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Science

Death Spiral First Evidence Of Black Hole 149

Posted by Hemos from the what-happens-next dept.
Porfiry writes "NASA's Hubble Space Telescope may have, for the first time, provided direct evidence for the existence of black holes by observing the disappearance of matter as it falls beyond the "event horizon." An event horizon is the mysterious region surrounding a black hole that forever traps light and matter straying nearby. By definition, no astronomical object other than a black hole can possess an event horizon. The discovery comes from a detailed statistical analysis of a 1992 observation of one of the first black holes ever discovered, Cygnus XR-1, which lies 6,000 light-years from Earth in the summer constellation Cygnus the Swan."

And Tackhead sends in this related information: "The folks at the Chandra X-Ray Observatory appear to have detected event horizons by comparing the X-ray luminosity of the accretion discs surrounding black-hole-based X-ray novae versus neutron-star-based X-ray novae during their phases of dormancy. X-ray novae are caused by ignition of fusion in the accretion discs of hot gas drawn from companion stars near black holes or neutron stars. While the novae were dormant, the discs surrounding black hole companions were observed and found to be 100 to 1000 times fainter than those surrounding neutron star companions. The conclusion: 'something' must be consuming the energy that would otherwise be expected from the disc; the most likely candidate being an event horizon."
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Death Spiral First Evidence Of Black Hole More

Death Spiral First Evidence Of Black Hole

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  • ..merely more indirect evidence....

  • ..actually it looks as though the person who was researching this could have done with a bit of distributed computing a la SETI screensaver et al.

    Apparently it took Dolan several years of processing the data from Hubble (1 billion data points) to find two examples of the pulse train he was looking for. If he'd knocked up a decent screensaver and distributed the processing he'd have got the answer in a couple of weeks....
  • Reminds me of the movie Event Horizon Moderators: Now is your chance to make my life even more worthless
  • That's like saying that, just because you can see things that are falling, that does nothing to prove gravity. This is as direct as the evidence can get without actually going and jumping into one.
  • ..I like the Artists concept [stsci.edu] of a black hole.

    Its just so.......black!!

    :-)
  • Chandra X-Ray Observatory is a name that just sounds like one of Dr. Evil's super-secret lairs.

    www.niceFire.com [nicefire.com]
  • How much more black could it be? None. None more black.
    Spot-the-quote
  • (IN A SPACESHIP APPROACHING EVENT HORIZON. Professor Tackhead is explaining the concepts of black hole detection to his fellow disbelievers.)

    Professor Tackhead: The folks at the Chandra X-Ray Observatory appear to have detected event horizons by comparing the X-ray luminosity of the accretion discs surrounding black-hole-based X-ray novae versus neutron-star-based X-ray novae during their phases of dormancy. X-ray novae are caused by ignition of fusion in the accretion discs of hot gas....

    (horrible sucking-slurping sound)

    Black Hole: SURRRRLLUPRRRPPPPPPPPP....

    Professor and the rest: AIIIIAAARRRGGGHHHHH...

    Black Hole: Blech! Ahhhhhh....
  • So _that's_ where all my karma went, must be there visiting my missing socks. :-)

  • This isn't seeing a black hole, it's seeing certain phenomena that might indicate the presence of a black hole. Until somebody actually sees one of these things, they're still purely speculation, and a somewhat dubious one at that, despite the amount of public attention they have managed to capture.

    Surely there's a problem when your theories mean that the topology of the Universe is punctured not just once, but many, many times with points of infinite density? Where the very laws that the Lord decreed cannot be used to determine behaviour? This strikes me as a somewhat flawed design, because if laws apply, they should apply everywhere! And because black holes would mean this was not the case, I personally don't see how they could exist in a well-formed Universe.

    I think that when we are able to shed some more light on these areas of the Universe, we'll see some logical explaination for them than holes in the fabric of the Universe.

  • > An event horizon is the mysterious region surrounding a black hole

    "mysterious" indeed. That sounds like a lame Discovery Channel way of describing scientific discoveries.

    > By definition, no astronomical object other than a black hole can possess an event horizon.

    But for terrestrial objects, we have the Management Zone and the Conference Room, where work slows to a complete stop.


    --
  • > Couldn't Rob or Hemos or SOMEBODY who has their fingers in the source to Slash make it so that people making references to first posts, goatse.cx, trolls or other lame ass shit can't even post at all?

    It seems like their filter for ASSCII art should already be catching goatse.cx.

    --
  • Cynic!

    It's not just indirect evidence - there's an "Artist's Concept" too.

    Peanut butter comes in jars. Jam comes in jars. Therefore peanut butter is jam. (Jello)

    FP.
    -- Real Men Don't Use Porn. -- Morality In Media Billboards
  • Set your user preferences to 'Browse at +1' and you'll be amazed at how much crap disappears....

    ..actually I like some of the AC posts, even the silly ones, but I do wish for a little more imagination and less repetition.

  • Re:Still more indirect "evidence" (Score:5)

    by sachsmachine ( 124186 ) on Friday January 12, 2001 @12:50AM (#512115) Homepage
    I'm not entirely sure this isn't a troll,but... it's either this or finish an essay on Bertrand Russell.

    What is your criterion for direct evidence? Part of the idea of a black hole is that I can't really see it in front of me, since it's black. Any good view of evidence would treat visual perceptions as different in degree, rather than kind, from evidence of the sort that these telescopes have turned up. I see tables in front of me all the time, but the way by which I should argue for the existence of tables and the way by which I should argue for the existence of black holes is precisely the same.

    What you say about laws applying everywhere is absolutely meaningless. I can create a list of laws for *any* universe that I can describe, no matter how chaotic it may appear -- there may be a whole lot of non-computable functions in those laws, and the list might not be finite, but that doesn't mean that universe is any less bound by laws.

    What's unusual about the laws in this universe is that there seem to be relatively few of them, and they're relatively simple -- at least compared to what they might be. There's no reason, though, why they *must* be so simple, or must be equally simple everywhere; the fact that we expect them to be is merely more evidence of the simplicity.

  • [...] it's seeing certain phenomena that might indicate the presence of a black hole [...]

    Consideringt this is only supposed to be evidence of a black hole, what other explanations can you offer for this phenomena?

    ----------------------------
  • Yes, and you can read my other comment about the artists concept here [slashdot.org]
  • It's one louder

    FP.
    -- Real Men Don't Use Porn. -- Morality In Media Billboards
  • ... once you understand what the principles behind them are. And, of course, we don't understand the principles behind them, in large part because we've never had the opportunity to test our theories in the laboratory, nor the opportunity to see direct evidence of our theories in the heavens.

    As Yogi Berra said, "In theory, there is no difference between theory and practice. In practice, there is."

    Black holes certainly do follow basic physical laws; they follow much of the same laws that the rest of the cosmos follows. Inside the event horizon of a black hole, the laws of physics still apply just as they do outside the event horizon.

    But if we don't know the laws outside the event horizon, it's hardly surprising to find that we can't tell what happens within, is it?

    Einstein's theory of relativity is a brilliant stroke of genius, but it is not a complete theory. Forgetting that leads us down a path of scientific hubris, in believing that we've found the One True Law of the Cosmos.
  • Obviously you are unfamiliar with Godel's theorem, which states (in essence) that no system can be both complete and consistent. In other words, you are either in an incomplete system, containing objects not produceable by the basic rules of the system, or you are in a system accepting paradox, where the rules of the system produce conflicting objects. Therefore, we can do one of two things: Not be able to describe the phenonenom, or describe it noting that the physics used to describe it are completely insane.

    "The very laws that the Lord decreed"? Dude, these "laws" are all interpretations based on limited human perception.

    Who said the Universe was well formed? Who said you could even describe the universe in those terms? For that matter, if we used Godel's notion of "well-formed", we'd have no problems with the apparent paradoxes introduced.

    Why do you have problems with paradox? Are you really that limited?
  • This isn't seeing a black hole, it's seeing certain phenomena that might indicate the presence of a black hole. Until somebody actually sees one of these things, they're still purely speculation, and a somewhat dubious one at that, despite the amount of public attention they have managed to capture.

    There's a ton of stuff that we can't see that we accept due to available evidence. Example: Gravity. Why do you need to "see" the black hole to know it exists?

  • What you say about laws applying everywhere is absolutely meaningless. I can create a list of laws for *any* universe that I can describe, no matter how chaotic it may appear -- there may be a whole lot of non-computable functions in those laws, and the list might not be finite, but that doesn't mean that universe is any less bound by laws.

    Strawman. We're not talking about some vague "other universes", we're talking about our Universe. I too could make up a whole set of data to support my point, but that wouldn't make it valid.

    What's unusual about the laws in this universe is that there seem to be relatively few of them, and they're relatively simple -- at least compared to what they might be. There's no reason, though, why they *must* be so simple, or must be equally simple everywhere; the fact that we expect them to be is merely more evidence of the simplicity.

    Again, how can you say this is "unusual"? Have you been to any of these other universes? And how does our expectations of simplicity constitute evidence of simplicity? If I expect that writing a modern operating system is simple, does that make it so? Of course not, that's another strawman argument.

    As for why this Universe is simple enough for us to understand, well I think that's obvious. It was created to be so.

  • There's a lot more to distributed processing than knocking up a decent screensaver. The client side is the easy part, its the actual distribution part that is a huge amount of effort.

    But you wouldn't know that, being a clueless Linux user.

  • "
    Where the very laws that the Lord decreed cannot be used to determine behaviour?
    "

    Troll. I'll bite.
    Not that line though, but this one:

    "
    ... if laws apply, they should apply everywhere!
    "

    We don't have "laws" as such. We have models. The models apply well in most situations. Black holes break our normal models. That doesn't mean that any intrinsic laws of physics are broken, it means our present model isn't capable enough, that's all.

    FatPhil
    -- Real Men Don't Use Porn. -- Morality In Media Billboards

  • The theiving cartoon bear is not someone I'd have thought of as good quoting material, but maybe that's just me...

    Black holes certainly do follow basic physical laws; they follow much of the same laws that the rest of the cosmos follows. Inside the event horizon of a black hole, the laws of physics still apply just as they do outside the event horizon.

    But they don't do they? Because if black holes existed then we'd end up with singularities at their centre which would violate physical laws by producing infinite discontinuities. Any theory which breaks itself cannot be a valid theory outside of esoteric mathematical journals.

    Einstein's theory of relativity is a brilliant stroke of genius, but it is not a complete theory. Forgetting that leads us down a path of scientific hubris, in believing that we've found the One True Law of the Cosmos.

    It may not be complete, but it's not wrong is it? Any new theory will have to include Einstein's theory in it, and so my point still stands.

  • Why bring pure maths into a physics thread?

    FatPhil
    (a pure mathematician)
    -- Real Men Don't Use Porn. -- Morality In Media Billboards

  • Godel proved that if you have a formal system with a fixed set of axioms that are sufficient to encode ordinary arithmetic, there will either be an inconsistency, or there will be statements that are undecidable within the system. You can prove that the formal system is internally consistent (cannot prove any pair of contradictory statements) provided you accept that some statements are undecidable.

    What does this have to do with anything? There's a difference between abstract mathematical systems and the physical universe, and Godel only talks about one.

    "The very laws that the Lord decreed"? Dude, these "laws" are all interpretations based on limited human perception.

    So you're a cultural relativist that believes that science is only the latest way for humans to make sense of the Universe around them? Whether you believe in the Lord or not, I think any rational human being should believe that the laws of physics are really real!

  • > This strikes me as a somewhat flawed design,
    > because if laws apply, they should apply
    > everywhere!

    Well they do. It is just that the definition of 'everywhere' isn't as obvious as you might think.

    Physical laws apply where they are supposed to, in space-time - all of it (which is my working definition of 'everywhere').

    The only oddity is that it is possible for things to leave 'everywhere', which is, I admit, a fairly strange property.

    Your reference to topology is the clue here. Lets drop back to the 2-d analogues for convenience of terminology.

    People would be happy with an 'infinite plane' of spacetime. If you are used to that idea, then the fact the space-time might be bounded (like the 2-d surface of a sphere or even a torus) seems really odd, but with analogies like this one people can get their head round it.

    (Although it is easy even then to get into mental traps. "What do you mean I can't go further North? I can just keep walking can't I? Thats not going to suddenly stop being North is it?")

    But both of those (2-d) surface mentioned above lack 'holes'. But we only expect that because we aren't near one.

    But if we lived in a chunk of flat space-time (i.e. no gravity) we would probably find the idea of curved space time prepostorous. ("What do you mean, things would just move 'on their own'? Yeah right").
  • I think any rational human being should believe that the laws of physics are really real!
    i don't think ANY physicist would ever dare to say that.

  • Well my knowledge of the subject is obviously not cutting-edge, but whilst general relativity has been experimentally proven to be correct there are alternative formulations [slashdot.org] which give equivalent experimental results but do not include black hole solutions, instead allowing for super-massive stellar objects. In these cases, it would be quite possible to have neutron stars that acted similar to what a "black hole" would appear to.

  • This is exactly right. When you take the dynamics equations from special relativity and apply them to everyday situations, they look identical to traditional Newtonian mechanics. Which is what you would expect, becuase Newtonian mechanics works in everyday situations. Newton's equations are therefore "laws" for such cases. It's just that in unusual situations (high relative velocity, or the area surrounding a black hole), things are now different, and you have to fall back on the "more fundamental" laws provided by relativity.

    Newton wasn't wrong, he just didn't have the full picture. By seeing what happens in unusual and extreme situations, we find out whether our models are correct, or whether they are specific cases in more accurate models, or rather, models that more completely describe physical reality.

  • Strawman. We're not talking about some vague "other universes", we're talking about our Universe. I too could make up a whole set of data to support my point, but that wouldn't make it valid.

    Not at all. Your argument was that in a universe bound by laws, those laws must be uniform. My argument is that if you don't put a bound on the complexity of the laws, all universes must be bound by laws -- not as a scientific principle, but as a tautology. This means it's without content.

    Again, how can you say this is "unusual"? Have you been to any of these other universes?

    I apologize. What I should have said was, "There's no reason for us to assume that a universe is bound by a small (or even finite) number of laws, or that they would be within human comprehension. The fact that it is, is spiffy."

    And how does our expectations of simplicity constitute evidence of simplicity?

    Well, it's certainly possible that our expectation is wrong, but given that "simple" is a completely arbitrary term, the fact that some people feel accustomed to simple rules for the universe does give us some reason to go along with their description.

    Of course not, that's another strawman argument.

    I can't see any connection between the two arguments you've labeled "straw men" that could be serving as your definition.:) So at this point I'm convinced you're a troll. I suppose the line between a troll and a very opinionated person isn't well-defined; it all depends on whether you're writing in bad faith, which isn't something I can check from my end. Heck, I might be some kind of reverse-psychology troll pretending to be a clueless newbie and laughing at you all behind my hand. Ah well; another night, another few precious minutes wasted on slashdot.

    Good night.


  • This strikes me as a somewhat flawed design, because if laws apply, they should apply everywhere!

    It may not be complete, but it's not wrong is it?

    Exactly! You're contradicting yourself. Einstein's theory works, but not for everything.

    ----------------------------

  • i don't think ANY physicist would ever dare to say that.

    So you think that no scientist would say that the universe actually exists outside of human conscioussness? I don't think solipsism is the number one philosophy for more physicists...

  • "The laws of physics are really real"?

    Thus, something is real if humans define it?

    I think it's pretty clear that if the "laws of physics are really real", then "science is the only way for humans to make sense of the Universe around them."

    If you have a hard time accepting rules with exceptions when we describe blackholes, how is it that you can believe laws of physics are really real yet also believe that there is a god?

    If the rules of physics do not allow for a blackhole, they do not allow for a god.

    Either way you're trolling.
  • I'm no physics major either, and these are valid arguments, the outcome will be very interesting. I personally still believe that photons have mass and therefore are affected by gravity. If the gravity is strong enough photons will not escape, hence black holes.

    ----------------------------

  • Thus, something is real if humans define it?

    No, real if experimentally proven. And real in the sense of existing independent of human existance.

    I think it's pretty clear that if the "laws of physics are really real", then "science is the only way for humans to make sense of the Universe around them."

    True. I haven't argued against that.

    If you have a hard time accepting rules with exceptions when we describe blackholes, how is it that you can believe laws of physics are really real yet also believe that there is a god?

    Yes, where's the contradiction? God created the Universe and thus the laws that define how the Universe works, hence God is real and so are the laws of physics. No problem there.

    If the rules of physics do not allow for a blackhole, they do not allow for a god.

    *sigh* Nonsense, because God is outside the Universe, black holes are inside it. So the laws of physics cannot say anything about the existance or non-existance of God, but they can about black holes.

    Either way you're trolling.

    That would make it easy for you wouldn't it?


  • So much for the Yilmaz variant of General Relativity,
    which predicts that black holes do not exist
    more... [washington.edu]

  • This strikes me as a somewhat flawed design, because if laws apply, they should apply everywhere!

    Well, no. The normal laws of physics break down when you get down to quantumn mechanics. Well, so I've read, I'm no expert in it.

  • FYI: The quote is from Yogi Berra, catcher and manager for the Yankees among other things.

    You are thinking of Yogi Bear, the cartoon bear.

  • Well, no. The normal laws of physics break down when you get down to quantumn mechanics. Well, so I've read, I'm no expert in it.

    So you're saying that quantum mechanics is not part of the laws of physics? I don't think that's what you meant, but still...

    And QM provides no solutions either. My point still remains.

  • Fusion is marginal in X-ray novae (Score:4)

    by Caid Raspa ( 304283 ) on Friday January 12, 2001 @02:21AM (#512142)
    X-ray novae are caused by ignition of fusion in the accretion discs

    [Kwatz!]

    Fusion is not an important factor in X-ray novae. Hydrogen-to-Helium fusion yields about 0.7% of the rest mass (E = mc2). Dropping something to a neutron star yields about 20% of rest mass, or about 280 times more energy than fusion. For black holes the yield is about 10%, as there is no solid surface to slam against.

    X-ray novae are ignited when the accretion disk gets ionised. This makes the gas more viscous, leading to a faster lose of angular momentum and thus a faster infall. Eventually, most of the disk falls on the neutron star, producing an X-ray nova outburst.

  • I don't think that it is a matter of belief - there's proof. Einstein had a theory about gravitational lenses, meaning light being bend by heavy objects. This theory has already been proven.
    How to make a sig
    without having an idea
  • From the article: The observation yielded 1 billion data-points, which, if printed out on a chart recorder, would stretch 600 miles! ... Dolan "mined" the enormous database on and off for years.

    Is that really an "enormous" database? If you have 1 byte/data point, you will just get something like 950 GB worth of data? That isn't much compared to what you get from many scientific observations or simulations.

    And what is the deal with "600 miles of chart recorder printout"? If it's a scientific article, write size in bytes, kB,MB or GB, goddamnit...

    --

    "I'm surfin the dead zone

  • There's nothing 'mysterious' about it at all (the theories have been revised over and over since the late '60s) if your expierence with black holes isn't limited to the Disney movie of the same name and that travesty with Sam Neill in it

    Provided they exist at all, they are most likely collapsed neutron stars, so think of the event horizon as the surface of the black hole, the same way the neutron star had a surface before it collapsed. The escape velocity (speed at which you must travel in order to escape the gravitational pull of the body) on earth is about 11km/s. The escape velocity on a black hole at this 'surface' is the speed of light, hence 'black'.

    By the way, I know you weren't claiming it to be mysterious, you were just slamming the Discovery Channel, but it seemed like a good opening for me to ramble a bit.

  • According the theory of Autodynamics (http://www.autodynamics.org/) black holes, being objects with infinite mass in a singularity, don't exist. Very dense object with enough mass to prevent light from escaping can exist however. This doesn't seem to be in conflict with the new data which the /.-story is about.

    Though the Autodynamics website is quite chaotic it's certainly an interesting read. Don't we all want to believe that the lightspeed-barrie is just bogus. On the other hand, I always tend to immediately believe some scientific-looking talk claiming that something is this way (or another way)
  • This reply has real physics, not blather. It should get a higher score than 2.

  • "by definition" (Score:3)

    by OlympicSponsor ( 236309 ) on Friday January 12, 2001 @03:11AM (#512148)
    "By definition, no astronomical object other than a black hole can possess an event horizon. The discovery comes from a detailed statistical analysis of a 1992 observation of one of the first black holes ever discovered, Cygnus XR-1, which lies 6,000 light-years from Earth..."

    Also "by definition": statistical analysis of data from a black hole will give evidence of a black hole.
    --
    MailOne [openone.com]

  • Re:Still more indirect "evidence" (Score:3)

    by Anonymous Coward on Friday January 12, 2001 @03:23AM (#512149)
    You can't see a black hole, moron. That's the fundamental property of a black hole.

    Vision is the process of your brain interpreting impulses from your retina, which are created by photons reflected off the object you are seeing.

    In the case of a black hole, the very definition of a black hole is an object with so high density, that the gravity well is strong enough that even light that gets inside a certain area (the even horizon) will be sucked in, and unable to escape.

    Thus, any photon that comes in contact with the black hole itself will never be reflected.

    You can see effects of a black hole. You can observe mass entering the event horizon. But you can never see the black hole itself.

    Also, your other points are inexact. Black holes does not indicate infinite density. They indicate a density high enough that photons can't escape.

    In addition, your argumentation is full of conjecture. For instance you don't give any argument for why it would be a problem if the topology of the universe is punctured with points of inifinite density, except by claiming this in some weird way violates "the very laws that the Lord decreed".

    Can you point me to any works that specify "the Lord"'s views on physics, with an emphasis on astrophysics, relativity and quantum mechanics? Thought so.

    The point is, our scientific theories are just that: Theories. Models that give a coherent view of the data we observe. If the models doesn't fit the data, then the models and theories have to be revised, not the data.

    In the same way, could you please point me to any religious texts that explain this "well-formed universe" of yours? If you have such fait in "the Lord", surely you should have faith that whatever we observe in the universe is by his device and design, and to his liking?

  • It seems like many times when a "breakthrough" like this comes about, it is always tied to the study of older data. Makes me think they should crank out a screen saver ala seti and crank through all of their old data.
  • But they don't do they? Because if black holes existed then we'd end up with singularities at their centre which would violate physical laws by producing infinite discontinuities. Any theory which breaks itself cannot be a valid theory outside of esoteric mathematical journals.

    But yes, they do. Our failure to understand the nature of those laws does not mean they don't exist. They violate *our* laws, the ones based on observation, experimentation and speculation, but that is not the same thing. You have to be smarter than the phenomenon you're trying to explain. We aren't yet.

    Naeser's Law:

  • Points of infinite density? Is that what black holes are supposed to be? I don't know much about the current percieved physics of blackholes, but I didn't think they were infinitely dense.

    Can someone fill me in on this.
  • Statistics?? Now, now. Don't throw the statistics card.

    "Nine out of ten dentists recommend Crest."
    -as compared to what...vasoline?
    -how many dentists were surveyed? 10? 1000? 10000?
    -were there choices other than Crest?

    Now I've done experiments where you "tweak" the stats to look *a little* better. All statistics provide is a means for us to examine phenomena and come to the conclusion "..hey..we just might have something here. Let's investigate further."

    Statistics *prove* nothing. Nor do they imply causality. If we were to go on statistics alone, Crest would be the only/best brand of toothpaste.

  • Seems to me, just about every time you guys post a story relating to black holes, in some way or another you always say "this is the first real evidence of the existence of black holes!

    How much "first real evidence" can we have from separate researchers? It seems that different people have each been coming up with the "first real evidence" for the existence of black holes for years now, and every couple of months some new researcher claims that he's finally proven it, and then it seems another couple of months down the road someone else stakes the claim.

    Why? What's going on here?

  • Instead, the gas crossed over into a twilight-zone realm when time and space no longer have any practical meaning

    Yep, that's the executive conferance room alright.
  • Where the very laws that the Lord decreed cannot be used to determine behaviour? This strikes me as a somewhat flawed design, because if laws apply, they should apply everywhere! And because black holes would mean this was not the case, I personally don't see how they could exist in a well-formed Universe.

    Surely laws of universe apply everywhere in the universe. Our aproximation of those laws just don't determine behaviour inside black holes.

    Jari Mustonen

  • He's NOT talking about statistics? Hmm...now I'm confused.

    "The discovery comes from a detailed statistical analysis of a 1992 observation of one of the first black holes ever discovered..."

    Error level? Probability? Statistical significance? Its all part of the scientific method.

    But - I could be wrong, after all, I'm an idiot.

  • GRT (Score:1)

    by Anonymous Coward
    "By definition, no astronomical object other than a black hole can possess an event horizon." Uhm, well. Every astronomical object have a schwartzhild radius (the Earth: 9mm) and as long as the radius of the mass is larger than that, everything is fine. But, if it goes below that we have an event horizon. Thus, compressing Earth to a marble of 9mm, we get an event horizon too! :-) Another thing: How can they observerve chunks of gas pass the event horizon when it is clear from GRT that it takes an infinite amount of time for an external observer to watch something to fall inside the black hole... Hmm.
  • After further analysis of these "pulse trains" a brief radio transmission was detected: "We keep tubs clean so you don't have toooooooooooo!"
  • If I remember my general relativity, to an observer at rest matter falling into a black hole will seem to take an infinite time to pass the event horizon.

    It's the one who needs more time (the observer falling in the black hole) who will experience becoming a very curved and very thin pancake in a finite amount of time.

    I suggest everyone interested to go read John Baez's GR Tutorial [ucr.edu]
  • Fun Troll First: Nobody ever claimed to have actually discovered the real laws that govern the universe. (e.g. F=ma is only a first order approximation and not even a mathematically rigorous law either(because m and F can't be defined independently)) Second: We don't have to live in a "well-formed"(whatever that means) universe. Just as we don't have to have a solar system with circular orbits. It sounds like you have some "my place in the universe" issues you need to work on. :)

  • Hail the mighty Astronomer! (Score:4)

    by jayhawk88 ( 160512 ) <jayhawk88@gmail.com> on Friday January 12, 2001 @04:40AM (#512162)
    Astronomers never cease to amaze me. This guy found an event that happened for 0.2 seconds, approximately 35,194,176,000,000,000 miles away, that happened 6000 years ago. And could actually recognize the significance of the event.
  • i will tell you how you can believe in god and physics......i dont see how someone cannot cancel out the premise behind physics if it works if they believe in god, but i can see how you can doubt god comming from a physics back ground and if you are not christian ((there is no slap in the face evidence of god, just things we say are god relics and views and oppinions and books which could be man made) i myself am christian in a none true way, i believe but dont practice per se), if there is a god and he (he because its quicker to type than anything else) made everything that we know of and more, he therefore made physics the way it works and so they both can exist in conjunction together due to the fact that he made it, just because physics explains that something is there but not how it got there from the begining of time until the present does not cancel out the probability of both coexisting in the same universe or space. just because physics cannot explain if god exists does that mean he doesn't, just because physics cannot explain why my programming book is on page 420 does that mean it doesn't exist? See where im comming from, you cant cancel something out until you have utter confirmation that it doesn't exist. Does that explain it to yah?
  • However, how can you SEE a black hole? It absorbs all the light and matter near it. That's the evidence. If you see light and matter being drawn towards a dark spot in space, what do you think? That it's being drawn towards a white-hot neutron star? Hell no, you think, "This is interesting, let me call my colleauges to see what they think." This sort of thing has long been suspected to be evidence for a black hole, and it looks like they're right. By the way, physical and chemical laws that you say should be applicable everywhere, have you heard about something called Quantum Theory? The world of the atom, and smaller, is bizzare. To give a example, a photon traveling through time and space, will turn into a electron, emit the electrons anti-particle, the positron; go back in time, pick up a positron, and turn back into a photon. This has to do with Quantum Electro-Dynamics, pioneered by Richard Feynman. Obviously, you don't often see something just go *pop* and travel back in time? That's what's happening on a quantum level all the time. Look! it just happened several thousand times!
  • > NASA's Hubble Space Telescope may have, for the
    > first time, provided direct evidence for the
    > existence of black holes by observing the
    > disappearance of matter as it falls beyond
    > the "event horizon."

    I doubted this from the beginning, as Relativity Theory clearly predicts that external observers cannot watch anything fall beyond the event horizon. It's only in the time-frame of reference of the falling object that eventually it'll cross the event horizon. In the time-frame of reference of any external observer the object will need infinite time to reach the horizon. This is because object time goes slower and slower as the object dives deeper and deeper into the gravity field. This is associated with the object becoming shorter and shorter (Lorentz contraction). All as seen from an external observer of course.

    Reading through the entire article, I finally found:

    > Because of the gravitational stretching of
    > light (an effect called redshift), the fragment
    > disappeared from Hubble's view before it ever
    > actually reached the event horizon. The
    > pulsation of the blob - an effect caused by the
    > black hole's intense gravity -- also shortened
    > as it fell closer to the event horizon.

    Which basically does not say that the object ("fragment") was observed to fall beyond the horizon, what it says is that is was observed to approach the horizon ! Note it also observed "shortened pulsation" which is a direct consequence of the time slowing down.

    So again a headline that's plain wrong. I really wonder if the author knew that.
  • I don't even pretend to understand this kind of stuff, but what do they mean by "disappear" and "vanish"? Is the amount of information in the universe reduced? Or do they just mean that you can't see the stuff any more?

    Also, the article says, "About 1,000 miles above the event horizon (in the case of stellar-mass black holes)." What does "stellar-mass" mean?

    jeb.

  • Yeah, just think of how many punchcards that would be to enter all of that data. That must have taken quite a long time...
    --
  • This has nothing to do with a black hole, it's simply two Holzman field generators turned back-to-back and switched out of phase 180 degrees. If they're only a few degrees out of phase, you end up with a No-room. In this case, however, you end up with what appears to be an infinitely dense point in space.

    I'd suspect that this actually has something to do with early versions of Kamen's IT. Which is exactly why we shouldn't let these things get out of control -- if they come together in a particular way, it will mean the end of the Earth.

    Sheesh.

    -Chris
    ...More Powerful than Otto Preminger...
  • black holes aren't the only things that look infinitely dense. Electrons, as far as we can tell, have NO volume, giving them infinite mass and charge density. Hmmmmm...
  • "Infinite density" is crap...

    In fact, considering you may live in an hyperspheric universe (closed topology), if you wannna see a black hole from the inside just look around!

    Black holes can be very sparse, if they are very big. In a sense, they are universes on their own...
  • The point is that altough it fits the theory of how matter should behave around a black hole, this does not preclude some unknown phenomenon from being the cause. The best they can say is that this fits the model really well. Astronomers still encounter unexpected and unusual things. It could be that it isn't a black hole, but something much more exotic.
  • As long as all of the black holes stay far away from earth and the sun, I really don't care about them.

  • Rush (Score:1)

    by guinsu ( 198732 )
    Pages of comments and no one has made a Rush reference? They knew there was a black hole there back in 1975. :)
  • I thought black holes can't exist [slashdot.org].
  • <gripe>
    I dont' know how many of you out there noticed (I'd suspect at least half of you) but they had no image or data from the Hubble on that page. Only an "Artists Concept" Hubble is a telescope for Bob's sake! It makes images (or at least pretty graphs if its a raido telescope) When a theorist is telling me about black holes, then I like to see artists concepts, but when I hear about evidence of black holes from a huge telescope, I want to see the pictures!

    </gripe>
  • No, but the bass-line to that song (I play) has been stuck in my head since reading the headline :)

    "spinning, whirling, still descending, like a spiral sea unending!!!!"
    --
  • Or more accurately: "The folks at the Channdraaa.. Exxx... Rraaaaaaaaaaaayyyyyyyyy...." ;-)

    (Good call - it serves me right for being verbose to the point of Katzianness!)

  • Whatever we do, let's not name a spaceship after it, because MAN, it is bound to end up running on an engine powered by Satan, and then the ship will probably come to life and try to kill the crew, with cameos by hell minions Pinhead, Freddy, Jason, and CarrotTop...

    "Uh, Mission Control...there is some crazy red-haired maniac killing my crewmates with idiotic inventions..."

  • I thought blick holes can't exist.
    -Want an iguana?

    Is an iguana the only other option?

  • > alternative formulations which give equivalent experimental results but do not include black hole solutions, instead allowing for super-massive stellar objects

    Question: In these formulations, what happens to matter when it hits the surface? (Or do they allow for "things big and dense enough to have event horizons, just without singularities inside 'em"?)

    (To be absolutely precise, both the Chandra study and the Cygnus XR-1 data support the hypothesis that event horizons exist; what's inside the event horizon is an open question. Is a "black hole" a "thing from which light cannot escape" or a "thing with a singularity in the middle"?)

  • From our perspective outside a black hole, matter never quite passes through a black hole's event horizon. That is because time slows down near the event horizon and it takes an infinite amount of our time for the matter to pass through the event horizon. From the perspective of the matter falling through the event horizon, the passage is uneventful; the matter experiences no sudden changes as it passes through that surface of no return. Instead, the matter continues to accelerate toward the singularity at the center of the black hole to a point of infinite density and infinitely small size. Its approach to the singularity completely destroys the matter's structure. The gravitational tidal forces caused by the differences in gravity at different locations in space tear the matter apart so that it contributes only mass, charge, momentum, and angular momentum to the singularity. The black hole is usual identified with the event horizon rather than the singularity contained inside it. Passage through that event horizon erases any memory of the structure of the matter, leaving only its mass, charge, momentum, and angular momentum observable in the properties of the black hole.

  • Re:Fusion is marginal in X-ray novae (Score:3)

    by Tackhead ( 54550 ) on Friday January 12, 2001 @07:00AM (#512186)
    >X-ray novae are ignited when the accretion disk gets ionised [not because o f fusion, as Tackhead had incorrectly guessed]

    The thing I like most about Slashdot is that when you make a mistake, people cal l you on it, and you learn.

    The thing I like most about the 'net is that I can hop over to Google, enter "x- ray novae mechanism" and find a paper on a site in Japan - Black-Hole X-Ray Transients: Th e Effect of Irradiation on Time-Dependent Accretion Disk Structure [riken.go.jp] (OK, I had to use the Google cached copy) - and discover once again that the universe is not only more weird than I do imagine, it's more weird than I can imagine:

    The disk instability due to the ionization of hydrogen and helium re mains the most plausible cause of the outburst of the black-hole candidate X-ray novae. For the orbital periods and mass-transfer rates inferred from observations,the disk is predicted to be unstable. A steady state is very unlikely.

    High-energy astrophysics rocks.

  • Black Holes vs. Singularities (Score:3)

    by gnfnrf ( 39155 ) on Friday January 12, 2001 @07:03AM (#512188) Homepage
    I'd just like to point out to those who want to engage in the "do black holes exist?" debate, that there are two questions.

    1.) Do massive objects exist that collapse beyond their own Schwartzchild radii, thus forming an event horizon?

    The answer to this one is very probably yes. Neutron stars maintain hydrostatic equilibrium by the counterbalance of the gravitational inward pressure and the outward pressure of neutron degeneracy. After a certain (debatable, but between 2 and 10 solar masses) point, gravtity overcomes the neutron degeneracy and the star collapses under it's Schwartzchild radius. At this point, it can be called a "black hole" because the escape velocity at the surface of the object, whatever it is, is greater than the speed of light. Unless some process prevents neutron stars from growing by matter accretion past a certain point (and Type Ia supernovae seem to contradict this) or another source of outward pressure than neutron degeneracy exists, this process can and probably has happened.

    2.) Once collapsed, do such objects become mathematical singularities within the event horizon?

    This is where all of the scary stuff happens, with the math predicting a space coordinate rotating into time, infinite density, etc. The answer to this question is, WE DON'T KNOW, and furthermore, IT DOESN'T MATTER. A black hole will look exactly the same if it is a singularity or just REALLY DENSE.
    We talk about black holes as singularities because we don't know of any outward force that can overcome the neutron degeneracy pressure at any point, but once under the event horizon, it doesn't matter if there is a new hydrostatic equilibrium, because it does not effect the rest of the universe.

    As for the "evidence" issue, astronomers have observed a handful of massive X-ray sources in tight binary systems (the mass is found by the period of the system) which are really probably black holes. From earth, that is probably the best we can do.

    And in case you wonder what my credentials are, I just finished an in-depth course in astrophysics.
    --
    gnfnrf
  • By definition, no astronomical object other than a black hole can possess an event horizon.

    Depends on your definition of black hole. I believe I've heard of some theories which suggested the existence of "cosmic strings" or something like that. Think string-like black holes, except different mechanism... Apparently, they would have an event horizon, but it might not completely conceal the singularity (oh no! a naked singularity! where's CyberPatrol when you need it).
  • You're correct when you say that the objects that scientists like to call "black holes" are nothing of the kind. They are sin receptacles created by the Lord and Savior Jesus Christ [jesus-is-lord.com]. Just as His death on the cross cleansed Earthly believers of all their sins nearly 2000 years ago, His cosmic sin receptacles suck all of the sin out of the Universe itself, leaving a moral and wholesome cosmos for all to enjoy.

    I hope this clears a few things up.
  • Strawman. We're not talking about some vague "other universes", we're talking about our Universe. I too could make up a whole set of data to support my point, but that wouldn't make it valid.

    You're missing the point. Just because the functions in our laws are not computable at the singularity of a black hole doesn't mean they don't still apply. We can't calculate them, true, but it doesn't matter because nature has conveniently concealed the singularity with an event horizon. His point about other universes was to demonstrate this.

    As for why this Universe is simple enough for us to understand, well I think that's obvious. It was created to be so.

    Oh, stop trolling. Created? By who? Who created that entity? Nobody? That entity must be pretty damn complex, then. Or I could just postulate that a simple universe came into being (or has always existed). Occam's Razor, you lose, I win.
  • The theiving cartoon bear is not someone I'd have thought of as good quoting material, but maybe that's just me...

    Yogi Berra, not Yogi Bear. Sometime baseball player, sometime commentator, and full-time professional mangler of the English language. He's the one who came up with such profundities as "nobody ever goes [to that nightclub] anymore, it's too crowded". When a colleague asked him what time it was, he asked "You mean right now?"

    Perhaps most famously, when a reporter asked him how he comes up with all these great quotes, he answered with "I really didn't say all those things I said."

    When his son, Dale Berra, was asked if he was going to continue his father's tradition of philosophically mangling the language, Dale Berra answered that "... the similarities between my father and me are really quite different".

    Etc. Yogi Bear, the Hanna-Barbara cartoon, was inspired largely by Yogi Berra.

    (If you couldn't tell, I'm a fan of Yogi Berra. Now, on to the rest of your email.)

    Because if black holes existed then we'd end up with singularities at their centre which would violate physical laws by producing infinite discontinuities.

    1. Find me a law which forbids infinite discontinuities. I've never been able to find one that says it can't happen. Philosophically, I find myself thinking that discontinuities are strongly implied by the nature of the cosmos.

    2. Which laws do we end up violating if black holes exist? The cosmos is incapable of breaking its own laws--it can only break what laws we attempt to enforce upon it.

    Any theory which breaks itself cannot be a valid theory outside of esoteric mathematical journals.

    Never heard of quantum mechanics, have you? Schroedinger's Cat is a brilliant example of quantum mechanics breaking itself. Or, in mathematics, there's Goedel's Incompleteness Theorem, which broke all of mathematics in half and left mathematicians scurrying to pick up the pieces.

    An essential part of any theory is falsifiability--that is to say, can this theory be proven wrong? Can this theory break itself? For relativity, it can be demonstrated wrong by showing that mass and energy are not equivalent, or that the speed of light is attainable by mass particles.

    Already in the cosmos we see tantalizing hints that relativity is not the end-all be-all of the universe. Black holes are one of the places where, if you peer down the rabbit-hole for long enough, you see the inconsistencies in the theory.

    But don't let that dissuade you; relativity correctly predicts 99.9% of the visible universe.

    It may not be complete, but it's not wrong is it?

    Relativity is absolutely wrong.

    Look, Newton's physics correctly explained 99.9% of the phenomena of his day, too. Then people started to look at the precession of Mercury and discovered, hey, this doesn't mesh with Sir Isaac. Newtonian mechanics said Mercury would be in one place, and Mercury wasn't, and the difference between the two places was far greater than could be accounted for by observational error.

    When theory and reality conflict... stake your money on reality.

    Newtonian Mechanics is wrong. Absolutely, utterly, wrong. However, despite the fact that it's unarguably wrong, it's a very useful approximation of the real laws (whatever they are) for anything that's moving slower than 0.1c and isn't in a huge gravity well. But don't go about thinking that Newton is correct, when the reality is Newtonian physics is a mere useful approximation of reality.

    Relativity is in the exact same boat. It's far and away better than Newtonian mechanics, but it's still an approximation of reality. In any approximation, there will be things that just aren't quite right.
  • There has GOT to be a black hole somewhere under my office building, because my job sucks harder than anything in the solar system...
    Sean
  • All depends on your perspective. I know some mathematicians (largely older ones) who still stew over Goedel, because they feel that he broke the beauty and truth of mathematics. I know a great many QMech students (typically younger ones, who haven't quite wrapped their brains around the impossibilities of it) who find cats that are both dead and alive to be counterintuitive and contrafactual.

    That being said, correct, neither example breaks their discipline (as in proving it wrong); both examples do break their discipline, though, in the context of shattering people's preconceptions of what can and cannot occur as a result of that theory.

    As I said--when reality and theory conflict, smart money is on reality.
  • A Universe simply came into being? That's pretty far fetched. You can't get something from nothing. Yeah, a debate of creationism here on Slashdot! If this were usenet, I think someone should mention Hitler soon...
  • Consider, for a moment, a black hole... what does it look like? It's absolutely black. Were it of small enough mass, and far enough away from other stellar bodies, it wouldn't even have the destinctive characteristic of an accretion disc surrounding it. How, then, can we detect such a non-descript phenomenon from afar? That's right! INDIRECTLY. Because their very nature, we can't see a black hole directly because there isn't anything to see! Instead, we have to look for the lensing effect that a black hole's gravity will have on stars behind it. Instead, we have to look for accretion disks, we have to look for inexplicable deviances in the orbits of other stellar bodies.

    You can't say "merely" more indirect evidence, because not only is indirect evidence sometimes a *VERY* good indicator of what is out there, but in this case, it's essentially all there is.

    ----
  • As for Occams razor, you are as close-minded and hypocritical bringing up the argument that God doesn't exist because who created Him? Can't answer it? Of course not. But it's perfectly logical to have a divide-by-zero error flow the wrong way in time for no reason and spontaneously erupt into our Universe. Come on that just sounds silly.

    I'm not arguing that my point of view is undoubtably right, simpy that, being the simplest answer that explains all the facts, is the most likely to be right (or, at least, is the most scientifically useful). For all we know, the universe was created 5 minutes ago by Invisible Keebler Elves. You can't disprove the Elf theory, but it's not very useful.

    It's been proven that with sufficient system resources, any Turing machine can simulate any other Turing machine not more complex than itself. Since we can build Turing machines, it means the universe is Turing-complete and therefore

    There's a serious flaw in your argument here. You point out that any Turing machine can simulate a less-complex Turing machine. This does not mean that any system containing a Turing machine can be simulated by a Turing machine. There's more to life than computers, you know. Take a look at quantum mechanics for some crazy stuff that is probably beyond any Turing machine.

    If you dismiss somebody else's as being ridiculous without examining your own to see if it has the same flaws, you just sound like an ass.

    Maybe you should have taken a second look at your Turing argument. :-)

    Every theory is just as silly as the next.

    From a purely philosophical point of view, perhaps. From a scientific point of view, some theories are better than others. The markings of a good theory are as follows: a) it is falsifiable, b) it makes verifiable predictions, c) it is no more complex than necessary. Let's analyze religion from the scientific point of view. You can't disprove God, so (a) is false. Religion hasn't been particularly good at making predictions, so it's not doing too well on (b). As for (c), well, an omnipotent god is a pretty simple explanation for everything ("it is God's will..."). One out of three ain't so hot. This doesn't mean religion is wrong, simply that it's not very useful as a scientific theory.
  • 1 - This known to be finite Universe simply... started.

    It's also possible that the universe goes in "cycles", and that what we perceive as the age of the universe is actually the time since the beginning of this cycle. It could very well still be an infinite universe.


    2 - This known to be finite Universe was created. By whom or what, there is no proof. A finite thing being created is more plausible than a finite thing simply appearing from nothing.

    It only seems more plausible because you're ignoring the question of where that creator came from. The creationist point of view requires the eternal existence or spontaneous appearance of a creator (which is surely a more complex entity than the universe it creates), and the creation of the universe. My theory (not that I can take credit for it) requires much simpler assumptions--the eternal existence or spontaneous creation of only the universe.

    As for spontaneous particles in quantum mechanics, they could just be echoes of other particles at the other side of the universe, or perhaps all atoms in the universe pop from one location to another constantly. Nobody knows what they are or what they mean. The phenomenon has only been observed, not deciphered.

    It was predicted by the Standard Model, and verified experimentally. There are numerous interpretations of what the mathematics of the Standard Model mean (most notably the Copenhagen Interpretation), but, for all but philosophical purposes, they're equivalent.

    Spontaneous creation of particle-antiparticle pairs is allowed under certain circumstances by the Heisenberg Uncertainty Principle relation for energy and time. Basically, you can violate the law of conservation of energy, as long as you do it really quickly. The energy "difference" (E) times the time interval over which the particles exist (t) must be less than or equal to Planck's constant over 2, or something like that.

    It has been shown that the semblance of an atom can be projected into a space without there actually being an atom there.[snip]They arranged atoms in an elipse, and placed another atom at one of the foci. What seemed to be an atom appeared at the other focus.

    This is probably just an experimental effect due to the geometry of electric fields of the atoms, or something like that--no mysterious profound explanations necessarily required.

  • From our perspective outside a black hole, matter never quite passes through a black hole's event horizon. That is because time slows down near the event horizon and it takes an infinite amount of our time for the matter to pass through the event horizon.

    Correct me if I'm wrong, but wouldn't this be true only for a static black hole? Since the black hole is gaining matter (or at the very least there is more matter near the event horizon which should be good enough), the black hole's event horizon should be growing, thus "swallowing" the mass that would otherwise appear to be stuck.

  • Or was it...

    Oh my god, Becky, look at her butt.
    It is so big!
    She looks like one of those rap guys' girlfriends.
    Who understands those rap guys?
    They only talk to her because she looks like a total prostitute.
    I mean, her butt! It's just so big!
    I can't believe it; it's so round.
    It's just out there.
    I mean, it's gross.
    Look, she's just so -- black.

    I like big butts and I cannot lie
    You other brothas can't deny...

    ("Baby Got Back," by Sir Mix-A-Lot
  • That's not technically true. Nothing in the universe is truly 'pure black' except for a black hole itself - it's a perfect absorber, of which none other exists in nature. Direct evidence would be seeing one - a giant, probably nearly spherical hole of 'nothingness'. Put yourself in orbit around it and watch stars wink out in each direction. Look at the CMBR and you'll see a hole exactly where the black hole is. Or, irradiate the sucker with a wide band of frequencies, and watch that nothing comes back (something will come back from everywhere *except* a black hole, due to the ISM/IGM/dust).

    You are, however, correct about the strength of indirect information, as that is all that astronomers have, anyway. Hell, astronomers can make ridiculously strong statements about things just based on spectroscopy, simply because we know that it *must* work, or else all of humanity is fooling itself.
  • Who are you to tell God what he can and cannot do?

    I'm sorry to say that, well, basically, your logic is entirely flawed. OK: It would be possible to truly see one, unfortunately for
    incontrovertable proof, we'd need to actually be able to be on multiple sides of it and confirm that all forms of radiation cannot pass through
    it. However, we're not likely to travel to Cyg X1 for sightseeing purposes! It's easy enough to confirm that we've got an object with a mass over the neutron star limit - it can't be anything else. A black hole might as well be defined to be something with a mass over the NS limit that we can't see. But, besides that...

    There are no problems with black holes, whatsoever. God didn't decree laws which can't be used with black holes - not unless God is Einstein. The only reason singularities are problems is because we don't have the math to handle it. We really don't. No one really knows how to handle 'pure' singularities.

    But then again, what is a 'pure' singularity? Do we know if it really goes to infinite density? It might not. If it goes to below the Planck length, there might not be any difference in saying that it *does* have the size of the Planck length, therefore giving it, not an infinite density, just a god awfully obscene one. And it's not like humans haven't had to deal with ultra-massive scales before - look at stellar distances.

    Besides, your ideas of a well-formed universe are useless. Unfortunately, your argument is about as persuasive as Einstein's, when he said that God didn't play dice. My first line response was a paraphrase of Bohr's. The problem is that human ideas of a well-formed universe are based on a universe where things move much much slower than c, and all energies are small compared to rest masses. Guess what? The Universe is not required to remain there.
  • Hawking radiation is particle radiation, not electromagnetic radiation. It is also completely independent of the incident energy upon the black hole. That still makes them 'pure black', since in some sense, they are similar to a pure blackbody - any outgoing radiation is of a universal form, completely independent of any energy incident on the object. There's still nothing else like that in the universe - just close approximations to it.
  • That would be why I had pure black in quotes - there's no term for an object whose emission spectrum is completely independent of any incident energy spectrum (This is not the definition of a blackbody... but it is close). However, the only other object with this characteristic is a true blackbody, which the black hole is (probably... there may be deviations from this due to quantum gravity type effects... possible resonance spikes at thermal energies equal to a pair, etc. Without any observational evidence, we can say virtually anything. Still, no matter what, a black hole's emission spectrum is completely determinable by theory - black holes have no hair, so the
    spectrum must be determinable from the mass, charge, and angular momentum. Thus, even if it is not a true blackbody, it is 'pure black').

    The reason I said 'particle radiation' rather than electromagnetic radiation is that typically when one thinks of a radiator of astrophysical origin, the object typically radiates omnidirectionally and continuously - i.e. the radiation is significant enough that the energy quantum of the radiation is insignificant compared to the luminosity of the object. In any black hole save a primordial black hole, this is not the case, and thus, if one were *observing* a black hole, one would not get a continuous spectrum, but occasional 'blips' from Hawking radiation. Thus, the object would, for the most part, never emit *any* radiation. (Obviously *any* electromagnetic radiation is particle radiation! The distinction is that in one case, we can ignore photon structure, and in the other case, we cannot. Typical black holes fall under particle radiation.)

    Thus, direct evidence of a black hole would be observation of an object whose emission spectrum is a pure blackbody at the temperature equal to the Hawking temperature of the radius of the
    'hole' visible in the CMBR.
  • Black holes can have hair if you're dealing with Brans-Dicke theory, as well - I do realize that. However, I'm not sure if they would alter its emission spectrum. In any case, all I was using the no-hair theorem for was to indicate that a black hole's emission spectrum must be universal, even if it isn't a true blackbody (which it most likely is not... but it's close).

    As I said before, there isn't a *word* to describe an object whose emission spectrum is independent of incident radiation, and unfortunately, color isn't well defined in layman usage, since color isn't intrinsic to an object, but depends on its surroundings. (For instance, what color is the sky? Most people would say blue, but that's simply because we're looking at the sky through a blue-green light - the Sun. If a uniform spectrum was incident upon the sky, what color would it appear? Probably purple: the sky scatters purple light best, however the human eye is less sensitive to purple light, so it might still be blue) Thus, I didn't use 'black', which would imply that it doesn't emit anything, but used 'pure black', which implies that it doesn't *reflect* anything (which is where the analogy with black comes in) and added the emission spectrum bit later. I've been trying to figure out a better word for this, but I can't come up with a good one.

    This discussion started out as trying to figure out if there were a way to directly tell if a black hole is observable - the answer is yes, since a black hole is the only object which reflects no light whatsoever, and for most stellar mass or higher black holes, emits (virtually) no light. Hawking radiation doesn't enter into the discussion here, because a detector almost guaranteedly wouldn't have the sensitivity to detect one photon every few minutes or so against the stellar backdrop and other noise.

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