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I Why are stars grouped in galaxies?

  1. Sep 25, 2016 #1
    I have been thinking at this for a couple of days now: why are stars grouped in the massive collections that we call galaxies?

    I can assume that in the very early Universe, matter was grouped in these areas, that matter interacted thus resulting in the formation of stars. Then, the gravitational pull between these stars made possible grouping them in what we call galaxies.

    But why was the matter scattered in these clusters in the early Universe? Why this uneven distribution throughout the Universe?

  2. jcsd
  3. Sep 25, 2016 #2


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    The belief is that dark matter, for whatever reason, "clumped" on huge scales and these clumps were the seeds for normal matter forming galaxies. It was NOT the case the the stars formed and then the galaxies formed.
  4. Sep 26, 2016 #3
    Another way to think about this question: If the universe did not have galaxies, we probably wouldn't be here.

    From Ken Croswell's book Planet Quest:

    "[Heavy] elements do no good unless they are recycled back into new stars and planets. This is why the second prerequisite for life is a galaxy. Not just any galaxy will work, however. If the galaxy is too small, as most galaxies are, then a dying star's harvest of heavy elements escapes the galaxy's weak gravitational grasp and drifts into intergalactic space, where their potential is completely wasted. Fortunately, a few galaxies, such as our own Milky Way, are giants that dwarf the rest. These galaxies harbor hundreds of billions of stars whose collective gravity retains stellar ejecta. Brimming with heavy elements, this life-giving debris can then enrich the beautiful interstellar clouds of gas and dust that give birth to new stars and planets."

    --Planet Quest by Ken Croswell, page 3.
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