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View Full Version : Dark matter and moving away galaxies



mgsirius
2014-Mar-16, 10:38 PM
If the galaxies are linked or connected to each other by dark matter or gravity, then why are they moving away from each other ?

http://arstechnica.com/science/2012/07/dark-matter-is-the-thread-connecting-galaxy-clusters/

( I understand Andromeda and Milkyway are moving towards each other but most of the rest of the galaxies are moving away !)

antoniseb
2014-Mar-17, 12:12 AM
I moved this to Q&A.

Cougar
2014-Mar-17, 01:06 AM
If the galaxies are linked or connected to each other by dark matter or gravity, then why are they moving away from each other ?

The clusters in that article are not moving apart. But when we see galaxies billions of lightyears away (in any direction), they appear to be moving away. We say the Universe is expanding. Exactly what that means depends on the details of the model you're using to explain it.

Big clusters of galaxies make up a huge amount of mass. All that mass, and the accompanying dark matter, makes for a lot of "local" gravity, and that overwhelms the expansion in that region. The expansion is extremely small judging locally. But it adds up over the huge expanses of space between distant clusters.

mgsirius
2014-Mar-20, 09:35 PM
Thanks.