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.'"

A million times brighter than black?

[jomegat]

How bright is a million times brighter than black?

of course a black hole can give off light

[pclminion]

Anything within the event horizon of the hole, by definition, cannot escape to the outside universe again. But that doesn't mean that matter OUTSIDE the horizon, falling into the hole, doesn't get heated up unbelievably hot and radiate like hell.

I suppose you could make a pedantic argument that it isn't the hole glowing, it's the matter falling into it, but it's certainly the hole which causes it.

Re:A million times brighter than black?

[wattrlz]

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.

Well, in a few senses [reference.com] of the word it does. The American Heritage® Dictionary of the English Language, Fourth Edition 2nd definition of ignite as a verb includes to make luminous with heat and the 2nd definition as an intransitive verb is to begin to glow.

New extinction event hypothesis?

[PoliTech]

Consider the hypothesis about the layer of enriched iridium in rocks formed at the boundary between the Triassic and Jurassic geologic periods and the associated extinction event... 200 million years ago.

And the similar hypothesis about the layer of enriched iridium in rocks formed at the boundary between Cretaceous and those of the Tertiary periods and the associated extinction event ... 65.5 million years ago.

Could that suggest an alternative to the "impact from an asteroid or comet" hypothesis? Could this actually be the observance of a 100 million year "or so" natural galactic cycle?

If that is indeed the case, we should expect our local galactic black hole to go "milky white" in 15 to 35 million years or so.

Keep your sunglasses handy!

BTW, if you couldn't already tell ... IANAAP and IANAPG

Re:"300 years ago"

[Roger W Moore]

There's only a tiny fraction of c relative velocity between us and the center [sic] of the galaxy.

True but not really relevant. Unless the readership of Slashdot is wider than I'm aware of the only frame of reference of relevance is that of the Earth. Hence that is the only frame you need to concern yourself with is that one.

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.

Not actually true: they are larger at those relative speeds but are certainly present and noticeable at far lower velocities e.g. atomic clocks on Concord, GR corrections to GPS satellite clocks etc.

(Physics degree speaking here).

Physics professor speaking here :-).