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

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Charles Francis - 29 Dec 2005 10:06 GMT

Thus spake John Baez <baez@math.removethis.ucr.andthis.edu>

>I checked and read there are 100 known "polar-ring galaxies". Here's a
>nice one called NGC 4650:
>
>18) Ring around a galaxy, HubbleSite News Archive, May 6, 1999,
>http://hubblesite.org/newscenter/newsdesk/archive/releases/1999/16/imag
>e/a
>
>I can imagine this thing looking like Hoag's object if we viewed it
>head-on.
>
>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/imag
>e/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!

In spite of this one, which is not symmetrical, the explanation seems to
imply that quite regularly a small galaxy has to pass bang through the
middle and perpendicular to a large galaxy. Yes, it can happen, but
surely not if there are loads of them. The thing that struck me about
these things was that they seemed more like a galaxy which had had its
middle blasted out by some massive explosion. Could they be the remnants
of dead quasars? I know it sounds wrong, because the inner contains old
stars, while the outer contains new ones, but we are seeing a lot of new
stars forming at the outside of galaxies generally. If there is more
matter in the outer ring, that is also where hydrogen will gather and
stars will ignite?

Regards

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Jonathan Silverlight - 30 Dec 2005 21:24 GMT

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:
>>
[quoted text clipped - 9 lines]
>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.
[quoted text clipped - 17 lines]
>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
[quoted text clipped - 7 lines]
>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
[quoted text clipped - 23 lines]
>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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Space Forum / Astronomy / December 2005

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