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First off, I realize how hard this is to even come close to estimating, but I'm trying to get a "general feel" for the distribution of galaxies by star count. I realize everything from rogue stars to super massive galaxies with trillions of stars exist... but I'd really love to see an estimated percentage of galaxies in the observable universe with:

  • <10^5 stars
  • 10^5 - 10^6 stars
  • 10^6 - 10^7 stars
  • 10^7 - 10^8 stars
  • 10^8 - 10^9 stars
  • 10^9 - 10^10 stars
  • 10^10 - 10^11 stars
  • 10^11 - 10^12 stars
  • 10^12 - 10^13 stars... etc.

Does anyone know where I could find some estimates on this... Or even on galactic mass

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    $\begingroup$ Richard Mushotzky has a nice page on the luminosity function of galaxies. astro.umd.edu/~richard/ASTRO620/LumFunction-pp.pdf $\endgroup$
    – eshaya
    Sep 23, 2023 at 12:52
  • $\begingroup$ @eshaya how was this function obtained? Is it empirical or is it derived from some physical considerations? $\endgroup$
    – dtn
    Jan 11 at 3:57
  • $\begingroup$ The Luminosity Function is derived empirically by measuring the brightness of all galaxies within a certain distance from us. It requires good distance determination to groups and clusters. $\endgroup$
    – eshaya
    Jan 11 at 14:50

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Interesting question, but it is quite difficult to provide an accurate estimate for each order of magnitude without a comprehensive survey.

Most galaxies in the universe are likely dim dwarfs that are hard to see and catalog. So it's not easy to give a percentage based on star count since we don't really have perfect numbers either, but I can try to give you a general idea of the distribution.

Our own absolute monster of a galaxy has just over 60 confirmed galaxies within 1.4 million light-years, either orbiting us or not. We may be an exception for having so many satellite (or at least nearby) galaxies because the Milky Way's mass is thought to be quite high, even compared to many other major ones - but if we assume this figure is generally uniform throughout major galaxies, without considering independent dwarf galaxies, we can see that they out-populate massive galaxies by at least 60 to 1.

So most galaxies would fall on the lower end of star count and galactic mass. I'd estimate that well over 98% have $<10^9$, while the remaining few have $>10^{10}$. But as I said, it's hard to come up with an accurate ratio since we don't really know how many compact galaxies exist, simply because they are hard to observe. So take that figure with a grain of salt since it came from some generalizations.

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