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Black Holes

Discussion in 'Science & Technology' started by Drone, Sep 24, 2011.

  1. Drone

    Drone

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    Astronomers have mapped dark matter on the largest scale ever observed

    Good news:

    Those tiny distortions in the images of distant galaxies, called cosmic shear.

    And here's Dark Matter map and the full moon to scale.

    [​IMG]

    The observations show that dark matter in the Universe is distributed as a network of gigantic dense (light) and empty (dark) regions, where the largest dense regions are about the size of several Earth moons on the sky.

    [​IMG]

    The densest regions of the dark matter host massive clusters of galaxies. To get these accumulated images over five years scientists used the wide field imaging camera MegaCam, a 1 degree by 1 degree field-of-view 340 Megapixel camera on the CFHT in Hawaii.

    The scientists are optimistic:

    http://www.physorg.com/news/2012-01-astronomers-universe-dark-unprecedented-scale.html

    http://www.physorg.com/news/2012-01-clearest-picture-dark-energy.html

    The bigger more accurate and better Dark Matter map they get the better we will understand our Universe. It will shed some light on dark energy as well.

    I just hope there will be more and more of new tools available to physicists in their study so we could get more info. :)

    [​IMG]

  2. jihadjoe

    jihadjoe

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    There are no such stars.
    The most massive star, a blue giant called R136a1 is only about 250-320 times the mass of our sun.
    The biggest stars, like VV Cephei or VY Canis Majoris may be 2000 times the radius of our sun, but they have just 30-40 times the mass. These stars are literally less dense than even the uppermost part of the Earth's atmosphere.

    Supermassive black holes are by necessity also primordial, and were essentially formed at the same time the universe was created. The law of conservation of angular momentum limits the speed at which matter can fall into a black hole, and essentially means the age of the universe isn't enough time for any stellar mass black hole to grow to such a size.
  3. FordGT90Concept

    FordGT90Concept "I go fast!1!11!1!"

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    "Dark matter" is whatever is located at the center of galaxies that hold the galaxy together (much like stars hold solar systems together). For the Milky Way, it is likely Sagittarius A*.

    I think a better word for it than "black hole" is a "fission star"--that is, a star composed mostly of extremely heavy metals like uranium and plutonium (but likely substantially heavier).
    Crunching for Team TPU
  4. Drone

    Drone

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    Can you post a source for this info?
  5. jihadjoe

    jihadjoe

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    http://iopscience.iop.org/1538-4357/701/2/L133
    Here's an interesting paper on accretion of matter into early stellar-mass blackholes, and details many of the limiting factors to black hole growth. Novel mechanisms are also explored which would account for possible growth of a stellar mass black hole into a massive entity, but not a true supermassives such as those found in galactic centers.

    IMO the elephant in the room is that we have data for a lot of stellar mass black holes of up to 30 or more solar masses, and then we have supermassives but there are no intermediate mass black holes at all. If stellar mass black holes were slowly accreting matter and growing into supermassives, then we should see plenty of black holes in the 1000M range, but there aren't any. We basically go from 0-33, and then skip right into the supermassive range. This suggests a completely different method of formation for the two black hole classes.
  6. jihadjoe

    jihadjoe

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    http://iopscience.iop.org/1538-4357/701/2/L133
    Here's an interesting paper on accretion of matter into early stellar-mass blackholes, and details many of the limiting factors to black hole growth. Novel mechanisms are also explored which would account for possible growth of a stellar mass black hole into a massive entity, but not a true supermassives such as those found in galactic centers.

    Here's a quote from the abstract:
    IMO the elephant in the room is that we have data for a lot of stellar mass black holes of up to 30 or more solar masses, and then we have supermassives but there are no intermediate mass black holes at all. If stellar mass black holes were slowly accreting matter and growing into supermassives, then we should see plenty of black holes in the 1000M range, but there aren't any. We basically go from 0-33, and then skip right into the supermassive range. This suggests a completely different method of formation for the two black hole classes.
    digibucc and Drone say thanks.
  7. Widjaja

    Widjaja

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    I believe there are other names needed other than 'Dark Matter' for these things we see.

    I personally consider dark matter to be a substance which the galaxy is kept within rather than what IS any sort of black hole.
  8. twilyth Guest

    I just want to say that the first person with this idea was Roger Penrose - sort of. OK, he ascribed the circular patterns in the CMBR to "leaks" from the last big crunch, but it seems that this theory lines up with his original idea.

  9. trickson

    trickson OH, I have such a headache

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    If black holes suck every thing in including light , Then why is it that jets can come out of the center of them . I mean if the gravity is so intense as to suck in light and every thing then why are jets of hot gas and radiation allowed to escape ?
  10. qubit

    qubit Overclocked quantum bit

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    The jets don't come out of the black hole - nothing can get out.

    They're caused by the motion of the disc of gas and dust falling in and the intense gravity. I don't think that scientists have quite figured out how the jets at 90 degrees to the plane of the discs are formed though.
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  11. Drone

    Drone

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    qubit is right but there's also another kind of radiation:


    Black holes have energy and they always emit it as photons. So Black Holes constantly lose their energy and eventually they will evaporate. It's called Hawking radiation. You ask how it happens? There's quantum tunnelling (See here: http://phys.educ.ksu.edu/vqm/html/qtunneling.html). Non-quantum (classic) objects can't escape but quantum objects (wave–particle duality of matter and the Heisenberg uncertainty principle can explain this easily) can use quantum tunnelling to break the "barriers" and escape the Black Hole. BTW quantum tunnelling also occurs in the nuclear fusion of Sun or any other star.

    So Black Holes are not "some big suckers that don't ever emit". Close to event horizon of a black hole there's strong gravitational field which generates pairs of particles and anti-particles. See the pic below:

    [​IMG]

    Some can escape to infinity, some can annihilate and some can get sucked in.

    [​IMG]

    http://casa.colorado.edu/~ajsh/hawk.html
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  12. Inceptor

    Inceptor

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    As I understand it, if Sagittarius A* is offset slightly, but still within the small 'region' of the black hole at galactic center (as it would have to be in order for stars to appear to be orbiting it and the black hole), there is no way to know what it is without a clever astrophysicist coming up with clever mathematical inferences, based upon observations, that they would be willing to publish.

    It could be a massive clump of dark matter, I suppose. But still less massive than the central black hole, which it seems to be closely orbiting.

    I think it's more likely to be another black hole in close orbit, the old core of a galaxy devoured by the Milky way sometime in the distant past. Which it probably is, if the central black hole is showing a slight 'wobble'. Which would not be good for future life in our galaxy, depending on how close they are to merging.
    Or, a supernova remnant (black hole or neutron star) doing its own post-death death-spiral into the massive black hole.
    Or, superheated plasma in the region around the massive black hole -- which could produce radio emissions.
  13. trickson

    trickson OH, I have such a headache

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    Ok so if a black hole dies what is left then ? Shouldn't there be some thing like a ball of iron ? After all it is a sun burn all them elements and making iron that leads to the end of the star then creating the black hole right ? Then once it has died shouldn't there be some thing left after the death of the black hole ?
  14. Drone

    Drone

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    ^ The crust of a neutron star is made of iron. And eventually neutron stars quantum-tunnel and become black holes. Yes, there's a theory that everything in the universe after 10^1500 years (can you imagine all those zeros) will lose the energy, cool down and turn to iron because iron has the nucleus with the least binding energy. But after 10^10^26 (lol all these zeros, this is the last time I promise) years all that iron collapse into black holes. But this will happen if proton decay won't occur before this.

    Some interesting thoughts here:

    http://en.wikipedia.org/wiki/Future_of_an_expanding_universe

    and especially here:

    http://math.ucr.edu/home/baez/end.html

    The end of the universe will be dark and cold, really cold (literally). But as always take this with a grain of salt. No one knows yet how the real END will look like.
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  15. trickson

    trickson OH, I have such a headache

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    Mind boggling !
  16. Drone

    Drone

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    Intermediate-mass black hole

    [​IMG]

    http://www.physorg.com/news/2012-02-black-hole-shredded-galaxy.html

    The fate of this black hole ain't too optimistic.
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  17. qubit

    qubit Overclocked quantum bit

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    Black holes are indestructible, so I'm not sure what you mean by that?
  18. Drone

    Drone

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    ^

    And no, they are not indestructible
  19. qubit

    qubit Overclocked quantum bit

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    Yes, it is. Black holes can only merge with each other to make a bigger one. All the article is saying is that it doesn't know where it's going and that it won't be detectible when the x-rays from infalling gas dry up.
  20. Drone

    Drone

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    Black holes evaporate as they lose their energy
  21. qubit

    qubit Overclocked quantum bit

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    That's splitting hairs. For anything other than a teeny tiny one, they'll take longer than the age of the universe to evaporate. And anyway, the effect is overridden because it's really really small and there's always something for a black hole to munch on and it doesn't have to be much, either, just a little gas and dust will do. :)

    So, consider a black hole as existing forever for all practical purposes. And once again, the article said nothing about the black hole dying.
  22. Drone

    Drone

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    It's not. Getting "owned" by other bigger black hole is the same as dying. Because other black hole will use smaller black holes energy. The article says that it can happen. Reminds me how bigger corporations eat up smaller corporatrions.
  23. qubit

    qubit Overclocked quantum bit

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    No, it's just a merge, ragardless of size - they eat each other you could say, I guess. And honestly, no one knows what happens at those singularities and we may never will. Bummer. :( I love science and I really want to know.
  24. Inceptor

    Inceptor

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    To get back to the Dark matter conversation thread:

    The ESA's Planck mission which is going to be measuring the Cosmic Microwave Background radiation to higher degrees of accuracy than previously achieved, discovered something while observing the 'foreground' in order to subtract it from its main observations --- a 'haze' of microwaves in a 35 000 ly region around the core of the Milky way.

    There ya go, possible annihilation of dark matter particles.

    http://www.centauri-dreams.org/?p=21757
  25. Drone

    Drone

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    [​IMG]

    Contrary to the popular perception of black holes pulling in all of the material that gets close, 95% of the matter in the disk around IGR J17091 is expelled by the wind. And other interesting fact is production of winds can stifle radio jets.

    They said this because jet from the black hole was not present when the ultra-fast wind was seen, although a radio jet is seen at other times. Fascinating!

    http://www.physorg.com/news/2012-02-chandra-fastest-stellar-mass-black-hole.html
    qubit says thanks.

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