The Milky Way's Black Hole Is Not So Quiescent 152
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.'"
"300 years ago" (Score:4, Informative)
Comment removed (Score:4, Informative)
Re:A million times brighter than black? (Score:5, Informative)
The Two Things Rule (Score:5, Informative)
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.
Re:A million times brighter than black? (Score:4, Informative)
Re:Matter ingestion (Score:3, Informative)
Re:Now I'm completly lost (Score:4, Informative)
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).
Re:A million times brighter than black? (Score:3, Informative)
Re:Other deadly core issues? (Score:5, Informative)
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.
Re:A million times brighter than black? (Score:4, Informative)
Re:A million times brighter than black? (Score:5, Informative)
Re:"300 years ago" (Score:5, Informative)
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).
Re:A million times brighter than black? (Score:4, Informative)
Since it's a million times brighter in X-rays, not much as far as your eye is concerned.
Re:"300 years ago" (Score:2, Informative)