Milky Way's Black Hole Wasn't Always Such a Wimp

scibri writes "Sagittarius A*, the dormant supermassive black hole that lies at the center of our galaxy, was much more active not that long ago. Astronomers using the Fermi Gamma-ray Space Telescope have picked up some faint gamma-ray signals that suggest Sagittarius A* was emitting a pair of powerful gamma-ray jets like other galactic black holes as recently as 20,000 years ago (arXiv paper). If our black hole was more active in the past, it could explain why Sagittarius A* seems to be growing about 1,000 times too slowly for it to have reached its current mass of about four million solar masses since the Galaxy formed about 13.2 billion years ago."

dormant black hole?

[ZombieBraintrust]

What makes a black hole dormant? Lack of gamma ray jets... ?

quieted by mass

[__aaltlg1547]

It was explained in my astrophysics class that when a black hole reaches a certain mass that whole stars pass inside the event horizon before being torn up by tidal force. Then the singularity no longer has a big accretion disk and the radiation emitted by infalling matter is trapped within the event horizon. So it goes quiet.

They Merge

[Anonymous Coward]

From the view of an outside observer, the larger (greater mass) black hole will appear to draw the smaller one in. In reality, they're drawn to each other, and eventually merge, like two drops of water meeting on a window pane. The singularities become one. Simulations suggest that the merger will radiate massive quantities of energy in the form of gravity waves, a major ringing of the bell.

The ringing quickly dies down, and the only evidence of the merger being 1) the changed direction of movement relative to other nearby objects and 2) major disruptions of whatever was orbiting the two holes, from stars down to the accreation disc gas.