Category: black holes

Scientists have long known that when two black holes collide, they merge to create a more massive black hole. These events are so violent that they set the very fabric of space ringing with ripples called gravitational waves.

Now, new research suggests that the opposite may happen, too: single black holes may be able to split in two. But this can only happen if that progenitor black hole is spinning at maximum possible speed. That speed prevents the black holes from immediately falling back on each other.

There are physical laws in place that would usually prevent black holes from splitting in two; the team behind this research investigated whether there are conditions in which these laws can be temporarily bypassed.

One of the key aspects of physics that prevents black holes from bifurcating comes from thermodynamics. Black holes possess a characteristic called "entropy," which is essentially a measure of disorder within a system.

Imagine a toddler's crayon box. When entropy is low, the crayons are neatly arranged by color. As entropy is increased, the crayons are scattered and no longer in order. To get the crayons back in order, it requires a parent to put energy into the system and neatly reorder the crayons. In other words, the entropy of a system can't be reduced without some intervention and energy being added from outside that system. Parenting would be a little easier if it could.

A black hole splitting in two would represent a decrease in entropy, strongly disfavored by the laws of thermodynamics, but only if the black hole is not rotating. The situation could be different for a rapidly rotating black hole.

This team of scientists found that a loophole exists for such a black hole.

"The two resulting black holes must also be able to separate rather than immediately fall back together," team member Francesco Sannino of the University of Naples Federico II in Italy said in a statement. "When we include this requirement, the window largely closes again, except possibly for black holes rotating close to their maximum possible rate."

Black hole trousers?

The team calculated just how such a black hole split could occur, finding that the division of the black hole's outer boundary, or "event horizon," proceeds in an oddly trouser-like shape, with one resulting black hole slipping down each "leg."

They termed this "pair-of-pants topologies."

The researchers also determined that a split is more likely to take place if one of the resultant black holes is considerably smaller than its newly born twin.

"We cannot yet give a single probability for a black hole to split. It depends on how gravity behaves beyond Einstein's theory, and we are working to quantify this," Sannino said. "We expect small primordial black holes to be more prone to splitting than much larger astrophysical black holes."

Sannino added that such black hole splits may be detectable in high-energy light called gamma-rays.

"We may detect a split indirectly: gamma-ray telescopes such as Fermi-LAT can search for signals from tiny black-hole fragments that might form during mergers," the researcher concluded.

The team's research was published on Oct. 22 in the journal Physical Review D.

Astronomers estimate that our home galaxy, the Milky Way, has churned out more than 10 million black holes over its 13-billion-year history. Yet so far, they have found only 70.

Now, a group of astronomers in the U.K. is trying to close that vast gap by enlisting the public. Their project, called Black Hole Hunters, is looking for volunteers with a computer and a few spare minutes to sift through troves of data gathered by a NASA space telescope. By flagging recognizable patterns that could point to a "missing" black hole, volunteers can help fast-track a search that would otherwise take years, the team says.

"You'll be narrowing down precisely where we need to point our telescopes next," project co-lead Adam McMaster, an astronomer at the University of Southampton in the U.K., said in a statement, "and you might be the one to discover a black hole."

Cosmic magnifying glasses

Black holes form when massive stars roughly 20 times heavier than our sun run out of fuel and collapse, leaving behind an abyss with gravity so immense that even light cannot escape. While invisible themselves, these cosmic behemoths reveal their presence by bending the light of nearby objects, and the Black Hole Hunters project is searching for one specific manifestation of this effect.

It happens thanks to the fact that massive stars often form in pairs, and a star can sometimes survive the violent supernova explosion that turns its companion into a black hole. When that happens, the two bodies continue to orbit each other. If such a duo aligns just right with Earth, the black hole will periodically pass directly between its companion star and our planet. And when it does, the black hole's gravity acts like a cosmic magnifying glass, bending and magnifying the star's light, causing it to briefly appear brighter to watchful telescopes.

To find these hidden giants, the project relies on data from NASA's Transiting Exoplanet Survey Satellite, or TESS. Although the satellite's primary mission is to hunt for planets beyond our solar system, its method of data collection — tracking tiny, continuous changes in a star's brightness over time — is ideally suited for identifying black hole magnification events, the project description notes.

"It's a simple task with no expertise required," McMaster said in the statement. "We will show volunteers examples of what to look for so all they have to do is recognise the right patterns."

Automated algorithms conduct a preliminary sweep of the TESS data, screening millions of potential stars for the most obvious black hole candidate locations, according to the project description. But, the researchers say, artificial intelligence struggles with the messy realities of the cosmos, such as stellar flares and the natural pulsations of stars that can trick the algorithms into false positives.

The human touch

That makes human volunteers a key part of the search. To keep errors in check, each graph is shown to multiple volunteers, and their answers are combined so that individual mistakes average out, according to the project's website.

"I can search for black holes on my laptop from my bedroom — and could make a real impact on real space science," Grace Clarke, an undergraduate student of physics and astronomy at the University of Southampton who's involved with the project, said in the same statement. "The data's easy to understand — it's just pattern recognition — and you don't need a degree in astronomy to read it."

The crowdsourced shortlist of promising signals lets astronomers aim follow-up observations at specific stars, such as precise measurements of whether a star is being tugged at by an unseen companion. Those measurements take time and are expensive, so a good shortlist helps researchers spend scarce telescope time wisely, the team says.

Since launching on the Zooniverse platform in October 2021, the project has attracted nearly 23,000 volunteers, who have completed more than 12 million classifications, according to its website.

Before turning to TESS, the team ran a similar search using data from SuperWASP, a ground-based survey that, like TESS, monitored stars for signs of planets from 2004 to 2016. Those results are still being analyzed and are expected to be published soon.

The team also plans to widen its search with observations from other instruments, including the European Space Agency's Euclid mission and NASA's recently launched Nancy Grace Roman Space Telescope.

"With potentially thousands of new discoveries, we need all the help we can get," McMaster said in the statement.

What looks like a neon pink treble clef floating out in space is actually a bizarre source of radio waves spotted deep in the cosmos.

What is it?

Scientists using NASA's Chandra X-ray Observatory have peered far out into space to look at strange radio waves coming from what they have nicknamed the "treble clef" because of its distinct shape, which looks a lot like the musical notation.

Using Chandra, as well as the German Extended RÖntgen Survey with an Imaging Telescope Array (eROSITA) X-ray telescope, researchers looking at this strange sight spotted a big cloud of blue gas, which we can see in this image, along with radio signals (seen here in bright pink). They think that this object is actually a huge galaxy cluster made up of two different clusters that are in the process of merging.

Why is it incredible?

The researchers think they may have gotten to the bottom of where these radio waves are coming from, they report in a new study.

The team thinks that the treble clef-shaped radio signals were created by an outburst from a supermassive black hole. They believe that this outburst pushed clouds of charged particles and magnetic fields away from the galaxy cluster's center, producing bright radio waves.

According to the scientists, following this bright outburst, there was likely an extreme collision between two galaxy clusters. This cosmic smash-up either compressed or somehow reenergized these charged particles to amplify the radio signal.

When we see beautiful images of objects in space such as this, they can seem just like peaceful, colorful, cosmic clouds. But when you look a bit deeper, these spectacular scenes can actually be evidence of violent, chaotic events.

This work was described in a study published in the journal Astronomy & Astrophysics.

Using the NASA X-ray spacecraft Swift combined with radio observations, astronomers have observed a supermassive black hole burping radio jets 300 days after a heavy cosmic meal. The team was also able to roughly estimate the mass of this feeding cosmic titan, which sits at the heart of the Perseus Cluster, a massive collection of thousands of galaxies.

The black hole sits at the center of the galaxy NGC 1275, located around 225 light-years away, and is the brightest galaxy of the Perseus Cluster. The supermassive black hole first flared in X-rays, which indicated an increase in the rate at which it was accreting matter. Actively feeding supermassive black holes sit in regions called active galactic nuclei (AGNs), with their immense gravity heating surrounding matter, causing them to glow brightly. These emissions are boosted by material channeled to the poles of the central black hole, from where it is blasted out as powerful twin jets that shine across the electromagnetic spectrum, particularly in radio waves.

The observation of the following radio jet from the AGN at the heart of NGC 1275 via flaring in radio waves is crucial for understanding the relationship between the disk of matter that surrounds and feeds the black hole, called an accretion disk, and the jets it launches. This so-called disk-jet coupling is key to developing a better picture of how black holes influence star formation in the galaxies in which they sit, and thus the growth of those galaxies.

Making these observations is no mean feat. The ideal spacecraft for observing X-ray emissions is Chandra, but it doesn't observe NGC 1275 frequently enough to observe its long-term behaviour. NASA's Neil Gehrels Swift Observatory may lack the power of Chandra, but having launched in 2004, it has collected a vast amount of data regarding NGC 1275 and its central supermassive black hole.

"It is fairly difficult to see the inner region of this AGN because NGC 1275 is at the center of the massive Perseus cluster of galaxies, which adds additional light to our observations," team leader Sarah Ketchum of the University of Michigan told Space.com. "We developed a model that allowed us to remove the cluster emission from archival Swift data, and in doing so, we were able to see the changes in the X-ray flux from gas accreting onto the black hole in NGC 1275, from 2007 to 2025."

Ketchum added that the capabilities of Swift were key to this investigation of NGC 1275, which is the ideal laboratory for the study of disk-jet coupling.

"There have been studies on other galaxies with AGN that show evidence of coupling between gas accretion traced in X-ray light and gas ejection in jets, traced in radio light. But NGC 1275 reveals the impact of black hole jets on large spatial scales better than any other system," the University of Michigan researcher continued.

This black hole didn't eat a star

Ketchum and colleagues saw the strongest ever X-ray flare from NGC 1275 in Feb. 2023. Lasting less than 60 days and consisting of two 5-day blasts, this episode saw a doubling of the X-ray brightness of the AGN at the heart of NGC 1275.

The flaring was so extreme that the team had to rule out a tidal disruption event (TDE) as the cause. These occur when an unfortunate star's orbit brings it too close to the immense gravitational influence of a supermassive black hole. This influence generates intense tidal forces that simultaneously squash and squeeze the star, "speghettifying" it and allowing the black hole to snack on some plasma pasta.

"We were able to rule out TDEs as a cause," Ketchum said. "Thus, the flaring was likely caused by a spike in the rate at which matter accreted onto the black hole."

Using Swift data, the team was able to infer the radius over which the AGN emits radiation. Because the size of a black hole is directly correlated with its mass, this meant that the researchers were able to constrain the mass of the black hole at the heart of NGC 1275. They determined that this supermassive black hole has a mass somewhere between 100 million times the mass of the sun and 1 billion solar masses.

The team then compared their data to known radio data to better understand the relationship between the X-ray emission and the radio jets that disrupt gas in NGC 1275.

Ketchum added that she and her colleagues found tentative evidence of around a 300-day delay between the X-ray flaring and the radio wave emission. This indicates the time it takes plasma to travel from the base of the jet to a knot or shock created when it hits surrounding gas or dust.

"This should be tested further in the future. Our X-ray data only sparsely sample the changes in NGC 1275," Ketchum said. "This makes it difficult to determine an exact relationship between the X-ray and radio radiation for large portions of our light curve, so we would need more X-ray data to further study this connection."

The researcher added that if the X-ray flares are produced close to the black hole, an echo of these flares should be seen coming from the accretion disk.

"An emission line from neutral iron is seen in data from NGC 1275, and this may be the echo. However, we likely need many observations with XMM-Newton and XRISM ( X-Ray Imaging and Spectroscopy Mission) to really establish that connection," Ketchum concluded.

The team's research has been accepted for publication in the Astrophysical Journal Letters, with a pre-peer-review version available on the repository site arXiv.

Astronomers have discovered the most distant and earliest blazar, comprised of an erupting supermassive black hole aiming its plasma jets directly at Earth.

Blazars occur when supermassive black holes are surrounded by vast amounts of gas and dust that they feed on, in regions called active galactic nuclei (AGNs). The immense gravity of these cosmic titans causes the surrounding gas and dust to glow brightly, meaning that AGNs can outshine the combined light of every star in the galaxies that house them. But that isn't all; matter that isn't feasted upon is channeled to the poles of the black hole, from where it is blasted out as twin jets of plasma moving at near-light speed.

These events are called quasars, but when the jets are directed straight down our line of sight, the quasar is classified as a blazar. Light from this high-energy blazar, designated Blazar OP 313, has been travelling to Earth for 8 billion years, meaning it is seen as it was just 5 billion years after the Big Bang during a crucial transitional phase in cosmic history.

"Around 11 billion years ago, the universe experienced a period of peak activity known as the 'cosmic noon,' characterised by an intense rate of star and galaxy formation," research team member Axel Arbet-Engels said in a statement."When this phase of intense activity slowed down and galaxies began to evolve and mature, the universe entered a calmer phase, which continues to this day."

The dawn of cosmic noon

Cosmic noon marked the period during which OP 313 emitted its powerful burst of very high-energy photons in the form of gamma-rays.

That emission was first observed in December 2023, with astronomers following up on the discovery with the Large-Sized Telescope (LST-1) prototype and the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescope, both of which are located at the Roque de los Muchachos Observatory, La Palma, Spain.

This revealed high-energy gamma-rays originating 8 billion light-years away. The analysis of these gamma-rays revealed how the supermassive black hole at the heart of this blazar is acting as a cosmic particle accelerator.

As these gamma rays traversed the cosmos, they interacted with the total accumulated radiation from all the stars, galaxies, and other AGNs throughout cosmic history, known as the extragalactic background (EBL).

When gamma rays interact with this fossil light, they create electron-positron pairs, a process known as pair production. This depletes the number of gamma-ray photons in this signal. Using the LST-1 and MAGIC, the team was able to characterize this depletion, revealing that the intense gamma-ray emission was fueled by a dense population of so-called 'relativistic' electrons. Relativistic means travelling at speeds near that of light, with the blazar's central supermassive black hole as the engine that accelerated these particles.

"In what is known as the leptonic scenario, electrons have been accelerated to speeds close to the speed of light within a powerful plasma jet ejected by the central supermassive black hole of OP 313," team member Domenico Della Volpe of the University of Geneva said. "Upon colliding with lower-energy photons surrounding the black hole, the electrons transfer part of their considerable energy to these photons, thereby propelling them to energy levels corresponding to very high-energy gamma rays."

That means these findings could represent a major step forward for our understanding of quasars, some of the most powerful cosmic events ever detected by humanity.

The team's research was published on Tuesday (Oct. 6) in the journal Astronomy & Astrophysics.

Though their origins may be shrouded in mystery, fast radio bursts (FRBs) could be used to probe some of the universe's biggest puzzles. This includes probing the nature of dark matter, the invisible sort of matter that somehow dominates the universe, and dark energy, the mysterious force causing the expansion of our universe to accelerate. They could even shed light on the mysteries of neutrinos, or "ghost particles." Let's dive into how.

FRBs are brief but intense blasts of radio waves currently thought to erupt from rapidly rotating dead stars with the universe's strongest magnetic fields, called magnetars. As FRBs travel billions of light-years to reach Earth, they pass through dense clouds of gas and dust in galaxies. This "cosmic fog" changes the original FRB signal. What this means is these blasts of radio waves carry the fingerprints of how matter in the universe is distributed.

Mapping the distribution and "clumpiness" of ordinary matter in galaxies can then help trace the distribution of dark matter, the effect of dark energy and the mass of neutrinos.

"We've established that FRBs are a leading probe of the distribution of matter in the universe," team leader Kritti Sharma, a graduate student working with Vikram Ravi, a professor of astronomy at the California Institute of Technology (Caltech) and also part of the team, said in a statement. "These FRB data can be used to enhance cosmology experiments that are trying to answer questions about dark matter, dark energy, and the mass of neutrinos."

For this research, Ravi and Sharma analyzed a sample of about 100 FRBs. This represents the first time scientists have used FRBs to directly measure the impact of so-called "feedback" from galaxies on the clumpiness of matter in the large-scale regions between galaxies.

Cosmic ghosts and the dark universe

Ordinary matter, composed of atoms made up of electrons, protons and neutrons, accounts for just around 5% of the universe's energy/matter budget despite comprising stars, planets, moons, our bodies, next door's cat and everything we see around us on a day-to-day basis.

Of this budget, the other 95% is composed of dark energy (68%) and dark matter (27%). It's little wonder that scientists are very keen to better understand these two aspects of the cosmos, sometimes collectively referred to as the "dark universe."

Things get even more murky when considering how, of that 5%, the second most abundant particles in the universe, aside from particles of light or photons, are neutrinos. These get their nickname of "ghost particles" because they interact with other matter particles so infrequently that approximately 100 trillion neutrinos pass through your body every second without leaving any trace. This is possible because neutrinos are virtually massless, and scientists are keen to accurately measure the mass of these cosmic ghosts.

These three mysterious elements of the cosmos have played a vital role in the evolution of large-scale cosmic structures like galaxies and galaxy clusters. That means, in turn, that measuring the clustering of matter can reveal details about the aspects of the universe that influenced that clustering.

However, to do that, scientists also have to understand how other factors smooth out cosmic clumpiness. That includes the energy pumped out from the hearts of galaxies by feeding supermassive black holes, a type of cosmic feedback that smooths out clumpy cosmic matter lying outside galaxies.

"The feedback process thins the gas around the galaxies, redistributing matter across vast distances. It smooths out clumps of matter in a way that looks astonishingly similar to what massive neutrinos do, or what dark energy or dark matter theories predict," Ravi said. "Unless scientists can independently measure this contribution from feedback, they can't tell these effects apart."

That's where FRBs come in.

The researchers found that, while galactic feedback does indeed smooth surrounding material, making it less clumpy, the effect is weaker than has previously been measured.

"Our analysis of FRBs reveals how gas ejected by astrophysical feedback suppresses cosmic structure," team member Elisabeth Krause of the University of Arizona said in the statement. "This is amazing considering we only had about 100 FRBs in our sample. It's only the beginning."

The investigation of the universe with FRBs could get a major boost in 2029 when Caltech's Deep Synoptic Array (DSA) begins operating in Nevada. This powerful radio telescope is expected to find tens of thousands of FRBs, a major boon for cosmology.

The team's research was published on Tuesday (Sept. 8) in the journal Nature Astronomy.

A "forbidden" merger between two massive black holes may not have been quite as impossible as previously thought. That's according to new research that suggests the black holes involved were smaller than expected.

On Nov. 23, 2023, the gravitational wave detector LIGO (Laser Interferometer Gravitational-Wave Observatory) detected tiny ripples in spacetime caused by the merger of two black holes. What was incredible about this signal, designated GW231123, was that it seemed to be the result of a black hole with 140 times the mass of the sun colliding with another that holds 100 solar masses.

This raised eyebrows among researchers because usual models of stellar evolution struggle to account for such massive black holes, especially ones that seemed to be spinning as fast as these two. While scientists have been attempting to explain how such an odd black hole binary could form. The team behind this new research suggests it doesn't need to be explained at all. They think that the masses of these black holes were an illusion.

The key to this illusion is a phenomenon called gravitational lensing, first predicted by Albert Einstein's 1915 theory of gravity, general relativity, which also first predicted the existence of gravitational waves. This theory says objects with mass cause the curvature of space and time, united as a four-dimensional entity called "spacetime." The more mass an object possesses, the greater the curvature, and because gravity arises from this curvature, the greater the gravitational influence.

Gravitational lensing occurs when light from a background object passes a massive foreground object. The foreground object can warp the fabric of spacetime in such a way that the light's path is curved. This means light from the same background source can reach Earth at different times, depending on how much that light was diverted.

This difference in travel time can magnify a background source, and it has been used to great effect to observe distant and ancient galaxies ordinarily too faint to be seen.

This research team thinks the effect also applies to gravitational waves, suggesting the signal GW231123 is an example of gravitationally lensed ripples in spacetime that made the black holes appear larger than they actually are.

"Like light, gravitational waves can also be deflected, magnified and split into multiple signals by massive objects," team member Miguel Zumalacárregui, group leader in the Astrophysical and Cosmological Relativity Department at the Albert Einstein Institute (AEI), said in a statement. "For gravitational waves, diffraction and interference effects give us an additional way to identify and study lensed signals."

To investigate this possibility, the team developed a mathematical model of gravitational lensing and created software powerful and fast enough to analyze it.

"If we assume that GW231123 was deflected and distorted by a compact object of about 190 to 850 solar masses — or by an extended structure such as a globular cluster — we can understand the observed high masses," said team member Srashti Goyal, who was based at the AEI when conducting the research. "Moreover, the lensing interpretation does not require unusually high spins."

When the team modeled the event with that consideration factored in, they found the merger involved a system with a mass of 140 solar masses, rather than the 240-solar-mass system initially theorized.

The team doesn't quite know what massive object is responsible for lensing the gravitational wave signal GW231123. But no matter what it is, if the team is correct, the lens could be something quite special.

"The nature of the lens remains a major mystery in our analysis, as individual compact lenses with 100 to 1,000 solar masses should be exceedingly rare," Zumalacárregui said. "Future work will need to establish whether such lenses can form, or whether an ensemble of lighter objects, including stars, can explain this event."

The team can't yet conclusively say if GW231123 is the first gravitationally lensed gravitational wave signal. Finding future signals of the sort will require upgrades to the sensitivity of detectors like LIGO.

Though even before that happens, the research does point to the utility of gravitational wave astronomy to study some of the universe's most violent events.

The team's research was published on August 25 in the Astrophysical Journal Letters.

In the four years that the James Webb Space Telescope (JWST) has been making observations of the early universe, it has been delivering one scientific milestone after another. However, the $10 billion telescope has also left astronomers with a massive problem  — literally.

The JWST has been routinely spotting supermassive black holes in the early universe that, at hundreds of millions of times the mass of the sun, are too big to have grown to such monstrous sizes before the universe was even 1 billion years old. These cosmic titans are also too massive in comparison to the masses of their small host galaxies, challenging what astronomers know about the relationships between supermassive black holes and their galactic homes that are usually observed in the modern universe.

Now, new research suggests this isn't such a massive problem after all. The team behind this research thinks that it is all a matter of perspective, and that these early supermassive black holes aren't as monstrous as scientists have estimated.

"We estimate masses of roughly one to ten million solar masses, compared with the tens or hundreds of millions previously inferred," team leader Alessandro Trinca of the Italian National Institute for Astrophysics (INAF) Astronomical Observatory of Rome told Space.com. "These are still enormous objects, comparable to the four-million-solar-mass black hole at the center of the Milky Way, or a few times larger, but they lie at the lower end of the supermassive black hole population rather than among the most extreme examples.

"Importantly, these masses are much more consistent with the small galaxies that host them."

The answer to this puzzle may lie in missing X-rays

While considering the mystery of "overmassive" black holes in the early universe, Trinca and colleagues picked up on another puzzle associated with these objects.

To reach such sizes, these black holes must be voraciously feeding on surrounding gas and dust. Such feeding black holes and the cosmic larders of gas and dust that surround them are usually extremely bright emitters of X-rays. But this doesn't seem to be the case with the supermassive black holes in the early universe seen by the JWST. The team looked at 14 X-ray-silent supermassive black holes, finding that there is another way of considering this lack of emission.

"Almost none of them are detected in X-rays, even in very deep observations with NASA's Chandra X-ray Observatory," Trinca said. "We interpreted this lack of X-rays as a clue rather than a problem. By incorporating it into our analysis, we find that these objects are likely much less massive than previously estimated. This brings their estimated masses into better agreement with the properties of their host galaxies."

This led Trinca and the team to another conclusion: these early supermassive black holes may not be as massive as previously theorized, but they are feeding even more rapidly than was thought.

If feeding supermassive black holes blast out a lot of X-rays, then it might seem somewhat counterintuitive that ravenously feeding black holes could be X-ray "quiet."

Trinca explains that this apparent contradiction is related to what happens when a black hole accretes matter at extremely high rates. The disk of gas around the black hole becomes geometrically thick, forming a donut-like structure with a narrow funnel along the rotation axis. The hot inner region that would normally produce strong X-rays becomes surrounded by this thick disk.

"As the X-rays escape, they are repeatedly scattered by the surrounding gas, losing energy before they can emerge. As a result, the black hole appears much fainter in X-rays than we would normally expect," Trinca continued. "Therefore, the lack of X-rays is not unexpected in this scenario; it is actually a prediction of the model.

"In addition, this very high feeding might help explain how these black holes could already have grown to millions of times the sun's mass when the universe was only a few hundred million years old."

Out-eating Eddington

One of the reasons that supermassive black holes are so troubling in the early universe is the fact that they grow by consuming matter and through merging with other black holes. However, there exists a limit to how rapidly a black hole, or any astronomical body, can gather or "accrete" matter.

Called the "Eddington limit," this exists because the more matter a body accretes, the more radiation it blasts out. So as the disk around a feeding black hole gathers enough mass to feed a rapidly growing black hole, it should emit so much radiation that it pushes away more matter, preventing it from being replenished.

Eventually this cuts off the food supply to the black hole and curtails its growth. However, this research suggests that supermassive black holes can enter brief phases of "super-Eddington" feeding.

"If these black holes are up to thirty times less massive than previously estimated, there is much less mass to build up within the available time, and their growth history becomes much less extreme," Trinca said. "Instead of requiring continuous, uninterrupted growth over hundreds of millions of years, the picture becomes one of shorter episodes of very rapid accretion, which is exactly the kind of behavior we might expect in the gas-rich and dynamically active galaxies of the early universe."

Confirming the team's theory about bouts of extreme feeding for supermassive black holes will require astronomical evidence, which may be tough to obtain at least for now.

"The most direct test would be to study similar objects that are accreting very rapidly but are located at lower redshifts, where we can observe and characterize their environments in much greater detail. However, such objects are quite rare," Trinca said. "For the more distant population observed with JWST, future missions providing deeper X-ray observations and improved spectra will be of crucial importance and might potentially detect the weak X-ray emission predicted by this scenario."

The INAF researcher added that in the longer term, obtaining direct and independent measurements of black hole masses at progressively earlier cosmic times will provide the strongest test of the team's theory. For now, the research is a striking example of what scientists can do when they don't detect something, rather than when they make a positive detection.

"What was interesting was seeing how much information could be extracted from something we did not observe," Trinca concluded. "A non-detection may appear to be the least informative type of observation, but in this case the absence of X-rays provided a strong constraint and helped define the physical picture more clearly than the detections alone."

The team's research was published in the June edition of the journal Astronomy & Astrophysics.

Some stars encounter supermassive black holes and live to tell the tale. New research shows why the flares these encounters cause dim over repeated episodes, and it may be down to the way these stars spin and an escaping binary partner that leaves them to be a stellar snack for a black hole.

Some stars are unfortunate enough to encounter the supermassive black holes that sit at the heart of every galaxy, being subjected to immense tidal forces that turn them into a strand of stellar spaghetti, a process called "spaghettification." This plasma pasta wraps around the black hole and is gradually fed to it, with some former star stuff being ejected as near-light-speed jets. These occurrences are called tidal disruption events (TDEs).

However, other stars get a reprieve, passing close enough to a supermassive black hole for the cosmic titan to take a bite and strip off material, but not close enough to be fully destroyed. As the star orbits the supermassive black hole, it takes repeated "bites," with this stellar snacking called a repeating partial tidal disruption event (rpTDE).

Each incident causes a flare of light from the vicinity of the black hole, as would be expected from the brightening seen during a standard TDE. But a strange pattern has emerged in rpTDES; each successive flare can become dimmer. Scientists have struggled to explain this dimming for some time, but finally a team of researchers from Syracuse University may have solved this puzzle.

To reach an answer to black hole flare dimming, the team considered a factor that hadn't been thought of before: the spin of the star itself. This element explained the dimming of black hole flaring and also helped to explain why not all rpTDEs play out the same.

"We were puzzled by this for two years," team leader Ananya Bandopadhyay of Syracuse University said in a statement.

A new spin on stellar snacking

Bandopadhyay and colleagues previously determined that how much material a star loses during repeated rpTDE episodes depends partially on its internal structure, which in turn depends on its mass.

Bandopadhyay compares a low-mass star to a fluffy meringue, which makes it more susceptible to the tidal forces generated by the black hole, allowing more material to be stripped from deeper within the star.

In contrast, a high-mass star has a structure more like an onion. That means that when such a stellar body buzzes a black hole in a rpTDE, its outer layers are stripped, but its core resists the influence of the black hole. Thus, as that outer layer is whittled away, there is less and less material to be stripped away in subsequent episodes.

However, that alone can't fully account for the dimming of flares from four of the ten currently discovered rpTDEs, because of the influence the black hole has on the star as it passes.

The team's prior work had identified that during rpTDEs, supermassive black holes exert a torque on the passing star that causes the star to spin faster during each passage.

That means even though less material falls to the black hole during each passage, the star returns over shorter and shorter periods of time. That helps keep flaring consistently bright. Thus, a recipe for dimming requires a new ingredient.

Bandopadhyay determined that this element could be a star that was already spinning rapidly before its first encounter with a supermassive black hole.

If a star is already rapidly spinning when it first encounters a black hole, the torque experienced doesn't increase that spin much. And without that increase in spin, there is no shortening of periods between episodes, meaning less and less material being stripped would result in dimming.

Of course, that leaves another question: why would a star be spinning so rapidly in the first place?

Rogue stars could be the answer

The key to this mystery could lie in the fact that most stars don't orbit the centers of their galaxies where supermassive black holes dwell alone, instead existing in binary partnerships.

"It is also extremely difficult to 'bind' a star to a supermassive black hole so tightly that it orbits the black hole in a matter of months, and yet they seem to do so in rpTDEs," team member Eric Coughlin of Syracuse University said.

The loss of a partner star, could cause a stellar body to be tightly bound to a supermassive black hole, completing an orbit once every few months.

During a process called Hills capture, as a stellar binary orbits a supermassive black hole and the gravitational influence of the black hole rips the binary apart, ejecting one star while capturing the other.

If this stellar binary was particularly tight, with the stars closely orbiting each other, this ejection and capture process could leave the trapped star rapidly spinning on a tight orbit.

"This work demonstrates that each of these peculiarities can be explained by the same underlying phenomenon: the tidal destruction of a binary system and the capture of one of the stars," Coughlin said. "From a theoretical standpoint, this is a major step forward in our understanding of the physics at play in these systems."

The discovery may have implications closer to home too. Though the supermassive black hole of the Milky Way, Sagittarius A* (Sgr A*), isn't currently involved in a rpTDE, it is orbited by many rapid stars. These findings may explain how they came to be there.

The team's research was published on August 18 in The Astrophysical Journal.

Astronomers have discovered a hitherto unseen population of so-called "radio galaxies" with fading "radio lobes." The discovery reveals what happens when the supermassive black hole engines that power these vast, blooming outflows of plasma stall. This discovery increases our understanding of the life cycles of galaxies.

The team behind this research studied 14 candidates for faded or remnant radio galaxies found in a region of the sky over Earth, studied intensely by the XMM-Newton X-ray spacecraft, called the XMM–Newton Large-Scale Structure (XMM–LSS) field.

Radio galaxies are extremely bright in radio waves and feature vast lobes of gas that can stretch out for millions of light-years. Remnant radio galaxies represent the final stage in the evolution of radio galaxies, at which point the jets from the galaxies' central regions, or active galactic nuclei (AGNs) powered by feeding supermassive black holes, have switched off. Therefore, these jets can no longer replenish the vast radio lobes, causing them to gradually fade.

The researchers studied the XMM–LSS field using the MeerKAT radio telescope, an array of 64 antennas located in the desert-like region of the Northern Cape, South Africa, the Jansky Very Large Array, and the LOFAR (Low-Frequency Array) network.

This powerful combination of observations allowed them to study how radio emissions from the lobes of radio galaxies change as the particles within them "age" and lose energy.

This allowed the researchers to determine that 12 of the 14 candidates actually are remnant radio galaxies, while the other two remain active radio galaxies.

The team also discovered something striking about the 12 confirmed radio galaxy remnants.

One thing that really stood out in this study was the ages of these remnants, which appeared to have been fading for between 8 million and 42 million years, with the average "fade age" being 12 million years.

This age is younger than the ages measured for radio galaxy remnants, which could indicate that astronomers have been missing a population of short-lived remnants.

This wasn't the only extraordinary finding in this study. The scientists also found that the remnants they looked at exist in a wide range of evolutionary stages, with some having jets that have only just switched off, while others are more evolved, having "powered down" long ago.

The new findings represent a major step forward in understanding the life cycles of radio galaxies, and also how supermassive black holes function as the engines powering jets that drive vast radio lobes.

The team's research was published on July 14 in the Monthly Notices of the Royal Astronomical Society.