Researchers at the Center for Astrophysics / Harvard & Smithsonian have identified the clearest case to date of a supermassive black hole in motion, which they publish in the Astrophysical Journal. The scientists have long theorized that supermassive black holes can roam space, but catching them in the act has proven difficult.
“We don’t expect most supermassive black holes to move; they are generally content to sit,” says Dominic Pesce, the astronomer who led the study, in a statement. “They are so heavy that it is difficult to get them going. Consider how much more difficult it is to kick a bowling ball in motion than it is to kick a soccer ball, realizing that in this case, the ‘bowling ball’ is several million times the mass of our Sun. That will require a pretty powerful kick. ”
Pesce and his collaborators have been working to observe this rare occurrence for the past five years by comparing the speeds of supermassive black holes and galaxies. “We ask ourselves: Are the speeds of black holes the same as the speeds of the galaxies in which they reside?” Explain. “We hope they have the same speed. If not, that implies that the black hole has been disturbed.”
For their search, the team initially examined 10 distant galaxies and the supermassive black holes at their cores. They specifically studied black holes that contained water within their accretion discs, the spiral structures that rotate into the black hole.
As the water orbits the black hole, it produces a laser-like beam of radio light known as a maser. When studied with a combined array of radio antennas using a technique known as very long baseline interferometry (VLBI), masers can help measure the speed of a black hole very precisely, says Pesce. The technique helped the team determine that nine of the 10 supermassive black holes were at rest, but one stood out and appeared to be in motion.
Located 230 million light-years from Earth, the black hole is at the center of a galaxy called J0437 + 2456. Its mass is approximately 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 moves at a speed of approximately 177,000 kilometers per hour within the galaxy J0437 + 2456.
But what is causing the movement is unknown. The team suspects there are two possibilities. “We may be looking at the consequences of the merger of two supermassive black holes“says Jim Condon, a radio astronomer at the National Radio Astronomy Observatory who participated in the study.” The result of such a merger may cause the newborn black hole to recede, and we may be watching it in the act of receding or while stabilizing again. But there is another possibility, perhaps even more exciting: the black hole can be part of a binary system.
“Despite all the expectations that they really should be there in abundance, scientists have struggled to identify clear examples of binary supermassive black holes,” says Pesce. “What we could be seeing in the galaxy J0437 + 2456 is one of the black holes in that pair, and the other remains hidden from our radio observations due to its lack of maser emission. “Ultimately, however, more observations will be needed to pin down the true cause of the unusual motion of this supermassive black hole.