Exoplanets have captured the imagination of public and scientists alike and, as the search continues for more, researchers have turned their attention to the evolution of metallicity in the Milky Way. With this answer comes more of an idea about where planets are likely to form in our Galaxy. They have found that stars with high-mass planets have higher metallicity than those with lower amounts of metals. They also found that stars with planets tend to be younger than stars without planets. This suggests planetary formation follows the evolution of a galaxy with a ring of planet formation moving outward over time.
The search for exoplanets has largely been one of surveying nearby stars. That generally means we are exploring stars in our region of the Galaxy. As technology develops, our ability to detect them improves and to date, nearly 6,000 planets have been discovered around other stars. A number of different techniques have been used to find them such as the transit method – which detects the dimming of a star’s light due to the presence of the passage of a planet, or the radial velocity method which measures the wobble of a star due to the gravitational tug of a planet.
This artist’s impression depicts the exomoon candidate Kepler-1625b-i, the planet it is orbiting and the star in the centre of the star system. Kepler-1625b-i is the first exomoon candidate and, if confirmed, the first moon to be found outside the Solar System. Like many exoplanets, Kepler-1625b-i was discovered using the transit method. Exomoons are difficult to find because they are smaller than their companion planets, so their transit signal is weak, and their position in the system changes with each transit because of their orbit. This requires extensive modelling and data analysis.One key aspect of planetary development in the Galaxy is the presence of metals (elements heavier than hydrogen and helium.) known as metallicity. These elements are formed during the life cycle of a star, especially during supernova explosions. They are scattered through space and form part of the interstellar medium. Understanding the abundance and distribution of metals provides an insight into the age, history and formation rates of stars and planets.
The Milky Way. This image is constructed from data from the ESA’s Gaia mission that’s mapping over one billion of the galaxy’s stars. Image Credit: ESA/Gaia/DPACA team of researchers led by Joana Teixeira from the University of Porto in Portugal have been exploring something known as the Galactic Birth Radii (rBirth) This term relates to the distance from galactic centre that stars and therefore planets are forming. Using photometric, spectroscopic and astrometric data, the team were able to estimate the ages of two groups of stars, those with planets and those without. This enabled them to rBirth for exoplanets based upon the original star positions (having calculated them from their age and levels of metals present within.)
The results of the analysis showed that stars hosting planets had a higher [Fe/H], are younger and were born closer to the centre of the galaxy than those without (Fe/H refers to the amount of iron relative to the amount of hydrogen in a star or galaxy, where the Sun is [Fe/H]=0.3.) The team went further to state that from one data set (from the Stellar Parameters of Stars with Exoplanets Catalog,) the results suggest that stars hosting high mass planets have a different iron to hydrogen radio and age distribution than stars with at least one low mass planet and those with only low mass planets.
The ESA/NASA Solar Orbiter has given us our highest resolution images of the Sun ever. They show us sunspots, plasma, and magnetic fields, and more. Image Credit: ESAThe research reveals that high mass planets or in other words terrestrial planets tend to form around stars with higher [Fe/H] and younger stars compared to low mass. Similarly, those with a mixture of high and low mass planets also formed around higher [Fe/H], young stars.
It’s an interesting study worthy of further investigations. Understanding that Earth-like planets tend to form around star systems that formed around the inner regions of the Galaxy. Here the supply of metals is more abundant and, even though the stellar systems can migrate to outer regions of the Milky Way it gives a better focus on the hunt for planetary systems beyond our own.
Source : Where in the Milky Way Do Exoplanets Preferentially Form?
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Just as important as the question of how much the livestock industry contributes to global warming is whether your giving up meat will have any real impact.
Learn about your ad choices: dovetail.prx.org/ad-choicesAstronomers have found two planets around two separate stars that are succumbing to their stars’ intense heat. Both are disintegrating before our telescopic eyes, leaving trails of debris similar to a comet’s. Both are ultra-short-period planets (USPs) that orbit their stars rapidly.
These planets are a rare sub-class of USPs that are not massive enough to hold onto their material. Astronomers know of only three other disintegrating planets.
USPs are known for their extremely rapid orbits, some completing an orbit in only a few hours. Since they’re extremely close to their stars, they’re subjected to intense heat, stellar radiation, and gravity. Many USPs are tidally locked to their star, turning the star-facing side into an inferno. USPs seldom exceed two Earth radii, and astronomers think that about 1 in 200 Sun-like stars has one. They were only discovered recently and are pushing the boundaries of our understanding of planetary systems.
There are plenty of unanswered questions about USPs. Their formation mechanism is unclear, though they likely migrated to their positions rather than formed there. They’re difficult to observe because of their proximity to their stars, making questions about their structures difficult to answer.
Fortunately, two separate teams of researchers have spotted the two disintegrating USPs. As they spill their contents out into space in tails, they’re giving astronomers an opportunity to see what’s inside them.
The new observations are in two new papers available at the pre-press site arxiv.org. One is “A Disintegrating Rocky Planet with Prominent Comet-like Tails Around a Bright Star.” The lead author is Marc Hon, a postdoctoral researcher at the MIT TESS Science Office. This paper is referred to hereafter as the MIT study.
“We report the discovery of BD+054868Ab, a transiting exoplanet orbiting a bright K-dwarf with a period of 1.27 days,” the authors write. The TESS spacecraft found the planet, and its observations “reveal variable transit depths and asymmetric transit profiles,” the paper states. Those are characteristics of dust coming from the doomed planet and forming tails: one on the leading edge and one on the trailing edge. Dust particle size in each tail is different, with the leading trail containing larger dust and the trailing tail containing finer grains.
This figure from the team’s modelling illustrates some of their findings. “A view from above the planetary orbit, looking down at the x ? y plane in which the planet is orbiting counterclockwise. The trails indicate the accumulated trajectories of the dust grains over time. There are two distinct trails that correspond to the leading and trailing dust tails,” the authors explain. The planet is not to scale in this image, but the host star is. Image Credit: Hon et al. 2025.“The rate at which the planet is evaporating is utterly cataclysmic, and we are incredibly lucky to be witnessing the final hours of this dying planet’,'”
Marc Hon, MIT TESS Science Office“The disintegrating planet orbiting BD+05 4868 A has the most prominent dust tails to date, “said lead author Hon. “The dust tails emanating from the rapidly evaporating planet are gigantic. Its length of approximately 9 million km encircles over half the planet’s orbit around the star every 30 and a half hours,” he added.
The MIT study shows that the planet is losing mass at the rate of 10 Earth masses of material per billion years. Since the object is probably only roughly the size of Earth’s Moon, it will be totally destroyed in only a few million years. “The rate at which the planet is evaporating is utterly cataclysmic, and we are incredibly lucky to be witnessing the final hours of this dying planet,” said Hon.
The host star is probably a little older than the Sun and has a companion red dwarf separated by about 130 AU. The authors think that the planet is a great candidate for follow-up studies with the JWST. Not only is the star bright, but the transits are deep. Because of the leading and trailing tails, the transits can last up to 15 hours.
The Las Cumbres Observatory captured this image of the two stars. The main sequence star is on the right, and its red dwarf companion is on the left. Image Credit: LCO/Hon et al. 2025.“The brightness of the host star, combined with the planet’s relatively deep transits (0.8?2.0%), presents BD+054868Ab as a prime target for compositional studies of rocky exoplanets and investigations into the nature of catastrophically evaporating planets,” they explain.
“What’s also highly exciting about BD+05 4868 Ab is that it has the brightest host star out of the other disintegrating planets —about 100 times brighter than K2-22—establishing it as a benchmark for future disintegrating studies of such systems,” said Avi Shporer, a Research Scientist at the MIT Kavli Institute for Astrophysics and Space Research and a co-author of the MIT paper. “Prior to our study, the three other known disintegrating planets were around faint stars, making them challenging to study,” he added.
The second paper is “A Disintegrating Rocky World Shrouded in Dust and Gas: Mid-IR Observations of K2-22b using JWST.” The lead author is Nick Tusay, a PhD student at Penn State working in the Center for Exoplanets and Habitable Worlds. This paper is hereafter referred to as the Penn State study.
“The effluents that sublimate off the surface and condense out in space are probably representative of the formerly interior layers convectively transported to the molten surface,” the authors write. In this work, astronomers were able to observe its debris with the JWST’s MIRI and also with other telescopes. The observations show that the material coming from the USP is not likely to be iron-dominated core material. Instead, they’re “consistent with some form of magnesium silicate minerals, likely from mantle material,” the authors explain.
“These planets are literally spilling their guts into space for us, and with JWST we finally have the means to study their composition and see what planets orbiting other stars are really made of,” said lead author Tusay.
We can’t see what’s inside the planets in our Solar System, though seismic waves and other observations give scientists a pretty good idea about Earth’s interior. By examining the entrails coming from K2-22b, astronomers are learning not only about the planet but, by extension, about other rocky planets. The irony is that they’re so far away.
“K2-22b has an asymmetric transit profile, as the planet’s dusty cloud of effluents comes into view in front of the star, showing evidence of extended tails like a comet.”
“It’s a remarkable and fortuitous opportunity to
understand terrestrial planet interiors.”
“It’s remarkable that directly measuring the interior of planets in the Solar System is so challenging—we have only limited sampling of the Earth’s mantle, and no access to that of Mercury, Venus, or Mars—but here we have found planets hundreds of light years away that are sending their interiors into space and backlighting them for us to study with our spectrographs,” said Jason Wright, Professor of Astronomy and Astrophysics, co-author of the Penn State study, and Tusay’s PhD supervisor. “It’s a remarkable and fortuitous opportunity to understand terrestrial planet interiors,” he added.
While TESS discovered the disintegrating planet in the previous paper, Kepler found this one during its extended K2 mission. This one orbits its M-dwarf star in only 9.1 hours. Evidence of its tail is in the variability of its light curve. “The dramatic variability in lightcurve transit depth (0–1.3%) combined with the asymmetric transit shape suggests we are observing a transient cloud of dust sublimating off the surface of an otherwise unseen planet,” the MIT paper states.
As this figure from the research shows, each of K2-22b’s transits lasts about 46 minutes. Each blue point represents 8 minutes. Image Credit: Tusay et al. 2025.According to the authors, this could be the first time we’ve seen outgassing from a vaporizing planet. “The shorter MIRI wavelength features … may constitute the first direct observations of gas features from an evaporating planet,” the paper states.
“Unexpectedly, the models that best fit these measurements seem to be ice-derived species (NO and CO2),” the authors write. Though the spectrum is broadly consistent with a rocky body, the presence of NO and CO2 is a bit of a curveball. These materials are more similar to icy bodies like comets rather than rocky planets.
“It was actually sort of a ‘who-ordered-that?’ moment,” Tusay said about finding the icy features. For this reason, the researchers are eager to point the JWST at the planet again to obtain more and better data. Multiple pathways can generate these results, and only better data can help astronomers determine what’s going on.
According to the authors, the wavelength features in the spectrum “may constitute the first direct observations of gas features from an evaporating planet.” Rather unexpectedly, the results indicate ice-derived chemical species. Image Credit: Tusay et al. 2025.Though we’re in the early days of observing planets like this one, scientists still have some expectations. These results defy those expectations since many expected to find only the iron-core remnants of these USPs.
“We didn’t know what to expect,” said Wright, who also co-authored an earlier study on how to use JWST to probe these exoplanetary tails. “We were hopeful they might still have their mantles, or potentially even crust material that was being evaporated. JWST’s mid-infrared spectrograph MIRI was the perfect tool to check, because crustal, silicate mantle, and iron core materials would all transmit light in different ways that JWST could distinguish spectroscopically,” Wright added.
Next, both teams of scientists hope to point the JWST at BD+05 4868 Ab from the MIT study. Its star is far brighter than the other stars known to host disintegrating USPs. A bright light source makes it much easier for the JWST to get stronger results.
“What’s also highly exciting about BD+05 4868 Ab is that it has the brightest host star out of the other disintegrating planets —about 100 times brighter than K2-22—establishing it as a benchmark for future disintegrating studies of such systems,” said Avi Shporer, a Research Scientist at the MIT Kavli Institute for Astrophysics and Space Research and a co-author of the MIT project. “Prior to our study, the three other known disintegrating planets were around faint stars, making them challenging to study,” he added.
When the JWST was launched, it wasn’t aimed at observing disintegrating exoplanets. But this research shows off a new way of using the powerful telescope. Surprises like this are a part of every new telescope or observing effort, and researchers often look forward to them.
“The data quality we should get from BD+05 4868 A will be exquisite,” said Shporer. “These studies have proven the validity of this approach to understanding exoplanetary interiors and opened the door to a whole new line of research with JWST.”
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Exoplanet exploration has taken off in recent years, with over 5500 being discovered so far. Some have even been in the habitable zones of their stars. Imaging one such potentially habitable exoplanet is the dream of many exoplanet hunters, however, technology has limited their ability to do that. In particular, one specific piece of technology needs to be improved before we can directly image an exoplanet in the habitable zone of another star – a starshade. Christine Gregg, a researcher at NASA Ames Research Center, hopes to contribute to the effort of developing one and has received a NASA Institute for Advanced Concepts (NIAC) grant as part of the 2025 cohort to work on a star shade that is based on a special type of metamaterial.
To understand the goal of Dr. Gregg and her team, it’s best first to understand what starshades do and what’s holding them back from being deployed. A starshade is designed to float in tandem with a space telescope and block out the light from a specific star, allowing the telescope to capture light directly from the much-less bright planet that is orbiting the star. That light can contain information about its size, orbital period, and even its atmospheric composition that would otherwise be lost in the overwhelming brightness of the planet’s star.
The shape of a starshade, which traditionally looks like a flower petal, might seem counterintuitive at first – if you’re trying to block a star’s light, why not just make the shape circular? But starlight coming from far away can diffract around a simple circle structure. The petals are explicitly designed to stop that from happening and completely block out even diffracted light around the shape’s edges.
Fraser interviews another Starshade expert – Dr. Markus Janson from Stockholm UniversityBut it’s not the shape that makes it hard to deploy—it’s its size. Starshades are typically designed to be hundreds of meters across. Therefore, they are impossible to fit inside a traditional rocket fairing fully assembled. What’s more, they have to move along with the telescope—if the telescope the starshade is meant to accompany is pointed at another star and redirected, the starshade has to move with it.
The wrinkle is that the starshade is likely tens of thousands of kilometers from the telescope it is designed to assist. So, a slight change of a few degrees of inclination for the telescope would mean hundreds of thousands of kilometers of travel for its associated starshade. That kind of movement requires a lot of fuel, which is also costly due to the weight requirements of launching these objects so far away.
No wonder a starshade has yet to be successfully deployed in space. Combining gigantic sizes that don’t fit inside rocket fairings and massive amounts of fuel to relocate every time the telescope needs to look at a different star are significant strikes against the concept. However, if humanity wants to directly image an exoplanet in the habitable zone of another star, there is still no better way to do so.
NASA animation of the deployment of a starshadeEnter Dr Gregg’s idea—she proposes using metamaterials for her starshade, which is robotically constructed in orbit. Metamaterials have several advantages over existing proposed starshades (one of which, by Nobel Prize winner John Mather, is another NIAC recipient this year).
First, metamaterials are lighter. As with all things launched into space, being lighter means less cost – or, in this case, the ability to bring more fuel, allowing the starshade to operate longer than alternatives.
Second, the specific kinds of metamaterials she proposes to use are much less likely to break. As she mentioned to Fraser in an interview, “The more stiffness a material has, the less damping it has. It’s just sort of a natural trade-off”. So, if a starshade is made from traditional materials, it would either be stiff and rigid but prone to vibrational strain when moving between positions or being deployed, or it would be very flexible but would have difficulty holding its shape when it’s supposed to.
This video shows phononic materials in action.The metamaterial Dr. Gregg and her colleagues have proposed uses a type of material that both holds its structure well but also suppresses vibration by a unique use of a material called a phononic crystal. These were initially engineered to dissipate sound waves. This means that when used as a material in a starshade, it could dampen any feedback on the structure from things like micrometeoroid impacts, solar radiation, or even the process of deployment and assembly.
Using robots to deploy the starshade is another focal point of Dr. Gregg’s work, as she discusses with Fraser. Still, for this Phase I NIAC project, she is focusing on developing the model for starshade itself and selecting the appropriate material. As with all NIAC projects, she can apply for more funding in a Phase II round upon completion of her Phase I. If she receives it, humanity will be one step closer to seeing a giant floating petal in space – but one with very particular mechanical and structural properties.
Learn More:
NASA / C. Gregg – Dynamically Stable Large Space Structures via Architected Metamaterials
UT – In Order to Reveal Planets Around Another star, a Starshade Needs to Fly 40,000 km Away from a Telescope, Aligned Within Only 1 Meter
UT – Starshade Prepares To Image New Earths
UT – To Take the Best Direct Images of Exoplanets With Space Telescopes, we’re Going to Want Starshades
Lead Image:
Artist concept highlighting the novel approach proposed by the 2025 NIAC awarded selection of the Dynamically Stable Large Space Structures via Architected Metamaterials concept. NASA/Christine Gregg
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Star formation in the early Universe was a vigorous process that created gigantic stars. Called Population 3 stars, these giants were massive, extremely luminous stars, that lived short lives, many of which were ended when they exploded as primordial supernovae.
But even these early stars faced growth limitations.
Stellar feedback plays a role in modern star formation. As young stars grow, they emit powerful radiation that can disperse nearby gas they need to keep growing. This is called protostellar radiative feedback, and it takes place in addition to the restrictive effect their magnetic fields have on their growth.
However, new research shows that the growth of Pop 3 stars was limited by their magnetic fields.
The research is titled “Magnetic fields limit the mass of Population III stars even before the onset of protostellar radiation feedback.” The lead author is Piyush Sharda, an astrophysicist at the Leiden Observatory in the Netherlands. It’s available on the pre-print server arxiv.org.
Scientists observe stars forming in the modern Universe to understand how the process plays out. This is difficult because stars take so much time to form, while we’ve only been watching young stars from a great distance for a few decades. Stars are massive, energetic, complex objects that don’t give up their secrets easily.
There are many unanswered questions about star formation, but a general picture has emerged. It starts with a cloud of cold molecular hydrogen that collapses into dense cores. These cories become protostars, also called young stellar objects (YSOs). Accretion disks form around the young stars, and this is where radiative feedback comes in.
This artist’s concept shows a young stellar object and the whirling accretion disk surrounding it. NASA/JPL-CaltechAs young stars accrete mass, they heat up. They radiate this heat outward into their own accretion disks. As the material in the disk heats, it slows or even stops the accretion process. So radiative feedback limits their growth.
YSOs also rotate more rapidly than more mature stars. The rotation creates powerful magnetic fields, and these fields drive jets from the YSO’s poles. These jets steal away some of the accretion energy, limiting the stars’ growth. The jets can also disperse some of the surrounding gas, further limiting their growth.
However, the picture may look different for Pop 3 stars. To begin with, their existence is hypothetical at this point in time, though theory supports it. If they’re real, astrophysicists want to know how they formed and what their growth limits were. If they’re real, Pop 3 stars played a critical role in the Universe by forging the first metals and spreading them out into space.
According to the authors of the new research, simulations haven’t been thorough enough to explain the masses of Population 3 stars.
“The masses of Population III stars are largely unconstrained since no simulations exist that take all relevant primordial star formation physics into account,” the authors write. “We evolve the simulations until 5000 years post the formation of the first star.”
In the team’s more thorough simulations, which include magnetic fields and other factors, these early stars are limited to about 65 solar masses. “In 5000 yrs, the mass of the most massive star is 65 solar masses in the RMHD <radiation magnetohydrodynamics> simulation, compared to 120 solar masses in simulations without magnetic fields,” they write.
This figure from the research shows a panel from each type of simulation: HD (hydrodynamic), MHD (magneto-hydrodynamic), RHD (radiation-hydrodynamics including ionizing and dissociating radiation feedback), RMHD (radiation-magnetohydrodynamics). They show each simulation at 5,000 years after the first star forms. White dots show the positions of Population 3 stars. Image Credit: Sharda et al. 2025The results show that both simulation runs that included magnetic fields are fragmented, leading to the formation of Pop 3 star clusters. That means that the evolution of the most massive Pop 3 stars in both runs is influenced by the presence of companion stars.
The difference comes down to gravity and magnetic fields working against each other. As young stars accrete mass, their gravitational power increases. This should draw more material into the star. But magnetic fields counteract the gravity. This all happens before radiative feedback is active.
The results also show that in both simulations that include magnetic fields, the amount of mass that reaches the envelope initially increases, then declines. However, the results were different in the simulations without magnetic fields. In those simulations, mass transfer from the envelope to the accretion disk is fast at first, creating a decline in the mass in the envelope and a build-up of mass in the disk. “This mass is consequently accreted by the star at a high rate,” the authors write.
This figure from the research illustrates some of the simulation results. It shows the mass enclosed within a disk of radius 500 au and height 50 au (from the midplane) around the most massive star. “The mass reservoir that can be accreted onto the central star in the MHD and RMHD runs eventually decreases as magnetic fields suppress gravitational collapse,” the authors explain.“We learn that magnetic fields limit the amount of gas infalling onto the envelope at later stages by acting against gravity, leading to mass depletion within the accretion disk,” the authors explain. “The maximum stellar mass of Population III stars is thus already limited by magnetic fields, even before accretion rates drop to allow significant protostellar radiative feedback.”
Though Population 3 stars are only hypothetical, our theories of physical cosmology rely on their existence. If they didn’t exist, then there’s something fundamental about the Universe that is beyond our grasp. However, our cosmological theories do a good job of explaining what we see around us in the Universe today. If we’re putting money on it, place your bets on Pop 3 stars being real.
“Radiation feedback has long been proposed as the primary mechanism that halts the growth of Pop III stars and sets the upper mass cutoff of the Pop III IMF (initial mass function),” the authors write in their conclusion. They show that magnetic fields can limit stellar growth before feedback mechanisms come into play.
“This work lays the first step in building a full physics-informed mass function of Population III stars,” the authors conclude.
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I’m feeling grotty today, probably because of dysthymia compounded by lack of sleep. I hope to be okay tomorrow, but in the meantime we have show and tell. The show and tell today involves the Alpine Ibex (Capra ibex), the subject of a nice seven-minute video. It concentrates on their remarkable ability to climb on ledges that look unclimbable, something the many goat species can do as well. The videos mentions that young goats must “overcome their fear,” but I wonder if they really feel fear.
Note the morphological traits that have evolved in concert with this behavior, including body shape. Surely the ability to climb (a behavioral trait) preceded the evolution of things like those split hooves with soft pads, supporting Ernst Mayr’s claim that many key adaptations begin not as changes in morphology, but changes in behavior that give a premium to later morphological evolution. I just opened a book that was perhaps the most influential volume of my career, Mayr’s 1963 Animal Species and Evolution. I found this sentence on p. 604:
“A shift into a new niche or adaptive zone is, almost without exception, initiated by a change in behavior.”
Mayr was a smart guy, and was probably right. The important question, though, is, though, “do those changes in behavior have a genetic basis“? It’s hard to see, for example, how a goat with a greater propensity to climb, but not one based on genetic differences from other individuals, could possibly kick off a bout of evolutionary change, for there would be no increase of climbing behavior unless it came with an adaptive advantage that could be passed on via genes. If the first climbers did have genetic differences from non-climbers, and climbing resulted in more of your genes being passed on, you would get an increase in the behavior over time since it conferred a reproductive advantage. (This didn’t start with some individuals climbing sheer cliffs, of course!). After that, any mutations changing the hoof or body shape would be subject to natural selection. In this case, simple behavioral variation not based on genes wouldn’t, I think, kick off behaviors and morphologies like those shown below.
I can think of one exception: the famous case of cultural evolution of milk-drinking in British birds, first noted by Fisher and Hinde in 1949 (they studied blue and great tits). This was apparently a case of cultural evolution, which started with one or a few individuals prying the tops off milk bottles left on doorsteps and drinking the cream. This spread rapidly throughout the UK, so rapidly that it must have been a spread via imitation—that is, cultural evolution, not genetic evolution. Of course that would be followed by natural selection leading to things like prying the caps off better (beak changes?), locating milk bottles more readily, and digesting the milk. I don’t think anybody has studied any subsequent evolution in the birds (for one thing, milk isn’t delivered on doorsteps any more!); but this is one case in which a potential change in an “adaptive zone”—however you describe it—began with a simple behavioral change not based on genetic differences.
Sorry, I was just thinking on paper. Watch the video, which is amazing and instructive: