'Restless' Supermassive Black Hole Discovered Wandering in Space Mysteriously


(Sloan Digital Sky Survey)

We typically think of supermassive black holes as being relatively stationary objects, sitting in the center of a galaxy while everything else swirls around it.

However, this isn't always the case, and now scientists have the best proof yet for a supermassive black hole that's not only traveling through space but also inside its own galaxy. It has ants in its pants and witches in its britches, and while the reason for this is unknown, the possibilities are fascinating.

According to astronomer Dominic Pesce of the Harvard & Smithsonian Center for Astrophysics, "we don't expect the bulk of supermassive black holes to be moving; they're normally happy to just sit there."

It's difficult to get them moving because they're so big. Consider how much more difficult it is to set a bowling ball in motion than it is to set a soccer ball in motion, particularly when you consider that the 'bowling ball' in this case is several million times the mass of our Sun. That's going to take some serious kicks.

It's not easy to capture a peripatetic supermassive black hole in the act. They can only be found through vast gulfs of space, millions to billions of light-years apart; at such distances, isolating the motion of one object in a galaxy, even though that object is a supermassive black hole, is difficult.

Pesce and his team hoped to find success with a form of galactic nucleus known as a mega maser. This is a form of active supermassive black hole that has an accretion disk of gas and dust slurping onto it, creating enormous quantities of heat and light.

There's an extra component in a super maser's formula: molecules like hydroxyl, water, formaldehyde, and methine, which improve the nucleus' luminosity in microwave wavelengths.

The velocities of these mega masers can be determined very accurately using a technique called very long baseline interferometry, which incorporates measurements from a network of radio telescope antennas to essentially produce one large observing dish.

Pesce and his colleagues hoped to find some supermassive black holes traveling at a different speed than the galaxy around them by observing water mega masers in particular.

We asked if the black holes' velocities were the same as the velocities of the galaxies they resided in, and he said yes. We anticipate that they will travel at the same speed. If they don't, the black hole has probably been disturbed.

The team examined ten megamasers in detail, comparing black hole velocity data to observations of the entire galaxy. Nine of them, like a spider in a web, were consistent with our fears of supermassive black holes lurking in the galactic Center.

However, one of them acted in an unusual manner. A supermassive black hole about 3 million times the mass of the Sun has been discovered in the spiral galaxy J0437+2456, which is situated about 228 million light-years away and appears to be traveling at a slightly different velocity than the rest of the galaxy.

The supermassive black hole's velocity, according to the team's calculations, is around 4,810 kilometers per second (2,990 miles per second). On the other hand, the galaxy's neutral hydrogen tends to be receding at a rate of 4,910 kilometers per second. The velocity of the inner area of the galaxy is 4,860 kilometers per second, according to measurements of star and gas motions.

It's difficult to say why anything is wobbling around in there because all of these measurements vary so greatly from one another, and the galaxy's entire velocity structure seems to be very complicated.

There may be a number of reasons for this. It's possible that the galaxy is in the midst of a long-term interaction with another large entity, such as another galaxy. The supermassive black hole could have collided with another supermassive black hole, causing a rebound kick that moved it out of place; the wobbling may be the galaxy and black hole settling back down.

Alternatively, the black hole may be accompanied by an unknown binary companion, the two objects orbiting a common gravitational center inside the galactic nucleus.

Despite all expectations that they should be plentiful, scientists have had difficulty finding specific instances of binary supermassive black holes, according to Pesce.

What we might be seeing in the galaxy J0437+2456 is one of a pair of black holes, with the other remaining concealed from our radio observations due to its lack of maser emission.

If it's a binary companion or a recoil kick, it will be fantastic news for astrophysics. Many questions about supermassive black holes remain unanswered, including how they grow so large and whether supermassive black hole binaries will close the final parsec of gap between them. Evidence for supermassive black hole mergers and binaries may assist in answering these questions.

It's also good news for us here in the Milky Way: since we're only a few billion years away from a galactic merger, our supermassive black hole, Sagittarius A*, is unlikely to grow wanderlust too soon.

More observations of the galaxy and its mysterious nucleus are hoped for by the team in order to narrow down the cause of its strange activity.

The research has been published in The AstrophysicalJournal.

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