The center of our home galaxy, the Milky Way, is hidden behind clouds of dust. But its location is easy to find -- it's above the spout of teapot-shaped Sagittarius, which scoots low across the south on summer evenings.
The galaxy's core is home to a supermassive black hole. But it's one of the puniest yet discovered, and it's also the quietest.
The second-quietest supermassive black hole is in the Andromeda galaxy. But a few years ago, it got a lot more conspicuous. And even though it's faded some since then, it's still brighter than it was before.
The black hole doesn't produce any energy of its own, of course. Its gravity is so strong that not even light can escape from it. But the black hole is encircled by a disk of superhot gas that emits X-rays and other forms of energy.
Astronomers have been using the orbiting Chandra X-Ray Observatory to keep a close eye on Andromeda's black hole for more than a decade. In early 2006, they found that it had flared to a hundred times its previous brightness. It soon began fading, but has remained about 10 times brighter than it was before the flare-up.
The flare might have been produced by processes like those on the surface of the Sun. As the disk rotates, it generates a strong magnetic field. Over time, the lines of magnetic force get tangled. Eventually, they snap, producing outbursts of particles and energy like solar flares -- making the black hole look a lot more impressive.
Script by Damond Benningfield, Copyright 2010