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Space Science

The Milky Way's Black Hole Is Not So Quiescent 152

Posted by kdawson
from the long-ago-in-a-galaxy-right-nearby dept.
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.'"
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The Milky Way's Black Hole Is Not So Quiescent

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  • by suso (153703) * on Tuesday April 15, 2008 @03:07PM (#23080982) Homepage Journal
    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.
  • by jomegat (706411) on Tuesday April 15, 2008 @03:07PM (#23080994)
    How bright is a million times brighter than black?
    • by explosivejared (1186049) <hagan.jaredNO@SPAMgmail.com> on Tuesday April 15, 2008 @03:14PM (#23081094)
      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.
      • by drerwk (695572) on Tuesday April 15, 2008 @03:19PM (#23081156) Homepage
        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.
        • Re: (Score:2, Funny)

          by Anonymous Coward
          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.

          Burning requires oxygen, but everyone knows there is no oxygen in space!

          Why else would the space-men wear those funny hats?

          QED
          • by interiot (50685)

            Why else would the space-men wear those funny hats?

            Otherwise the helium would make their voices squeaky, and having squeaky voices over the radio isn't very manly [wikipedia.org].

        • by evanbd (210358) on Tuesday April 15, 2008 @04:02PM (#23081798)
          In astonomy and astrophysics, ignition usually refers to fusion, rather than a chemical process.
          • by drerwk (695572)
            I'm not recalling that the accretion disk is supposed to sustain fusion, I don't think it is dense enough, nor do I think that the x-rays we see from AGN suggest that the are hot enough to support fusion. So including that definition I don't think we have ignition, just blackbody friction induced radiation.
            • by Evil Pete (73279)

              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.

            • If you call what happens in an atom smasher 'friction' then yes, but this is quite different to rubbing two sticks together. The vast majority of radiation from the disc is due to the conversion of mass into energy by particle collisions at near light speed (ie: fission and fusion). It has little or nothing to do with blackbody radiation which is the radiation emitted by an object until it reaches thermal equilibrium with it's surroundings.
              • by drerwk (695572)
                I'm calling what happens in a typical X-ray tube http://en.wikipedia.org/wiki/X-ray_tube [wikipedia.org] friction. I'm calling what happens in a plasma lamp http://en.wikipedia.org/wiki/Sodium_vapor_lamp [wikipedia.org] to keep the lamp lit friction. Everything I've read so far suggests that the relative velocities of particles in an accretion disc, and the mean free path of those particles, is not sufficient for fission or fusion. I've not done the calculation recently, but even for a small solar mass black hole I think the tidal force
                • Blobs of matter the size of Jupiter have been observed moving away from a black hole at near light speed (perpendicular to the disc's rotation). I always thought those beams were formed from the accretion disc as it falls toward the hole.

                  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.
                  • by drerwk (695572)
                    Hey TapeCutter - the blobs the size of Jupiter sounds pretty odd to me -- it would have to be an enormous black hole not to tear something that size up. Can you give me a reference?
                    • Ref [space.com]
                    • by drerwk (695572)
                      That is the joy of popular science writing. The author of the article takes what Glenn Piner says, "And the blobs of plasma in these jets are at least as massive as a large planet.", and turns it into "Jupiter-sized blobs". As I'm sure you know, mass and volume are related through density. If you go to what might be the paper Prof.Piner's was referring to when he was talking about these blobs: "http://arxiv.org/PS_cache/arxiv/pdf/0801/0801.2749v1.pdf" you will read that he only ever talks about measurements
                    • I understood what it meant the first time I read it, the reference was the first google hit to mention it. You seem hung-up on compression or perhaps I am missing something about the definitions, AFAIK a sustained chain reaction is not essential for fusion or fission ( the merging and splitting of atoms ) to take place, it just needs a hard enough collision. Also I am not saying that it is happenening in the blob, I am saying the blob's speed is largely due to the energy released from the destruction of the
        • Re: (Score:3, Interesting)

          by wattrlz (1162603)

          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.

          • by drerwk (695572)
            Oh, sure, use a dictionary against my Wikipedia definition. And beaten only with the second definition. Ok, in no sense of the word as I'm familiar with it from college physiscs 20 years ago.
            • Ok, in no sense of the word as I'm familiar with it from college physiscs 20 years ago.

              ...and 20 years ago, it was thought that no information ever escaped a black hole, either...

              Do keep up, dear boy...

              • by drerwk (695572)
                Making that effort to keep up, I see that my Ph. 136 professor has not yet conceded the bet. http://www.theory.caltech.edu/~preskill/jp_24jul04.html [caltech.edu] While I have the utmost respect for Prof. Preskill, and am inclined to prefer myself that information is not destroyed, if Prof. Thorne has not conceded I would suggest that the matter is not entirely resolved.
      • by evanbd (210358) on Tuesday April 15, 2008 @04:01PM (#23081786)
        Black holes of this size do not give off meaningful amounts of Hawking radiation. Their temperature is far, far below the cosmic microwave background temperature -- so even if they didn't capture matter, they would grow by absorbing background radiation. A one solar mass black hole is at only 60 nanokelvins; heavier black holes are colder. Perfect black bodies at that temperature glow very, very dimly.
        • by Evil Pete (73279)

          Black holes don't give off much radiation but the accretion disk around it usually gives off plenty.

    • blackish?
    • Re: (Score:3, Informative)

      by xPsi (851544) *
      I think he's right, there is something about this, that's...that's so black, it's like; "How much more black could this be?" and the answer is: "None, none... more black." Seriously, though, the term "black hole" is descriptive in some ways, but is not to be taken literally. There are a lot of interactions which radiate near the event horizon. In short Black holes aren't so black [physorg.com]
    • The answer is 'none'. None more bright.
    • by ArcherB (796902) on Tuesday April 15, 2008 @03:50PM (#23081674) Journal

      How bright is a million times brighter than black?
      Dark Gray

    • by ozbird (127571) on Tuesday April 15, 2008 @06:34PM (#23083306)
      How bright is a million times brighter than black?

      Since it's a million times brighter in X-rays, not much as far as your eye is concerned.
      • you can get some serious luminescence in the eye from x-rays. How do you think they used to find the beam at the old accelerators? (until everyone got cataracts that is.)
      • by RockDoctor (15477)

        How bright is a million times brighter than black?

        Since it's a million times brighter in X-rays, not much as far as your eye is concerned.

        At least, not until the X-ray blast has finished ablating the front 6cm off your face.
    • How bright is a million times brighter than black?
      Yeah, those Pioneer Kuros have great contrast ratios.
  • "300 years ago" (Score:4, Informative)

    by l2718 (514756) on Tuesday April 15, 2008 @03:08PM (#23080998)
    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.
    • Re:"300 years ago" (Score:5, Informative)

      by Beryllium Sphere(tm) (193358) on Tuesday April 15, 2008 @04:13PM (#23081956) Homepage Journal
      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).
      • Re:"300 years ago" (Score:5, Interesting)

        by Roger W Moore (538166) on Tuesday April 15, 2008 @07:09PM (#23083626) Journal

        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 :-).
        • by kestasjk (933987)

          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)

          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
          • by mykdavies (1369)
            Wow, that's a stunning image. Thanks for the link and the explanation.
          • 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)

        by SoVeryTired (967875)
        You need to be thinking in terms of general relativity, rather than special relativity here. Given that this material is falling into a black hole, we are emphatically not in the same reference frame.
  • by CRCulver (715279) <crculver@christopherculver.com> on Tuesday April 15, 2008 @03:08PM (#23081008) Homepage
    In Larry Niven's old Known Space story "At the Core" (collected in Neutron Star [amazon.com] , 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.
    • by meringuoid (568297) on Tuesday April 15, 2008 @03:47PM (#23081618)
      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.

      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.

    • There are several lines of evidence that point to a large black hole being at the core. The speed of things orbiting it points to so much mass being in so small a space that it would be a black hole.

      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.
  • 'The black hole was a million times brighter three centuries ago.'

    What is it about this phrase I just can't wrap my mind around? Black hole...Brighter?
    • I am by no means an expert here, but couldn't that mean that one million times more light was escaping before?

  • by CodeMunch (95290) * on Tuesday April 15, 2008 @03:13PM (#23081072) Homepage

    "'The black hole was a million times brighter three centuries ago.'"

    Damn global warming!

  • by Bob-taro (996889)

    Already posted [slashdot.org] a few days ago.

  • IANA astrophysicist, but a black hole might be said to be bright if it gives off radiation outside it's event horizon.

    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)

      This [physorg.com] 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.
  • The Two Things Rule (Score:5, Informative)

    by Anonymous Coward on Tuesday April 15, 2008 @03:17PM (#23081126)
    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.
    • by teasea (11940)
      My issue is not with blackness or holeness. As I have learned, light does not escape black holes. Therefore, the misnomer here is the term 'brighter.'

      ooof. I think I pulled a neuron. I need a nap now.
      • by frith01 (1118539)
        Only material / energy which is beyond the "Event Horizon" of a black hole no longer radiates back out. Matter / Energy which is in the process of being consumed is quite bright, due to the accelleration / compression process, and friction with other items being consumed. If all local matter had been consumed, then the black hole will not be "bright". If additional material in on the path towards the black hole, we will see the hole 'brighten' once the material starts to accellerate / compress as it
      • Light that crosses the event horizon does not escape (or at least in classical physics). However, the matter and energy that is falling into the black hole does give off radiation as it accelerates and compresses, and it is this radiation (ie. light) that can be seen.
    • by sm62704 (957197) on Tuesday April 15, 2008 @03:27PM (#23081290) Journal
      Sadly it extends way beyond just physics

      Pogo said it best: Nuclear physics ain't so new, and it ain't so clear.
  • In the original subject, IRTFA and came to some stupid conclusions. Blame having a bubble in my eye and being stoned on endorphins from the pain in my neck and back from holding my head down.

    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
    • "...the pain in my neck and back from holding my head down"

      huh... couldnt suck your own dick either eh?...lol /kidding
      • by sm62704 (957197)
        Heh, there's a cartoon about a guy jealous of his dog ;)

        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.
  • by Anonymous Coward
    We Didn't Start the Fire...
    • Billy Joel...???

      There's a thing called "it", which, it is my sad duty to impart, you are not and never will be with.
  • by pclminion (145572) on Tuesday April 15, 2008 @03:50PM (#23081660)

    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.

    • That's not true

      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
      • by pclminion (145572)

        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

    • by snaz555 (903274)

      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

      • by pclminion (145572)

        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? Isn't this equal to the Mayan Calendar that predicts the end of time in 2012?
    • by esocid (946821)
      That is just a misinterpreted end-time theory. Scholars have been trying to figure out the Mayan calendar in Gregorian terms for a long ass time. I've heard it best described as odometer like. When it hits the "end" around Dec. 21st 2012 it will roll over and begin a new "era" of the calendar, ending 1/5 (5,125.36 years) of the Platonic Year (about 26,000 years), which measures the length of the procession of equinoxes. Their calendar was all about mapping cycles, and on Dec. 21st 2012 there will be a prett
  • I always find the idea of the time/distance involved to be amazing, and it really kinds of gives you a good perspective on how big things are (small you are). Like a friend who pointed out that the half moon you could see in the sky was because of the shadow _of the earth_. That's just crazy talk, and even more interesting as it sinks in.

    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
  • by PoliTech (998983) on Tuesday April 15, 2008 @04:40PM (#23082288) Homepage Journal
    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

    • by ceoyoyo (59147)
      Why would the galaxy's black hole have anything to do with iridium layers on Earth?
      • by PoliTech (998983)
        Imagine we are now about 35 million years in the future, humans are but a legend among the nanobot population, and the event described in TFA happens.

        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

        • by ceoyoyo (59147)
          There's the hole in the theory: there's no reason the black hole would spew out heavy elements.

          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.
          • by PoliTech (998983)
            We can include a theorized Correlation between Compact Radio Quasars and Ultrahigh Energy Cosmic Rays. When the Quasi Quasars radio source ignites, it sends a blast wave out that clears out a lot of the gas (which contains heavy elements) out to the rim (our way). And the Ultra High Energy reaction creates a lot of iridium in the process. I was thinking about the cause of the Galactic warming myself. Wormhole energy taps by the Nano People perhaps? We can likely work that into chapter two.
  • ... oy. Why choose a word that means both "being at rest; quiet; still; inactive or motionless" and "Having the power or quality of acting; causing change; communicating action or motion; acting" for the news headline? (Dictionary.com Definitions [reference.com])
  • From the Title:The Milky Way's Black Hole Is Not So Quiescent

    If it's not so Quiescent, then perhaps it is Resplendent, or perhaps Exultant or maybe even Transcendent. ;-)
    • Which Baxter are you referring to? Wikipedia suggests "Charles Baxter" may be who you have in mind.

      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.
      • by theolein (316044)
        Stephen Baxter wrote a series of SF books on the far future and a lot of it has to do with a long war with a race of beings that own the center of the Milky Way and use its black hole for construction and computing.

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