:

-March 8th – Mercury is 18º east (dusk)

-April 21st – Mercury is 27º west (dawn, best for 2025)

-July 4th -Mercury is 26º east (dusk)

-August 19th – Mercury is 18º west (dawn)

-October 29th – Mercury is 24º east (dusk)

-December 8th – Mercury is 21º west (dawn)

Meanwhile, Venus is busy in 2025. The brilliant world starts off dominating the evening sky, reaching greatest elongation 47 degrees east of the Sun on January 10th and shining at magnitude -4.5. This is the best apparition of Venus since 2017. Venus then takes the plunge towards the Sun, passing less than nine degrees north of the Sun on March 21st-22nd. This is a good time to try the challenging feat of seeing Venus near inferior conjunction… just make sure that the Sun is physically blocked from view.

Venus near inferior conjunction in 2020. Credit: Shahrin Ahmad.

Venus then goes on to a fine dawn appearance for the remainder of 2025, reaching greatest elongation 46 degrees west of the Sun on June 25th.

The Outer Planets in 2025

The big ticket planetary event kicks off 2025, when Mars reaches opposition on January 16th. To be sure, this opposition is part of an unfavorable cycle as the Red Planet is currently moving away from us towards aphelion on April 16th, 2025, but noteworthy as it marks the biannual Mars observing season. At its best, Mars shines at -1.5 magnitude and presents a disk 15” across.

Mars from 2020. Credit: Andrew Symes.

Beyond opposition, Mars spends most of the rest of 2025 in the evening sky, and reaches solar conjunction on January 9th, 2026.

Jupiter in 2025

Jupiter reached opposition on December 7th, 2024, skips in 2025, and heads to opposition next on January 10th, 2026. Jupiter last performed such a bypass in 2013. Callisto (the only major moon that can ‘miss’ Jove) starts shadow-casting and passing back into Jupiter’s shadow on May 11th. This is a prelude to another bidecadal mutual eclipse season for Jupiter’s moons starting in 2026.

We have three double shadow transit seasons to watch for in 2025:

(Thanks to John Flannery and the late John O’Neill who edited the ‘Sky-High’ publication for the Irish Astronomical Society for years for calculating and passing this info on).

-February 25th (Ganymede-Europa)

-October 13th (Ganymede-Io)

-October 29th (Io-Europa)

-November 5th (Io-Europa)

-November 21st (Callisto-Io)

Also watch for a unique event, when only Callisto is visible on October 6th. Jupiter reaches solar conjunction on June 24th, transitioning from the dusk to dawn sky.

Saturn in 2025

Saturn starts off 2025 in the evening sky, and passes behind the Sun and into the dawn sky on March 12th. Saturn reaches opposition once on September 21st, marking the best time to spy the ringed world.

The changing tilt of Saturn’s rings. Credit: Shahrin Ahmad.

Saturn’s rings are edge on on March 23rd, 2025, providing us a twice every 29-year view of an apparently ‘ring-less’ Saturn… just think how bland the solar system would be, if Saturn always appeared thus?

Ring plane-crossing also means it’s time to see Saturn’s moons transiting across its disk. These are tougher to spot versus the Galilean moons of Jupiter, though shadow transits of 0.8” Titan are in the range of backyard telescopes. Use the IMCCE’s site to generate shadow transits for Titan in 2025.

Looking outward, Uranus reaches opposition on November 21st in the constellation Taurus, Neptune passes opposition on September 23rd in Pisces, and distant Pluto hits opposition on July 25th in Capricornus.

The Best Conjunctions and Groupings in 2025

2025 is an intriguing year for lunar-planetary meetups. First off, you have a rare chance to see all of the naked eye planets (from Mercury to Saturn) in the evening sky at once in mid-March, as Mercury briefly completes the scene.

The sky scene looking eastward on the morning of April 25th.

The best planet-versus-planet pairing occurs on August 12th with Jupiter and Venus just 54’ apart, 36 degrees from the Sun at dawn. The best planet-versus-bright star conjunction for the year happens when Venus passes 30’ north of Regulus on September 19th, also at dawn. Incidentally, a remote region in the Siberian Arctic will actually see the 5% illuminated waning crescent Moon cover the pair simultaneously, while the rest of us will see a skewed, ‘smiley face’ emoticon grouping hanging in the dawn sky, demonstrating that perhaps the Universe does indeed have a sly sense of humor.

Venus vs. Regulus on September 19th. Credit: Dave Dickinson

A triple conjunction grouping of this sort won’t grace the skies of our fair planet again until February 13th, 2056, when the Moon, Mars and Mercury meet up.

Looking eastward on the morning of August 20th. Credit: Stellarium Bright Planets vs. Clusters

Three planets that transit the Beehive Cluster (Messier 44) in 2025:

-May 4th Mars vs. M44 (83º from the Sun at dusk)

-July 2nd Mercury vs. M44 (25º from the Sun at dusk)

-August 31st Venus vs. M44 (31º from the Sun at dawn)

The Moon occults Saturn in 2014. Credit: Paul Stewart

Planets Occulted by the Moon in 2025

The Moon occults 4 naked eye planets (all except Jupiter) a total of 7 times in 2025:

DatePlanetMoon PhaseRegionNotesJan 4Saturn+25%Europe
Jan 14Mars+99%N. America/Africa
Feb 1Saturn+13%Alaskan Arctic
Feb 9Mars+91%N. Europe/Asia
Mar 1Mercury+2%Central Pacific
Jun 30Mars+24%S. America
Sep 19Venus-6%NW N. AmericaSee Venus (daytime) The visibility footprint for the January 14th occultation of Mars by the Moon. Bright Stars Occulted by the Moon in 2025

2025 is also rare in that the Moon will occult three of the four +1st magnitude stars that it can occult: Spica (11 times), Antares (12 times) and Regulus (6 times). Only Aldebaran sits this one out. Spica occultations are on their way out and headed towards the Antarctic region in 2025, while Regulus events are just sliding on to the scene to the north from the Arctic. Meanwhile, Spica occultations are still ongoing in 2025, and run out in November.

DateStarMoon PhaseRegionNotesJan 21Spica-51%W. Africa/Atlantic
Jan 25Antares-16%Indian Ocean
Feb 17Spica-77%South Pacific
Feb 21Antares-41%S. South America
Mar 16Spica-95%E. Africa/Indian Ocean
Mar 20Antares-67%Australia/New Zealand
Apr 13Spica-99%S. America/S. Atlantic
Apr 16Antares-88%S. Africa
May 10Spica+97%South Pacific
May 14Antares-96%S. Africa
Jun 6Spica+83%Antarctica
Jun 10Antares+99%Australia/New Zealand
Jul 3Spica+60%Antarctica
Jul 7Antares+91%S. Africa/SW Australia
Jul 26Regulus+5%Arctic1st of cycleJul 31Spica+44%Antarctica
Aug 4Antares+80%Antarctica/S. South America
Aug 23Regulus+0.5%ArcticNear NewAug 27Spica+20%Antarctica
Aug 31Antares+56%New Zealand/Antarctica
Sep 19Regulus-4%Arctic
Sep 23Spica+3%Antarctica
Sep 27Antares+28%Antarctica
Oct 16Regulus-22%NE North America
Oct 21Spica+0.5%AntarcticaNear NewOct 25Antares+15%S. South America
Nov 13Regulus-37%N. Europe
Nov 17Spica-7%AntarcticaFinal of cycleNov 21Antares+2%Southern Indian OceanDaytimeDec 10Regulus-64%N. North America
Dec 18Antares-3%Southern AtlanticDaytime Occultations of the Pleiades by the Moon in 2025

The Moon occults the Pleiades 14 times worldwide in 2025, in a series of ongoing occultations running all the way out to 2029:

DateLocation favoredMoon phaseNotesJanuary 10thNorth America/W. Europe/NW Africa+82%
February 6thWestern North America+69%
March 5thNE Asia+43%
April 1stEurope+17%
April 29thN. Pacific+4%
May 26thNorth America<1%Daytime, unobservableJune 23rdNE Africa-8%
July 20thNorth America-24%
August 16thNE Asia-45%
September 12thEurope-67%
October 10thW. North America-87%
November 6thN. Asia-98%
December 4thNW North America-99%
December 31stN. Asia+89%
Bright Comets to Watch for in 2025

Right now, there’s only one comet with real potential to reach naked eye visibility in 2025: Comet C/2024 G3 ATLAS. This comet reaches perihelion 0.094 AU from the Sun on January 13th, and ‘may’ top -1st magnitude or brighter. At magnitude +7 as of writing this in late December 2024, Comet G3 ATLAS could become a fine object low in the dawn sky for southern hemisphere observers… but only if it holds together and performs as expected.

A bright Geminid meteor over southern Arizona from 2024. Credit: Eliot Herman Meteor Showers to Watch For in 2025

Here are prospects for annual meteor showers in 2025:

Quadrantids – Peak at a Zenithal Hourly Rate (ZHR) of 80 on January 4th versus a +27% illuminated, waxing crescent Moon.

Lyrids – Peak on April 22nd with an ZHR of 18, versus a -32% illuminated, waning crescent Moon.

Eta Aquariids – Peak on May 5th with a ZHR of 50, versus a +64% illuminated, waxing gibbous Moon.

Southern Delta Aquariids – Peak on July 31st, with a ZHR of 25, versus a +44% illuminated, waxing crescent Moon.

Perseids – Peak on August 12th, with an expected ZHR of 100, versus a -87% illuminated, waning gibbous Moon.

Orionids – Peak on October 21st with an expected ZHR of 20, versus a New Moon.

Leonids – Peak on November 17th, with a ZHR of 10, versus a -5% illuminated, thin waning crescent Moon.

Geminids – Peak on December 14th, with a ZHR of 150, versus a -23% illuminated, waning crescent Moon.

Ursids – Peak on December 22nd, with a ZHR of 10, versus a 7% illuminated, waxing crescent Moon.

My money is on the Geminids for the best expected meteor shower of 2025.

Weirdness and More

Well, we’re now officially a quarter of the way into the 21st century. For fans and users of stellar cartography, 2050.0 coordinates will now slowly start to come into vogue versus 2000.0, as we inch ever closer to mid-century. It’s a strange thought, for those of us who still remember 1950.0 coordinates on star maps (and star maps in general!). Looking out of the solar system, we’re still waiting for the reclusive (and now overdue) recurrent nova T Coronae Borealis to finally pop.

Also, the white dwarf star Sirius b is now at apastron 11.5” from its brilliant primary, making this an excellent time to cross it off of your life-list… the +4 and +6 magnitude double star 70 Ophiuchus also reaches maximum separation of 6.7” in 2025. Finally, will the defunct Soviet Kosmos 482 Venus mission reenter in 2025? Should we alert the Six Million Dollar Man to stand-by to fight the ‘Venus Death Probe?’

…And a Teaser for 2026

The sky just keeps turning into 2026. Watch for mutual eclipse season for the major moons of Jupiter, as the moons pass one in front of the other. Also, the ongoing solar cycle is also still expected to be active into 2026, producing sunspots, space weather and more. And (finally!) we’ll see the return of total solar eclipses on August 12th, as the umbral shadow of the Moon crosses Greenland, Iceland and northern Spain.

Don’t miss all of these great sky-watching events and more, coming to a sky near you.

Credits: It has been a wild year, on the Earth and in the sky above. We always like to say that our sky watching almanac for the coming year is the one post that takes us six months to write, and this year’s is no exception. Lots of research goes into these, and we’ve picked the brains of lots of knowledgeable observers in the process. Thanks to John Flannery at the Irish Astronomical Society, Bob King, Robert Sparks, Andrew Symes, Paul Stewart, Eliot Herman, Guy Ottewell and everyone who contributed over the past year. Additionally, thanks go out to Universe Today Publisher Fraser Cain for hosting these looks at astronomy for the coming year, for going on over a decade now.

It’s going to be another great year for skywatching in 2025… and who knows? If the interest is out there, 2026 might see this half-a-year project grow into something bigger.

The post Top Astronomy Events for 2025 appeared first on Universe Today.

For decades cosmologists have wondered if the large-scale structure of the universe is a fractal: if it looks the same no matter the scale. And the answer is: no, not really. But in some ways, yes. Look, it’s complicated.

Our universe is unimaginably vast and contains somewhere around two trillion galaxies. These galaxies aren’t scattered around randomly, but are assembled into a series of ever-larger structures. There are the groups, containing at most a dozen galaxies are so. Then there are the clusters, which are home to a thousand galaxies and more. Above them are the superclusters, which twist and wind for millions of light-years.

Is this the end of the story?

In the mid 20th century Benoit Mandelbrot brought the concept of fractals into the mainstream. Mandelbrot didn’t invent the concept of fractals – mathematicians had been studying self-similar patterns for ages – but he did coin the word and usher in our modern study of the concept. The basic idea of a fractal is that you can use a single mathematical formula to define a structure at all scales. In other words, you can zoom in and out of a fractal and it still maintains the same shape.

Fractals appear everywhere in nature, from the branches of a tree to the edges of a snowflake. And Mandelbrot himself wondered if the universe is a fractal. If as we zoom out we will see the same kinds of structures appearing again and again.

And in a way, that’s what we see: a hierarchy of structures at ever-larger scales in the universe. But that hierarchy does come to an end. At a certain scale, roughly 300 million lightyears across, the cosmos becomes homogenous, meaning that there are no larger structures and the universe is (at that scale) roughly the same from place to place.

The universe is definitely not a fractal, but parts of the cosmic web still have interesting fractal-like properties. For example, clumps of dark matter called “halos”, which host galaxies and their clusters, form nested structures and sub-structures, with halos holding sub-haloes, and sub-sub-halos inside those.

Conversely, the voids of our universe aren’t entirely empty. They do contain a few, faint dwarf galaxies…and those few galaxies are arranged in a subtle, faint version of the cosmic web. In computer simulations, the sub-voids within that structure contain their own effervescent cosmic webs too.

So while the universe as a whole isn’t a fractal, and Mandelbrot’s idea didn’t hold up, we can still find fractals almost everywhere we look.

The post Is the Universe a Fractal? appeared first on Universe Today.

Within nearly every galaxy is a supermassive black hole. The beast at the heart of our galaxy contains the mass of millions of suns, while some of the largest supermassive black holes can be more than a billion solar masses. For years, it was thought that these black holes grew in mass over time, only reaching their current size after a billion years or more. But observations from the Webb telescope show that even the youngest galaxies contain massive black holes. So how could supermassive black holes grow so large so quickly? The key to the answer could be the powerful jets black holes can produce.

Although it seems counterintuitive, it is difficult for a black hole to consume matter and grow. The gravitational pull of a black hole is immensely strong, but the surrounding matter is much more likely to be trapped in orbit around the gravitational well than to fall directly in. To enter a black hole, material needs to slow down enough to fall inward. When a black hole has a jet of material speeding away from its polar region, this high-velocity plasma can pull rotational motion from the surrounding material, thus allowing it to fall into the black hole. For this reason, black holes with powerful jets also undergo the most powerful growth.

We can see many fast-growing black holes in the distant Universe as quasars, or active galactic nuclei. We know, then, that in the middle age of the cosmos, many supermassive black holes were gaining mass rapidly. One idea is that the youngest supermassive black holes also had active jets, which would allow them to gain a million solar masses or more quite quickly. But proving this is difficult.

The problem is that it’s extremely difficult to observe jets from the earliest period of the cosmos. Light from that distant time is so redshifted that their once brilliant beacon has become dim radio light. Before this recent study, the most distant jet we observed had a redshift of z = 6.1, meaning it traveled for nearly 12.8 billion years to reach us. In this new study, the team discovered a blazar with a redshift of z = 7.0, meaning it comes from a time when the Universe was just 750 million years old.

A blazar occurs when the jet of a supermassive black hole is lined up to be pointed directly at us. Since we’re looking directly into the beam, we see the jet at its most powerful. Blazars normally allow us to calculate the true intensity of a jet, but in this case, the redshift is so strong that our conclusions must be a bit more subtle.

How distant jets could be Doppler magnified. Credit: Bañados, et al

One possibility is that the jet of this particular supermassive black hole really is pointed directly our way. Based on this, the black hole is growing so quickly that it would easily gain more than a million solar masses within the first billion years of time. But it would be extremely rare for a black hole jet to point directly at us from that distance. So statistically, that would mean there are many more early black holes that are just as active and growing just as quickly. They just aren’t aligned for us to observe.

Another possibility is that the blazar isn’t quite aligned in our direction, but the cosmic expansion of space and time has focused its energy toward us over 12.9 billion years. In other words, the blazar may appear more energetic than it actually is, thanks to relativistic cosmology. But if that is the case, then the jet of this black hole is less energetic but still powerful. And statistically, that would mean most early black holes are equally powerful.

So this latest work tells us that either there was a fraction of early black holes that grew to beasts incredibly fast, or that most black holes grew quickly, beginning at a time even earlier than we can observe. In either case, it is clear that early black holes created jets, and these jets allowed the first supermassive black holes to appear early in cosmic time.

Reference: Bañados, Eduardo, et al. “A blazar in the epoch of reionization.” Nature Astronomy (2024): 1-9.

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The black hole information paradox has puzzled physicists for decades. New research shows how quantum connections in spacetime itself may resolve the paradox, and in the process leave behind a subtle signature in gravitational waves.

For a long time we thought black holes, as mysterious as they were, didn’t cause any trouble. Information can’t be created or destroyed, but when objects fall below the event horizons, the information they carry with them is forever locked from view. Crucially, it’s not destroyed, just hidden.

But then Stephen Hawking discovered that black holes aren’t entirely black. They emit a small amount of radiation and eventually evaporate, disappearing from the cosmic scene entirely. But that radiation doesn’t carry any information with it, which created the famous paradox: when the black hole dies, where does all its information go?

One solution to this paradox is known as non-violent nonlocality. This takes advantage of a broader version of quantum entanglement, the “spooky action at a distance” that can tie together particles. But in the broader picture, aspects of spacetime itself become entangled with each other. This means that whatever happens inside the black hole is tied to the structure of spacetime outside of it.

Usually spacetime is only altered during violent processes, like black hole mergers or stellar explosions. But this effect is much quieter, just a subtle fingerprint on the spacetime surrounding an event horizon.

If this hypothesis is true, the spacetime around black holes carries tiny little perturbations that aren’t entirely random; instead, the variations would be correlated with the information inside the black hole. Then when the black hole disappears, the information is preserved outside of it, resolving the paradox.

In a recent paper appearing in the journal preprint server arXiv, but not yet peer-reviewed, a pair of researchers at Caltech investigated this intriguing hypothesis to explore how we might be able to test it.

The researchers found that these signatures in spacetime also leave an imprint in the gravitational waves when black holes merge. These imprints are incredibly tiny, so small that we are not yet able to detect them with existing gravitational wave experiments. But they do have a very unique structure that stands on top of the usual wave pattern, making them potentially observable.

The next generation of gravitational wave detectors, which aim to come online in the next decade, might have enough sensitivity to tease out this signal. If they see it, it would be tremendous, as it would finally point to a clear solution of the troubling paradox, and open up a new understanding of both the structure of spacetime and the nature of quantum nonlocality.

The post Quantum Correlations Could Solve the Black Hole Information Paradox appeared first on Universe Today.

In April 2019, the Event Horizon Telescope (EHT) collaboration made history when it released the first-ever image of a black hole. The image captured the glow of the accretion disk surrounding the supermassive black hole (SMBH) at the center of the M87 galaxy, located 54 million light-years away. Because of its appearance, the disk that encircles this SMBH beyond its event horizon (composed of gas, dust, and photons) was likened to a “ring of fire.” Since then, the EHT has been actively imaging several other SMBH, including Sagittarius A* at the center of the Milky Way!

In addition, the EHT has revealed additional details about M87, like the first-ever image of a photon ring and a picture that combines the SMBH and its relativistic jet emanating from its center. Most recently, the EHT released the results of its latest observation campaign. These observations revealed a spectacular flare emerging from M87’s powerful relativistic jet. This flare released a tremendous amount of energy in multiple wavelengths, including the first high-energy gamma-ray outburst observed in over a decade.

The EHT is an international collaboration of researchers from thirteen universities and institutes worldwide that combines data from over 25 ground-based and space-based telescopes. The research, which was recently published in the journal Astronomy & Astrophysics, was conducted by the Event Horizon Telescope Collaboration, the Event Horizon Telescope- Multi-wavelength science working group, the Fermi Large Area Telescope Collaboration, the H.E.S.S. Collaboration, the MAGIC Collaboration, the VERITAS Collaboration, and the EAVN Collaboration.

The observatories and telescopes that participated in the 2018 multiband campaign to detect the high-energy gamma-ray flare from the M87* black hole. Credits: EHT Collaboration/Fermi-LAT Collaboration/H.E.S.S. Collaboration/MAGIC Collaboration/VERITAS Collaboration/EAVN Collaboration

The study presents the data from the second EHT observational campaign conducted in April 2018 that obtained nearly simultaneous spectra of the galaxy with the broadest wavelength coverage ever collected. Giacomo Principe, the paper coordinator, is a researcher at the University of Trieste associated with the Instituto Nazionale di Astrofisica (INAF) and the Institute Nazionale di Fisica Nucleare (INFN). As he explained in a recent EHT press release:

“We were lucky to detect a gamma-ray flare from M87 during this EHT multi-wavelength campaign. This marks the first gamma-ray flaring event observed in this source in over a decade, allowing us to precisely constrain the size of the region responsible for the observed gamma-ray emission. Observations—both recent ones with a more sensitive EHT array and those planned for the coming years—will provide invaluable insights and an extraordinary opportunity to study the physics surrounding M87’s supermassive black hole. These efforts promise to shed light on the disk-jet connection and uncover the origins and mechanisms behind the gamma-ray photon emission.”

The second EHT and multi-wavelength campaign leveraged data from more than two dozen high-profile observational facilities, including NASA’s Fermi Gamma-ray Space Telescope-Large Area Telescope (Fermi-LAT), the Hubble Space Telescope (HST), Nuclear Spectroscopic Telescope Array (NuSTAR), the Chandra X-ray Observatory, and the Neil Gehrels Swift Observatory. This was combined with data from the world’s three largest Imaging Atmospheric Cherenkov Telescope arrays – the High Energy Stereoscopic System (H.E.S.S.), the Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC), and the Very Energetic Radiation Imaging Telescope Array System (VERITAS).

During the campaign, the Fermi space telescope gathered data indicating an increase in high-energy gamma rays using its LAT instrument. Chandra and NuSTAR followed by collecting high-quality data in the X-ray band, while the Very Long Baseline Array (VLBA) and the East Asia VLBI Network (EAVN) obtained data in radio frequencies. The flare these observations revealed lasted approximately three days and occupied a region roughly three light-days in size, about 170 times the distance between the Sun and the Earth (~170 AU).

Light curve of the gamma-ray flare (bottom) and collection of quasi-simulated images of the M87 jet (top) at various scales obtained in radio and X-ray during the 2018 campaign. Credits: EHT Collaboration/Fermi-LAT Collaboration/H.E.S.S. Collaboration/MAGIC Collaboration/VERITAS Collaboration/EAVN Collaboration

The flare itself was well above the energies typically detected around black holes and showed a significant variation in the position angle of the asymmetry of the black hole’s ‘event horizon’ and its position. As Daryl Haggard, a professor at McGill University and the co-coordinator of the EHT multi-wavelength working group, explained, this suggests a physical relation between these structures on very different scales:

“In the first image obtained during the 2018 observational campaign, we saw that the emission along the ring was not homogeneous, instead it showed asymmetries (i.e., brighter areas). Subsequent observations conducted in 2018 and related to this paper confirmed that finding, highlighting that the asymmetry’s position angle had changed.”

“How and where particles are accelerated in supermassive black hole jets is a long-standing mystery,” added University of Amsterdam professor Sera Markoff, another EHT multi-wavelength working group co-coordinator. “For the first time, we can combine direct imaging of the near event horizon regions during gamma-ray flares caused by particle acceleration events and thus test theories about the flare origins.”

This discovery could create opportunities for future research and lead to breakthroughs in our understanding of the Universe.

Further Reading: EHT, Astronomy & Astrophysics

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Almost every large galaxy has a supermassive black hole churning away at its core. In most cases, these black holes spin in concert with their galaxy, like the central hub of a cosmic wagon wheel. But on December 18, 2024, NASA researchers announced they had discovered a galaxy whose black hole appears to have been turned on its side, spinning out of alignment with its host galaxy.

The galaxy, NGC 5084, was discovered centuries ago by German astronomer William Herschel, but it took new techniques, recently developed at NASA’s Ames Research Center, to reveal the unusual properties of the black hole.

The new method is called SAUNAS (Selective Amplification of Ultra Noisy Astronomical Signal). It enables astronomers to tease out low-brightness X-ray emissions that were previously drowned out by other radiation sources.

When the team put their new technique to the test by combing through old archival data from the Chandra X-ray observatory – a space telescope that acts as the X-ray counterpart to Hubble’s visible-light observations – they found their first clue that something unusual was going on in NGC 5084.

Four large X-ray plumes, made visible by the new technique, appeared in the data. These streams of plasma extend out from the centre of the galaxy, two in line with the galactic plane, and two extending above and below.

While plumes of hot, charged gas are not unusual above or below the plane of large galaxies, it is unusual to find four of them, rather than just one or two, and even more unusual to find them in line with the galactic plane.

NGC 5084, as seen by in visible light. Adam Block/Mount Lemmon SkyCenter/University of Arizona.

To make sure that they weren’t just seeing some error or artifact in the Chandra data, they started looking more closely at other images of the galaxy, including both the Hubble space telescope and the Atacama Large Millimeter Array (ALMA).

These observations revealed a dusty inner disk spinning in the centre of the galaxy at a 90-degree angle to the rest of NGC 5084.

The team also looked at the galaxy in radio wavelengths using the NRAO’s Expanded Very Large Array. All together, these observations painted a picture of a very strange galactic core.

“It was like seeing a crime scene with multiple types of light,” said Ames research scientist Alejandro Serrano Borlaff, lead author of the paper published this week in The Astrophysical Journal. “Putting all the pictures together revealed that NGC 5084 has changed a lot in its recent past.”

Borlaff’s coauthor and astrophysicist at Ames, Pamela Marcum, added that “detecting two pairs of X-ray plumes in one galaxy is exceptional. The combination of their unusual, cross-shaped structure and the ‘tipped-over,’ dusty disk gives us unique insights into this galaxy’s history.”

The plumes of plasma suggest that the galaxy has been disturbed in some way during its lifetime. It might be explained, for example, by a collision with another galaxy, which caused the black hole to tip on its side.

With this discovery, SAUNAS has demonstrated that it can bring new life to old data, uncovering new surprises in familiar galaxies. This surprise twist on a galaxy we’ve known about since 1785 offers tantalizing hope that there might be other weird and wonderful discoveries to come, even in places we thought we’d seen everything.

Learn more:

“NASA Finds ‘Sideways’ Black Hole Using Legacy Data, New Techniques.” NASA.

Alejandro S. Borlaff et al. “SAUNAS. II. Discovery of Cross-shaped X-Ray Emission and a Rotating Circumnuclear Disk in the Supermassive S0 Galaxy NGC 5084.” The Astrophysical Journal.

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Through the Artemis Program, NASA will send the first astronauts to the Moon since the Apollo Era before 2030. They will be joined by multiple space agencies, like the ESA and China, who plan to send astronauts (and “taikonauts”) there for the first time. Beyond this, all plan to build permanent habitats in the South Pole-Aitken Basin and the necessary infrastructure that will lead to a permanent human presence. This presents many challenges, the most notable being those arising from the nature of the lunar environment.

Aside from the extremes in temperature, a 14-day diurnal cycle, and the airless environment, there’s the issue of lunar regolith (aka moondust). In addition to being coarse and jagged, lunar regolith sticks to everything because it is electrostatically charged. Because of how this dust plays havoc with astronaut health, equipment, and machinery, NASA is developing technologies to mitigate dust buildup. Seven of these experiments will be tested during a flight test using a Blue Origin New Shepard rocket to evaluate their ability to mitigate lunar dust.

Another major problem with lunar regolith is how it gets kicked up and distributed by spacecraft plumes. With essentially no atmosphere and lower gravity (16.5% of Earth’s), this dust can remain aloft for extended periods of time. Its jagged nature, resulting from billions of years of meteor and micrometeoroid impacts and a total lack of weathering, is abrasive to any surface it comes into contact with, ranging from spacesuits and equipment to human skin, eyes, and lungs. It will also build up on solar panels, preventing missions from drawing enough power to survive a lunar night.

In addition, it can also cause equipment to overheat as it coats thermal radiators and accumulates on windows, camera lenses, and visors, making it harder to see, navigate, and acquire accurate images. Kristen John, the Lunar Surface Innovation Initiative technical integration lead at NASA’s Johnson Space Center, said in a NASA press release: “The fine grain nature of dust contains particles that are smaller than the human eye can see, which can make a contaminated surface appear to look clean.”

Addressing the Problem

These technologies were developed by NASA’s Game Changing Development program within the agency’s Space Technology Mission Directorate (STMD). The “Lunar Gravity Simulation via Suborbital Rocket” flight test will study regolith mechanics and lunar dust transport in a simulated lunar gravity environment. The payload includes projects for mitigating and cleaning dust using multiple strategies. They include:

ClothBot:
This compact robot is designed to simulate and measure how dust behaves in a pressurized environment, which astronauts could bring back after conducting Extravehicular Activities (EVAs). The robot relies on pre-programmed motions that simulate astronauts’ movements when removing their spacesuits (aka “doffing”), releasing a small dose of lunar regolith simulant. A laser-illuminated imaging system will then capture the dust flow in real-time while sensors record the size and number of particles.

Electrostatic Dust Lofting (EDL):
The EDL will examine how lunar dust is “lofted” (kicked up) when it becomes electrostatically charged to improve models on dust lofting. During the lunar gravity phase of the flight, a dust sample will be released that the EDL will illuminate using a UV light source, causing the particles to become charged. The dust will then pass through a sheet laser as it rises from the surface while the EDL observes and records the results. The EDL’s camera will continue to record the dust until the mission ends, even after the lunar gravity phase ends and the UV light is shut off.

The Lunar Lab and Regolith Testbeds at NASA’s Ames Research Center. Credit: NASA/Uland Wong.

Hermes Lunar-G:
The Hermes Lunar-G project, developed by NASA, Texas A&M, and Texas Space Technology Applications and Research (T-STAR), is based on a facility (Hermes) that previously operated on the International Space Station (ISS). Like its predecessor, the Lunar-G project will rely on repurposed Hermes hardware to study lunar regolith simulants. This will be done using four canisters containing compressed lunar dust simulants. When the flight enters its lunar gravity phase, these simulants will decompress and float around in the canisters while high-speed cameras and sensors capture data. The results will be compared to microgravity data from the ISS and similar flight experiments.

Dust Mitigation Strategies

The data obtained by these projects will provide information on regolith generation rates, transport, and mechanics that will help scientists refine computational models. This will allow mission planners and designers to develop better strategies for dust mitigation for future missions to the Moon and Mars. Already, this challenge informs several aspects of NASA’s technological developments, ranging from In-Situ Resource Utilization (ISRU) and construction to transportation and surface power. Said John:

“Learning some of the fundamental properties of how lunar dust behaves and how lunar dust impacts systems has implications far beyond dust mitigation and environments. Advancing our understanding of the behavior of lunar dust and advancing our dust mitigation technologies benefits most capabilities planned for use on the lunar surface.”

The test flight and vehicle enhancements that will enable the simulation of lunar gravity are being funded through NASA’s Flight Opportunities program.

Further Reading: NASA

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New research suggests that our best hopes for finding existing life on Mars isn’t on the surface, but buried deep within the crust.

Several years ago NASA’s Curiosity rover measured traces of methane in the Martian atmosphere at levels several times the background. But a few months later, the methane disappeared, only for it to reappear again later in the year. This discovery opened up the intriguing possibility of life still clinging to existence on Mars, as that could explain the seasonal variability in the presence of methane.

But while Mars was once home to liquid water oceans and an abundant atmosphere, it’s now a desolate wasteland. What kind of life could possibly call the red planet home? Most life on Earth wouldn’t survive long in those conditions, but there is a subgroup of Earthly life that might possibly find Mars a good place to live.

These are the methanogens, a type of single-celled organism that consume hydrogen for energy and excrete methane as a waste product. Methanogens can be found in all sorts of otherwise-inhospitable places on Earth, and something like them might be responsible for the seasonal variations in methane levels on Mars.

In a recent paper submitted for publication in the journal AstroBiology, a team of scientists scoured the Earth for potential analogs to Martian environments, searching for methanogens thriving in conditions similar to what might be found on Mars.

The researchers found three potential Mars-like conditions on Earth where methanogens make a home. The first is deep in the crust, sometimes to a depth of several kilometers, where tiny cracks in rocks allow for liquid water to seep in. The second is lakes buried under the Antarctic polar ice cap, which maintain their liquid state thanks to the immense pressures of the ice above them. And the last is super-saline, oxygen-deprived basins in the deep ocean.

All three of these environments have analogs on Mars. Like the Earth, Mars likely retains some liquid water buried in its crust. And its polar caps might have liquid water lakes buried underneath them. Lastly, there has been tantalizing – and heavily disputed – evidence of briny water appearing on crater walls.

In the new paper, the researchers mapped out the temperature ranges, salinity levels, and pH values across sites scattered around the Earth. They then measured the abundance of molecular hydrogen in those sites, and determined where methanogens were thriving the most.

For the last step, the researchers combed through the available data about Mars itself, finding where conditions best matched the most favorable sites on Earth. They found that the most likely location for possible life was in Acidalia Planitia, a vast plain in the northern hemisphere.

Or rather, underneath it. Several kilometers below the plain, the temperatures are warm enough to support liquid water. That water might have just the right pH and salinity levels, along with enough dissolved molecular hydrogen, to support a population of methanogen-like creatures.

Now we just have to figure out how to get there.

The post Where’s the Most Promising Place to Find Martian Life? appeared first on Universe Today.

Entanglement is perhaps one of the most confusing aspects of quantum mechanics. On its surface, entanglement allows particles to communicate over vast distances instantly, apparently violating the speed of light. But while entangled particles are connected, they don’t necessarily share information between them.

In quantum mechanics, a particle isn’t really a particle. Instead of being a hard, solid, precise point, a particle is really a cloud of fuzzy probabilities, with those probabilities describing where we might find the particle when we go to actually look for it. But until we actually perform a measurement, we can’t exactly know everything we’d like to know about the particle.

These fuzzy probabilities are known as quantum states. In certain circumstances, we can connect two particles in a quantum way, so that a single mathematical equation describes both sets of probabilities simultaneously. When this happens, we say that the particles are entangled.

When particles share a quantum state, then measuring the properties of one can grant us automatic knowledge of the state of the other. For example, let’s look at the case of quantum spin, a property of subatomic particles. For particles like electrons, the spin can be in one of two states, either up or down. Once we entangle two electrons, their spins are correlated. We can prepare the entanglement in a certain way so that the spins are always opposite of each other.

If we measure the first particle, we might randomly find the spin pointing up. What does this tell us about the second particle? Since we carefully arranged our entangled quantum state, we now know with 100% absolute certainty that the second particle must be pointing down. Its quantum state was entangled with the first particle, and as soon as one revelation is made, both revelations are made.

But what if the second particle was on the other side of the room? Or across the galaxy? According to quantum theory, as soon as one “choice” is made, the partner particle instantly “knows” what spin to be. It appears that communication can be achieved faster than light.

The resolution to this apparent paradox comes from scrutinizing what is happening when – and more importantly, who knows what when.

Let’s say I’m the one making the measurement of particle A, while you are the one responsible for particle B. Once I make my measurement, I know for sure what spin your particle should have. But you don’t! You only get to know once you make your own measurement, or after I tell you. But in either case nothing is transmitted faster than light. Either you make your own local measurement, or you wait for my signal.

While the two particles are connected, nobody gets to know anything in advance. I know what your particle is doing, but I only get to inform you at speed slower than light – or you just figure it out for yourself.

So while the process of entanglement happens instantaneously, the revelation of it does not. We have to use good old-fashioned no-faster-than-light communication methods to piece together the correlations that quantum entanglement demand.

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Neutrinos are tricky little blighters that are hard to observe. The IceCube Neutrino Observatory in Antarctica was built to detect neutrinos from space. It is one of the most sensitive instruments built with the hope it might help uncover evidence for dark matter. Any dark matter trapped inside Earth, would release neutrinos that IceCube could detect. To date, and with 10 years of searching, it seems no excess neutrinos coming from Earth have been found!

Neutrinos are subatomic particles which are light and carry no electrical charge. Certain events, such as supernovae and solar events generate vast quantities of neutrinos. By now, the universe will be teeming with neutrinos with trillions of them passing through every person every second. The challenge though is that neutrinos rarely interact with matter so observing and detecting them is difficult. Like other sub-atomic particles, there are different types of neutrino; electron neutrinos, muon neutrinos and tau neutrinos, with each associated with a corresponding lepton (an elementary particle with half integer spin.) Studying neutrinos of all types is key to helping understand fundamental physical processes across the cosmos. 

Chinese researchers are working on a new neutrino observatory called TRIDENT. They built an underwater simulator to develop their plan. Image Credit: TRIDENT

The IceCube Neutrino Observatory began capturing data in 2005 but it wasn’t until 2011 that it began full operations. It consists of over 5,000 football-sized detectors arranged within a cubic kilometre of ice deep underground. Arranged in this fashion, the detectors are designed to capture the faint flashes of Cherenkov radiation released when neutrinos interact with the ice. The location near the South Pole was chosen because the ice acts as a natural barrier against background radiation from Earth. 

A view of the IceCube Lab with a starry night sky showing the Milky Way and green auroras. Photo By: Yuya Makino, IceCube/NSF

Using data from the IceCube Observatory, a team of researchers led by R. Abbasi from the Loyola University Chicago have been probing the nature of dark matter. This strange and invisible component of the universe is thought to make up 27% of the mass-energy content of the universe. Unfortunately, dark matter doesn’t emit, absorb or reflect light making it undetectable by conventional means. One train of thought is that dark matter is made up of Weakly Interacting Massive Particles (WIMPs.) They can be captured by objects like the Sun leading to their annihilation and transition into neutrinos. It’s these, that the team have been hunting for. 

The paper published by the team articulates their search for muon neutrinos from the centre of the Earth within the 10 years of data captured by IceCube. The team searched chiefly for WIMPs within the mass range of 10GeV to 10TeV but due to the complexity and position of the source (the centre of the Earth,) the team relied upon running Monte Carlo simulations. The name is taken from casino’s in Monaco and involves running many random simulations. This technique is used where exact calculations are unable to compute the answer and so the simulations are based on the concept that randomness can be used to solve problems.

After running many simulations of this sort, the team found no excess neutrino flux over the background levels from Earth. They conclude however that whilst no evidence has been found yet, that an upgrade to the IceCube Observatory may yield more promising results as they can probe lower neutrino mass events and hopefully one day, solve the mystery of the nature of dark matter. 

Source : Search for dark matter from the centre of the Earth with ten years of IceCube data

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A team of astronomers have detected a surprisingly fast and bright burst of energy from a galaxy 500 million light years away. The burst of radiation peaked in brightness just after 4 day and then faded quickly. The team identified the burst, which was using the Catalina Real-Time Transient Survey with supporting observations from the Gran Telescopio Canarias, as the result of a small black hole consuming a star. The discovery provides an exciting insight into stellar evolution and a rare cosmic phenomenon. 

Black holes are stellar corpses where the gravity is so intense that nothing, not even light can escape. They form when massive stars collapse under their own gravity at the end of their life forming an infinitely small point known as a singularity. The region of space around the singularity is bounded by the event horizon, the point beyond which, nothing can escape. Despite the challenges of observing them, they can be detected by observing the effects of their gravity on nearby objects like gas clouds. There are still many mysteries surrounding black holes so they remain an intense area of study. 

3D rendering of a rapidly spinning black hole’s accretion disk and a resulting black hole-powered jet. Credit: Ore Gottlieb et al. (2024)

A team of astronomers led by Claudia Gutiérrez from the Institute of Space Sciences and the Institute of Space Studies of Catalina used data from the Catalina Real-Time Transient Survey (CRTS) to explore transient events. The CRTS was launched in 2004 and is a wide field survey that looks for variable objects like supernova and asteroids. It uses a network of telescopes based in Arizona to scan large areas of sky to detect short-lived events. It has been of great use providing insights into the life cycle of stars and the behaviour of distant galaxies. 

The 60 inch Mt. Lemmon telescope is one of three telescopes used in the Catalina Sky Survey. Image: Catalina Sky Survey, University of Arizona.

The team detected the bright outburst in a galaxy located 500 million light years away and published their results in the Astrophysical Journal. The event took place in a tiny galaxy about 400 times less massive than the Milky Way. The burst was identified as CSS161010, it reached maximum brightness in only 4 days and 2.5 days later had it’s brightness reduced by half. Subsequent work revealed that previous detection had been picked up by the All-Sky Automated Survey for SuperNovae. Thankfully the detection was early enough to allow follow up observations by other ground based telescopes. Typically these types of events are difficult to study due to their rapid evolution.

Only a handful of events like CSS161010 have been detected in recent years but until now  their nature was a mystery. The team led by Gutiérrez have analysed the spectral properties and found hydrogen lines revealing material travelling at speeds up to 10% of the speed of light. The changes observed in the hydrogen emission lines is similar to that seen in active galactic nuclei where supermassive black holes exist. The observation suggests it relates to a black hole, although not a massive one.

The brightness of the object reduced 900 times over the following two months. Further spectral analysis at this time still revealed blue shifted hydrogen lines indicating high speed gas outflows. This was not something usually seen from supernova events suggesting a different origin. The team believe that the event is the result of a small black hole swallowing a star. 

Source : Astronomers detected a burst caused by a black hole swallowing a star

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Meet the brown dwarf: bigger than a planet, and smaller than a star. A category of its own, it’s one of the strangest objects in the universe.

Brown dwarfs typically are defined to have masses anywhere from 12 times the mass of Jupiter right up to the lower limit for a star. And despite their names, they are not actually brown. The largest and youngest ones are quite hot, giving off a steady glow of radiation. In fact, the largest brown dwarfs are almost indistinguishable from red dwarfs, the smallest of the stars. But the smallest, oldest, and coldest ones are so dim they can only be detected with our most sensitive infrared telescopes.

Unlike stars, brown dwarfs don’t generate their own energy through nuclear fusion, at least not for very long. Instead they emit radiation from the leftover heat of their own formation. As that heat escapes, the brown dwarf continues to dim, sliding from fiery red to mottled magenta to invisible infrared. The greater the mass at its birth, the more heat it can trap and the longer it can mimic a proper star, but the ultimate end fate is the same for every single brown dwarf, regardless of its pedigree.

At first it may seem like brown dwarfs are just extra-large planets, but they get to do something that planets don’t. While brown dwarfs can’t fuse hydrogen in their cores – that takes something like 80 Jupiter masses to accomplish – they can briefly partake in another kind of fusion reaction.

In the cooler heart of a brown dwarf, deuterium, which is a single proton and neutron, can convert into Helium-3, and in the process release energy. This process doesn’t last long; in only a few million years even the largest brown dwarfs use up all their available deuterium, and from there they will just cool off.

As for their size, they tend not to be much larger in diameter than a typical gas giant like Jupiter. That’s because unlike a star, there isn’t an additional source of energy, and thereby pressure, to prop themselves up. Instead, all that’s left is the exotic quantum force known as degeneracy pressure, which means that you can only squeeze so many particles into so small a volume. In this case, brown dwarfs are very close to the limit for degeneracy pressure to maintain their size given their mass.

This means that despite outweighing Jupiter, they won’t appear much larger. And unlike Jupiter, they are briefly capable of nuclear fusion. After that, however, they spend the rest of their lives wandering the galaxy, slowly chilling out.

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In 1971, the Soviet Mars 3 lander became the first spacecraft to land on Mars, though it only lasted a couple of minutes before failing. More than 50 years later, it’s still there at Terra Sirenum. The HiRISE camera NASA’s Mars Reconnaissance Orbiter may have imaged some of its hardware, inadvertently taking part in what could be an effort to document our Martian artifacts.

Is it time to start cataloguing and even preserving these artifacts so we can preserve our history?

Some anthropologists think so.

Justin Holcomb is an assistant research professor of anthropology at the University of Kansas. He and his colleagues argue that it’s time to take Martian archaeology seriously, and the sooner we do, the better and more thorough the results will be. Their research commentary, “The emerging archaeological record of Mars,” was recently published in Nature Astronomy.

Artifacts of the human effort to explore the planet are littered on its surface. According to Holcomb, these artifacts and our effort to reach Mars are connected to the original human dispersal from Africa.

“Our main argument is that Homo sapiens are currently undergoing a dispersal, which first started out of Africa, reached other continents and has now begun in off-world environments,” said lead author Holcomb. “We’ve started peopling the solar system. And just like we use artifacts and features to track our movement, evolution and history on Earth, we can do that in outer space by following probes, satellites, landers and various materials left behind. There’s a material footprint to this dispersal.”

Tracks from Opportunity stretch across this vista taken by the rover on Sol 3,781 in September 2014. This is from only ten years ago, but those missions already seem historical. Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

It’s tempting to call debris from failed missions wreckage or even space junk like we do the debris that orbits Earth. But things like spent parachutes and heat shields are more than just wreckage. They’re artifacts the same way other cast-offs are artifacts. In fact, what archaeologists often do in the field is sift through trash. “Trash is a proxy for human behaviour,” said one anthropologist.

In any case, one person’s trash can be another person’s historical artifact.

Spacecraft that land on Mars have to eject equipment – like this protective shell from Perseverance and imaged by Ingenuity– on their way to the Martian surface. Spacecraft can’t reach the surface without protection. As time passes, trash and debris like this become important artifacts. NASA/JPL-Caltech

“These are the first material records of our presence, and that’s important to us,” Holcomb said. “I’ve seen a lot of scientists referring to this material as space trash, galactic litter. Our argument is that it’s not trash; it’s actually really important. It’s critical to shift that narrative towards heritage because the solution to trash is removal, but the solution to heritage is preservation. There’s a big difference.”

14 missions to Mars have left their mark on the red planet in the form of artifacts. According to the authors, this is the beginning of the planet’s archaeological record. “Archaeological sites on the Red Planet include landing and crash sites, which are associated with artifacts including probes, landers, rovers and a variety of debris discarded during landing, such as netting, parachutes, pieces of the aluminum wheels (for example, from the Curiosity rover), and thermal protection blankets and shielding,” they write.

This figure from the research shows fourteen missions to Mars, along with key sites and examples of artifacts. MER A and B are NASA’s Spirit and Opportunity. a) Basemap generated from data derived from the Mars Orbiter Laser Altimeter (MOLA) and the High-Resolution Stereo Camera (HRSC)12. b) Viking-1
lander (NASA/JPL). c) Trackways created by NASA’s Perseverance rover (NASA/JPL-Caltech/Arizona State University). d) Dacron netting used in thermal blankets, photographed by NASA’s Perseverance rover using its onboard Front Left Hazard Avoidance Camera A (NASA/JPL-Caltech/Arizona State University).
e) China’s Tianwen-1 lander and Zhurong rover in southern Utopia Planitia photographed by HiRISE (NASA/JPL-Caltech/University of Arizona). f) The ExoMars Schiaparelli Lander crash site in Meridiani Planum (NASA/JPL-Caltech/University of Arizona). g) Illustration of the Soviet Mars Program’s Mars 3
space probe (NASA). h) NASA’s Phoenix lander with digital video disc (DVD) in the foreground (NASA/JPL-Caltech).

Other features include rover tracks and rover drilling and sampling sites.

Curiosity captured this self-portrait at the ‘Windjana’ Drilling Site in 2014. The right panel shows its work. Image Credit: NASA/JPL-Caltech/MSSS

We’re already partway to taking our abandoned artifacts seriously. The United Nations keeps a list of objects launched into space called the Register of Objects Launched into Outer Space. It’s a way of identifying which countries are liable and responsible for objects in space (but not which private billionaires.) The Register was first implemented in 1976, and it says that about 88% of crewed spacecraft, elements of the ISS, satellites, probes, and landers launched into space are registered.

UNESCO also keeps a register of heritage sites, including archaeological and natural sites. The same could be done for Mars.

This UNESCO list of heritage sites shows both natural and cultural heritage sites, including ones that are considered to be in danger. Click the image to visit the site and explore the map. Image Credit: UNESCO

There’s already one attempt to start documenting and mapping sites on Mars. The Perseverance Rover team is documenting all of the debris they encounter to make sure it can’t contaminate sampling sites. There are also concerns that debris could pose a hazard to future missions.

According to one researcher, there is over 1700 kg (16,000) pounds of debris on Mars, not including working spacecraft. While much of it is just scraps being blown around by the wind and broken into smaller pieces, there are also larger pieces of debris and nine intact yet inoperative spacecraft.

So far, there have been only piecemeal attempts to document these Martian artifacts.

“Despite efforts from the USA’s Perseverance team, there exists no systematic strategy for documenting, mapping and keeping track of all heritage on Mars,” the authors write. “We anticipate that cultural
resource management will become a key objective during planetary exploration, including systematic surveying, mapping, documentation, and, if necessary, excavation and curation, especially as we expand
our material footprint across the Solar System.”

Holcomb and his co-authors say we must understand that our spacecraft debris is the archaeological record of our attempt to explore not just Mars but the entire Solar System. Our effort to understand Mars is also part of our effort to understand our own planet and how humanity arose. “Any future accidental destruction of this record would be permanent,” they point out.

The authors say there’s a crucial need to preserve things like Neil Armstrong’s first footsteps on the Moon, the first impact on the lunar surface by the USSR’s Luna 2, and even the USSR’s Venera 7 mission, the first spacecraft to land on another planet. This is our shared heritage as human beings.

A bootprint in the lunar regolith, taken during Apollo 11 in 1969. Credit: NASA.

“These examples are extraordinary firsts for humankind,” Holcomb and his co-authors write. “As we move forward during the next era of human exploration, we hope that planetary scientists, archaeologists and geologists can work together to ensure sustainable and ethical human colonization that protects
cultural resources in tandem with future space exploration.”

There are many historical examples of humans getting this type of thing wrong, particularly during European colonization of other parts of the world. Since we’re still at (we hope) the beginning of our exploration of the Solar System, we have an opportunity to get it right from the start. It will take a lot of work and many discussions to determine what this preservation and future exploration can look like.

“Those discussions could begin by considering and acknowledging the emerging archaeological record on Mars,” the authors conclude.

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In 2019, astronomers observed an unusual gravitational chirp. Known as GW190521, it was the last scream of gravitational waves as a black hole of 66 solar masses merged with a black hole of 85 solar masses to become a 142 solar mass black hole. The data were consistent with all the other black hole mergers we’ve observed. There was just one problem: an 85 solar mass black hole shouldn’t exist.

All the black hole mergers we’ve observed involve stellar mass black holes. These form when a massive star explodes as a supernova and its core collapses to become a black hole. An old star needs to be at least ten times the mass of the Sun to become a supernova, which can create a black hole of about 3 solar masses. Larger stars can create larger black holes, up to a point.

The first generation of stars in the cosmos were likely hundreds of solar masses. For a star above 150 solar masses or so, the resulting supernova would be so powerful that its core would undergo what is known as pair-instability. Gamma rays produced in the core would be so intense they decay into an electron-positron pair. The high-energy leptons would then rip apart the core before gravity could collapse it. To overcome the pair-instability, a progenitor star would need a mass of 300 Suns or more. This means that the mass range of stellar black holes has a “pair-instability gap.” Black holes from 3 solar masses to about 65 solar masses would form from regular supernovae, and black holes above 130 solar masses could form from stellar collapse, but black holes between 65-130 solar masses shouldn’t exist.

For GW190521, the 66 solar mass black hole is close enough to the limit that it likely formed from a single star. The 85 solar mass black hole, on the other hand, is smack-dab in the middle of the forbidden range. Some astronomers have argued that the larger black hole might have formed from a hypothetical boson star known as a Proca star, but if that’s true, then GW190521 is the only evidence that Proca stars exist. More likely, the 85 solar mass black hole formed from the merger of two smaller black holes, making GW190521 a staged merger. The difficulty with that idea is that black hole mergers are often asymmetrical, in a way that the resulting black hole is kicked out of its region of origin. Multiple black hole mergers would only occur under certain circumstances, which is where a new study in The Astrophysical Journal comes in.

The authors looked at how the mass, spin, and motion of a merging black hole pair determine the mass, spin, and recoil velocity of the resulting black hole. By creating a statistical distribution of outcomes, the team could then work backwards. Given the mass, spin, and velocity of a “forbidden” black hole relative to its environment, what were the properties of its black hole ancestors? When the authors applied this to the progenitors of GW190521, they found that the only possible ancestors would have given a relatively large recoil velocity. This means that the merger must have occurred within the region of an active galactic nucleus, where the gravitational well would be strong enough to hold the system together.

This work has implications for what are known as intermediate mass black holes (IMBHs), which can have masses of hundreds or thousands of Suns. It has been thought that IMBHs form within globular clusters, but if the recoil velocities of black hole mergers are large, this would be unlikely. As this study shows, GW190521 could not have occurred in a globular cluster.

Reference: Araújo-Álvarez, Carlos, et al. “Kicking Time Back in Black Hole Mergers: Ancestral Masses, Spins, Birth Recoils, and Hierarchical-formation Viability of GW190521.” The Astrophysical Journal 977.2 (2024): 220.

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Telling time in space is difficult, but it is absolutely critical for applications ranging from testing relativity to navigating down the road. Atomic clocks, such as those used on the Global Navigation Satellite System network, are accurate, but only up to a point. Moving to even more precise navigation tools would require even more accurate clocks. There are several solutions at various stages of technical development, and one from Germany’s DLR, COMPASSO, plans to prove quantum optical clocks in space as a potential successor.

There are several problems with existing atomic clocks – one has to do with their accuracy, and one has to do with their size, weight, and power (SWaP) requirements. Current atomic clocks used in the GNSS are relatively compact, coming in at around .5 kg and 125 x 100 x 40 mm, but they lack accuracy. In the highly accurate clock world terminology, they have a “stability” of 10e-9 over 10,000 seconds. That sounds absurdly accurate, but it is not good enough for a more precise GNSS.

Alternatives, such as atomic lattice clocks, are more accurate, down to 10e-18 stability for 10,000. However, they can measure .5 x .5 x .5m and weigh hundreds of kilograms. Given satellite space and weight constraints, those are way too large to be adopted as a basis for satellite timekeeping.

Rendering of a passive hydrogen maser atomic clock.

To find a middle ground, ESA has developed a technology development roadmap focusing on improving clock stability while keeping it small enough to fit on a satellite. One such example of a technology on the roadmap is a cesium-based clock cooled by lasers and combined with a hydrogen-based maser, a microwave laser. NASA is not missing out on the fun either, with its work on a mercury ion clock that has already been orbitally tested for a year.

COMPASSO hopes to surpass them all. Three key technologies enable the mission: two iodine frequency references, a “frequency comb,” and a “laser communication and ranging terminal.” Ideally, the mission will be launched to the ISS, where it will sit in space for two years, constantly keeping time. The accuracy of those measurements will be compared to alternatives over that time frame. 

Lasers are the key to the whole system. The iodine frequency references display the very distinct absorption lines of molecular iodine, which can be used as a frequency reference for the frequency comb, a specialized laser whose output spectrum looks like it has comb teeth at specific frequencies. Those frequencies can be tuned to the frequency of the iodine reference, allowing for the correction of any drift in the comb. 

engineerguy explains how atomic clocks work with the GNSS.
Credit – engineerguy YouTube Channel

The comb then provides a method for phase locking for a microwave oscillator, a key part of a standard atomic clock. Overall, this means that the stability of the iodine frequency reference is transferred to the frequency comb, which is then again transferred to the microwave oscillator and, therefore, the atomic clock. In COMPASSO’s case, the laser communication terminal is used to transmit frequency and timing information back to a ground station while it is active.

COMPASSO was initially begun in 2021, and a paper describing its details and some breadboarding prototypes were released this year. It will hop on a ride to the ISS in 2025 to start its mission to make the world a more accurately timed place—and maybe improve our navigation abilities as well.

Learn More:
Kuschewski et al – COMPASSO mission and its iodine clock: outline of the clock design
UT – Atomic Clocks Separated by Just a few Centimetres Measure Different Rates of Time. Just as Einstein Predicted
UT – Deep Space Atomic Clocks Will Help Spacecraft Answer, with Incredible Precision, if They’re There Yet
UT – A New Atomic Clock has been Built that Would be off by Less than a Second Since the Big Bang

Lead Image:
Benchtop prototype of part of the COMPASSO system.
Credit – Kuschewski et al

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Binary stars are common throughout the galaxy. Roughly half the stars in the Milky Way are part of a binary or multiple system, so we would expect to find them almost everywhere. However, one place we wouldn’t expect to find a binary is at the center of the galaxy, close to the supermassive black hole Sagittarius A*. And yet, that is precisely where astronomers have recently found one.

There are several stars near Sagittarius A*. For decades, we have watched as they orbit the great gravitational well. The motion of those stars was the first strong evidence that Sag A* was indeed a black hole. At least one star orbits so closely that we can see it redshift as it reaches peribothron.

But we also know that stars should be ever wary of straying too close to the black hole. The closer a star gets to the event horizon of a black hole, the stronger the tidal forces on the star become. There is a point where the tidal forces are so strong a star is ripped apart. We have observed several of these tidal disruption events (TDEs), so we know the threat is very real.

Tidal forces also pose a threat to binary stars. It wouldn’t take much for the tidal pull of a black hole to disrupt binary orbits, causing the stars to separate forever. Tidal forces would also tend to disrupt the formation of binary stars in favor of larger single stars. Therefore astronomers assumed the formation of binary stars near Sagittarius A* wasn’t likely, and even if a binary formed, it wouldn’t last long on cosmic timescales. So astronomers were surprised when they found the binary system known as D9.

Distance and age of D9 in the context of basic dynamical processes and stellar populations in the Galactic center. Credit: Peißker et al

The D9 system is young, only about 3 million years old. It consists of one star of about 3 solar masses and the other with a mass about 75% that of the Sun. The orbit of the system puts it within 6,000 AU of Sag A* at its closest approach, which is surprisingly close. Simulations of the D9 system estimate that in about a million years, the black hole’s gravitational influence will cause the two stars to merge into a single star. But even this short lifetime is unexpected, and it shows that the region near a supermassive black hole is much less destructive than we thought.

It’s also pretty amazing that the system was discovered at all. The center of our galaxy is shrouded in gas and dust, meaning that we can’t observe the area in the visible spectrum. We can only see stars in the region with radio and infrared light. The binary stars are too close together for us to identify them individually, so the team used data from the Enhanced Resolution Imager and Spectrograph (ERIS) on the ESO’s Very Large Telescope, as well as archive data from the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI). This gave the team data covering a 15-year timespan, which was enough to watch the light of D9 redshift and blueshift as the stars orbit each other every 372 days.

Now that we know the binary system D9 exists, astronomers can look for other binary stars. This could help us solve the mystery of how such systems can form so close to the gravitational beast at the heart of our galaxy.

Reference: Peißker, Florian, et al. “A binary system in the S cluster close to the supermassive black hole Sagittarius A.” Nature Communications 15.1 (2024): 10608.

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