Tag: black holes

The Mystery of How Supermassive Black Holes Merge

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However, modeling has shown that it is difficult to scatter enough stars toward the black holes to solve the final-parsec problem.

Alternatively, each black hole might have a small disk of gas around it, and these disks might draw in material from a wider disk that surrounds the empty region carved out by the holes. “The disks around them are being fed from the wider disk,” Taylor said, and that means, in turn, that their orbital energy can leak into the wider disk. “It seems a very efficient solution,” Natarajan said. “There’s a lot of gas available.”

In January, Blecha and her colleagues investigated the idea that a third black hole in the system could provide a solution. In some cases where two black holes have stalled, another galaxy could begin to merge with the first two, bringing with it an additional black hole. “You can have a strong three-body interaction,” Blecha said. “It can take away energy and greatly decrease the merger timescale.” In some scenarios, the lightest of the three holes is ejected, but in others all three merge.

Tests on the Horizon

The task now is to work out which solution is correct, or if multiple processes are at play.

Alonso-Álvarez hopes to test his idea by seeking a signal of self-interacting dark matter in upcoming pulsar timing array data. Once black holes get closer than the final parsec, they shed angular momentum primarily by emitting gravitational waves. But if self-interacting dark matter is at play, then we should see it sap some of the energy at distances around the parsec limit. This in turn would make for less energetic gravitational waves, Alonso-Álvarez said.

Hai-Bo Yu, a particle physicist at the University of California, Riverside who is a proponent of self-interacting dark matter, said the idea is plausible. “It’s an avenue to look for microscopic features of dark matter from gravitational wave physics,” he said. “I think that’s just fascinating.”

The European Space Agency’s Laser Interferometer Space Antenna (LISA) spacecraft, a gravitational wave observatory that’s set to launch in 2035, might give us even more answers. LISA will pick up the strong gravitational waves emitted by merging supermassive black holes in their final days. “With LISA we will actually see supermassive black holes merging,” Pacucci said. The nature of that signal could reveal “particular traits that show the slowing process,” solving the final-parsec problem.

Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.

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December 1, 2024
Super-bright black holes could reveal if the universe is pixelated

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Artist’s representation of a galaxy with a brilliant quasar at its centre

NASA, ESA and J. Olmsted (STScI)

Space-time, the so-called fabric of physical reality, may be made of tiny, discrete pieces stitched together. A preliminary analysis of the way matter orbits quasars suggests we could find evidence of this cosmic quilt in the universe’s most extreme neighbourhoods.

Much of the understanding we have of the make-up of our universe comes from probing matter at smaller and smaller scales. Think of fluids, says Jonathan Gorard…

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November 21, 2024
Solving Stephen Hawking’s black hole information paradox has raised new mysteries

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In March 1974, Stephen Hawking published the paper that made his name. It contained the revelation that black holes – gravitational giants from which nothing, not even light, can escape – don’t grow and grow until the end of time, but instead slowly shrink as they release particles in a phenomenon now called Hawking radiation.

The implications were mystifying. Hawking’s calculations showed that the radiation should be random, offering no way to predict what types of particles will emerge. The problem was that anything that falls into a black hole contains information – what sorts of particles it is made of, their configurations, their quantum states – and if what comes back out is random, that information is lost forever as soon as the object is sucked in. But physics operates on the idea that, if we know all the information about a system, we can reconstruct its past and predict its future.

Can black holes really do the impossible, destroying anything and everything they pull in? That prospect is called the black hole information paradox. It has occupied physicists for decades, not only because it highlights the profound disconnect between general relativity, Albert Einstein’s theory of gravity, and quantum theory – but also because it offers the hope of a reconciliation.

Now, 50 years after its inception, the paradox is all but solved. And yet physicists aren’t celebrating as you might expect because their solution hasn’t resulted in a long-sought quantum theory of gravity. In many ways, it has only deepened the mystery of what happens inside black…

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October 21, 2024
What does it mean to “look” at a black hole?

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A simulation of a black hole

Hotaka Shiokawa/EHT

General relativity teaches us that reality is, in some sense, a matter of perspective. Consider how someone who is “falling” into a black hole sees something completely different to an observer trying to watch that someone cross the event horizon, a black hole’s edge.

The person actually making the transition beyond this point of no return won’t see anything unusual, although they will notice gravity is getting stronger and stronger. By contrast, the observer will find that no matter how long they watch, the person never seems to actually cross the event…

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October 16, 2024
Sophie Koudmani: The astrophysicist unravelling the origins of supermassive black holes

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Supermassive black holes are, as you might expect, rather large – millions and sometimes billions of times as massive as the sun. They lurk at the centre of all large galaxies, including our Milky Way, shaping the growth of these cosmic structures. And yet we can say precious little for certain about how they form and why they grow so big.

These mysteries have come into sharper focus in recent years thanks to the James Webb Space Telescope (JWST), which has peered back in deep time to spot a surprising abundance of supermassive black holes in the early universe. Intriguingly, it seems that just a few hundred million years after the big bang brought our universe into being, the cosmos already contained black holes that were far too hefty to make sense under our current models of how the cosmos evolved. There simply hadn’t been enough time for anything that enormous to form.

Sophie Koudmani, an astrophysicist at the University of Cambridge, is among those trying to solve this conundrum. She uses supercomputer simulations to model galaxies and supermassive black holes in the early universe, testing ideas about their origins and growth and even predicting what we should be looking for in future observations.

Koudmani spoke to New Scientist about why supermassive black holes are so fascinating, the joy of discovering surprises in the early universe that throw up new questions, and…

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September 30, 2024
Black hole’s jets are so huge that they may shake up cosmology

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Illustration of the giant black hole jets known as Porphyrion

Caltech

A pair of jets blasting out of a black hole spans 23 million light years, the equivalent of 220 Milky Way galaxies in length. This is so large that it may change our understanding both of black holes and the structure of the universe.

“If you think of jets as a thing, then you could say this is the largest object that we know of in the universe,” says Martin Hardcastle at the University of Hertfordshire, UK.

The jets, which Hardcastle and his colleagues have named Porphyrion, come from a black hole in a distant galaxy, some 7.5 billion light years from Earth. The light reaching us from them now started its journey when the universe was just 6.3 billion years old, only about half the age it is now.

The researchers identified the jets, as well as at least 10 other sets of jets that are also millions of light years across, using the Low Frequency Array (LOFAR) telescope, which consists of thousands of radio antennas across many European countries. Follow-up observations using telescopes in India and Hawaii then helped to locate the host galaxy.

To produce such vast jets, the black hole responsible would have needed to ingest about a sun’s worth of matter each year for a billion years, says Hardcastle. As matter falls into the black hole over this time frame, some of it will be twisted and accelerated by the black hole’s magnetic field, blasting it out into space to form the jets.

In the early universe, matter was more closely bunched together than it is in our current cosmos, which makes the persistence of the jets over such a long time period without being interrupted by another cosmological object unusual, says Hardcastle. “This is back in a period of the universe where galaxies are quite active. There’s a lot going on, and yet this black hole has managed just to keep blasting away more or less unchecked for a billion years,” he says.

“I would have thought something like this was impossible,” says Laura Olivera-Nieto at the Max Planck Institute for Nuclear Physics in Germany. “Simply because it seems too big to have maintained the [jet] for so long.”

Even simulating how such a vast beam formed or what its effects might be is extremely difficult because of the distances involved, she says. “It’s truly a challenge to try to understand how this is physically possible. We cannot put it in a computer, it’s too big.”

Porphyrion extends so far that it could affect the formation of other galaxies, injecting energy and magnetic fields into other regions, says Hardcastle. This could also help explain the mystery of where the universe gets its magnetic fields from. “It dumps energy and magnetic fields and particles into the voids between the galaxies,” says Hardcastle. “That’s a mechanism for transporting magnetic fields from very, very small scales to very large scales.”

These jets might also shake up some cosmological theories, which assume that objects like black holes don’t have influence across so much of the universe.

“A result like this one shows that if you want to understand how the universe’s large-scale structure forms and evolves, you then also have to think about how the smaller components of it, like the systems that would make such an outflow, influence it,” says Olivera-Nieto.

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September 18, 2024
Dark matter may allow giant black holes to form in the early universe

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The long-standing mystery of how supermassive black holes grew so huge so quickly could be solved by decaying dark matter

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September 16, 2024
Stephen Hawking Was Wrong—Extremal Black Holes Are Possible

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Now two mathematicians have proved Hawking and his colleagues wrong. The new work—contained in a pair of recent papers by Christoph Kehle of the Massachusetts Institute of Technology and Ryan Unger of Stanford University and the University of California, Berkeley—demonstrates that there is nothing in our known laws of physics to prevent the formation of an extremal black hole.

Their mathematical proof is “beautiful, technically innovative, and physically surprising,” said Mihalis Dafermos, a mathematician at Princeton University (and Kehle’s and Unger’s doctoral adviser). It hints at a potentially richer and more varied universe in which “extremal black holes could be out there astrophysically,” he added.

That doesn’t mean they are. “Just because a mathematical solution exists that has nice properties doesn’t necessarily mean that nature will make use of it,” Khanna said. “But if we somehow find one, that would really [make] us think about what we are missing.” Such a discovery, he noted, has the potential to raise “some pretty radical kinds of questions.”

The Law of Impossibility

Before Kehle and Unger’s proof, there was good reason to believe that extremal black holes couldn’t exist.

In 1973, Bardeen, Carter, and Hawking introduced four laws about the behavior of black holes. They resembled the four long-established laws of thermodynamics—a set of sacrosanct principles that state, for instance, that the universe becomes more disordered over time, and that energy cannot be created or destroyed.

Christoph Kehle, a mathematician at the Massachusetts Institute of Technology, recently disproved a 1973 conjecture about extremal black holes.

Image: Dan Komoda/Institute for Advanced Study

In their paper, the physicists proved their first three laws of black hole thermodynamics: the zeroth, first, and second. By extension, they assumed that the third law (like its standard thermodynamics counterpart) would also be true, even though they were not yet able to prove it.

That law stated that the surface gravity of a black hole cannot decrease to zero in a finite amount of time—in other words, that there is no way to create an extremal black hole. To support their claim, the trio argued that any process that would allow a black hole’s charge or spin to reach the extremal limit could also potentially result in its event horizon disappearing altogether. It is widely believed that black holes without an event horizon, called naked singularities, cannot exist. Moreover, because a black hole’s temperature is known to be proportional to its surface gravity, a black hole with no surface gravity would also have no temperature. Such a black hole would not emit thermal radiation—something that Hawking later proposed black holes had to do.

In 1986, a physicist named Werner Israel seemed to put the issue to rest when he published a proof of the third law. Say you want to create an extremal black hole from a regular one. You might try to do so by making it spin faster or by adding more charged particles. Israel’s proof seemed to demonstrate that doing so could not force a black hole’s surface gravity to drop to zero in a finite amount of time.

As Kehle and Unger would ultimately discover, Israel’s argument concealed a flaw.

Death of the Third Law

Kehle and Unger did not set out to find extremal black holes. They stumbled on them entirely by accident.

They were studying the formation of electrically charged black holes. “We realized that we could do it”—make a black hole—“for all charge-to-mass ratios,” Kehle said. That included the case where the charge is as high as possible, a hallmark of an extremal black hole.

After proving that highly charged extremal black holes are mathematically possible, Ryan Unger of Stanford University is now trying to show that fast-spinning ones are, too. But it’s a much harder problem.

Photograph: Dimitris Fetsios

Dafermos recognized that his former students had uncovered a counterexample to Bardeen, Carter, and Hawking’s third law: They’d shown that they could indeed change a typical black hole into an extremal one within a finite stretch of time.

Kehle and Unger started with a black hole that doesn’t rotate and has no charge, and modeled what might happen if it was placed in a simplified environment called a scalar field, which assumes a background of uniformly charged particles. They then buffeted the black hole with pulses from the field to add charge to it.

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September 15, 2024
Our galaxy may host strange black holes born just after the big bang

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The Milky Way may be home to strange black holes from the first moments of the universe, and the best candidates are the three closest black holes to Earth

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August 23, 2024
Why we need to save the Chandra space telescope

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Chandra X-ray Observatory

NASA/CXC & J. Vaughan

On 23 July 1999, just months before I started university, NASA’s space shuttle Columbia launched with precious cargo on board. Not only was it carrying the first crew to be led by a woman, Eileen Collins, but its primary goal was to launch a new flagship space telescope, the Chandra X-ray Observatory. Chandra was the heaviest payload that NASA’s space shuttles ever carried, and it turned out to be one of the last two completed missions by Columbia before it tragically exploded after launch on 1 February 2003.

Chandra was the first, and so far only, NASA mission named for a person of colour, the late theoretical astrophysicist and Nobel laureate Subrahmanyan Chandrasekhar, known to his friends and family as Chandra. Chandrasekhar, whose family name means “moon crown”, made many significant contributions to astrophysics. His most important was figuring out the Chandrasekhar limit, the maximum mass a white dwarf stellar remnant can be before it collapses and forms a black hole.

It is appropriate to name an X-ray telescope mission after a scientist who spent his life thinking about the physics of black holes, because X-ray telescopes play a key role in black hole research. X-rays are high-energy light waves. This means they are produced in extremely energetic environments like the regions around black holes, where the strong gravitational pull due to space-time’s extreme distortion causes particles to accelerate to very high speeds. In other words, we see a whole other universe when we look at it through the lens of X-ray astronomy rather than the visible wavelengths of more traditional telescopes.

Importantly, X-ray astronomy can’t be done from Earth’s surface because our atmosphere blocks X-rays. That is good for human health, but not so great for astronomers. Thus, Chandra serves as a reminder of how important it is to keep low Earth orbit free of debris: we need to be able to safely launch space telescopes that do work we simply can’t manage from the ground.

I feel that I have grown up with Chandra, and not just because attending university at Chandra headquarters, now known as the Center for Astrophysics (CfA) in Massachusetts, meant being mistakenly called “Chandra” a lot. One of my undergraduate lab projects was calibrating the light-collecting part of a back-up camera for Chandra. The following year, I wrote my undergraduate thesis under the supervision of X-ray astronomy expert Martin Elvis. My research focused on winds of particles that fly out of galaxies that are home to supermassive black holes. I used Chandra data to analyse what structure these galaxies might take. I know for a fact that Martin’s letter secured my admission into at least one PhD programme. In other words, without Chandra, my career might never have launched.

I am one of thousands of scientists across physics and astronomy who can tell a similar story about how Chandra data has provided the foundation for their early career steps, or who have dedicated their lives to exploring cosmic mysteries using Chandra. Laura Lopez at The Ohio State University has long used Chandra to research supernovae. Daniel Castro, now a staff scientist at the CfA, does the same. The three of us were all postdoctoral researchers together at the Massachusetts Institute of Technology, part of a generation raised on the power of the Chandra X-ray Observatory.

Today, after 25 years in orbit, Chandra is under threat – not from space debris or the realities of ageing equipment, but instead from political winds. US President Joe Biden’s political appointees at the head of NASA recently sought to wind down the project, but the scientific community has worked with Congress to save the mission. But things won’t be the same. The compromise, yet to be signed into law, involves significantly defunding and limiting the scientific reach of Chandra. There is no scientific argument for doing this, especially against the recommendations of professional advisors. Even so, NASA has cut grants that were already promised to scientists, leaving PhD students and postdoctoral researchers without expected funding that covers the salaries they live on.

Chandra deserves better, and so does its global audience. Thanks to Chandra, we have discovered new neutron stars and learned about their interiors. Our knowledge of black holes has blossomed. We better understand the stellar life cycle and the history of our galaxy. We have been able to situate the Milky Way in context, studying galaxy clusters and learning about how dark matter is distributed in them. There is still time to save Chandra, which is a monument to human ingenuity. The fact it is still going strong after 25 years should be celebrated, and honoured by continuing the mission.

Chanda’s week

What I’m reading

A friend gave me a copy of Andreea Kindryd’s From Slavery to the Stars: A personal journey, and it’s beautiful.

What I’m watching

I’ve been watching classic episodes of Star Trek: The Next Generation like “Remember Me”.

What I’m working on

I’m developing a new course that will prepare students to understand science in social context.

Chanda Prescod-Weinstein is an associate professor of physics and astronomy, and a core faculty member in women’s studies at the University of New Hampshire. Her most recent book is The Disordered Cosmos: A journey into dark matter, spacetime, and dreams deferred

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August 21, 2024