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Thread: Black hole

  1. #1
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    Black hole

    When a black hole consumes a neighbouring star or other material in the surrounding universe, does the mass of the black hole increase?

    If light can not escape from a black hole, does that mean that the material that is beeing thrown out from the black hole in form of jets, does travel faster then light?


    Eta Carinae

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    For solar mass black holes (and bigger) 99% plus of the mass that passes inside the event horizon adds to the mass of the black hole. If there are any tiny black holes, they have significant to lots of Hawking radiation which could result in a decreasing mass for a black hole that is getting lots of input mass.
    The polar jets are produced outside the event horizon from accretion disk material, so the jet starts out at almost c, but decelerates considerably the first second out going. Neil

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    Quote Originally Posted by eta carinae View Post
    When a black hole consumes a neighbouring star or other material in the surrounding universe, does the mass of the black hole increase?

    If light can not escape from a black hole, does that mean that the material that is beeing thrown out from the black hole in form of jets, does travel faster then light?


    Eta Carinae

    In general when a BH swallows mass/energy of any sort, yes it will get bigger.
    It's worth noting that a BH in general will not swallow a star or any other object whole....That object more then likely will be torn to shreds and form part of the accretion disk which a BH that is swallowing mass/energy will have. The matter from the accretion disk will then gradually spiral into the BH.
    Not 100% sure on exactly where accretion disks do form, but I would say at least outside the photon sphere of that BH.
    The photon sphere is at 1.5 Schwarzchild radius and is where light would orbit.

    The polar jets that are observed are not coming from inside the BH, but is matter/energy that on its spiral path to the BH, may be affected by a BH's magnetic field and the associated magnetic field lines, which will be twisted around the BH, similar to the Lense Thirring effect we see with space/time itself around a spinning object.
    As the matter/energy is twisted around at near "c", it is flung away again at the polar regions and are the jets which we see.

    The Schwarzchild radius I referred to is the limit of the observed BH or gravitationally completely collapsed object, where the escape velocity is equal to "c"

    The Lense Thirring effect, or frame dragging, is the twisting of space/time around a spinning object.
    “Imagination will often carry us to worlds that never were, but without it we go nowhere.”
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    “Imagination will often carry us to worlds that never were, but without it we go nowhere.”
    ― Carl Sagan

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    Quote Originally Posted by ASTRO BOY View Post
    In general when a BH swallows mass/energy of any sort, yes it will get bigger.
    It's worth noting that a BH in general will not swallow a star or any other object whole....That object more then likely will be torn to shreds and form part of the accretion disk which a BH that is swallowing mass/energy will have. The matter from the accretion disk will then gradually spiral into the BH.
    Not 100% sure on exactly where accretion disks do form, but I would say at least outside the photon sphere of that BH.
    The photon sphere is at 1.5 Schwarzchild radius and is where light would orbit.

    The polar jets that are observed are not coming from inside the BH, but is matter/energy that on its spiral path to the BH, may be affected by a BH's magnetic field and the associated magnetic field lines, which will be twisted around the BH, similar to the Lense Thirring effect we see with space/time itself around a spinning object.
    As the matter/energy is twisted around at near "c", it is flung away again at the polar regions and are the jets which we see.

    The Schwarzchild radius I referred to is the limit of the observed BH or gravitationally completely collapsed object, where the escape velocity is equal to "c"

    The Lense Thirring effect, or frame dragging, is the twisting of space/time around a spinning object.
    My bold. The more massive the black hole, the less severe the tidal stress near the event horizon, which may be counterintuitive to some of us. This is because the event horizon radius is proportional to the mass while the Roche radius, at which it starts tearing up infalling bodies, is proportional to the cube root of the mass. A non-spinning supermassive black hole of a billion solar masses could swallow an infalling star without coming close to shredding it first. If we could watch it from afar, we would see the star rapidly fading and reddening, and then disappearing with no fireworks. A rapidly spinning black hole will have stronger ripping forces.

    Sky and Telescope, June 2013, has an article on this topic.

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    Quote Originally Posted by Hornblower View Post
    Sky and Telescope, June 2013, has an article on this topic.
    Actually, CosmoQuest (when it was BAUT) has an article on it! GRB 110328A - A possible beamed tidal disruption of a star by a supermassive BH!. SMBHs (super massive black holes) with a mass of less than 108 Msol can disrupt a star outside the event horizon, giving us a nice gamma ray burst (GRB).
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    Quote Originally Posted by eta carinae View Post
    When a black hole consumes a neighbouring star or
    other material in the surrounding universe, does the
    mass of the black hole increase?
    Yes.

    Quote Originally Posted by eta carinae View Post
    If light can not escape from a black hole, does that
    mean that the material that is being thrown out from
    the black hole in form of jets, does travel faster than
    light?
    No. Material that is thrown out is never at or inside
    the black hole's event horizon. It gets close enough
    to the event horizon to be accelerated to speeds
    approaching the speed of light, but that's all.

    -- Jeff, in Minneapolis

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