Universe size
12 Dec 2005 0:21:14 UTC
Topic 190356
(moderation:
Silly question:
Everyone has seen the pictures from the Hubble telescope where it shows hundreds of visible universes (sp)? Relatively speaking they all seem to be of a very large size (Milky Way size or there about). I wonder why they all tend to be very large (Milky Way) instead of some at least being much much smaller (say the size of our solar system, or planet size, or for that matter, why not the size of a basketball or marble)? Is this the result of Einstein's theory of an expanding universe? And did he not actually adjust his general theory of relativity to explain a constant universe?
Universe size
)
ECR
I assume you are talking about the Hubble Deep Field images. Most of the galaxies in those images are thought to fairly small. Their size is not influnced by the expansion of the universe attributed to the big bang. The gravitional forces binding the galaxy's components are great enough to prevent that.
ps dark energy could have that ultimate effect in some of the theories proposed.
Yes he did, when James Hubble produce evidence that the universe was in fact expanding he retracted the adjustment. It may just be he should have left it in and reversed the sign of his Cosmological Constant.
ECR: Do think you mean
)
ECR:
Do think you mean "visible galaxies?"
Actually, there are a lot of small galaxies around. In the Southern Hemisphere you can see two very close ones called the Magellanic Clouds. There are a few more of these "dwarf galaxies" orbiting the Milky Way, and there is actually good evidence that we ate one more not too long ago.
Here "small" means something like 100,000 stars. The US Army might call a single star a "galaxy of one" but astronomers don't. There is a minimum size (or mass) for a star, which is a lot bigger than Jupiter but smaller than the Sun. Below that size the nuclear reactions that make a star shine can't start, and you just get a planet with a warm interior. Like Jupiter.
And there are many galaxies much, much bigger than the Milky Way.
Hope this helps,
Ben
RE: ECR: Do think you mean
)
Thanks, that helps a bit.