But last year scientists noticed the nucleus of NGC 5548 had gotten noticeably dimmer. A year later, having closely analyzed imagery from a host of NASA and European Space Agency observatories, scientists think they know why -- a different, swifter stream of gas was being spewed out from the galaxy's center, blocking out and manipulating the x-rays that normally make 5548 much easier to see.
Shooting out from the black hole, the stream of gas moves at rates of more than 3,000 miles per second with unpredictable turbulence.
Scientists hope the newly observed stream of gas will offer new insight into the strange behaviors of active galaxies, where wind, cosmic matter and clumps of gas all swirl around a supermassive black hole -- all of them governed by the strange laws of extreme physics.
"Astronomers have been looking at this galaxy for decades, and everyone expected it to behave normally, so seeing this galaxy's center change to a completely different state was surprising and exciting," lead author Jelle Kaastra told Space.com.
Kaastra is an astronomer at the SRON Netherlands Institute for Space Research; she collaborated with astronomers from all over the world to produce the new study into NGC 5548's shiftless center, which was published this week in journal Science.
"There are other galaxies that show gas streams near a black hole, but they haven't changed as dramatically," explained Gerard Kriss, an astronomer at the Space Telescope Science Institute in Baltimore, Md. "This is the first time we've seen a stream like this move into the line of sight. We just happened to get lucky. With most objects like this, you don't normally see this kind of event."