Webb telescope

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Researchers spot black hole feeding at 40x its theoretical limit

astronomy, astrophysics, black holes, Chandra telescope, cosmology, eddington limit, Science, supermassive black holes, Webb telescope / /

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.

Nature Astronomy, 2024. DOI: 10.1038/s41550-024-02402-9  (About DOIs).

Photo of John Timmer

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.

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Webb confirms: Big, bright galaxies formed shortly after the Big Bang

astronomy, cosmology, galaxies, galaxy formation, Science, Webb telescope / /

They grow up so fast —

Structure of galaxy rules out early, bright objects were supermassive black holes.

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Image of a field of stars and galaxies.

Enlarge / Some of the galaxies in the JADES images.

One of the things that the James Webb Space Telescope was designed to do was look at some of the earliest objects in the Universe. And it has already succeeded spectacularly, imaging galaxies as they existed just 250 million years after the Big Bang. But these galaxies were small, compact, and similar in scope to what we’d consider a dwarf galaxy today, which made it difficult to determine what was producing their light: stars or an actively feeding supermassive black hole at their core.

This week, Nature is publishing confirmation that some additional galaxies we’ve imaged also date back to just 300 million years after the Big Bang. Critically, one of them is bright and relatively large, allowing us to infer that most of its light was coming from a halo of stars surrounding its core, rather than originating in the same area as the central black hole. The finding implies that it formed through a continuing burst of star formation that started just 200 million years after the Big Bang.

Age checks

The galaxies at issue here were first imaged during the JADES (JWST Advanced Deep Extragalactic Survey) imaging program, which includes part of the area imaged for the Hubble Ultra Deep Field. Initially, old galaxies were identified by using a combination of filters on one of Webb’s infrared imaging cameras.

Most of the Universe is made of hydrogen, and figuring out the age of early galaxies involves looking for the most energetic transitions of hydrogen’s electron, called the Lyman series. These transitions produce photons that are in the UV area of the spectrum. But the redshift of light that’s traveled for billions of years will shift these photons into the infrared area of the spectrum, which is what Webb was designed to detect.

What this looks like in practice is that hydrogen-dominated material will emit a broad range of light right up to the highest energy Lyman transition. Above that energy, photons will be sparse (they may still be produced by things like processes that accelerate particles). This point in the energy spectrum is called the “Lyman break,” and its location on the spectrum will change based on how distant the source is—the greater the distance to the source, the deeper into the infrared the break will appear.

Initial surveys checked for the Lyman break using filters on Webb’s cameras that cut off different areas of the IR spectrum. Researchers looked for objects that showed up at low energies but disappeared when a filter that selected for higher-energy infrared photons was swapped in. The difference in energies between the photons allowed through by the two filters can provide a rough estimate of where the Lyman break must be.

Locating the Lyman break requires imaging with a spectrograph, which can sample the full spectrum of near-infrared light. Fortunately, Webb has one of those, too. The newly published study involved turning the NIRSpec onto three early galaxies found in the JADES images.

Too many, too soon

The researchers involved in the analysis only ended up with data from two of these galaxies. NIRSpec doesn’t gather as much light as one of Webb’s cameras can, and so the faintest of the three just didn’t produce enough data to enable analysis. The other two, however, produced very clear data that placed the galaxies at a redshift measure roughly z = 14, which means we’re seeing them as they looked 300 million years after the Big Bang. Both show sharp Lyman breaks, with the amount of light dropping gradually as you move further into the lower-energy part of the spectrum.

There’s a slight hint of emissions from heavily ionized carbon atoms in one of the galaxies, but no sign of any other specific elements beyond hydrogen.

One of the two galaxies was quite compact, so similar to the other galaxies of this age that we’d confirmed previously. But the other, JADES-GS-ZZ14-0, was quite distinct. For starters, it’s extremely bright, being the third most luminous distant galaxy out of hundreds we’ve imaged so far. And it’s big enough that it’s not possible for all its light to be originating from the core. That rules out the possibility that what we’re looking at is a blurred view of an active galactic nucleus powered by a supermassive black hole feeding on material.

Instead, much of the light we’re looking at seems to have originated in the stars of JADES-GS-ZZ14-0. Most of those stars are young, and there seems to be very little of the dust that characterizes modern galaxies. The researchers estimate that star formation started at least 100 million years earlier (meaning just 200 million years after the Big Bang) and continued at a rapid pace in the intervening time.

Combined with earlier data, the researchers write that this confirms that “bright and massive galaxies existed already only 300 [million years] after the Big Bang, and their number density is more than ten times higher than extrapolations based on pre-JWST observations.” In other words, there were a lot more galaxies around in the early Universe than we thought, which could pose some problems for our understanding of the Universe’s contents and their evolution.

Meanwhile, the early discovery of the extremely bright galaxy implies that there are a number of similar ones out there awaiting our discovery. This means there’s going to be a lot of demand for time on NIRSpec in the coming years.

Nature, 2024. DOI: 10.1038/s41586-024-07860-9  (About DOIs).

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Webb directly images giant exoplanet that isn’t where it should be

astronomy, exoplanets, planetary science, Science, Webb telescope / /

How do you misplace that? —

Six times bigger than Jupiter, the planet is the oldest and coldest yet imaged.

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A dark background with read and blue images embedded in it, both showing a single object near an area marked with an asterisk.

Enlarge / Image of Epsilon Indi A at two wavelengths, with the position of its host star indicated by an asterisk.

T. Müller (MPIA/HdA), E. Matthews (MPIA)

We have a couple of techniques that allow us to infer the presence of an exoplanet based on its effects on the light coming from its host star. But there’s an alternative approach that sometimes works: image them directly. It’s much more limited, since the planet has to be pretty big and orbiting far away enough from its star to avoid having light coming from the planet swamped by the far more intense starlight.

Still, it has been done. Massive exoplanets have been captured relatively shortly after their formation, when the heat generated by the collapse of material into the planet causes them to glow in the infrared. But the Webb telescope is far more sensitive than any infrared observatory we’ve ever built, and it has managed to image a relatively nearby exoplanet that’s roughly as old as the ones in our Solar System.

Looking directly at a planet

What do you need to directly image a planet that’s orbiting a star light-years away? The first thing is a bit of hardware called a coronagraph attached to your telescope. This is responsible for blocking the light from the star the planet is orbiting; without it, that light will swamp any other sources in the exosolar system. Even with a good coronagraph, you need the planets to be orbiting at a significant distance from the star so that they’re cleanly separated from the signal being blocked by the coronagraph.

Then, you need the planet to emit a fair bit of light. While the right surface composition might allow the planet to be highly reflective, that’s not going to be a great option considering the distances we’d need the planet to be orbiting to be visible at all. Instead, the planets we’ve spotted so far have been young and still heated by the processes that brought material together to form a planet in the first place. Being really big doesn’t hurt matters either.

Put that all together, and what you expect to be able to spot is a very young, very distant planet that’s massive enough to fall into the super-Jupiter category.

But the launch of the Webb Space Telescope has given us new capabilities in the infrared range, and a large international team of researchers pointed it at a star called Epsilon Indi A. It’s a bit less than a dozen light years away (which is extremely close in astronomical terms), and the star is both similar in size and age to the Sun, making it an interesting target for observations. Perhaps most significantly previous data had suggested a large exoplanet would be found, based on indications that the star was apparently shifting as the exoplanet tugged on it during its orbit.

And there was in fact an indication of a planet there. It just didn’t look much like the expected planet. “It’s about twice as massive, a little farther from its star, and has a different orbit than we expected,” said Elisabeth Matthews, one of the researchers involved.

At the moment, there’s no explanation for the discrepancy. The odds of it being an unrelated background object are extremely small. And a reanalysis of data on the motion of Epsilon Indi A suggests that this is likely to be the only large planet in the system—there could be additional planets, but they’d be much smaller. So, the researchers named the planet Epsilon Indi Ab, even though that was the same name given to the planet that doesn’t seem to match this one’s properties.

Big, cold, and a bit enigmatic

The revised Epsilon Indi Ab is a large planet, estimated at roughly six times the mass of Jupiter. It’s also orbiting at roughly the same distance as Neptune. It’s generally bright across the mid-infrared, consistent with a planet that’s roughly 275 Kelvin—not too far off from room temperature. That’s also close to what we would estimate for its temperature simply based on the age of the planet. That makes it the coolest exoplanet ever directly imaged.

While the signal from the planet was quite bright at a number of wavelengths, the planet couldn’t even be detected in one area of the spectrum (3.5 to 5 micrometers, for the curious). That’s considered an indication that the planet has high levels of elements heavier than helium, and a high ratio of carbon to oxygen. The gap in the spectrum may influence estimates of the planet’s age, so further observations will probably need to be conducted to clarify why there are no emissions at these wavelengths.

The researchers also suggest that imaging more of these cool exoplanets should be a priority, given that we should be cautious about extrapolating anything from a single example. So, in that sense, this first exoplanet imaging provides an important confirmation that, with Webb and its coronagraph, we’ve now got the tools we need to do so, and they work very well.

Nature, 2024. DOI: 10.1038/s41586-024-07837-8  (About DOIs).

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A supernova caused the BOAT gamma ray burst, JWST data confirms

astronomy, astrophysics, B.O.A.T., Gamma ray bursts, nucleosynthesis, Physics, Science, Webb telescope / /

Still the BOAT —

But astronomers are puzzled by the lack of signatures of expected heavy elements.

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Artist's visualization of GRB 221009A showing the narrow relativistic jets — emerging from a central black hole — that gave rise to the brightest gamma ray burst yet detected.

Enlarge / Artist’s visualization of GRB 221009A showing the narrow relativistic jets—emerging from a central black hole—that gave rise to the brightest gamma-ray burst yet detected.

Aaron M. Geller/Northwestern/CIERA/ ITRC&DS

In October 2022, several space-based detectors picked up a powerful gamma-ray burst so energetic that astronomers nicknamed it the BOAT (Brightest Of All Time). Now they’ve confirmed that the GRB came from a supernova, according to a new paper published in the journal Nature Astronomy. However, they did not find evidence of heavy elements like platinum and gold one would expect from a supernova explosion, which bears on the longstanding question of the origin of such elements in the universe.

As we’ve reported previously, gamma-ray bursts are extremely high-energy explosions in distant galaxies lasting between mere milliseconds to several hours. There are two classes of gamma-ray bursts. Most (70 percent) are long bursts lasting more than two seconds, often with a bright afterglow. These are usually linked to galaxies with rapid star formation. Astronomers think that long bursts are tied to the deaths of massive stars collapsing to form a neutron star or black hole (or, alternatively, a newly formed magnetar). The baby black hole would produce jets of highly energetic particles moving near the speed of light, powerful enough to pierce through the remains of the progenitor star, emitting X-rays and gamma rays.

Those gamma-ray bursts lasting less than two seconds (about 30 percent) are deemed short bursts, usually emitting from regions with very little star formation. Astronomers think these gamma-ray bursts are the result of mergers between two neutron stars, or a neutron star merging with a black hole, comprising a “kilonova.” That hypothesis was confirmed in 2017 when the LIGO collaboration picked up the gravitational wave signal of two neutron stars merging, accompanied by the powerful gamma-ray bursts associated with a kilonova.

The October 2022 gamma-ray burst falls into the long category, lasting over 300 seconds. GRB 221009A triggered detectors aboard NASA’s Fermi Gamma-ray Space Telescope, the Neil Gehrels Swift Observatory, and Wind spacecraft, among others, just as gamma-ray astronomers had gathered for an annual meeting in Johannesburg, South Africa. The powerful signal came from the constellation Sagitta, traveling some 1.9 billion years to Earth.

Several papers were published last year reporting on the analytical results of all the observational data. Those findings confirmed that GRB 221009A was indeed the BOAT, appearing especially bright because its narrow jet was pointing directly at Earth. But the various analyses also yielded several surprising results that puzzled astronomers. Most notably, a supernova should have occurred a few weeks after the initial burst, but astronomers didn’t detect one, perhaps because it was very faint, and thick dust clouds in that part of the sky were dimming any incoming light.

Swift’s X-ray Telescope captured the afterglow of GRB 221009A about an hour after it was first detected.

Enlarge / Swift’s X-ray Telescope captured the afterglow of GRB 221009A about an hour after it was first detected.

NASA/Swift/A. Beardmore (University of Leicester)

That’s why Peter Blanchard of Northwestern University and his fellow co-authors decided to wait six months before undertaking their own analysis, relying on data collected during the GRB’s later phase by the Webb Space Telescope’s Near Infrared Spectrograph. They augmented that spectral data with observations from ALMA (Atacama Large Millimeter/Submillimeter Array) in Chile so they could separate light from the supernova and the GRB afterglow. The most significant finding was the telltale signatures of key elements like calcium and oxygen that one would expect to find with a supernova.

Yet the supernova wasn’t brighter than other supernovae associated with less energetic GRBs, which is puzzling. “You might expect that the same collapsing star producing a very energetic and bright GRB would also produce a very energetic and bright supernova,” said Blanchard. “But it turns out that’s not the case. We have this extremely luminous GRB, but a normal supernova.” The authors suggest that this might have something to do with the shape and structure of the relativistic jet, which was much narrower than other GRB jets, resulting in a more focused and brighter beam of light.

The data held another surprise for astronomers. The only confirmed source of heavy elements in the universe to date is the merging of binary neutron stars. But per Blanchard, there are far too few neutron star mergers to account for the abundance of heavy elements, so there must be another source. One hypothetical additional source is a rapidly spinning massive star that collapses and explodes into a supernova. Alas, there was no evidence of heavy elements in the JWST spectral data regarding the BOAT.

“When we confirmed that the GRB was generated by the collapse of a massive star, that gave us the opportunity to test a hypothesis for how some of the heaviest elements in the universe are formed,” said Blanchard. “We did not see signatures of these heavy elements, suggesting that extremely energetic GRBs like the BOAT do not produce these elements. That doesn’t mean that all GRBs do not produce them, but it’s a key piece of information as we continue to understand where these heavy elements come from. Future observations with JWST will determine if the BOAT’s ‘normal’ cousins produce these elements.”

Nature Astronomy, 2024. DOI: 10.1038/s41550-024-02237-4  (About DOIs).

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Study: Conflicting values for Hubble Constant not due to measurement error

astrophysics, expansion of the universe, Hubble constant, Science, Webb telescope / /

A long-standing tension —

Something else is influencing the expansion rate of the Universe.

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This image of NGC 5468, a galaxy located about 130 million light-years from Earth, combines data from the Hubble and James Webb space telescopes.

Enlarge / This image of NGC 5468, about 130 million light-years from Earth, combines data from the Hubble and Webb space telescopes.

NASA/ESA/CSA/STScI/A. Riess (JHU)

Astronomers have made new measurements of the Hubble Constant, a measure of how quickly the Universe is expanding, by combining data from the Hubble Space Telescope and the James Webb Space Telescope. Their results confirmed the accuracy of Hubble’s earlier measurement of the Constant’s value, according to their recent paper published in The Astrophysical Journal Letters, with implications for a long-standing discrepancy in values obtained by different observational methods known as the “Hubble tension.”

There was a time when scientists believed the Universe was static, but that changed with Albert Einstein’s general theory of relativity. Alexander Friedmann published a set of equations in 1922 showing that the Universe might actually be expanding, with Georges Lemaitre later making an independent derivation to arrive at that same conclusion. Edwin Hubble confirmed this expansion with observational data in 1929. Prior to this, Einstein had been trying to modify general relativity by adding a cosmological constant in order to get a static universe from his theory; after Hubble’s discovery, legend has it, he referred to that effort as his biggest blunder.

As previously reported, the Hubble Constant is a measure of the Universe’s expansion expressed in units of kilometers per second per megaparsec. So, each second, every megaparsec of the Universe expands by a certain number of kilometers. Another way to think of this is in terms of a relatively stationary object a megaparsec away: Each second, it gets a number of kilometers more distant.

How many kilometers? That’s the problem here. There are basically three methods scientists use to measure the Hubble Constant: looking at nearby objects to see how fast they are moving, gravitational waves produced by colliding black holes or neutron stars, and measuring tiny deviations in the afterglow of the Big Bang known as the Cosmic Microwave Background (CMB). However, the various methods have come up with different values. For instance, tracking distant supernovae produced a value of 73 km/s Mpc, while measurements of the CMB using the Planck satellite produced a value of 67 km/s Mpc.

Just last year, researchers made a third independent measure of the Universe’s expansion by tracking the behavior of a gravitationally lensed supernova, where the distortion in space-time caused by a massive object acts as a lens to magnify an object in the background. The best fits of those models all ended up slightly below the value of the Hubble Constant derived from the CMB, with the difference being within the statistical error. Values closer to those derived from measurements of other supernovae were a considerably worse fit for the data. The method is new, with considerable uncertainties, but it did provide an independent means of getting at the Hubble Constant.

Comparison of Hubble and Webb views of a Cepheid variable star.

Enlarge / Comparison of Hubble and Webb views of a Cepheid variable star.

NASA/ESA/CSA/STScI/A. Riess (JHU)

“We’ve measured it using information in the cosmic microwave background and gotten one value,” Ars Science Editor John Timmer wrote. “And we’ve measured it using the apparent distance to objects in the present-day Universe and gotten a value that differs by about 10 percent. As far as anyone can tell, there’s nothing wrong with either measurement, and there’s no obvious way to get them to agree.” One hypothesis is that the early Universe briefly experienced some kind of “kick” from repulsive gravity (akin to the notion of dark energy) that then mysteriously turned off and vanished. But it remains a speculative idea, albeit a potentially exciting one for physicists.

This latest measurement builds on last year’s confirmation based on Webb data that Hubble’s measurements of the expansion rate were accurate, at least for the first few “rungs” of the “cosmic distance ladder.” But there was still the possibility of as-yet-undetected errors that might increase the deeper (and hence further back in time) one looked into the Universe, particularly for brightness measurements of more distant stars.

So a new team made additional observations of Cepheid variable stars—a total of 1,000 in five host galaxies as far out as 130 million light-years—and correlated them with the Hubble data. The Webb telescope is able to see past the interstellar dust that has made Hubble’s own images of those stars more blurry and overlapping, so astronomers could more easily distinguish between individual stars.

The results further confirmed the accuracy of the Hubble data. “We’ve now spanned the whole range of what Hubble observed, and we can rule out a measurement error as the cause of the Hubble Tension with very high confidence,” said co-author and team leader Adam Riess, a physicist at Johns Hopkins University. “Combining Webb and Hubble gives us the best of both worlds. We find that the Hubble measurements remain reliable as we climb farther along the cosmic distance ladder. With measurement errors negated, what remains is the real and exciting possibility that we have misunderstood the Universe.”

The Astrophysical Journal Letters, 2024. DOI: 10.3847/2041-8213/ad1ddd  (About DOIs).

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