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The Milky Way's Black Hole Is Not So Quiescent
esocid writes in with a followup to the recent discussion about the possibility that our galaxy's central black hole could reignite. "Using NASA, Japanese, and European X-ray satellites, a team of Japanese astronomers has discovered that Sagittarius A* let loose a powerful flare three centuries before the time at which we are observing it (i.e., 26,000 years in the past). X-ray pulses emanating from just outside the black hole take 300 years to traverse the distance between the central black hole and a large cloud known as Sagittarius B2, so the cloud responds to events that occurred 300 years earlier. 'By observing how this cloud lit up and faded over 10 years, we could trace back the black hole's activity 300 years ago,' says team member Katsuji Koyama of Kyoto University. 'The black hole was a million times brighter three centuries ago.'"
Warning: that expression does not quite meant what it seems to. The "timeline" under discussion here is from our point of view as light from that area arrives here, after about 26,000 years. On the other hand, that doesn't quite mean that the events actually happened "26,300 years ago" -- there's no good global notion of time that is applicable here.
In Larry Niven's old Known Space story "At the Core" (collected in Neutron Star , he conjectures that because the stars at the core are so close together, one supernova-ing could cause a chain reaction that would bring killing radiation to all reaches of the galaxy. What do astrophysicists today think of this possibility? All the hype now seems to be on black holes.
The stuff that the black hole is sucking in is under great pressure and will often ignite, which is what this article is talking about. The pressurized gas being consumed by the black hole gives off very visible radiation, not the black hole itself. The black hole gives off Hawking radiation which is not with this is talking about though.
I got a catholic block.
To all those confused about black holes being bright - you need to learn the "two things rule" proposed by a colleague of mine - it runs like this:
There are two things you need to know about black holes: They're not black, and they're not holes.
There are two things you need to know about parallel universes: They're not parallel, and they're not universes.
There are two things you need to know about the big bang: It wasn't big and it didn't bang.
Sadly it extends way beyond just physics, but it does give an insight into why physicists have trouble communicating with the public - names come from the very early days of an idea and as often as not end up being misnomers.
It does not 'ignite' by any sense of the word. It does get very hot through friction, and emits black body radiation. But it does not burn.
This is what I think you are looking for. The black hole is essentially working as a particle accelerator. The article I linked to mentions that the forces involved can can produce rays in the trillions of electron volts.
I got a catholic block.
The black hole itself is, indeed, black for all intents and purposes. However, matter falling into the black hole (but still outside the horizon) heats up as it accelerates, emitting thermal radiation, typically in the X-ray spectrum. Thus one talks about "brightness", the brightness of the region right around the black hole.
An illustrative example: for an outside observer, the "temperature of the sun" can mean the temperature of the part one sees, that is the surface temperature (roughly 6000 kelvin). This is not the same as the core temperature of the sun (roughly 1.5x10^7 kelvin).
I think he's right, there is something about this, that's...that's so black, it's like; "How much more black could this be?" and the answer is: "None, none... more black." Seriously, though, the term "black hole" is descriptive in some ways, but is not to be taken literally. There are a lot of interactions which radiate near the event horizon. In short Black holes aren't so black
i\hbar\dot{\psi}=\hat{H}\psi
Black holes of this size do not give off meaningful amounts of Hawking radiation. Their temperature is far, far below the cosmic microwave background temperature -- so even if they didn't capture matter, they would grow by absorbing background radiation. A one solar mass black hole is at only 60 nanokelvins; heavier black holes are colder. Perfect black bodies at that temperature glow very, very dimly.
In astonomy and astrophysics, ignition usually refers to fusion, rather than a chemical process.
How bright is a million times brighter than black?
Since it's a million times brighter in X-rays, not much as far as your eye is concerned.