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What is the range of the number of stars possible in a galaxy? What is the rough average?

Googling leads to vague answers, things like "billions upon billions". But what is a more pinpointed set of numbers?

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  • $\begingroup$ There will be a different answer for the mean and the median $\endgroup$ – James K May 1 at 7:46
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    $\begingroup$ Please read astronomy.stackexchange.com/q/1083/43 - it will give you answers and the reason why you cannot have an accurate answer. $\endgroup$ – Rory Alsop May 1 at 13:12
  • $\begingroup$ Our galaxy is roughly an average one, it has about 250billion +/- 150billion stars. Surprisingly unexact count. $\endgroup$ – peterh - Reinstate Monica May 1 at 20:16
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The term galaxy can not be given an approximate number of stars since our galaxy has a 27,000 light-years radius while a dwarf galaxy is typically 130 light-years. On the other hand, for and old elliptical galaxy, it can happen that some of the stars are already dead and the creation rate is almost zero, but since those are probably made out of 2 spiral galaxies colliding, the number would be around the sum of the two initial spirals. For some young spiral galaxies, 2-3 stars per year are being created and very few die.

So there are many factors that play a role. Ironically, for our galaxy the number of stars is pretty uncertain since we are inside of it, and we can't infer it from the apparent mass knowing how it rotates, because the total mass and the dark matter both play a role on it. Plus the star mass range can be as wide as 0.1 to 150 (!) solar masses. So, an order of magnitude for our galaxy? $10^{11}$ assuming the population of stars is consistent with the H-R diagram and that half of the population are binary stars.

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  • $\begingroup$ The maximum number of stars in a galaxy is known, roughly, both observationally and theoretically. The average can be estimated as the first moment of the stellar mass function. $\endgroup$ – pela May 6 at 10:57

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