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The Sculptor Dwarf Galaxy is a small satellite Galaxy of the Milky Way. There are many such satellites galaxies and I'm trying to compile basic data on them.

However, I can't find an estimate for the number of stars in the Sculptor Dwarf (and many other satellite galaxies too). I'm disappointed that Wikipedia doesn't have this basic information, and that makes me suspicious that estimating the number of stars in other galaxies is not very easy or reliable for current astronomy.

Googling these things has resulted in nothing but a bunch of pop science sites...which is no surprise except that these sites don't seem to have the number of stars either. This lack of basic data is surprising and only adds to me worries that no reliable estimates exist.

Can anyone find a link to this info? It would also be very helpful to point me to a database that has the number of stars for all galaxies in the local group, if such a database exists.

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  • $\begingroup$ I searched a few websites but found nothing interesting facts about stars and it contains only 4% carbon.If you want more detailed information you can check this below link:ned.ipac.caltech.edu/cgi-bin/… $\endgroup$ – LightSaber Mar 18 '16 at 9:21
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Estimates of star numbers are difficult to obtain. Red dwarfs are too dim to be seen as individual points so star counts cannot be obtained. The best guesses come from obtaining the mass of the galaxy and then guessing how much of that mass is made of stars. It is usually a low proportion, between 1 and 3%. You then guess how big the stars are on average to obtain a rough estimated of the star count.

Sources

Dwarf galaxies tend to have a high mass to light ratio meaning that more of their mass is in the form of dust, gas and "dark matter". Sculptor has particularly high ratio, of about 160$\Upsilon_\odot$, and a mass of about about 200 million times the sun.

If 1% of that mass is in the form of stars, but the stars are on average half the mass of the sun then Sculptor would have about 4 million stars. The error bars on that number are very large: The mass could be as much as 320 million suns, and the other values are guessed by me (about 3% of the milky way is in stars, but the milky way has a much lower mass to light ratio)

Perhaps the final reason that this number is not easily available is that it is of relatively little use. While the size of a galaxy can be measured spatially or by mass, and the nature of the stars is of interest, the number of them is of less use.

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  • $\begingroup$ I'm sorry, but any pop science site that states "All galaxies are moving away from each other" and leaves it at that, immediately loses my trust. Andromeda and the Milky Way are on a collision course, just to name one example. Thank you for the second source though. Do you know where I can find pdfs like that for all the dwarf galaxies of the local group? $\endgroup$ – DrZ214 Nov 30 '15 at 20:56
  • $\begingroup$ I searched arxiv, for anything related to sculptor dwarf. You could also do an old fashioned literature search. $\endgroup$ – James K Nov 30 '15 at 21:30
  • $\begingroup$ I also found a old paper from someone who had done a manual star count of Scl adsabs.harvard.edu/full/1961AJ.....66..384H There weren't interested in the absolute number of stars, but in their distribution. $\endgroup$ – James K Nov 30 '15 at 22:12

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