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When I heard Stephen Hawking extoll the mysteries of black holes, I knew theoretical physics was what I wanted to do. There is still so much to learn about these strange regions, says Chanda Prescod-Weinstein
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Tag: black holes
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How the weird and powerful pull of black holes made me a physicist
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Tiny black holes hiding in the sun could trace out stunning patterns
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Primordial black holes could take on intricate orbits inside the sun and similar stars
Vitorio A. De Lorenci
Our solar system might be chock-full of tiny black holes, with some tracing out beautiful patterns resembling Spirograph drawings as they orbit inside the sun.
Invisible dark matter seems to account for the vast majority of mass in the universe, but scientists don’t know what exactly it is. Hypothetical black holes that formed shortly after the big bang, called primordial black holes, are one dark matter candidate. If they do exist, our solar system should be…
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Astronomers using AI to prepare for ton of data from new telescopes
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It’s a problem that will be repeated in other places over the coming decade. As astronomers construct giant cameras to image the entire sky and launch infrared telescopes to hunt for distant planets, they will collect data on unprecedented scales.
“We really are not ready for that, and we should all be freaking out,” says Cecilia Garraffo, a computational astrophysicist at the Harvard-Smithsonian Center for Astrophysics. “When you have too much data and you don’t have the technology to process it, it’s like having no data.”
In preparation for the information deluge, astronomers are turning to AI for assistance, optimizing algorithms to pick out patterns in large and notoriously finicky data sets. Some are now working to establish institutes dedicated to marrying the fields of computer science and astronomy—and grappling with the terms of the new partnership.
In November 2022, Garraffo set up AstroAI as a pilot program at the Center for Astrophysics. Since then, she has put together an interdisciplinary team of over 50 members that has planned dozens of projects focusing on deep questions like how the universe began and whether we’re alone in it. Over the past few years, several similar coalitions have followed Garraffo’s lead and are now vying for funding to scale up to large institutions.
Garraffo recognized the potential utility of AI models while bouncing between career stints in astronomy, physics, and computer science. Along the way, she also picked up on a major stumbling block for past collaboration efforts: the language barrier. Often, astronomers and computer scientists struggle to join forces because they use different words to describe similar concepts. Garraffo is no stranger to translation issues, having struggled to navigate an English-only school growing up in Argentina. Drawing from that experience, she has worked to put people from both communities under one roof so they can identify common goals and find a way to communicate.
Astronomers had already been using AI models for years, mainly to classify known objects such as supernovas in telescope data. This kind of image recognition will become increasingly vital when the Vera C. Rubin Observatory opens its eyes next year and the number of annual supernova detections quickly jumps from hundreds to millions. But the new wave of AI applications extends far beyond matching games. Algorithms have recently been optimized to perform “unsupervised clustering,” in which they pick out patterns in data without being told what specifically to look for. This opens the doors for models pointing astronomers toward effects and relationships they aren’t currently aware of. For the first time, these computational tools offer astronomers the faculty of “systematically searching for the unknown,” Garraffo says. In January, AstroAI researchers used this method to catalogue over 14,000 detections from x-ray sources, which are otherwise difficult to categorize.
Another way AI is proving fruitful is by sniffing out the chemical composition of the skies on alien planets. Astronomers use telescopes to analyze the starlight that passes through planets’ atmospheres and gets soaked up at certain wavelengths by different molecules. To make sense of the leftover light spectrum, astronomers typically compare it with fake spectra they generate based on a handful of molecules they’re interested in finding—things like water and carbon dioxide. Exoplanet researchers dream of expanding their search to hundreds or thousands of compounds that could indicate life on the planet below, but it currently takes a few weeks to look for just four or five compounds. This bottleneck will become progressively more troublesome as the number of exoplanet detections rises from dozens to thousands, as is expected to happen thanks to the newly deployed James Webb Space Telescope and the European Space Agency’s Ariel Space Telescope, slated to launch in 2029.
Processing all those observations is “going to take us forever,” says Mercedes López-Morales, an astronomer at the Center for Astrophysics who studies exoplanet atmospheres. “Things like AstroAI are showing up at the right time, just before these faucets of data are coming toward us.”
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Einstein was right about the way matter plunges into black holes
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We’ve seen the waterfall of matter plunging into a black hole
Buradaki / Alamy Stock Photo
A strange area around black holes called the “plunging region” has been spotted for the first time. This area, where matter stops circling a black hole and instead falls straight in, was predicted by Albert Einstein’s theory of general relativity, but it has never been observed before. Studying plunging regions could teach us about how black holes form and evolve, as well as reveal new information about the fundamental nature of space-time.
When any matter gets too close to a black hole, it rips apart and forms an orbiting ring around it called an accretion disc. General relativity predicts there should be an inner boundary to the accretion disc past which nothing can orbit the black hole – instead, it should plunge straight in, rapidly accelerating to near the speed of light as it falls.
“It’s like a river turning into a waterfall, and until now we’ve only been looking at the river,” says Andrew Mummery at the University of Oxford. “If Einstein was wrong, then it would be stable all the way down – there would only be a river.” Now we’ve gotten our first peek at the waterfall, suggesting Einstein was correct.
Mummery and his colleagues spotted evidence of the plunging region around a black hole in a binary system called MAXI J1820+070, which is about 10,000 light years from Earth. They used data from the Nuclear Spectroscopic Telescope Array (NuSTAR), a space-based X-ray telescope, to build models of the light from the black hole’s accretion disc.
They found the models only fit the data when they included the light emitted by matter in the plunging region in addition to light from the accretion disc. “Before, we sort of thought that anything that crosses this boundary would have no time to really radiate appreciably before it plunges into the black hole”, so researchers wouldn’t see anything, says Greg Salvesen at Los Alamos National Laboratory in New Mexico, who was not involved with this work. “But it turns out that this plunging region gives you extra light that you wouldn’t have expected.”
This extra light could solve a long-standing problem in X-ray astronomy, in which black holes appear to be spinning faster than theory predicts. The spin of a black hole and the brightness of the area around it are connected, so adding some extra light could bring the spins back in line with predictions. “Black hole spins tell us about all kinds of things, so if we could measure it better, we could answer loads of questions in astrophysics,” says Salvesen.
That includes questions about the nature of gravity and space-time itself, because plunging regions are some of the most extreme regions of space we can observe. The plunging region is just outside the event horizon, beyond which the gravitational forces are so strong, no matter or even light can escape.
“Technically, if the matter had a rocket it could escape the plunging region, but it’s doomed – its orbit has become unstable and it’s rapidly accelerating toward the speed of light,” says Mummery. “This stuff has about as much chance of coming back as water off the edge of a waterfall.” The researchers are now trying to make more observations of these strange cosmic waterfalls to illuminate the conditions in these extraordinary areas.
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How could we give boring blobby galaxies a new, exciting shape?
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Dead Planets Society is a podcast that takes outlandish ideas about how to tinker with the cosmos – from snapping the moon in half to causing a gravitational wave apocalypse – and subjects them to the laws of physics to see how they fare. Listen on Apple, Spotify or on our podcast page.
For the most part, galaxies only come in two shapes: spirals and blobs. While spirals can be majestic viewed from the right angles, the lack of variety can get boring over the cosmic eons. So in this episode of Dead Planets Society, it’s time to spice things up, galactically.
Our hosts Leah Crane and Chelsea Whyte are joined by Vivian U at the University of California, Irvine, an astronomer who studies how galaxies evolve when they smash together and warp one another. In the real world, galactic collisions can create strange swirls and many-armed behemoths, but over time the chaos from the smash-up results in just another blob. To make a lasting change, we’ll need tools with a bit more precision.
That’s where the supermassive black holes come in. They might be able to carve gaps through the dust and gas of a galaxy, creating more detailed images. But gravity tends to complicate things, and eventually even those black holes would devour too much matter and merge together, resulting in yet another blob. Perhaps dark matter could be used instead to create an invisible scaffold that shapes the distribution of the regular matter that we can see.
Building such a strange-shaped galaxy – especially one unlike anything that a natural galactic collision would create, such as a galaxy with sharp corners or one in a recognisable image like a giraffe – might be a way to signal to aliens or future astronomers that we are here and we have incredible cosmic powers.
In fact, perhaps this has already been done to the Milky Way by some strange alien force – after all, we can’t see our home galaxy from outside of it. We only know its shape by counting the stars that we can see in each direction and building theoretical models, so we can rule out that our galaxy is in the shape of a giraffe or something else wildly out of the ordinary. But if it were, say, a square instead of a spiral, it might be difficult for astronomers to tell the difference.
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Black holes scramble information – but may not be the best at it
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Previously, physicists theorised that black holes are the fastest possible scramblers of information
MARK GARLICK/SCIENCE PHOTO LIBRARY/Alamy
When two quantum objects interact, all the information they carry becomes scrambled. Now, physicists have calculated a fundamental limit for how quickly this can happen.
One striking example of information scrambling happens in black holes, says Victor Galitski at the University of Maryland. When objects fall into these super-dense bodies, some of the information they contain reemerges in the black hole’s emitted radiation – but in a highly scrambled form.
In fact, physicists have theorised that black holes…
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Kill the sun! How wild thought experiments drive scientific discovery
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Listen, it’s not that I actually want to kill the sun – I just want to figure out how. But when I told my colleagues at New Scientist that I was recruiting scientists to do just this, I was met with baffled looks. I write about space every single day, and I find it endlessly fascinating. I feel at home with the mysteries of the cosmos, so why would I want to ruin any part of it, let alone kill our beloved and essential star?
Despite their confusion, my colleagues indulged me and my partner in destruction, our US editor Chelsea Whyte. We started reaching out to free-thinking astrophysicists and planetary scientists, asking them to join us on our podcast, Dead Planets Society. With them we began tinkering with the universe – in our minds, at least – not only killing the sun but imagining a gravitational wave apocalypse, what would happen if sliced the moon in half or chiseled the Earth into a cube.
As we thought about questions to ask the guests we had on the show, who are all university professors and proper scientists, we found ourselves looking up tidbits about gravity and planetary science, doing calculations of escape velocities and Roche limits. As much as the podcast was a flight of fancy – a fun game to play – it also started to feel a bit like we were doing science. We realised that seemingly absurd thought experiments have always been at heart of the scientific method.
Science began with thought experiments rather than empirical experiments that are carried out with lab benches or telescopes, says philosopher H. Peter Steeves at DePaul University. Galileo Galilei, one of the founders of the modern scientific method in the 16th century, is remembered for dropping a feather and a hammer from the Leaning Tower of Pisa. By demonstrating they fell at the same rate, the story goes, Galileo overturned a 2000-year-old idea of how gravity worked. “[It] is as fanciful a story as Newton getting hit on the head with an apple,” says Steeves. “But there is evidence that he engaged in a thought experiment to demonstrate how Aristotle’s conception of gravity was incorrect.”
Over the course of history, we have become far better at performing practical experiments, but thought experiments remain important. For example, Albert Einstein, who also transformed our view of the universe by grappling with gravity, is renowned for conjuring absurd scenarios in his head. One evening as he was riding in a streetcar, he imagined what the world would look like if he were travelling at the speed of light. After years of frustration trying to explain the behaviour of light, this was the seed that grew into special relativity in 1905. “Imagining things on this grand scale presents the familiar in a different way,” says philosopher Guy Kahane at the University of Oxford.
At Dead Planets Society, we like to imagine what would happen if Earth were cube-shaped
Vitaga/Adobe Stock
This is no less true today. Indulging in thought experiments is common practice among theorists trying to understand black holes and what these extreme objects reveal about the nature of reality. For instance, the intense gravity of a black holes mean that you can’t place any scientific instruments right next to one or inside one in order transmit data back out. So theorists spend a whole lot of time thinking about and calculating what might happen to an observer in one of those positions – leading to all kinds of surprising insights about concepts like time and causality. “Once you’re thinking in this playful way, you start to see things that you wouldn’t see otherwise,” says Kahane.
In the first episode of season two of Dead Planets Society, we carry out our own black hole thought experiment. Black holes are often thought of as massive voids that swallow everything that comes near them – they are the ultimate destroyers. So what would we learn by trying to demolish one? Searching for the black hole’s weak spot, we considered using infinitely fast spacecraft to escape a black hole with some of its mass, or unrealistically powerful magnets to rip it apart. We can’t actually build these cosmic tools, but imagining them reframed how we thought about black holes.
Over the course of recording the episode, this led us to think of black holes in new ways. Using quantum mechanics, we can picture them as incredibly massive objects that happen to have escape velocities higher than the speed of light, or according to general relativity, they are infinitely deep divots in space-time itself. The latter, for the record, is much harder to destroy.
Freedom from seriousness is an opportunity that Chelsea and I run wild with in the podcast. Cosmologists can benefit from thinking like this too, says Wendy Freedman at the University of Chicago. As we observe more and more astronomical anomalies, jarring with the standard model of cosmology, it is becoming evident that our best empirical theory of the universe is due an overhaul. “As the data get better and better and the theories get more and more creative, something will fit,” says Freedman. “We need wacky ideas right now, because there are so many things that we don’t understand.”
Nobel prizewinning cosmologist Jim Peebles, one of the architects of the standard model, agrees that this sort of playful thinking “is an important part of science”, so long as you get the balance right. “I indulge in blue-sky thinking; it’s… a time sink if overdone and a loss if suppressed,” he says.
Mike Myers as Dr Evil
FlixPix / Alamy
Now, I am not claiming that Chelsea and I are going to solve the problems with the standard model of cosmology by considering how to give the Milky Way more arms. But I do think that something is lost when scientists take themselves too seriously. Sure, the conversations we had while making Dead Planets Society are a little goofy, but they are also some of the most thought-provoking exchanges I have ever had.
“If you cut the moon in half, blew up the sun or suddenly turned the Earth into a cube, well, this is all interesting – and not just to Dr Evil, a Bond villain or the Borg,” says Steeves. “It pushes us both to think about limit cases given our current understanding of science and to have fun while doing it. Both of these are important: the pushing and the fun.”
If we weren’t having fun, we never would have realised that if the sun were to disappear, whales would outlive humans. It turns out this is true for most other types of apocalypses too, so underwater life may have a better chance out there in the universe than land-based organisms. We certainly would never have thought of using aerogel as a sort of cosmic fly strip to catch asteroids.
Steeves quotes Rob Reiner’s cult movie This Is Spinal Tap, which he describes as a font of scientific truths: “It’s such a fine line between stupid and clever.” In other words, turning our silliness up to 11 doesn’t mean we won’t end up with clever or interesting ideas.
This Is Spinal Tap holds surprising scientific truths
Pictorial Press Ltd / Alamy
The universe is big and messy and sometimes it feels like anything that can happen, cosmically, probably is happening somewhere out there. That is the beauty of it. So idle speculation, no matter how outlandish, is not necessarily useless. It can help reveal the secrets of the universe – even if it does mean thinking like a cartoon villain and, sometimes, trying to kill the sun.
And as for my colleagues’ bafflement, I will let Steeves respond to that: “The sanity question is hard. Are you a maniac, Leah? Perhaps. But in the very best way.” I’ll carry that compliment with me as I continue to imagine exploring and occasionally ruining the cosmos.
Dead Planets Society is a hilariously destructive podcast about the cosmos from New Scientist. In each episode, hosts Leah Crane and Chelsea Whyte explore what would happen if they were given cosmic powers to rearrange the universe. They speak with astronomers, cosmologists and geologists to find out what the consequences would be if we punched a hole in a planet, unified the asteroid belt or destroyed the sun. Season two of Dead Planets Society is available to listen to here.
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Supermassive black holes may provide a nursery for mini ones to grow
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We may have a clearer understanding of why the accretion disc around large black holes is so bright
Dana Berry/SkyWorks Digital/NASA
Thousands of relatively small black holes may be circling the supermassive black holes that lurk at the centres of galaxies. The idea would not only help explain how small black holes grow larger, it would also give us a new understanding of why supermassive black holes appear so bright.
The centres of galaxies are extraordinarily dense, so matter – including relatively small, or stellar-mass, black holes – tends to accumulate there. Some of…
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How to destroy a black hole
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Dead Planets Society is a podcast that takes outlandish ideas about how to tinker with the cosmos – from snapping the moon in half to causing a gravitational wave apocalypse – and subjects them to the laws of physics to see how they fare. Listen on Apple, Spotify or on our podcast page.
Dead Planets Society is back for season two, and our intrepid hosts Chelsea Whyte and Leah Crane are going after the toughest adversaries in the universe: black holes. These cosmic behemoths are so big and so sturdy that they can devour pretty much anything that is thrown at them without so much as flinching – so is it even possible to destroy one?
Black holes are expected to evaporate on their own thanks to Hawking radiation, a process by which they emit a slow leak of particles, but this would take much longer than the age of the universe to happen naturally. Just waiting isn’t really an option, so our hosts are joined by black hole astronomer Allison Kirkpatrick at the University of Kansas in an attempt to find a faster way.
Throwing anything at the black hole won’t really help either, whether it is a planet made of TNT or clumps of antimatter – the black hole will just swallow it up and get even more massive.
That doesn’t mean it is impossible to dream up something that would destroy a black hole by falling in. The escape velocity of a black hole – the speed at which one would have to fly away from its centre to escape its gravitational influence – is faster than the speed of light, so a ship that could travel beyond that physical limitation might be able to escape, or a bomb that could explode faster than the speed of light might be able to make a dent.
That is only the beginning of the outlandish ways to potentially wreck a black hole. Theoretical objects called white holes might work, but that could mean sending the black holes back in time, which wouldn’t be great for the past or the future.
A black hole could perhaps be stretched out, but whether that works depends on the question of how quantum mechanics and general relativity mesh together, which may be the biggest unsolved question in physics. Our hosts find that giant magnets could help, with potentially horrifying results.
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A surprisingly enormous black hole has been found in our galaxy
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This artist’s impression shows the orbits of both a massive stellar black hole and its companion star
ESO/L. Calçada
Astronomers have found the largest stellar black hole ever spotted, dubbed Gaia-BH3. It has a mass 33 times that of the sun, dwarfed only by supermassive black holes and those that formed through mergers of other black holes.
At about 2000 light years away, Gaia-BH3 is also the second-nearest black hole to Earth ever discovered. George Seabroke at University College London and his colleagues found this stellar black hole, meaning it formed from a star that had reached the end of its life, using the Gaia space telescope.
No light can escape a black hole, so most of them are found by spotting the glow of the hot material orbiting them and falling in. However, BH3 is dormant, not devouring any material. Instead, the researchers found it by noticing the strange motion of a star that seemed to be orbiting a patch of empty space.
This star itself is unusual, too – it is made almost entirely of hydrogen and helium. Most stars contain at least some heavier elements, which formed in the hearts of massive stars and were distributed throughout space by supernovae. But the first generations of stars would have had very low amounts of heavy elements. The composition of BH3’s partner star suggests that the enormous star that eventually collapsed to form BH3 was also one of these primitive objects, which may have evolved differently from the way massive stars do today. This would explain how the black hole got so huge. Its size would be difficult to account for if it had evolved more like regular stars do.
Finding such a massive black hole wasn’t a complete surprise – experiments that hunt for gravitational waves, which are ripples in space-time caused by the motions of heavy objects, have found signs of them in other galaxies.
“From these gravitational wave measurements, we should be expecting to see such black holes in our own galaxy, but we hadn’t until now,” says Seabroke. And this should just be the beginning, he says: “The star is extremely bright, and generally if you find something this bright, you expect to find many more fainter.”
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