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Post by abacus9900 on Mar 11, 2011 13:36:49 GMT 1
Why is there an almost empty area of space next to the centre of our galaxy?
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Post by speakertoanimals on Mar 11, 2011 16:31:31 GMT 1
Can you be more specific as to which void you mean?
A reference would be best.
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Post by abacus9900 on Mar 15, 2011 11:23:29 GMT 1
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Post by speakertoanimals on Mar 15, 2011 15:34:29 GMT 1
Well, since that source confuses a black hole at the centre of our galaxy, with a black hole at the centre of the universe, still not sure. Plus any links from it don't make it clear WHAT is being referred to either................ abyss.uoregon.edu/~js/ast122/lectures/lec26.htmlAnd this page refers to increasing stellar density as we go in, plus the central accretion disk -- no mention of a void. Hence I suggest you need to use better sources (and junk ones where the writer doesn't appear to know the difference between our galaxy and the universe..............) |
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Post by abacus9900 on Mar 15, 2011 15:47:43 GMT 1
Well, since that source confuses a black hole at the centre of our galaxy, with a black hole at the centre of the universe, still not sure. Plus any links from it don't make it clear WHAT is being referred to either................ abyss.uoregon.edu/~js/ast122/lectures/lec26.htmlAnd this page refers to increasing stellar density as we go in, plus the central accretion disk -- no mention of a void. That's a lot of material to get through. Can't you just summarize for me please? |
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Post by speakertoanimals on Mar 15, 2011 16:14:28 GMT 1
No, because the point is it DOESN'T make ANY MENTION of a void....................
Hence WHAT is the void that is supposedly a problem? No one can answer the question until you come up with a decent source as to what the problem supposedly is...................
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Post by abacus9900 on Mar 15, 2011 17:11:25 GMT 1
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Post by speakertoanimals on Mar 15, 2011 17:28:34 GMT 1
Nope the local void is a void within our local group of galaxies, NOT a void supposedly within our galaxy, which is the question YOU ASKED. Try again................... Common knowledge that distribution of galaxies is full of voids etc, but that wasn't what you asked about. Seems you don't kniow what you asked about either............. I suggest a better source for big problems in cosmology than the one you used................. en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics#Cosmology_and_astronomy |
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Post by abacus9900 on Mar 15, 2011 18:10:32 GMT 1
Nope the local void is a void within our local group of galaxies, NOT a void supposedly within our galaxy, which is the question YOU ASKED. Try again................... Common knowledge that distribution of galaxies is full of voids etc, but that wasn't what you asked about. Seems you don't kniow what you asked about either............. I suggest a better source for big problems in cosmology than the one you used................. en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics#Cosmology_and_astronomyHow can I trust what I see on the net now? |
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Post by principled on Mar 15, 2011 18:12:33 GMT 1
Now I'm confused. I thought that space expands by the space between celestial bodies expanding. Yet in Abacus' link they say the following: So is the galaxy moving "through" space that exists or is it moving because space is expanding.  If the former, then where is this expanding space occurring that the galaxy is moving through? P |
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Post by speakertoanimals on Mar 15, 2011 18:43:17 GMT 1
Expanding space occurs everywhere.
A real galaxy has two motions -- the motion due to expansion (best evidence is the CMB, which gives you a frame where you are at rest with respect to the average of local expansion in effect), then you have the proper motion on top of that -- because our galaxy isn't all on its own, it moves as part of a collection of galaxies (the local group), which are gravitationally-linked.
Hence that is where the 'moving through space bit' comes in -- moving relative to the CMB locally, in effect.
(CMB: cosmic microwave background. The frame in which the temperature is equal in all directions represents the 'at rest' frame averaged over our bit of the universe -- or at least as far back as we can see which is the CMB)
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Post by principled on Mar 15, 2011 19:05:43 GMT 1
So, a (2 dimensional)analogy could be :
We have a gnat on a bicycle (=galaxy). We place the gnat with its bike on a piece of knicker elastic(space). The gnat starts riding as we start stretching the elastic. Its velocity relative to us (our position is unchanging) is the sum of the rate of extension of the elastic plus the bike's forward velocity. Whereas the space in front of it is expanding (relative to us) at the extension rate of the knicker elastic.
There's just one problem, what happens if the gnat can pedal faster than the elastic can stretch?
P
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Post by abacus9900 on Mar 15, 2011 19:47:01 GMT 1
If fact, although space is still expanding, individual galaxies are moving within it. The Andromeda galaxy is due to collide with the Milky Way at some distant point in the future!
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Post by speakertoanimals on Mar 15, 2011 21:12:23 GMT 1
I think that would be called -- getting CLOSER to us. Not hard, the speed of the expansion for nearby objects is pretty small.
Which still doesn't get us any closer to whatever void the original question was about..................Because I think it was just plain wrong, and confused the larger-scale voids on the scale of galaxies and clusters of galaxies, with some supposed void within our galaxy.
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Post by abacus9900 on Mar 21, 2011 21:19:57 GMT 1
So, a (2 dimensional)analogy could be : We have a gnat on a bicycle (=galaxy). We place the gnat with its bike on a piece of knicker elastic(space). The gnat starts riding as we start stretching the elastic. Its velocity relative to us (our position is unchanging) is the sum of the rate of extension of the elastic plus the bike's forward velocity. Whereas the space in front of it is expanding (relative to us) at the extension rate of the knicker elastic. There's just one problem, what happens if the gnat can pedal faster than the elastic can stretch? P principled, all space is expanding but it only becomes appreciable over very large distances. The Hubble Constant states that it is expanding at the rate of 72km/sec. per megaparsec. A megaparsec equals one million parsecs (3.26 million light-years). |
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If the former, then where is this expanding space occurring that the galaxy is moving through?