New research just published will help astrophysicists understand the formation of jets of matter ejected from supermassive black holes. This, in turn, will help understand conditions in the early universe, when such phenomena were much more common than now.
The galaxy M87 is one of the strongest sources of radio waves in the sky. Its black hole, accretion disk, and radio jet have been studied in the past, but it has been difficult to pin down the relative positions of the black hole and the base of the jets. Until now, at least: in today’s Nature, scientists report observations that map out the shape of the jet and, from that, extrapolate the position of the black hole—the two appear to be much closer than in other galaxies.
The black hole’s ejected material forms a jet, located in the galaxy known as M87. This galaxy is quite interesting for a number of reasons. Its distance from us is about 53.5 million light years, which is relatively quite nearby, making M87 easy to study. M87 is also a very large elliptical galaxy, whose central black hole is extremely massive. The galaxy’s total mass is hard to estimate but may be ten or more times that of our Milky Way, whose mass is pretty large itself. The mass of the central black hole has been measured fairly precisely – about 6.6×109 solar masses, making it one of the most massive black holes known. Curiously, the black hole is not in the exact center of the galaxy – it’s offset by about 22 light years, which isn’t a lot compared to the size of the galaxy, but still surprising.
The new research uses a new method of estimating the distance from the black hole at which the jet originates, which turns out to be about .023 light years, a little over 8 light days. That’s a lot smaller than previous estimates of distances between black holes and their jets in M87 and other galaxies. It’s important to know this distance, because the mechanism that forms jets of this kind from supermassive black holes is not understood. This information will help test models of jet dynamics. That, in turn, is important, because there are many galaxies having this kind of activity, including the most energetic examples: quasars. Quasars were much more common in the early universe than they are now, and because they are so bright they are visible at extreme distances, back to times when the universe was only a few hundred million years old. Thus understanding how black hole jets form indirectly helps understand the early universe itself.