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

1. Nov 4, 2006

Jonathan Silverlight

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
>matter.

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
>http://hubblesite.org/newscenter/newsdesk/archive/releases/2002/21/image/a
>
>says,
>
>"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
>form."
>
>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
away.

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