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Two black holes locked in cosmic dance near galaxy's center are doomed to crash

Two huge black holes are locked together by gravity as they inevitably spiral towards a collision, researchers have found in a new study.

Researchers in a new study have spotted two supermassive black holes that whip around each other every two Earth years, on average, with respective masses each of hundreds of millions of times that of our sun. They found that the pair are also relatively close, being only about 2,000 Earth-sun distances apart (or about 50 times the distance between the sun and Pluto.)

"When the pair merge in roughly 10,000 years, the titanic collision is expected to shake space and time itself, sending gravitational waves across the universe," the California Institute of Technology said of the objects in a statement (opens in new tab).

Related: Did astronomers see light from two black holes colliding for the first time?

Described in the statement as the tightest-knit supermassive black hole duo yet observed, the study provides a unique laboratory to understand the dynamics of a quasar involved, called PKS 2131-021. 

Quasars are distant objects powered by black holes a billion times as massive as our sun. Astronomers are interested in these super-bright objects in part because quasars may give insight into the physics of the early universe.

Two supermassive black holes are seen orbiting each other in this artist's loopable animation. (Image credit: Caltech/R. Hurt (IPAC))

If the findings from this study are confirmed, PKS 2131-021 is not alone in having a pair of supermassive black holes merging. The first suggested pair in quasar OJ 287, however, are much further apart and take nine years to circle each other.

Researchers in this study used 45 years of observations from multiple radio observatories to catch a powerful jet in action within PKS 2131-021, which appears to be moving back and forth as the pair of black holes orbit each other. The movement in turn causes changes in the brightness of radio waves observed at Earth.

"When we realized that the peaks and troughs of the light curve detected from recent times matched the peaks and troughs observed between 1975 and 1983, we knew something very special was going on," Sandra O'Neill, lead author of the new study and an undergraduate astronomy student at Caltech, said in the same statement. 

Artist's animation of a supermassive black hole circled by a spinning disk of gas and dust.  (Image credit: Caltech/R. Hurt (IPAC))

Galaxies commonly have huge black holes in their centers, including our own Milky Way. Galaxy mergers, when they occur, tend to see their respective black holes "sink" to the middle of the now combined, new galaxy and create an accordingly combined and more massive supermassive black hole.

The effects of such mergers create huge ripples across space and time, known as gravitational waves. Gravitational waves have been observed multiple times using the National Science Foundation's LIGO (Laser Interferometer Gravitational-Wave Observatory) that is jointly managed by Caltech and the Massachusetts Institute of Technology.

That said, the supermassive black holes would not be visible to LIGO, as the black holes produce lower frequencies of gravitational waves that are undetectable in LIGO's sensors. Caltech researchers say that the way to catch this in the future would be to use pulsar timing arrays, referring to radio telescopes that look at blinking stars called pulsars, according to the statement. In the meantime, light waves can show supermassive black holes in action.

A study (opens in new tab) based on this research was published Wednesday (Feb. 23) in the Astrophysical Journal Letters.

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Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell, Ph.D., is a staff writer in the spaceflight channel since 2022. She was contributing writer for Space.com (opens in new tab) for 10 years before that, since 2012. As a proud Trekkie and Canadian, she also tackles topics like diversity, science fiction, astronomy and gaming to help others explore the universe. Elizabeth's on-site reporting includes two human spaceflight launches from Kazakhstan, three space shuttle missions in Florida, and embedded reporting from a simulated Mars mission in Utah. She holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, and a Bachelor of Journalism from Canada's Carleton University. Elizabeth is also a post-secondary instructor in communications and science since 2015. Her latest book, Leadership Moments from NASA, is co-written with astronaut Dave Williams. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday.