A supermassive black hole at the center of a distant galaxy is emitting an unusual stream of gas at high speed that's blocking about 90 percent of its emitted X-rays, scientists say.
The extremely odd and rare behavior may offer clues to how such cosmic objects interact with the galaxies within which they live, they said.
Revealed by an unexpected dimming at the galaxy's heart, it may be the first direct sign of a long-predicted shielding effect that permits powerful gas winds to be accelerated to high speeds out of a black hole, researchers said.
Scientists using both NASA and European Space Agency space telescopes, including the Hubble instrument, first noticed the effect.
"There were dramatic changes since the last observation with Hubble in 2011," said researcher team member Gerard Kriss of the Space Telescope Science Institute.
As matter is pulled toward a black hole, it spirals into a flat plane dubbed the accretion disc. The disd becomes heated to a point where it emits X-rays near the hole and ultraviolet radiation further away.
That UV radiation can generate cosmic winds so strong some of the gases that would normally fall into the black hole are blown away -- but that can happen only if their starting point is shielded from the X-rays, the researchers say.
That seems to be the case with black hole at the center of the galaxy NGC 5548.
"There are other galaxies with similar streams of gas flowing outward from the direction of its central black hole, but we've never before found evidence that a stream of gas changed its position as dramatically as this one has," researcher Gerard Kriss said. "This is the first time we've seen a stream like this move into our line of sight. We got lucky."
Most supermassive black holes centered in active galaxies expel large amount of matter through powerful and persistent winds of ionized gas, as does NGC 5548 at about 600 miles a second, but an additional wind from this one is more powerful than normally seen, the researchers said.
"These new winds reach speeds of up to 3,107 miles per second, but is much closer to the [galaxy] nucleus than the persistent wind," researcher Jelle Kaastra, said. "The new gas outflow blocks 90 percent of the low-energy X-rays that come from very close to the black hole, and it obscures up to a third of the region that emits the ultraviolet radiation at a few light-days distance from the black hole."
Scientists say they suspect such winds are involved in regulating the growth of both a supermassive black hole and its host galaxy.
