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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.'"
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.
No, Niven wrote before we knew that the Milky Way *HAD* a central black hole. He was assuming that there were a whole bunch of really large stars hidden behind the gas clouds (that we couldn't see through from ground level).
At the time he wrote it, it was plausible. Now he'd probably write about a huge gamma burst instead. Not quite as destructive. Or he could write about a cluster of stars that had been merged into the accretion disk, and were now feeding into the central black hole.
Don't try to make what he wrote then match with current possibilities. It doesn't mesh. If you want to find really blatant mismatches, look at his really early stories that take place within the solar system, and before the interstellar drive. (More particularly, before the "Gil the Arm" stories.) Try "Becalmed in Hell".
Niven made reasonable guesses given what was known at the time. Don't try to stuff his guesses into what was later discovered. They don't fit.
I think we've pushed this "anyone can grow up to be president" thing too far.
In astonomy and astrophysics, ignition usually refers to fusion, rather than a chemical process.
There's only a tiny fraction of c relative velocity between us and the center of the galaxy. For practical purposes we're in the same reference frame, and in any one reference frame you can do a clock synchronization algorithm that gets everybody to agree.
The weird effects that relativity is famous for come into play when you're comparing clocks between two reference frames that are moving relative to each other at relativistic speeds.
(Physics degree speaking here).