“In addition to stars, gas clouds can also be disrupted by SMBHs and their binaries,” they said in the same study. “The key difference is that the clouds can be comparable to or even larger than the binary separation, unlike stars, which are always much smaller. “
Looking at the results of a previous study that numerically modeled this type of situation also suggested a gas cloud. Just like the hypothetical supermassive black hole binary in the model, AT 2021hdr would accrete large amounts of material every time the black holes were halfway through orbiting each other and had to cross the cloud to complete the orbit—their gravity tears away some of the cloud, which ends up in their accretion disks, every time they cross it. They are now thought to take in anywhere between three and 30 percent of the cloud every few cycles. From a cloud so huge, that’s a lot of gas.
The supermassive black holes in AT 2021hdr are predicted to crash into each other and merge in another 70,000 years. They are also part of another merger, in which their host galaxy is gradually merging with a nearby galaxy, which was first discovered by the same team (this has no effect on the BSMBH tidal disruption of the gas cloud).
How the behavior of AT 2021hdr develops could tell us more about its nature and uphold or disprove the idea that it is eating away at a gaseous cloud instead of a star or something else. For now, it seems these black holes don’t just get gas from what they eat—they eat the gas itself.
Similar feeding events could explain the rapid growth of supermassive black holes.
How did supermassive black holes end up at the center of every galaxy? A while back, it wasn’t that hard to explain: That’s where the highest concentration of matter is, and the black holes had billions of years to feed on it. But as we’ve looked ever deeper into the Universe’s history, we keep finding supermassive black holes, which shortens the timeline for their formation. Rather than making a leisurely meal of nearby matter, these black holes have gorged themselves in a feeding frenzy.
With the advent of the Webb Space Telescope, the problem has pushed up against theoretical limits. The matter falling into a black hole generates radiation, with faster feeding meaning more radiation. And that radiation can drive off nearby matter, choking off the black hole’s food supply. That sets a limit on how fast black holes can grow unless matter is somehow fed directly into them. The Webb was used to identify early supermassive black holes that needed to have been pushing against the limit for their entire existence.
But the Webb may have just identified a solution to the dilemma as well. It has spotted a black hole that appears to have been feeding at 40 times the theoretical limit for millions of years, allowing growth at a pace sufficient to build a supermassive black hole.
Setting limits
Matter falling into a black hole generally gathers into what’s called an accretion disk, orbiting the body and heating up due to collisions with the rest of the disk, all while losing energy in the form of radiation. Eventually, if enough energy is lost, the material falls into the black hole. The more matter there is, the brighter the accretion disk gets, and the more matter that gets driven off before it can fall in. The point where the radiation pressure drives away as much matter as the black hole pulls in is called the Eddington Limit. The bigger the black hole, the higher this limit.
It is possible to exceed the Eddington Limit if matter falls directly into the black hole without spending time in the accretion disk, but it requires a fairly distinct configuration of nearby clouds of gas, something that’s unlikely to persist for more than a few million years.
That creates a problem for supermassive black holes. The only way we know to form a black hole—the death of a massive star in a supernova—tends to produce them with only a few times the mass of the Sun. Even assuming unusually massive stars in the early Universe, along with a few black hole mergers, it’s expected that most of the potential seeds of a supermassive black hole are in the area of 100 times the Sun’s mass. There are theoretical ideas about the direct collapse of gas clouds that avoid the intervening star formation and immediately form a black hole with 10,000 times the mass of the Sun or more, but they remain entirely hypothetical.
In either case, black holes would need to suck down a lot of matter before reaching supermassive proportions. But most of the early supermassive black holes spotted using the Webb are feeding at roughly 20 percent of the Eddington limit, based on their lack of X-ray emissions. This either means that they fed at well beyond the Eddington Limit earlier in their history or that they started their existences as very heavy black holes.
The object that’s the focus of this new report, LID-568, was first spotted using the Chandra X-ray Telescope (an observatory that was recently threatened with shutdown). LID-568 is luminous at X-ray wavelengths, which is why Chandra could spot it, and suggests the possibility that it is feeding at an extremely high rate. Imaging in the infrared shows that it appears to be a point source, so the research team concluded that most of the light we’re seeing comes directly from the accretion disk, rather than from the stars in the galaxy it occupies.
But that made it difficult to determine any details about the black hole’s environment or to figure out how old it was relative to the Big Bang at the time we’re viewing it. So, the researchers pointed the Webb at it to capture details that other observatories couldn’t image.
A fast eater
Use of spectroscopy revealed that we were viewing LID-568 as it existed about 1.5 billion years after the Big Bang. The emissions from gas and dust in the area were low, which suggests that the black hole resides in a dwarf galaxy. Based on the emission of hydrogen, the researchers estimate that the black hole is roughly a million times the mass of the Sun—nothing you’d want to get close to, but small compared to many supermassive black holes.
It’s actually similar in mass to a number of black holes the Webb was used to identify in galaxies that are considerably older. But it’s much, much brighter (as bright as something 10 times heavier) and includes the X-ray emissions that those lack. In fact, it’s so bright compared to its mass that the researchers estimate that it could only produce that much radiation if it were feeding at well above the Eddington Limit. Ultimately, they estimate that it’s exceeding the Eddington Limit by a factor of over 40.
Critically, the Webb was able to identify two lobes of material that were moving toward us at high velocities, based on the blue shifting of hydrogen emissions lines. These suggest that the material is moving at over 500 kilometers a second and stretched for tens of thousands of light years away from the black hole. (Presumably, these obscured similar blobs of material moving away from us.) Given their length and apparent velocity, and assuming they represent gas driven off by the black hole, the researchers estimated how long it was emitting this intense radiation.
Working back from there, they estimate the black hole’s original mass was about 100 times that of the Sun. “This lifetime suggests that a substantial fraction of the mass growth of LID-568 may have occurred in a single, super-Eddington accretion episode,” they conclude. For that to work, the black hole had to have ended up in a giant molecular cloud and stayed there feeding for over 10 million years.
The researchers suspect that this intense activity interfered with star formation in the galaxy, which is one of the reasons that it is relatively star-poor. That may explain why we see some very massive black holes at the center of relatively small galaxies in the present Universe.
So what does this mean?
In some ways, this is potentially good news for cosmologists. Forming supermassive black holes as quickly as the size/age of those observed by Webb would seemingly require them to have fed at or slightly above the Eddington Limit for most of their history, which was easy to view as unlikely. If the Eddington Limit can be exceeded by a factor of 40 for over 10 million years, however, this seems to be less of an issue.
But, at the same time, the graph showing mass versus luminosity of supermassive black holes the research team generated shows that LID-568 is in a class by itself. If there were a lot of black holes feeding at these rates, it should be easy to identify more. And it’s a safe bet that these researchers are checking other X-ray sources to see if there are additional examples.
John is Ars Technica’s science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots.
Enlarge/ The Milky Way’s central black hole is in a very crowded neighborhood.
Supermassive black holes are ravenous. Clumps of dust and gas are prone to being disrupted by the turbulence and radiation when they are pulled too close. So why are some of them orbiting on the edge of the Milky Way’s own supermassive monster, Sgr A*? Maybe these mystery blobs are hiding something.
After analyzing observations of the dusty objects, an international team of researchers, led by astrophysicist Florian Peißker of the University of Cologne, have identified these clumps as potentially harboring young stellar objects (YSOs) shrouded by a haze of gas and dust. Even stranger is that these infant stars are younger than an unusually young and bright cluster of stars that are already known to orbit Sgr A*, known as the S-stars.
Finding both of these groups orbiting so close is unusual because stars that orbit supermassive black holes are expected to be dim and much more ancient. Peißker and his colleagues “discard the en vogue idea to classify [these] objects as coreless clouds in the high energetic radiation field of the supermassive black hole Sgr A*,” as they said in a study recently published in Astronomy & Astrophysics.
More than just space dust
To figure out what the objects near Sgr Amight be the, researchers needed to rule out things they weren’t. Embedded in envelopes of gas and dust, they maintain especially high temperatures, do not evaporate easily, and each orbits the supermassive black hole alone.
The researchers determined their chemical properties from the photons they emitted, and their mid- and near-infrared emissions were consistent with those of stars. They used one of them, object G2/DSO, as a case study to test their ideas about what the objects might be. The high brightness and especially strong emissions of this object make it the easiest to study. Its mass is also similar to the masses of known low-mass stars.
YSOs are low-mass stars that have outgrown the protostar phase but have not yet developed into main sequence stars, with cores that fuse hydrogen into helium. These objects like YSO candidates because they couldn’t possibly be clumps of gas and space dust. Gaseous clouds without any objects inside to hold them together via gravity could not survive so close to a supermassive black hole for long. Its intense heat causes the gas and dust to evaporate rather quickly, with heat-excited particles crashing into each other and flying off into space.
The team figured out that a cloud comparable in size to G2/DSO would evaporate in about seven years. A star orbiting at the same distance from the supermassive black hole would not be destroyed nearly as fast because of its much higher density and mass.
Another class of object that the dusty blobs could hypothetically be—but are not—is a compact planetary nebula or CPN. These nebulae are the expanding outer gas envelopes of small to medium stars in their final death throes. While CPNs have some features in common with stars, the strength of a supermassive black hole’s gravity would easily detach their gas envelopes and tear them apart.
It is also unlikely that the YSOs are binary stars, even though most stars form in binary systems. The scorching temperatures and turbulence of SGR Awould likely cause stars that were once part of binaries to migrate.
Seeing stars
Further observations determined that some of the dust-obscured objects are nascent stars, and while others are thought to be stars of some kind, but haven’t been definitively identified.
The properties that made G2/DSO an exceptional case study are also the reason it has been identified as a YSO. D2 is another high-luminosity object about as massive as a low-mass star, which is easy to observe in the near- and mid-infrared. D3 and D23 also have similar properties. These are the blobs near the black hole that the researchers think are most likely to be YSOs.
There are other candidates that need further analysis. These include additional objects that may or may not be YSOs, but still show stellar characteristics: D3.1 and D5, which are difficult to observe. The mid-infrared emissions of D9 are especially low when compared to the other candidates, but it is still thought to be some type of star, though possibly not a YSO. Objects X7 and X8 both exhibit bow shock—the shockwave that results from a star’s stellar wind pushing against other stellar winds. Whether either of these objects is actually a YSO remains unknown.
Where these dusty objects came from and how they formed is unknown for now. The researchers suggest that the objects formed together in molecular clouds that were falling toward the center of the galaxy. They also think that, no matter where they were born, they migrated towards Sgr A*, and any that were in binary systems were separated by the black hole’s immense gravity.
While it is unlikely that the YSOs and potential YSOs originated in the same cluster as the slightly older S-stars, they still might be related in some way. They might have experienced similar formation and migration journeys, and the younger stars might ultimately reach the same stage.
“Speculatively, the dusty sources will evolve into low-mass S stars,” Peißker’s team said in the same study.
Even black holes look better with a necklace of twinkling diamonds.
Artist’s animation of the black hole at the center of SDSS1335+0728 awakening in real time—a first for astronomers.
In December 2019, astronomers were surprised to observe a long-quiet galaxy, 300 million light-years away, suddenly come alive, emitting ultraviolet, optical, and infrared light into space. Far from quieting down again, by February of this year, the galaxy had begun emitting X-ray light; it is becoming more active. Astronomers think it is most likely an active galactic nucleus (AGN), which gets its energy from supermassive black holes at the galaxy’s center and/or from the black hole’s spin. That’s the conclusion of a new paper accepted for publication in the journal Astronomy and Astrophysics, although the authors acknowledge the possibility that it might also be some kind of rare tidal disruption event (TDE).
The brightening of SDSS1335_0728 in the constellation Virgo, after decades of quietude, was first detected by the Zwicky Transient Facility telescope. Its supermassive black hole is estimated to be about 1 million solar masses. To get a better understanding of what might be going on, the authors combed through archival data and combined that with data from new observations from various instruments, including the X-shooter, part of the Very Large Telescope (VLT) in Chile’s Atacama Desert.
There are many reasons why a normally quiet galaxy might suddenly brighten, including supernovae or a TDE, in which part of the shredded star’s original mass is ejected violently outward. This, in turn, can form an accretion disk around the black hole that emits powerful X-rays and visible light. But these events don’t last nearly five years—usually not more than a few hundred days.
So the authors concluded that the galaxy has awakened and now has an AGN. First discovered by Carl Seyfert in 1943, the glow is the result of the cold dust and gas surrounding the black hole, which can form orbiting accretion disks. Gravitational forces compress the matter in the disk and heat it to millions of degrees Kelvin, producing radiation across the electromagnetic spectrum.
Alternatively, the activity might be due to an especially long and faint TDE—the longest and faintest yet detected, if so. Or it could be an entirely new phenomenon altogether. So SDSS1335+0728 is a galaxy to watch. Astronomers are already preparing for follow-up observations with the VLT’s Multi Unit Spectroscopic Explorer (MUSE) and Extremely Large Telescope, among others, and perhaps even the Vera Rubin Observatory slated to come online next summer. Its Large Synoptic Survey Telescope (LSST) will be capable of imaging the entire southern sky continuously, potentially capturing even more galaxy awakenings.
“Regardless of the nature of the variations, [this galaxy] provides valuable information on how black holes grow and evolve,” said co-author Paula Sánchez Sáez, an astronomer at the European Southern Observatory in Germany. “We expect that instruments like [these] will be key in understanding [why the galaxy is brightening].”
There is also a supermassive black hole at the center of our Milky Way galaxy (Sgr A*), but there is not yet enough material that has accreted for astronomers to pick up any emitted radiation, even in the infrared. So, its galactic nucleus is deemed inactive. It may have been active in the past, and it’s possible that it will reawaken again in a few million (or even billion) years when the Milky Way merges with the Andromeda Galaxy and their respective supermassive black holes combine. Only much time will tell.
Enlarge/ The star’s orbit, shown here in light, is influenced by the far more massive black hole, indicated by the red orbit.
As far as black holes go, there are two categories: supermassive ones that live at the center of the galaxies (and we’re unsure about how they got there) and stellar mass ones that formed through the supernovae that end the lives of massive stars.
Prior to the advent of gravitational wave detectors, the heaviest stellar-mass black hole we knew about was only a bit more than a dozen times the mass of the Sun. And this makes sense, given that the violence of the supernova explosions that form these black holes ensures that only a fraction of the dying star’s mass gets transferred into its dark offspring. But then the gravitational wave data started flowing in, and we discovered there were lots of heavier black holes, with masses dozens of times that of the Sun. But we could only find them when they smacked into another black hole.
Now, thanks to the Gaia mission, we have observational evidence of the largest black hole in the Milky Way outside of the supermassive one, with a mass 33 times that of the Sun. And, in galactic terms, it’s right next door at about 2,000 light-years distant, meaning it will be relatively easy to learn more.
Mapping the stars
Although stellar-mass black holes are several times the mass of the Sun, they aren’t really all that heavy in the grand scheme of things. The sorts of stars that tend to leave black holes behind also tend to lead violent existences, spewing a lot of themselves into space before dying. And the supernova that forms the black hole obviously expels a lot of the star’s mass, rather than feeding it into the black hole. It had been thought that these processes set limits on how big a stellar mass black hole could be when it forms.
The discovery of larger black holes through gravitational wave detectors suggested that this wasn’t true. While there are ways for black holes to get bigger after they form—excessive feeding, mergers—it wasn’t clear that these events occurred often enough to explain the frequency of heavy black holes that we were seeing. And detecting them via gravitational waves doesn’t tell us anything about the history of how they got that large.
Which is why the discovery of Gaia BH3 (which is what the research team is using to avoid having to retype Gaia DR3 4318465066420528000 all the time) is so intriguing. The black hole is sitting calmly in a binary system, not doing anything in particular. But we know it’s there due to its gravitational influence.
Gaia is an ESA mission to map the location and movement of many of the Milky Way’s brighter stars by imaging them multiple times from different perspectives. It also gathers basic data on the stars’ light, allowing us to estimate things like age and composition. And, in addition to their movement across the galaxy, Gaia can measure their movement relative to Earth, a method that is useful for the detection of orbital interactions, such as the presence of companion stars or exoplanets.
The Gaia team was busy preparing for the fourth release of the data from the spacecraft and were running validation tests on the software used to detect binary star systems when they stumbled across Gaia BH3. While normally they’d publish its discovery at the same time as the data release, they consider the new object too important to wait: “We took the exceptional step of the publication of this paper based on preliminary data ahead of the official DR4 due to the unique nature of the discovery, which we believe should not be kept from the scientific community until the next release.”
Finding the invisible
Every star in our galaxy is in motion relative to every other. They orbit the center of our galaxy and may have a history that has imparted additional momentum—gravitational interactions with neighbors, having been part of a smaller galaxy that was consumed by the Milky Way, and so on. But that motion only changes on very long time scales. By contrast, any star in an orbit experiences regular changes in its motion in addition to its overall travel through the galaxy. As part of processing its data, the Gaia team attempts to identify both overall motion and any indications that a star is orbiting as part of a binary system.
The star that is orbiting Gaia BH3 is similar in mass to the Sun but shows the sort of periodic wobbles that indicate it’s in a mutual orbit with a companion. The companion itself, however, was completely invisible, which means it is almost certainly a black hole (the Gaia data had already been used to identify black holes this way). And, based on the mass and orbital motion of the visible star, it’s possible to estimate the mass of the invisible companion.
The estimate ended up being 32 solar masses, which is significantly larger than anything else identified in the Gaia dataset. So, the Gaia team wanted to confirm this wasn’t a software issue and used Earth-based telescopes to observe the same system. Three different observatories confirmed it was there, and the resulting mass estimates were slightly larger than those derived from the Gaia data alone: just under 33 solar masses.
Assuming it’s a single object and not two black holes orbiting each other closely, that makes it the largest non-supermassive black hole known in the Milky Way. And it places it in the mass range that had been difficult to explain via formations in supernovae.
Enlarge/ Scientists have found a large black hole that “hiccups,” giving off plumes of gas.
Jose-Luis Olivares, MIT
In December 2020, astronomers spotted an unusual burst of light in a galaxy roughly 848 million light-years away—a region with a supermassive black hole at the center that had been largely quiet until then. The energy of the burst mysteriously dipped about every 8.5 days before the black hole settled back down, akin to having a case of celestial hiccups.
Now scientists think they’ve figured out the reason for this unusual behavior. The supermassive black hole is orbited by a smaller black hole that periodically punches through the larger object’s accretion disk during its travels, releasing a plume of gas. This suggests that black hole accretion disks might not be as uniform as astronomers thought, according to a new paper published in the journal Science Advances.
Co-author Dheeraj “DJ” Pasham of MIT’s Kavli Institute for Astrophysics and Space research noticed the community alert that went out after the All Sky Automated Survey for SuperNovae (ASAS-SN) detected the flare, dubbed ASASSN-20qc. He was intrigued and still had some allotted time on the X-ray telescope, called NICER (the Neutron star Interior Composition Explorer) on board the International Space Station. He directed the telescope to the galaxy of interest and gathered about four months of data, after which the flare faded.
Pasham noticed a strange pattern as he analyzed that four months’ worth of data. The bursts of energy dipped every 8.5 days in the X-ray regime, much like a star’s brightness can briefly dim whenever an orbiting planet crosses in front. Pasham was puzzled as to what kind of object could cause a similar effect in an entire galaxy. That’s when he stumbled across a theoretical paper by Czech physicists suggesting that it was possible for a supermassive black hole at the center of a galaxy to have an orbiting smaller black hole; they predicted that, under the right circumstances, this could produce just such a periodic effect as Pasham had observed in his X-ray data.
Computer simulation of an intermediate-mass black hole orbiting a supermassive black hole and driving periodic gas plumes that can explain the observations.
Petra Sukova, Astronomical Institute of the CAS
“I was super excited about this theory and immediately emailed to say, ‘I think we’re observing exactly what your theory predicted,” Pasham said. They joined forces to run simulations incorporating the data from NICER, and the results supported the theory. The black hole at the galaxy’s center is estimated to have a mass of 50 million suns. Since there was no burst before December 2020, the team thinks there was, at most, just a faint accretion disk around that black hole and a smaller orbiting black hole of between 100 to 10,000 solar masses that eluded detection because of that.
So what changed? Pasham et al. suggest that a nearby star got caught in the gravitational pull of the supermassive black hole in December 2020 and was ripped to shreds, known as a tidal disruption event (TDE). As previously reported, in a TDE, part of the shredded star’s original mass is ejected violently outward. This, in turn, can form an accretion disk around the black hole that emits powerful X-rays and visible light. The jets are one way astronomers can indirectly infer the presence of a black hole. Those outflow emissions typically occur soon after the TDE.
That seems to be what happened in the current system to cause the sudden flare in the primary supermassive black hole. Now it had a much brighter accretion disk, so when its smaller black hole partner passed through the disk, larger than usual gas plumes were emitted. As luck would have it, that plume just happened to be pointed in the direction of an observing telescope.
Astronomers have known about so-called “David and Goliath” binary black hole systems for a while, but “this is a different beast,” said Pasham. “It doesn’t fit anything that we know about these systems. We’re seeing evidence of objects going in and through the disk, at different angles, which challenges the traditional picture of a simple gaseous disk around black holes. We think there is a huge population of these systems out there.”
Enlarge/ A new image from the Event Horizon Telescope has revealed powerful magnetic fields spiraling from the edge of a supermassive black hole at the center of the Milky Way, Sagittarius A*.
EHT Collaboration
Physicists have been confident since the1980s that there is a supermassive black hole at the center of the Milky Way galaxy, similar to those thought to be at the center of most spiral and elliptical galaxies. It’s since been dubbed Sagittarius A* (pronounced A-star), or SgrAfor short. The Event Horizon Telescope (EHT) captured the first image of SgrAtwo years ago. Now the collaboration has revealed a new polarized image (above) showcasing the black hole’s swirling magnetic fields. The technical details appear in two new papers published in The Astrophysical Journal Letters. The new image is strikingly similar to another EHT image of a larger supermassive black hole, M87*, so this might be something that all such black holes share.
The only way to “see” a black hole is to image the shadow created by light as it bends in response to the object’s powerful gravitational field. As Ars Science Editor John Timmer reported in 2019, the EHT isn’t a telescope in the traditional sense. Instead, it’s a collection of telescopes scattered around the globe. The EHT is created by interferometry, which uses light in the microwave regime of the electromagnetic spectrum captured at different locations. These recorded images are combined and processed to build an image with a resolution similar to that of a telescope the size of the most distant locations. Interferometry has been used at facilities like ALMA (the Atacama Large Millimeter/submillimeter Array) in northern Chile, where telescopes can be spread across 16 km of desert.
In theory, there’s no upper limit on the size of the array, but to determine which photons originated simultaneously at the source, you need very precise location and timing information on each of the sites. And you still have to gather sufficient photons to see anything at all. So atomic clocks were installed at many of the locations, and exact GPS measurements were built up over time. For the EHT, the large collecting area of ALMA—combined with choosing a wavelength in which supermassive black holes are very bright—ensured sufficient photons.
In 2019, the EHT announced the first direct image taken of a black hole at the center of an elliptical galaxy, Messier 87, located in the constellation of Virgo some 55 million light-years away. This image would have been impossible a mere generation ago, and it was made possible by technological breakthroughs, innovative new algorithms, and (of course) connecting several of the world’s best radio observatories. The image confirmed that the object at the center of M87is indeed a black hole.
In 2021, the EHT collaboration released a new image of M87showing what the black hole looks like in polarized light—a signature of the magnetic fields at the object’s edge—which yielded fresh insight into how black holes gobble up matter and emit powerful jets from their cores. A few months later, the EHT was back with images of the “dark heart” of a radio galaxy known as Centaurus A, enabling the collaboration to pinpoint the location of the supermassive black hole at the galaxy’s center.
SgrAis much smaller but also much closer than M87*. That made it a bit more challenging to capture an equally sharp image because SgrAchanges on time scales of minutes and hours compared to days and weeks for M87*. Physicist Matt Strassler previously compared the feat to “taking a one-second exposure of a tree on a windy day. Things get blurred out, and it can be difficult to determine the true shape of what was captured in the image.”
Enlarge/ A model of a tidal disruption, along with some observations of one.
Supermassive black holes appear to be present at the core of nearly every galaxy. Every now and again, a star wanders too close to one of these monsters and experiences what’s called a tidal disruption event. The black hole’s gravity rips the star to shreds, resulting in a huge burst of radiation. We’ve observed this happening several times now.
But we don’t entirely know why it happens—”it” specifically referring to the burst of radiation. After all, stars produce radiation through fusion, and the tidal disruption results in the spaghettification of the star, effectively pulling the plug on the fusion reactions. Black holes brighten when they’re feeding on material, but that process doesn’t look like the sudden burst of radiation from a tidal disruption event.
It turns out that we don’t entirely know how the radiation is produced. There are several competing ideas, but we’ve not been able to figure out which one of them fits the data best. However, scientists have taken advantage of an updated software package to model a tidal disruption event and show that their improved model fits our observations pretty well.
Spaghettification simulation
As mentioned above, we’re not entirely sure about the radiation source in tidal disruption events. Yes, they’re big and catastrophic, and so a bit of radiation isn’t much of a surprise. But explaining the details of that radiation—what wavelengths predominate, how quickly its intensity rises and falls, etc.—can tell us something about the physics that dominates these events.
Ideally, software should act as a bridge between the physics of a tidal disruption and our observations of the radiation they produce. If we simulate a realistic disruption and have the physics right, then the software should produce a burst of radiation that is a decent match for our observations of these events. Unfortunately, so far, the software has let us down; to keep things computationally manageable, we’ve had to take a lot of shortcuts that have raised questions about the realism of our simulations.
The new work, done by Elad Steinberg and Nicholas Stone of The Hebrew University, relies on a software package called RICH that can track the motion of fluids (technically called hydrodynamics). And, while a star’s remains aren’t fluid in the sense of the liquids we’re familiar with here on Earth, their behavior is primarily dictated by fluid mechanics. RICH was recently updated to better model radiation emission and absorption by the materials in the fluid, which made it a better fit for modeling tidal disruptions.
The researchers still had to take a few shortcuts to ensure that the computations could be completed in a realistic amount of time. The version of gravity used in the simulation isn’t fully relativistic, and it’s only approximated in the area closest to the black hole. But that sped up computations enough that the researchers could track the remains of the star from spaghettification to the peak of the event’s radiation output, a period of nearly 70 days.
