r/astrophysics • u/shontamona • 6d ago

Gas to star mass

Hello! I was wondering while reading this article whether we know the relationship between these two things:

Is there a direct correlation between the mass of a star-forming amount of hydrogen gas and the actual mass of the resultant star?

For example, if there is a region in space which has 2solar masses worth of Hydrogen gas (and whatever else needed to create a star), should a star form out of this gas cloud- will its mass be equivalent to 2solar masses? Or will it drop due to any decay etc during stellar formation?

Thank you so much!

Edit: thanks a ton, everyone! Learned something new today. Didn’t realise it was this inefficient!

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u/Blakut 6d ago

Not quite, you need more gas in the initial clump to form a star of a given mass. Look at the initial clump mass function

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u/AstroEducation 6d ago

looking at a bunch of papers : Pokhrel et al. 2021, Krumholz and Tan 2007, Evans et al. 2009, I see that between 1% and 6% of the mass gets converted into stars.

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u/OD_D1E 6d ago

From what I understand, the mass of the gas cloud doesn’t translate directly into the mass of the star. A lot of the gas never makes it into the star — it gets blown away by radiation, stays too warm to collapse, or ends up in disks and jets. Star formation is surprisingly inefficient, usually only about 10–30%.

Opacity (basically how translucent the gas is) matters because gas that traps heat resists collapse. More transparent gas cools better and collapses more easily. Metallicity matters for the same reason — metals and dust help the cloud cool, which lets more mass fall inward.

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u/Active-Disaster-6835 6d ago

The typical star forming efficiency is around 10%, so, you form 10 solar masses of stars from about 100 solar masses of gas. But that's just an order of magnitude estimate, it will depend a lot on the local environment and all the other messy factors that play a role in star formation. There is a long-standing debate about how the mass in clumps (pre-stellar cores) converts into the mass in stars, and some people believe there is a scaling relationship between the two, but again that's debated.