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Galaxy and Stars

  1. Nov 16, 2015 #1
    I have a few questions. Would a given galaxy contain same amount of stars and gas through its lifetime? I want to say no, but I was thinking for every dead star, there will be a new star forming, and the gases would be preserved in the galaxy. And would the spiral disk component of the Milky Way contain all of the stars in its galaxy? I was wondering if this disk covers the diameter of the Milky Way. Lastly, do newly formed stars usually have disks?

    Thank you!
  2. jcsd
  3. Nov 17, 2015 #2


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    Stars form when a clump of gas becomes concentrated enough. The gas in stars is moving all of the time so stars are being formed all of the time. The rate of star formation slows down but it will be a very long time before it ends. The gas in a galaxy isn't necessarily constant either because galaxies often merge with other galaxies.
    There are often stars outside of the spiral disk. As galaxies merge with each other, they don't necessarily align with each other. So, you get existing stars from the two galaxies flying off in all kinds of directions. Lots of new stars are formed where their gasses collide.
    Yes. Star formation is a messy business.
  4. Nov 17, 2015 #3


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    Keep in mind that the type of stars that make up the largest proportion of a galaxies population are M class red dwarfs which can remain in the main sequence for over a trillion years (much longer than the age of the universe.) So any M class stars born when the galaxy was young would still be around, and any new ones being born would add to the population. Even stars like our own Sun remain in the main sequence for ~10 billion years, followed by a ~2 billion yrs as a red giant before settling down as a white dwarf for trillions of years. It is really only the more massive stars that live "hard and fast" so to speak and die young. So on the long term, I would say that the total number of stars in a galaxy increases, as would its population distribution of old vs. young stars.
    The spiral arms contain the youngest stars in the galaxy, as this is where the majority of star formation is presently taking place. The bulge is dominated by older stars, and the oldest stars are found in the globular clusters in the galactic halo.
  5. Nov 18, 2015 #4
    As stated before the long lived stars like M stars and white dwarfs not to mention neutron stars and black holes would hold on to the original gas mass of the galaxy and not give it back. So as more of those stars form the less and less gas you will have. In the end you will have very little gas in the galaxy and very many old stars.
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