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.'"
Black(hole)box joke. (Score:5, Funny)
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.
Sounds like the Brown Note? (Score:2, Funny)
"26,000 Hz tone"...
Sounds like the Brown Note [wikipedia.org]...
A million times brighter than black? (Score:4, Interesting)
Re:A million times brighter than black? (Score:5, Informative)
Re:A million times brighter than black? (Score:4, Informative)
Re: (Score:2, Funny)
Burning requires oxygen, but everyone knows there is no oxygen in space!
Why else would the space-men wear those funny hats?
QED
Re: (Score:2)
Otherwise the helium would make their voices squeaky, and having squeaky voices over the radio isn't very manly [wikipedia.org].
Re:A million times brighter than black? (Score:5, Informative)
Re: (Score:2)
Re: (Score:2)
Warning: vague half-baked memory retrieval detected. So I'm not certain about what follows.
I seem to recall that in some circumstances, eg very large black holes, some fusion in the accretion disk is possible. Though probably not much. Sorry haven't got a reference for that.
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
The matter that gets sucked into the disc from the surroundings would not be all arriving from the same direction therefore I can't see how the relative speeds of the particles would be so low as to rule out fusion.
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
Rapid proton capture on accreting neutron stars: It has been widely accepted that type I X-ray bursts from low mass X-ray binaries (LMXBs) are due to thermonuclear runaways in accreted materials on the surface of neutron stars (e.g. Taam 1985, Lewin et al. 1993, Bildsten 1998).
The key here is that material is accreting on the surface of the neutron star, it collects in a layer that becomes thick/dense enough (1-10meters?) to sustain fusion. http://www.nasa.gov/centers/goddard/news/topstory/2004/0220stardisk.html [nasa.gov]
This fusion is on the surface of the star, not in the accretion disk. There is no equivalent surface on a black hole.
Re: (Score:3, Interesting)
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.
Re: (Score:2)
Re: (Score:2)
...and 20 years ago, it was thought that no information ever escaped a black hole, either...
Do keep up, dear boy...
Re: (Score:2)
Re:A million times brighter than black? (Score:4, Informative)
Re: (Score:2)
Black holes don't give off much radiation but the accretion disk around it usually gives off plenty.
Re: (Score:1)
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
Re: (Score:3, Informative)
Re: (Score:2)
Re:A million times brighter than black? (Score:5, Funny)
Re: (Score:2)
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: (Score:2)
Re: (Score:2)
At least, not until the X-ray blast has finished ablating the front 6cm off your face.
Re: (Score:2)
"300 years ago" (Score:4, 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:"300 years ago" (Score:5, Interesting)
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.
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 professor speaking here
Re: (Score:2)
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.
True but not really relevant; relativistic effects matter for the tiny differences in time which make atomic clocks and GPS satellites possible, but for 300 years the relativistic effects talked about here aren't significant.
(Physics degree speaking here).
Physics professor speaking here :-).
God speaking here *condescending look*
Light echo (Score:3, Insightful)
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
Re: (Score:2)
Re: (Score:2)
Remember that the Earth frame is arbitrary.
True - but as far as we know it is the only frame with any observers in so while the other frames you mention exist the only one that matters to us is the frame we are in.
...if the Earth were at rest in it then we would see a sky with a uniform temperature in all directions.
The Earth's motion relative to the CMB only accounts for the dipole moment. The higher order multi-pole moments would not disappear and so the temperature would still not be uniform.
Re: (Score:2, Informative)
Comment removed (Score:4, Informative)
Re:Other deadly core issues? (Score:4, Funny)
It's not thought likely. Supernovae are triggered by the collapse of a star's core; external phenomena don't have a great deal to do with it. However, active galactic nuclei have been known about for quite some time. Perhaps when Niven was writing, the idea that active galaxies were powered by chained supernova swarms was current in the literature.
The contemporary model for such phenomena is that the gas swirling around the black hole is heated by friction and by compression as it moves inward. Consider: you're dropping thousands of solar masses through the deepest gravity well in the universe. That releases an awful lot of energy. It makes little difference to Niven's nightmare scenario: it's entirely possible that our Galaxy was active in this way in the past, may become so again in the future, and may even be a little bit active right now. If anyone were to go to the galactic core today in a General Products #3 hull with a quantum-II hyperdrive and discover that the X-ray flux was way, way higher than it ought to be... then we'd better start making plans to run to Andromeda, now.
Re: (Score:2)
I don't know what astrophysical thinking would be, but one of the reasons to doubt the possibility of a supernova chain reaction is that it takes thousands of years for energy to travel between the core of a star and its surface. The core of a star might never know that a supernova had happened outside it.
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: (Score:2)
Tell that to THIS guy... [wikipedia.org]
Phrasing? (Score:2)
What is it about this phrase I just can't wrap my mind around? Black hole...Brighter?
Re: (Score:2)
I am by no means an expert here, but couldn't that mean that one million times more light was escaping before?
yet more evidence of human interferance (Score:5, Funny)
Damn global warming!
dup (Score:2)
Already posted [slashdot.org] a few days ago.
Re: (Score:2, Troll)
RTFA next time before shouting wolf. I mean dupe.
Re: (Score:2)
Sorry, I'll be more careful in the future.
Matter ingestion (Score:2)
I suspect this mostly happens when normal or superdense (neutronic) matter nears and passes the event horizon. The bigger/better question is: Any estimate on the amount of matter ingested to produce the fireworks? How many solar masses? Just what is going on around that drainhole?
Re: (Score:3, 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: (Score:2)
ooof. I think I pulled a neuron. I need a nap now.
Re: (Score:1)
Re: (Score:2)
Re: (Score:2)
Re:The Two Things Rule (Score:5, Funny)
Pogo said it best: Nuclear physics ain't so new, and it ain't so clear.
Re: (Score:2)
"There are X number of people in the world", followed by a list?
I'm dumb (Score:2)
Anyway, I didn't say that we're safe because the black hole is fifty thousand light years away and if it started spewing radiation, whatever was left of humanity (whether already wiped out, anything like ourselves, or what we may have evolved into would see the result.
However, the thing could have exploded fifty thousan
Re: (Score:1)
huh... couldnt suck your own dick either eh?...lol
Re: (Score:2)
But I had a vitrectomy [slashdot.org] and had a gas bubble in my left eye, had to keep my head down 50 minutes out of every hour. Literal pain in the neck! And back as well.
OB Billy Joel reference (Score:1, Funny)
Re: (Score:2)
There's a thing called "it", which, it is my sad duty to impart, you are not and never will be with.
of course a black hole can give off light (Score:3, Interesting)
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: (Score:1)
Anti matter radiates out from the center of the black hole caused by matter being annilated by the black hole inside the event horizon of the black hole. Hubble photos of black holes have shown this IE the hubble space photo of the black hole in the center of the andromoda galaxy.
Black holes also shed mass slowly when not active.
So it's not true that anything within the event horizon cannot escape out into the universe again when it has been show
Re: (Score:2)
You are wrong. Hawking radiation arises when a virtual particle/antiparticle pair pops into existence very near the horizon. One particle is inside the horizon and falls in. The other particle is outside, and escapes. Had the virtual pair come into existence entirely within the horizon, both particles would have fallen in and no radiation would have escaped. Nothing, not even a virtual particle, can escape the event horizon of a black hole. Hawking radiation is "strange" but it cannot defy the basic physics
Re: (Score:2)
Re: (Score:1)
Anything within the event horizon of the hole, by definition, cannot escape to the outside universe again.
But it can still be observed in some ways, no? Matter inside the horizon exerts gravitational pull on matter outside - so matter inside the horizon still in the process of accreting should produce gravitational effects that can be observed in the matter still outside. We should be able to observe what goes on inside, in some ways. Similarly, a star cluster getting sucked in should be able to cause
Re: (Score:2)
Matter inside the horizon exerts gravitational pull on matter outside - so matter inside the horizon still in the process of accreting should produce gravitational effects that can be observed in the matter still outside.
No. The key is, "Black holes have no hair." What this means is that there are only three properties which can be distinguished for a black hole: Electrical charge, spin, and mass. Once a piece of matter or energy has penetrated the event horizon, the only observable effect on the hole i
26,000 years? (Score:2)
Re: (Score:2)
wut?
Re: (Score:2)
Re: (Score:2)
Relative Time (Score:2)
This type of thing though is interesting in how it may have already reignited. Maybe just this morning, maybe 20000 years ago. We have no idea, it's not as easy as ju
New extinction event hypothesis? (Score:3, Interesting)
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: (Score:2)
Re: (Score:2)
It is not actually a Quasar event, but the Black Hole does as predicted in TFA where, "The relatively quiet black hole at the center of our Milky Way galaxy could one day reignite, spewing forth so much radiation that the sky would never darken." As the reigniting occurs the Milky Way Black Hole begins emitting heavy elements as part of the reaction as it be
Re: (Score:2)
There ARE extinction events (some of the worst ones, actually) that don't have corresponding evidence of an impact. They have a suspiciously regular timing, and it's long been hypothesized that they might have something to do with our orbit around the galaxy.
Re: (Score:2)
Re: (Score:2)
Re: (Score:2, Funny)
It isn't an issue of stupidity no matter how much you wish it was, just an issue of posting too fast. Besides, I do have a signature but my post didn't, that is all. Anyway, here it is: Failure to question fundamental statements, even when made by eminent authorities, is a key feature of poor science. - Simon Singh
Quiescent... (Score:2)
Baxteresque (Score:2)
If it's not so Quiescent, then perhaps it is Resplendent, or perhaps Exultant or maybe even Transcendent.
Re: (Score:2)
I'm just curious because the set of words you've chosen reminds me of the writing style I've seen used in another context.
Re: (Score:2)
Re:Now I'm completly lost (Score:4, Funny)
Ni.
Re: (Score:2)
Re:Now I'm completly lost (Score:5, Funny)
Re: (Score:2)
Re:Now I'm completly lost (Score:5, Funny)
Re: (Score:2)
Over here in sunny ZA, it's: "Previously Disadvantaged Holes".
Of course, we also don't refer to "blackouts" (which have become quite common in recent months), but rather "Previously Lit Areas".
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: (Score:2)
Re: (Score:2)