Can a supermassive black hole have wanderlust? That’s something astronomers have been wondering about for years, and a new study from the Harvard and Smithsonian Center for Astrophysics might have arrived at an answer: yep. By comparing the movement of black holes and their surrounding home galaxies, the researchers discovered one that appears to drift around. This could resolve some long-standing questions about the nature of these enormous dead stars.
Supermassive black holes are usually found in the centers of galaxies, and they don’t have a reputation for moving around much. After all, they weigh as much as millions or billions of suns! It takes a lot of energy to get something that big moving, but the monster black hole in spiral galaxy J0437+2456, some 228 million light-years away, is almost definitely mobile.
To spy on black holes, the team used a technique called very long baseline interferometry that relies on networks of radio telescopes. This technique allows scientists to measure the velocity of distant objects, but black holes don’t emit detectable radiation. That’s why the team focused its efforts on a class of active galactic nuclei known as megamaser — supermassive black holes with an accretion disk of material swirling around them. There are several molecules in megamasers that can be measured with high accuracy, including water.
The analysis included 10 megamaser-type galaxies, and nine of them came up normal — the galaxy and the black hole are moving at the same velocity. However, J0437+2456 (top) showed a ton of variation. The neutral hydrogen floating around in the galaxy was moving away at 4,910 kilometers per second, but the water molecules in the black hole’s disk were only moving at 4,810 kilometers per second. What’s more, the inner part of the galaxy is moving at 4,860 kilometers per second. All those different velocities make for a very wobbly galaxy.
There are several possible explanations for this wobble, including a past collision with another supermassive black hole. It’s also possible the varying velocity is due to another unseen supermassive black hole in a binary system. Scientists believe binary systems like this should exist, but there’s very little observational evidence. In either case, this galaxy could teach us a lot about black holes. It’s also feasible that the galaxy has been disrupted by a nearby massive object like another galaxy. That would be less interesting, but it would still show that central black holes can be nudged off course. The team plans to conduct more observations of J0437+2456 in hopes of figuring out which it is.
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