Messier 96 (APOD 15 June 2007)

Comments and questions about the APOD on the main view screen.
jcbaty
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Messier 96 (APOD 15 June 2007)

Post by jcbaty » Fri Jun 15, 2007 2:41 pm

Here's the last part of the caption from today's pic:

"Background galaxies and smaller Leo I group members can be found by examining the picture, but accomplished astro-imager Adam Block notes he is most intrigued by the edge-on spiral galaxy that apparently lies behind the outer spiral arm near the 10 o'clock position. The edge-on spiral appears to be about 1/5 the size of M96. If the spiral is similar in actual size to M96, then it lies about 5 times farther away."

The last sentence doesn't make sense to me and here's why: The background galaxy is easily visible in this pic, even though it's approx 190 million light years away from us (M96 is approx 38 million light years away). Since this background galaxy is so easily visible to us in this picture, it would take up a huge portion of the sky to an observer living in M96, even though it would be nearly 150 million light years away from them. At the same time, even though M96 is only 38 million light years from us, we cannot even see it without a telescope. Can someone explain this? Thanks.
John Baty
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makc
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Re: APOD 6/15/07

Post by makc » Fri Jun 15, 2007 3:39 pm

jcbaty wrote:Since this background galaxy is so easily visible to us in this picture, it would take up a huge portion of the sky to an observer living in M96, even though it would be nearly 150 million light years away from them.
Bring in some math please?

Image

jcbaty
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Post by jcbaty » Fri Jun 15, 2007 3:51 pm

Your question doesn't make any sense to me, so maybe I didn't explain myself clearly. I'll try again. Thanks for your patience:

M96 is 38M light-years from us, yet we cannot go out and see it in the night sky. The background galaxy that lies beyond M96 in today's APOD pic is supposedly 150M miles from M96 and is supposedly approx the same size as M96, yet since it is so big in today's APOD picture, it would be easily visible in the night sky if you lived in M96.

My question is, "How could a 100K light-year (LY) in diameter galaxy, 150M LY away be easily visible in the night sky to an observer in M96, but a 100K LY in diameter galaxy only 38M LYs away is not visible in the night sky to a Milky Way resident?"

This does not seem possible, so my conclusion is that the background galaxy must be far larger than 100K LY in diameter or lies much closer to M96 than 150M LY. If not, I'm missing something here. Thanks.
John Baty
Arizona

jcbaty
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Post by jcbaty » Fri Jun 15, 2007 3:53 pm

Ok, now I see your diagram and it all makes perfect sense. Because of the distances involved, an M96 oberver will see the background galaxy at virtually the same size we do, observing from the Milky Way. Thanks.
John Baty
Arizona

jimmysnyder
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Post by jimmysnyder » Fri Jun 15, 2007 5:08 pm

What is so intriguing about that smaller galaxy. I googled "Adam Block" m96 and got this:

http://www.noao.edu/outreach/aop/observers/m96.html

which repeats the "intriguing" comment, but still doesn't say what the intrigue is.
Making mistakes since 1950.

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Case
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Post by Case » Fri Jun 15, 2007 5:48 pm

jimmysnyder wrote:What is so intriguing about that smaller galaxy.
Maybe it is just aesthetically fascinating, to see through a spiral arm and see this object that is almost hiding in there. Anyway, that's what I make of it. Without any elaboration, I don't think the intrigue is deeply scientific.

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JohnD
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Post by JohnD » Fri Jun 15, 2007 6:02 pm

Jimmy,
Thanks for that link - the picture is so much better on there that the question I was going to ask - is that an edge-on galaxy or a gravity lensed image of something - is redundant.
On the NOAO page it is clearly - an edge-on galaxy!

John

TimeTravel123456789
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Dark Matter Relationship with Galaxies Close UP

Post by TimeTravel123456789 » Sat Jun 16, 2007 2:14 pm

Something I had written about in an article on Mistakes in Astronomical Imaging which no one, except a professor who did not have enough recent posts on arxiv, would post for me is that galaxy collisions can be a factor in dark matter. Unlike the argument of Vera Rubin, Dr. Krauss, others that the source of increased velocity of the distant edges of galaxies is dark matter, I argued that galaxy collisions were a factor.

When two galaxies collide, the spin rate of the outer edge of the galaxies increase their speed. Dark matter is not a factor in increased spin or velocity rates in some cases.

With this M96 object we can see more concrete observable matter near the distant galaxy. Galaxies in interaction do interact the idea is. The more observable matter at the 9:45 to 10:15 position may, of course, be due to other factors. If the more concrete matter at 9:45 to 10:15 or so is due to the other galaxies, the distance may be problematic.

Still the thesis stands, galaxies in collision or interacting are the source of some outer galaxy increased spin or velocity rates. Dark matter in some cases is not a factor in some of the increased velocities at galaxy edges. At this point, this is just a logical argument based on ideas like weather systems in interaction change their velocities. A hurricane frequently changes its speed based on factors like interacting weather systems completely independent of dark matter.
James T. Struck