View Full Version : Dark Matter First, Then a Galaxy

2006-Jun-16, 04:30 PM
A new study from NASA's Spitzer Space Telescope suggests that galaxies form within clumps of dark matter. This mysterious substance emits no light, but it does have mass, so it can pull on matter with its gravity. Astronomers believe there's 5 times as much dark matter in the Universe as regular matter. This new Spitzer survey found that the amount of dark matter surrounding distant galaxies is surprisingly consistent.

Read the full blog entry (http://www.universetoday.com/2006/06/16/dark-matter-first-then-a-galaxy/)

2006-Jun-16, 05:57 PM
This is an interesting story, though I get the impression that opinion is going to keep swaying back and forth on this topic.

2006-Jun-16, 06:55 PM
Galaxies are born inside dark matter clumps.


Try mixing caramel into vanilla ice cream -- you will always end up with globs and swirls of caramel. Scientists are finding that galaxies may distribute themselves in similar ways throughout the universe and in places where there is lots of so-called dark matter.

"Our findings suggest that unseen dark matter -- which emits no light but has mass -- has had a major effect on the formation and evolution of galaxies, and that bright active galaxies are only born within dark matter clumps of a certain size in the young universe" - Duncan Farrah, Cornell University research associate, the lead author of a paper on spatial clustering that appeared in the April 10 issue of Astrophysical Journal Letters.


2006-Jun-16, 06:58 PM
Oh-oh. It might call for a Genesis revision:

And God said, Let there be dark, and, eventually, there was light.

2006-Jun-16, 08:18 PM
Why do I get the impression that this is circular reasoning?

1. Galaxies have flat rotation curves, so there must be fairy dust dark matter... whose characteristics are derived from the characteristics of the galaxies.

2. So by definition, dark matter must play a part in the formation and characteristics of galaxies.

Am I missing something?

Ian Tresman

2006-Jun-16, 09:37 PM
I think there really needs to be more of an understanding of what dark matter is and how it effects things before you can start throwing off half-baked theories about which comes first the chicken or the egg.

2006-Jun-19, 05:57 PM
I find it interesting that the amount of dark matter is consistant and varies little from galaxy to galaxy, what does this mean exactly? Is there any elaboration on this anywhere?

2006-Jun-19, 06:35 PM
Am I missing something?
That's my guess.

We observe what we observe, and then try to understand what we see based on the physics we know. We suggest other things to try and observe based on what we're seeing, to determine more of its nature.

In this case we had a reason to think there is a lot of dark matter, and we looked for it in other places and found it. Specifically in the lensing by Galaxy clusters.