Watch, as black holes spiral closer
NASA released the two videos on this page on October 2, 2018. Both are based on a new computer simulation by scientists, showing what happens when two supermassive black holes orbit closely, spiraling toward each other before merging. The scientific simulation is described in a paper published this month in the peer-reviewed Astrophysical Journal. The new work depicts three orbits of a pair of supermassive black holes, only 40 orbits from merging. The videos on this page stem from this simulation, and they’re a lot of fun to watch!
Meanwhile, scientists are most excited by new results of the work, showing which kinds of light – mostly ultraviolet (UV) light with some high-energy X-rays – are emitted as two supermassive black holes spiral closer. They’re excited because – if scientists can understand what to look for – they might be able to observe supermassive black holes prior to merging. They haven’t accomplished this yet or anything close to it; in fact, so far, although supermassive black hole mergers should be relatively common in space, astronomers haven’t yet observed one. What’s been seen, so far, are gravitational waves originating in the merger of two stellar-mass black holes. More about that below.
These researchers said that, based on their new simulation, they expect X-rays emitted by a near-merger of supermassive black holes will be brighter and more variable than X-rays seen from single supermassive black holes. NASA also said in a statement that the new simulation:
… fully incorporates the physical effects of Einstein’s general theory of relativity.
And that’s why, for example, in the video above, we see complex effects caused by gravitational lensing, when one supermassive black hole passes in front of the other. The degree to which light is bent can be predicted via Einstein’s theory.
Scientists also said some exotic features came as a surprise, such as the eyebrow-shaped shadows one black hole occasionally creates near the horizon of the other.
This next video is a result of the new simulation, too. It’s an interactive 360-degree video, which places the viewer in the middle of two circling supermassive black holes around 18.6 million miles (30 million km) apart with an orbital period of 46 minutes. The simulation shows how the black holes distort the starry background and capture light, producing black silhouettes. A distinctive feature called a photon ring outlines the black holes. The entire system would have around a million times the sun’s mass.
As you may know, scientists have detected merging stellar-mass black holes — which range from around three to several dozen solar masses — using the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO). The mergers produce gravitational waves, which are space-time ripples traveling at the speed of light.
But supermassive black holes should be merging, too, in various places across the universe. Astrophysicist Scott Noble at NASA’s Goddard Space Flight Center in Greenbelt, Maryland – a co-author on the study – explained:
We know galaxies with central supermassive black holes combine all the time in the universe, yet we only see a small fraction of galaxies with two of them near their centers. The pairs we do see aren’t emitting strong gravitational-wave signals because they’re too far away from each other.
Our goal is to identify – with light alone – even closer pairs from which gravitational-wave signals may be detected in the future.
Stéphane d’Ascoli, a doctoral student at École Normale Supérieure in Paris, is lead author of the new paper. These scientists’ statement further explained:
… supermassive binaries nearing collision may have one thing stellar-mass binaries lack – a gas-rich environment. Scientists suspect the supernova explosion that creates a stellar black hole also blows away most of the surrounding gas. The black hole consumes what little remains so quickly there isn’t much left to glow when the merger happens.
Supermassive binaries, on the other hand, result from galaxy mergers. Each supersized black hole brings along an entourage of gas and dust clouds, stars and planets. Scientists think a galaxy collision propels much of this material toward the central black holes, which consume it on a time scale similar to that needed for the binary to merge.
As the black holes near, magnetic and gravitational forces heat the remaining gas, producing light that astronomers should be able to see.
At least, they hope that will someday be so. At the moment, much is unknown. And that’s one reason co-author Manuela Campanelli, director of the Center for Computational Relativity and Gravitation at the Rochester Institute of Technology in New York, who initiated this project nine years ago, said:
It’s very important to proceed on two tracks. Modeling these events requires sophisticated computational tools that include all the physical effects produced by two supermassive black holes orbiting each other at a fraction of the speed of light.
Knowing what light signals to expect from these events will help modern observations identify them.
Modeling and observations will then feed into each other, helping us better understand what is happening at the hearts of most galaxies.
Bottom line: A new simulation by scientists lets you witness supermassive black holes about to collide. One shows them from outside the system, just 40 orbits from merging. The other places you in their midst.