Scientists have long theorized that supermassive black holes can wander through space, but they have proven difficult to catch in the act.
Now, researchers at the Center for Astrophysics | Harvard & Smithsonian have identified the clearest case yet of a supermassive black hole moving. Their results are published today (March 12, 2021) in The Astrophysical Journal
“We don’t expect most supermassive black holes to be in motion; they are usually content to just sit there, ”said Dominic Pesce, an astronomer at the Center for Astrophysics who led the study. “They are just so heavy that it is difficult to get them going. Think how much more difficult it is to get a bowling ball moving than kicking a soccer ball – realizing that in this case the ‘bowling ball’ is a few million times the mass of our sun. It takes quite a powerful staircase. “
Pesce and his associates have worked for the past five years to observe this rare occurrence by comparing the speeds of supermassive black holes and galaxies.
“We asked, are the speeds of the black holes the same as the speeds of the galaxies in which they are located?” he explains. “We expect them to have the same speed. If they don’t, it means the black hole has been disrupted. “
Galaxy J0437 + 2456 is believed to be home to a supermassive moving black hole. Credit: Sloan Digital Sky Survey (SDSS)
For their search, the team initially examined 10 distant galaxies and the supermassive black holes in their cores. They specifically studied black holes that contain water in their accretion discs – the spiral structures that spin inward toward the black hole.
As the water orbits around the black hole, it produces a laser-like beam of radio light known as a maser. When studied with a combined network of radio antennas using a technique known as Very Long Baseline Interferometry (VLBI), masers can help measure the speed of a black hole very accurately, Pesce says.
The technique helped the team determine that nine of the 10 supermassive black holes were at rest – only one stood out and appeared to be moving.
At 230 million light years from Earth, the black hole is at the center of a galaxy called J0437 + 2456. Its mass is about three million times that of our sun.
Using follow-up observations with the Arecibo and Gemini Observatories, the team has now confirmed their initial findings. The supermassive black hole is moving at about 110,000 miles per hour in the galaxy J0437 + 2456.
But what causes the movement is not known. The team suspects there are two possibilities.
“We may be observing the aftermath of two supermassive black holes merging,” said Jim Condon, a radio astronomer at the National Radio Astronomy Observatory who was involved in the study. “The result of such a fusion can make the newborn black hole recoil, and we can watch it recoil or settle down.”
But there is one more, perhaps even more exciting possibility: the black hole can be part of a binary system.
“Despite all expectations that they really should be plentiful, scientists have had a hard time identifying clear examples of binary supermassive black holes,” said Pesce. “What we might see in the galaxy J0437 + 2456 is one of the black holes in such a pair, while the other remains hidden from our radio observations due to the lack of maser emission.”
However, further observations are ultimately needed to determine the true cause of this supermassive black hole’s unusual movement.
Reference: “A Restless Supermassive Black Hole in the Galaxy J0437 + 2456” by Dominic W. Pesce, Anil C. Seth, Jenny E. Greene, James A. Braatz, James J. Condon, Brian R. Kent and Davor Krajnović, 12 March 2021, The Astrophysical Journal
DOI: 10.3847 / 1538-4357 / abde3d
Co-authors of the new study are Anil Seth from the University of Utah; Jenny Greene from Princeton UniversityJim Braatz, Jim Condon and Brian Kent of the National Radio Astronomy Observatory; and Davor Krajnović from the Leibniz Institute for Astrophysics in Potsdam, Germany.