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The Hubble Deep Field and its successor, the Hubble Ultra-Deep Field, showed us how vast our Universe is and how it teems with galaxies of all shapes and sizes. They focused on tiny patches of the sky that appeared to be empty and revealed the presence of countless galaxies. Now, astronomers are using the Hubble Ultra-Deep Field and follow-up images to reveal the presence of a large number of supermassive black holes in the early Universe.

This is a shocking result because, according to theory, these massive objects shouldn’t have been so plentiful billions of years ago.

The Hubble Ultra-Deep Field (HUDF) was released in 2004 and required almost one million seconds of exposure over 400 of the telescope’s orbits. Over the years, the same region has been imaged with other wavelengths and been updated and refined in other ways.

The Hubble has re-imaged the region multiple times, and astronomers have compared the new images to older images and identified more SMBHs from the Universe’s early times.

The results are in a paper titled “Glimmers in the Cosmic Dawn: A Census of the Youngest Supermassive Black Holes by Photometric Variability, ” which was published in The Astrophysical Journal Letters. Matthew Hayes, an associate professor in the Department of Astronomy at Stockholm University, Sweden, is the lead author.

Supermassive Black Holes (SMBHs) sit in the center of large galaxies like ours. While the hole itself isn’t visible, material being drawn into the hole collects in an accretion disk. As that material heats, it gives off light as an active galactic nucleus (AGN). Since black holes feed sporadically, only a portion of them were visible in the original HUDF. By re-imaging the same field at different times, the Hubble captured additional SMBHs that weren’t originally visible.

Our understanding of the ancient Universe and how it and its galaxies evolved depends on several factors. One of them is the requirement for an accurate idea of the number of AGN. AGN can be difficult to spot, and this method overcomes some of the obstacles.

AGN can emit X-ray, radio, and other emissions, but they don’t always stand out. “The challenge to this field comes from the fact that identifying AGN at the luminosity regimes of typical galaxies is observationally difficult,” the authors write. “This leads to SMBHs probably being undercounted, with potentially large numbers going unnoticed among the ostensibly star-forming galaxy population at high-z.”

The authors’ photometric variability method circumvents that. Since AGN accrete material at variable rates, observing changes in output from AGN is a better method of determining how many there are. “Here, we argue that the photometric variability that results from changes in the mass accretion rate of SMBHs can provide a completely independent and complementary probe of AGN,” Hayes and his co-authors write. “Monitoring for variability selects AGN from imaging data directly by phenomena related to the SMBH, without any biases of photometric preselection (color, luminosity, compactness, etc).”

This figure from the research article shows how effective photometric variability can be at detecting SMBH. It shows the photometric variability of two objects found in the field: 1051264 at z = 2 (upper panels) and 1052126 at z = 3.2. Image Credit: Hayes et al. 2024.

The new paper presents preliminary results and reports the detection of eight interesting targets that display variability. Three of the eight are probably supernovae, two are clear AGN at about z = 2–3, and three more are likely AGN at redshifts greater than 6.

These findings are significant because they impact our understanding of black holes, how they form, and their place in the history of the Universe.

Astronomers understand how stellar-mass black holes form. They also believe that supermassive black holes grow so massive through mergers with other black holes. They’re even making progress in finding the in-between black holes called intermediate-mass black holes (IMBHs).

Since astronomers think that SMBHs grow through mergers, there should be more of them in the modern Universe and comparatively few, if any, in the ancient Universe. There simply hadn’t been enough time for enough mergers to take place to create SMBHs. That’s why there are alternate theories to explain black holes in the early Universe.

Astronomers theorize that a different type of star existed in the early universe. These massive, pristine stars could only form in the conditions that dominated the early Universe. They could’ve collapsed and become massive black holes.

Another theory suggests that massive gas clouds in the early Universe could have collapsed directly into black holes. Yet another theory suggests that so-called ‘primordial black holes’ could have formed in the first seconds after the Big Bang through purely speculative mechanisms.

The Hubble Ultra Deep Field with annotation showing the location of a supermassive black hole. Image Credit: Hayes et al. 2024.

The new observations should help clarify some of these ideas.

“The formation mechanism of early black holes is an important part of the puzzle of galaxy evolution,” said study lead author Hayes. “Together with models for how black holes grow, galaxy evolution calculations can now be placed on a more physically motivated footing, with an accurate scheme for how black holes came into existence from collapsing massive stars.”

“These sources provide a first measure of nSMBH in the reionization epoch by photometric variability,” the authors explain in their paper. They say the sources identified in their work indicate the largest black hole population ever reported for these redshifts. “This SMBH abundance is also strikingly similar to estimates of nSMBH in the local Universe,” the authors write.

Some theoretical models suggest that there were large numbers of AGN in the reionization epoch. The JWST shows us that there seem to be more SMBHs and AGN than astronomers thought. By finding more SMBHs and AGN, this research is adding to our understanding of black holes and the evolution of the Universe.

But there’s still more work to be done. The researchers think that a larger sample of AGN at high redshifts is needed to reduce uncertainties and strengthen their results, and the JWST can help. “JWST is required to push to detection of fainter AGN via variability,” the authors explain, adding that it would take years of monitoring for the space telescope to do so.

This work also underlines the HST’s ongoing contribution to astronomy. It may not be as powerful as the JWST, but it has the benefit of many years of observations already under its belt and keeps proving its worth as a powerful observatory in its own right.

“In contrast, HST’s legacy of deep NIR imaging already stretches back about 15 yr, providing an excellent baseline for monitoring.”

The post The Early Universe Had a Lot of Black Holes appeared first on Universe Today.

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If you are going to look for intelligent life beyond Earth, there are few better candidates than the TRAPPIST-1 star system. It isn’t a perfect choice. Red dwarf stars like TRAPPIST-1 are notorious for emitting flares and hard X-rays in their youth, but the system is just 40 light-years away and has seven Earth-sized worlds. Three of them are in the potentially habitable zone of the star. They are clustered closely enough to experience tidal forces and thus be geologically active. If intelligent life arises easily in the cosmos, then there’s a good chance it exists in the TRAPPIST-1 system.

But finding evidence of intelligent life on a distant planet is difficult. Unless Mr. Mxyzptlk or the Great Gazoo want to talk about your car’s extended car warranty, any signal we detect will likely be subtle, similar to the stray radio signals we emit from Earth. So the challenge is to distinguish actual signals from aliens, known as technosignatures, from the naturally occuring emissions of stars and planets. Recently a team used the Allen Telescope Array to capture 28 hours of TRAPPIST-1 signals in an effort to find the elusive aliens.

The study began with a few assumptions. The biggest one was to presume that if TRAPPIST-1 has an intelligent civilization it is likely spread across more than one world. Given how compact the system is, that isn’t too outlandish. Getting from one world to another wouldn’t be much more difficult than it is for us to get to the Moon. With that assumption, the team then assumed that the worlds would transmit radio messages between each other. Since the signals would need to transverse interplanetary distances, they would be the strongest and most clear technosignatures in the system. So the team focused on signals during a planet-planet occultation (PPO). That is when two planets line up from our vantage point. During a PPO any signal sent from the far planet to the closer planet would spill over and eventually reach us.

Illustration of a PPO event. Credit: Tusay, et al

With 28 hours of observation data in hand, the team filtered out more than 11,000 candidate signals. Signals that were stronger than the expected range for natural signals. Then using computer models of the system they determined 7 possible PPO events and further narrowed things down to about 2,200 potential signals occurring during a PPO window. From there they went on to determine whether any of those signals were statistically unusual enough to suggest an intelligent origin. The answer to that was sadly no.

Alas, if there are aliens in the TRAPPIST-1 system, we haven’t found them yet. But the result shouldn’t minimize this study. It is the longest continuous survey of the system to date, which is pretty cool. And it’s kind of amazing that we’ve reached the point where we’re able to do this study. We are actively searching known exoplanets in detail.

Reference: Tusay, Nick, et al. “A Radio Technosignature Search of TRAPPIST-1 with the Allen Telescope Array.” arXiv preprint arXiv:2409.08313 (2024).

The post SETI Scientists Scan TRAPPIST-1 for Technosignatures appeared first on Universe Today.

Scientists at MPI-IS have developed electrically driven robotic components, called HEXEL modules, which can snap together into high-speed reconfigurable robots. Magnets embedded along the outside of the modules allow them to electrically and mechanically connect to other modules, forming robots with diverse shapes and capabilities. HEXEL modules are a promising technology for use in resource-limited environments, such as on space or rescue missions, and can be used to construct versatile robots from redundant parts, altogether promoting a sustainable robot design.

Scientists at MPI-IS have developed electrically driven robotic components, called HEXEL modules, which can snap together into high-speed reconfigurable robots. Magnets embedded along the outside of the modules allow them to electrically and mechanically connect to other modules, forming robots with diverse shapes and capabilities. HEXEL modules are a promising technology for use in resource-limited environments, such as on space or rescue missions, and can be used to construct versatile robots from redundant parts, altogether promoting a sustainable robot design.

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A set of knee exoskeletons, built with commercially available knee braces and drone motors, has been shown to help counteract fatigue in lifting and carrying tasks. They helped users maintain better lifting posture even when tired, a key factor in defending against on-the-job injuries, the researchers say.

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Astronomers have solid evidence for the existence of stellar-mass black holes and supermassive black holes. However, evidence for Intermediate Black Holes (IMBHs) is more elusive. Their existence remains hypothetical.

However, study by study, evidence is accumulating for IMBHs. The latest comes from the globular cluster M15, where a fast-moving star suggests the presence of something massive. Could it be an elusive IMBH?

IMBHs bridge the gap between stellar-mass black holes, which have up to about 100 solar masses, and supermassive black holes (SMBHs), which have millions to billions of solar masses. Though their existence still isn’t proven, many astronomers expect they’ll be found one day. Scientists think they can form in three different ways: the merger of multiple stellar-mass black holes, the direct collapse of huge gas clouds in the early Universe, or through collisions in dense stellar environments.

Globular clusters are prime locations where IMBHs could form because the stellar density is so high in their cores. In Omega Centauri, the largest Globular Cluster (GC) in the Milky Way, estimates show there may be several thousand stars per cubic parsec, an incredible density of stars. In our solar neighbourhood, the stellar density is only 0.004 stars per cubic parsec.

Several studies pointed to the existence of an IMBH in Omega Centauri, and in the summer of 2024, astronomers found more evidence with the Hubble Space Telescope.

This is Omega Centauri, the largest and brightest globular cluster that we know of in the Milky Way. An international team of astronomers used more than 500 images from the NASA/ESA Hubble Space Telescope spanning two decades to detect seven fast-moving stars in the innermost region of Omega Centauri. These stars provide compelling new evidence for the presence of an intermediate-mass black hole. Now, evidence shows that another Milky Way globular cluster, M15, may also host an IMBH. Image Credit: ESA/Hubble & NASA, M. Häberle (MPIA)

New research shows that M15, another of the Milky Way’s GCs, may also host an IMBH. It’s based on observations of a runaway high-velocity star.

The research, titled “A high-velocity star recently ejected by an intermediate-mass black hole in M15,” has been accepted for publication in the National Science Review. Yang Huang, from the School of Astronomy and Space Science, University of Chinese Academy of Sciences, is the lead author.

“The existence of intermediate-mass black holes (IMBHs) is crucial for understanding various astrophysical phenomena, yet their existence remains elusive, except for the LIGO-Virgo detection,” the authors write. They’re referring to GW190521, the most massive gravitational wave binary observed. It was in 2020 and created a black hole remnant of 142 solar masses. Some call this the first detection of an IMBH.

“We report the discovery of a high-velocity star J0731+3717, whose backward trajectory about 21 Myr ago intersects that of globular cluster M15 within the cluster tidal radius,” the researchers write. They hypothesize that gravitational interactions with an IMBH in M15 are responsible for the star’s ejection.

This figure shows the backward orbits of J0731+3717 (blue arrow) and the globular cluster M15 (magenta arrow). The black hourglass marks the position of the encounter that ejected the star 21 Myr ago. Image Credit: Huang et al. 2024.

The cluster tidal radius is the distance from the center of a GC where the GC’s gravitational influence gives way to that of the surrounding galaxy. This is strong evidence that the star may have originated in M15. However, it’s not the researchers’ only evidence; the star’s metallicity also suggests it came from M15. “Both its metallicity [Fe/H] and its alpha-to-iron abundance ratio [?/Fe] are consistent with those of M15,” Huang and his colleagues write.

The researchers compared the metallicity and alpha-to-iron abundance of M15 and the runaway star with stars from APOGEE (Apache Point Observatory Galactic Evolution Experiment). APOGEE is a large-scale spectroscopic survey of stars in the Milky Way. Its data are used to measure stellar populations, star chemistry, and the history of star formation in our galaxy, so it makes a useful comparison for M15 and the runaway star.

This figure shows the [Fe/H]–[?/Fe] for the escaped star and M15 compared to APOGEE-targeted stars. Image Credit: Huang et al. 2024.

“It is extremely unlikely for the association of J0731+3717 and M15 to be by pure chance, given the probability for random association, chemical and age similarities,” the authors explain.

This is good evidence that the runaway star originated in M15. However, metallicity can’t tell us whether an IMBH is responsible for ejecting the star. For that, the researchers looked at the star’s speed and trajectory. They started by examining known hypervelocity stars in the Milky Way.

“To discover high-velocity stars ejected from globular clusters, backward orbital integrations are carried out for 934 high-velocity (VGSR ? 400 km s?1) halo stars in the searching volume within 5 kpc from the Sun and 145 Galactic globular clusters,” the authors explain. They traced the backward trajectories of the stars and the clusters to 250 million years ago. Then, they calculated the closest distance for each pair of stars and GCs.

“Amongst the hundred thousand pairs, only J0731+3717 has the closest distance smaller than the tidal radius of M15, making it a rare candidate of cluster ejected high-velocity star,” the authors write.

There are other ways that a GC can eject a star. Interactions with other stars, a supernova explosion, interactions with a massive gas cloud, or even passing too close to the Milky Way’s galactic disk are all potential causes. But none of those fit, according to the researchers. “In summary, the above alternative ejection mechanisms are not viable to kick-off J0731+3717 from M15,” the authors conclude.

By rejecting alternative explanations for the star’s ejection, they were left with an IMBH as the only viable cause.

Like other GCs, M15 has an extremely high stellar density in its core, one of the highest of any known GCs. Astronomers think that M15 underwent a process called core collapse, which created its extremely compact center packed full of stars. M15’s core is about one million times more dense than our stellar neighbourhood. It’s so dense that even our most powerful telescopes struggle to resolve individual stars. In this crowded environment, stars are expected to collide and merge frequently, and interactions between all types of stellar objects are more likely. That makes it a prime area for the mergers of stellar-mass black holes into IMBHs.

The evidence for IMBHs is mounting, but there’s still no widespread agreement that their existence is proven. However, we may not have to wait long for the scientific community to gather enough convincing evidence. “With the increasing power of ongoing Gaia and large-scale spectroscopic surveys, we expect to discover dozens of cases within the 5 kpc volume and ten times more within a 10 kpc volume, which should shed light on the understanding of the evolutionary path from stellar-mass BHs to SMBHs,” the authors explain.

It’s even possible that the Event Horizon Telescope or something similar that succeeds it will be able to image an IMBH. A lot would have to go right for that to happen, but it’s a possibility.

For now, we can watch as researchers gather incremental evidence of IMBH’s existence and watch as the story unfolds.

The post A Star Was Kicked Out of a Globular Cluster by an Intermediate-Mass Black Hole appeared first on Universe Today.

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