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Re: This Week's Finds in Mathematical Physics (Week 224)

  1. Nov 4, 2006 #1
    In message <Pine.LNX.4.62.0512262224020.12621@lab44.ma.utexas.edu>, Kwok
    Man Hui <kmhui@math.utexas.edu> writes
    >On Tue, 27 Dec 2005, Jonathan Silverlight wrote:
    >> Why should it be any less clear than the other distant galaxies in the
    >> picture? It's just a background object that happens to be in line of sight,
    >> and inside the ring.

    >Hubble moves around the Earth, which orbits the Sun. So Hubble can take
    >pictures at different time and can detect any abberation. Then it may
    >eliminate this kind of parallel background light. You may further argue
    >that the Earth movement compares with the distance from the background
    >object we observed is very small. So Hubble may not be able to distinguish
    >any abberation. If that is the case, I think we need an expert on this

    I'm no expert, but you have _got_ to be joking :-) Have you tried
    calculating the parallax of an extragalactic object?

    >Second, I know the astronomists can filter some background light if
    >the source is far enough away from, say, the Hoag's object.
    >> And are you sure we are seeing it exactly head-on? People thought we were
    >> seeing Ring Nebula in Lyra head-on, but that's not so.

    >The commentary from
    >"A nearly perfect ring of hot, blue stars pinwheels about the yellow
    >nucleus of an unusual galaxy known as Hoag's Object. This image from
    >NASA's Hubble Space Telescope captures a face-on view of the galaxy's ring
    >of stars, revealing more detail than any existing photo of this object.
    >The image may help astronomers unravel clues on how such strange objects
    >A "face-on" view or a "head-on" view is up to your choice of word. This
    >picture was taken on July 9, 2001. May be they should take a second
    >picture now.

    I have the impression that you have no idea of the distances involved
    here. It would take thousands of years to see a change.

    >>> 2.) About "Ring Around a Galaxy", the vertical bluish ring is warped and
    >>> does not lie in one plane according to the accompanying commentary. The
    >>> lower clump should have more young stars. It is hardly as symmetrical as
    >>> the one we saw. The Haog's ring is more evenly bluish and has shown a
    >>> slight clockwise spiral roatation. Is it easy to get such a higher level
    >>> of plane symmetry by colliding two galaxies? I doubt it.

    >> Don't simulations show exactly that sort of ring?

    >Are the two colliding galaxies having exact plane symmetry? No way you can
    >get such perfect galaxies.

    Again, why not? Don't forget that this object has aroused interest
    because of its symmetry. Without doing a survey of a lot of galaxies you
    can't even say if it's unusual. If you want a less symmetric example,
    consider AM 0644-741, which has already been mentioned here.

    >>> Look at the polar ring shown, let me emphasize again about the commentary:
    >>> "The polar ring appears to be highly distorted. No regular spiral pattern
    >>> stands out in the main part of the ring, and the presence of young stars
    >>> below the ring is warped and does not lie in one plane" from the side view.
    >>> So the head-on view should be as symmetrical as the Haog's ring we saw.
    >>> Not so easy to explain the Haog's object.
    >>>> Here's another ring galaxy, called AM 0644-741:
    >>>> 19) The lure of the rings, Hubblesite News Archive, April 22, 2004,
    >>>> http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/15/image/a
    >>>> It's the result of a collision involving a galaxy that's not in this
    >>>> picture. So, maybe Hoag's object is just a specially pretty case of
    >>>> a galaxy collision!
    >>> Still doesn't explain "The weirdest thing is that inside the ring, in the
    >>> upper right, you can see *another* ring galaxy in the distance!"
    >>> I think it is quite hard to form a ring galaxy within another ring galaxy.

    >> But why should it be "within" the closer galaxy?

    >OK. Collide two galaxies and form two ring galaxies nearby or one within
    >another if the smaller galaxy is not engulfed at all. Try 1000 simulations
    >and see how many results fall in this scenario. Don't just argue for
    >argument sake. I hope you get my point.

    You don't get _my_ point, which George Dishman has made more clearly.
    The small ring has nothing to do with the big ring. It's much further
  2. jcsd
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