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So, I've always heard that the Milky Way hosts between 100 billion to 400 billion stars.

My problem is very simple: I'm unable to find any research papers on that topic or giving those estimates. I'm starting to think that this has become common knowledge but all comes from a back-of-the-envelope calculation instead from a true attempt to obtain that number.

Are there any scientific publication on this? Gaia data might have improved that number to some extent I guess thus there should be something recent in the ADS but I'm unable to find anything. Also more accurate IMFs in the last decade and estimates of the mass content should have probably improved the accuracy of this value.

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    $\begingroup$ The problem is, any measurement of the IMF is local. It is an extrapolation to apply it throughout the Galaxy. In addition, it is not enough to know the present-day IMF; you need the history of the IMF too, which is not readily measurable. Finally, you have to know things about multiplicity, since a large fraction of "stars" are unresolved multiples. $\endgroup$
    – ProfRob
    Commented Sep 19, 2021 at 21:54
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    $\begingroup$ @ProfRob I think this comment basically constitutes at least half an answer. Throw in a common guestimate for the IMF and multiplicity and ... that's how good it can get. $\endgroup$
    – planetmaker
    Commented Sep 23, 2021 at 10:12
  • $\begingroup$ @ProfRob Yes, I also agree that there is little room for improvement on these numbers but I would like to know if there's any scientific publication mentioning these estimates. I also read: "there are estimates that even give a trillion stars", well then where are those taken from? $\endgroup$
    – Swike
    Commented Sep 25, 2021 at 12:51

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Interesting that you ask this question after reading this article from NASA. The same agency also published this article on the number of stars in the Milky Way. The article then links to three other interesting articles.

I don't want to repeat the article in this post, please read it, but the main take away of the article is that there is no exact number of starts in the Milky Way, or even galaxy, like this article on the ESA site. All estimates are based on statistical analysis where a know value, like mass or luminosity are used to estimate an new value. The estimation is then based on averages and big number rounding. If I know the mass of the Milky Way and define that on average stars have a mass of x with a normal distribution and we define that y% of the mass is made up by stars, we can guess the number of stars in the Milky Way.

We can also look at other galaxies, with a certain luminosity and a mass and then say that based on the mass and luminosity the mass of the that galaxy is made up by y% by stars and the average star has x mass and z luminosity. That galaxy would then have so many stars. This might than also be right for our Milky Way.

However, as you pointed out. There is no exact number and the articles posted on NASA and ESA are the most scientific I could find.

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  • $\begingroup$ There's no need to plagurise. That is when you claim to have written something that was actually written by another. Since you already said "Article from NASA", it is literally impossible for you to plagerise it. If you only quote a small amount from the article there is no issue of copyright either, moreover as NASA is a federal agency, all its works are in the public domain. So you literally can't violate copyright. So please feel free to quote from the article! $\endgroup$
    – James K
    Commented Sep 25, 2021 at 20:47
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    $\begingroup$ Second pararaph is not how you estimate the number of stars in the Galaxy, since very little of that mass is in the form of stars. Neither do stellar masses follow a normal distribution. $\endgroup$
    – ProfRob
    Commented Oct 27, 2021 at 10:44
  • $\begingroup$ It gets even worse, considering we don't really have an established boundary for our own solar system that is widely agreed upon, let alone for the entire Milky Way. How far into the intergalactic medium does the galaxy actually extend? At what radius do we stop counting? How can we be sure that that's the right radius? How many stars will changing the measurement include or exclude? These are all very good questions and a little off the topic that you really want to know, which I interpret as "What is the primary source for the statement?" $\endgroup$
    – GrasshopperTaji
    Commented Dec 21, 2021 at 21:17

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