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SESK: Stuff Everyone Should Know · sesk.info/astro-brown-dwarf-mass-limit

Below about what mass can an object never get hot enough to fuse ordinary hydrogen?

About 0.075 solar masses (7.5% of the Sun). Below that you get a brown dwarf.

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  1. About 0.075 solar masses ✔
  2. About 1.4 solar masses
  3. About 3 solar masses

Why: An object less than about 7.5% of the Sun's mass never reaches the temperature needed for hydrogen fusion. It glows faintly as a brown dwarf. 1.4 solar masses is the white dwarf limit.

Huh, didn't know that: Brown dwarfs give off most of their light in the infrared, so they are hard to find.

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Brown dwarfs tried to be stars but just didn't have the mass appeal.
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References

Answer: About 0.075 solar masses. An object less than about 7.5% of the Sun's mass never reaches the temperature needed for hydrogen fusion. It glows faintly as a brown dwarf. 1.4 solar masses is the white dwarf limit.

  1. Astronomy 2e, 17.3 The Spectra of Stars (and Brown Dwarfs) openstax.org/books/astronomy-2e/pages/17-3-the-spectra-of-stars-and-brown-dwarfs
    less than about 7.5% of the mass of our Sun (about 0.075 M Sun ) do not become hot enough for hydrogen fusion
    Checked 2026-10-10.

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