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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.'"
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)
That's a bit of a confusing sentence but I think I understand. What they really meant to say is that if Sagittarius A's flare produces a 26,000 Hz tone, it
will interfere with GT&T's subspace carrier signal and allow you to send free messages to the gamma quadrant.
How bright is a million times brighter than black?
In theory, practice and theory are the same. In practice, they're not.
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.
Damn global warming!
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.
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.
You may refer to it as "the hole who so recently was known as black".
Ni.
Yeah? Well I think you're overrated too.
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).
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.
The term black is offensive to some, We say African American Holes
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
"let loose a powerful flare"...
"26,000 Hz tone"...
Sounds like the Brown Note...
Move all sig!
That's one of my favorite movies.
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.
Remember that the Earth frame is arbitrary. Although relativity stipulates that there is no privileged frame, strictly speaking there is only one intertial frame which is at rest with respect to the cosmic microwave background radiation; if the Earth were at rest in it then we would see a sky with a uniform temperature in all directions. Instead we can observe a dipole moment in the sky's CMB spectrum consistent with motion at 380 km/s toward the direction of Virgo. The inertial frame of the black hole would also be worthy of consideration. But of course this is all just Slashdot nitpicking, you do your calculations in the Earth's frame because you want your result to come out in Earth proper time, and realistically this means you don't do anything different.
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.
Those effects are negligible with this level of approximation. Basically everything can be considered to be at rest; you guys are making this way harder than it is. This is a simple problem of geometric optics. We're seeing this glowing cloud, with a region 10 light years across, brightening and darkening within the space of 5 light years. That's very hard to explain as anything other than a light echo from a source nearby that must have been bright, and small, and rapidly varying in brightness. And look, there's this supermassive black hole sitting here 300 light years away. You don't have to be Einstein to figure this one out.
The star V838 Mon is a good example of a light echo. This star emitted a huge flash in 2002 that made it the brightest star in the galaxy for a couple months. Then it dimmed to a normal brightness. Once it did, starting in mid-late 2002, we started to see a huge reflection of the flash begin to expand out from the star as it lit up the gas and dust in the vicinity. At any given time we see a glowing sheet of gas shaped like a paraboloid open towards us with the star at its focus, and every year this paraboloid gets bigger. Now that it's 2008 this thing has become a Firefox logo 12 light years wide that continues to expand outward in all directions at the speed of light.