Stories
Slash Boxes
Comments
Search

News for nerds, stuff that matters

Slashdot Log In

Log In

Create Account  |  Retrieve Password

The Milky Way's Black Hole Is Not So Quiescent

Posted by kdawson on Tue Apr 15, 2008 02:03 PM
from the long-ago-in-a-galaxy-right-nearby dept.
Space Science
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.'"
+ -
story

Related Stories

[+] Milky Way Black Hole Could Reignite 117 comments
sciencehabit sends us to Sciencemag.org for an account of a survey of nearby galaxies that points to the possibility that once-quiescent galactic nuclei could wake up and become active again. If the Milky Way's dormant black hole should become active, it could be bad news for life on Earth (and elsewhere in the neighborhood). The paper (PDF) is up on the arXiv.
Submission: Why the Milky Way's black hole is so quiescent by esocid (946821)
This discussion has been archived. No new comments can be posted.
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.

The Milky Way's Black Hole Is Not So Quiescent 50 Comments More /

 Full
 Abbreviated
 Hidden
More
Loading... please wait.

  • Black(hole)box joke. (Score:5, Funny)

    by suso (153703) * on Tuesday April 15 2008, @02:07PM (#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.

  • A million times brighter than black? (Score:4, Interesting)

    by jomegat (706411) on Tuesday April 15 2008, @02:07PM (#23080994)
    How bright is a million times brighter than black?
    • 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.

      • Re:A million times brighter than black? (Score:4, Informative)

        by drerwk (695572) on Tuesday April 15 2008, @02:19PM (#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

          • 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].

        • Re:A million times brighter than black? (Score:5, Informative)

          by evanbd (210358) on Tuesday April 15 2008, @03:02PM (#23081798)
          In astonomy and astrophysics, ignition usually refers to fusion, rather than a chemical process.

        • 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.

      • Re:A million times brighter than black? (Score:4, Informative)

        by evanbd (210358) on Tuesday April 15 2008, @03:01PM (#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.

    • 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.

    • Re:A million times brighter than black? (Score:5, Funny)

      by ArcherB (796902) on Tuesday April 15 2008, @02:50PM (#23081674) Journal

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

    • Re:A million times brighter than black? (Score:4, Informative)

      by ozbird (127571) on Tuesday April 15 2008, @05:34PM (#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.

  • "300 years ago" (Score:4, Informative)

    by l2718 (514756) on Tuesday April 15 2008, @02:08PM (#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, @03:13PM (#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, @06:09PM (#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 :-).
        • 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

  • Other deadly core issues? (Score:4, Informative)

    by CRCulver (715279) <crculver@christopherculver.com> on Tuesday April 15 2008, @02:08PM (#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.

    • Re:Other deadly core issues? (Score:4, Funny)

      by meringuoid (568297) on Tuesday April 15 2008, @02:47PM (#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.
      • No, Niven wrote before we knew that the Milky Way *HAD* a central black hole. He was assuming that there were a whole bunch of really large stars hidden behind the gas clouds (that we couldn't see through from ground level).

        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.
  • '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?

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

    Damn global warming!

  • 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?

    • 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, @02:17PM (#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.
    • 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.
      • 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.

    • Re:The Two Things Rule (Score:5, Funny)

      by sm62704 (957197) on Tuesday April 15 2008, @02:27PM (#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
      • 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.

  • of course a black hole can give off light (Score:3, Interesting)

    by pclminion (145572) on Tuesday April 15 2008, @02:50PM (#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.

      • 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

      • 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?
    • 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

  • New extinction event hypothesis? (Score:3, Interesting)

    by PoliTech (998983) on Tuesday April 15 2008, @03:40PM (#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

    • Billy Joel...???

      There's a thing called "it", which, it is my sad duty to impart, you are not and never will be with.

All trademarks and copyrights on this page are owned by their respective owners. Comments are owned by the Poster. The Rest © 1997-2009 Geeknet, Inc.