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Re: This Week's Finds in Mathematical Physics (Week 238)

  1. Nov 4, 2006 #1
    Some updates on the Bullet Cluster / dark matter saga.
    You can now see a picture of the Bullet Cluster here:

    http://math.ucr.edu/home/baez/week238.html

    I've also updated a bunch of information and fixed some mistakes
    in the initial version of "week238", thanks in part to Matt Owers.

    >Markevitch and company have been studying the "Bullet Cluster", a
    >a bunch of galaxies that has a small bullet-shaped subcluster zipping
    >away from the center at 4,500 kilometers per second.


    >It seems that one of the rapidly moving galaxies in this subcluster
    >has hit a bystander galaxy - I'm not sure, but a high-speed collision
    >of galaxies occurred.


    In fact, the whole subcluster hit another subcluster!

    So, the picture is a picture of colliding bunches of galaxies.
    The individual galaxies in these bunches mainly shoot right past
    each other - but the intergalactic gas in one bunch is hitting
    the gas in the other, and getting so hot it emits X-rays.

    >So, dark matter is seeming more and more real. In fact, last year
    >folks found evidence for "ghost galaxies" made mainly of dark matter
    >and cold hydrogen, with very few stars:
    >
    >6) PPARC, New evidence for a dark matter galaxy,
    >http://www.interactions.org/cms/?pid=1023641


    Apparently the consensus is now that this ghost, VIRGOHI 21,
    is hydrogen stripped off from a galaxy by the "wind" it felt
    as it fell into the Virgo Cluster. This effect is called
    "ram pressure stripping" - the gas of a galaxy can be stripped
    off if the galaxy is moving rapidly through a cluster, due
    to interaction with the gas in the cluster.
     
  2. jcsd
  3. Nov 4, 2006 #2
    On Thu, 17 Aug 2006, John Baez wrote:
    >
    >> Markevitch and company have been studying the "Bullet Cluster", a
    >> a bunch of galaxies that has a small bullet-shaped subcluster zipping
    >> away from the center at 4,500 kilometers per second.

    >
    >> It seems that one of the rapidly moving galaxies in this subcluster
    >> has hit a bystander galaxy - I'm not sure, but a high-speed collision
    >> of galaxies occurred.

    >
    > In fact, the whole subcluster hit another subcluster!
    >
    > So, the picture is a picture of colliding bunches of galaxies.
    > The individual galaxies in these bunches mainly shoot right past
    > each other - but the intergalactic gas in one bunch is hitting
    > the gas in the other, and getting so hot it emits X-rays.
    >
    >> So, dark matter is seeming more and more real. In fact, last year
    >> folks found evidence for "ghost galaxies" made mainly of dark matter
    >> and cold hydrogen, with very few stars:
    >>
    >> 6) PPARC, New evidence for a dark matter galaxy,
    >> http://www.interactions.org/cms/?pid=1023641

    >
    > Apparently the consensus is now that this ghost, VIRGOHI 21,
    > is hydrogen stripped off from a galaxy by the "wind" it felt
    > as it fell into the Virgo Cluster. This effect is called
    > "ram pressure stripping" - the gas of a galaxy can be stripped
    > off if the galaxy is moving rapidly through a cluster, due
    > to interaction with the gas in the cluster.
    >
    >



    Along with your above comment on "ram pressure stripping",
    I would like to talk about an old This Week's Finds, Week 224, about a
    mono knotted jet from a hypothesized supermassive blackhole in M87 galaxy.

    The three pictures from NASA do not show two knotty jets. There is only
    one jet revealed. I have reviewed several times that the Chandra X-ray
    telescope picture has shown that there is dim blue light around the
    brightest center spot. So there are matters or gases around the
    hypothesized supermassive blackhole. Therefore, there should have another
    jet (synchrotron radiation) from the acretion disk of the blackhole and
    that jet should x-ray the inter-galaxtic matters/gases on the other side
    of the acretion disk as well. However, none is seen.

    Would it be possible that there was a high speed small dense dark matter
    (High speed ,dense and small are required so that it didn't cause a
    prolonged microlensing effect that can be observable nowaday.)
    "ram pressure stripping" some tiny galaxies and brought those gases to the
    current scene? And the small dense dark matter finally hit the center
    of the M87 galaxy and formed a blackhole (if there is a blackhole)?
    Look at the Chandra x-ray picture, and notice the blurryness and a very
    bright spot near the jet tail. Do they look like the remaining part of the
    "bullet cluster"?
     
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