# Relative masses of Binary Systems

I'm writing a sci-fi novel and I have an some astrophysics questions. First, is it possible for a binary system to be made up of a large gaseous planet and a dwarf star?

I know it's possible to have two stars orbit each other, and a planet around those (since there is still a center of mass that the system orbits) but could one of the stars be replaced with a planet of sufficient mass without the planet becoming a star itself?

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Dec 12, 2021 at 20:20
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The mass of Jupiter is around $$\approx 10^{-4} M_{sun}$$.
A super-jupiter type of planet, is roughly $$80$$ times the mass of Jupiter, so, $$\approx 10^{-2} M_{sun}$$.
The least massive white dwarf star, is roughly $$\approx 0.17 M_{sun}$$.
So we are talking about a mass ratio of roughly $$5\%$$. According to wikipedia, the Charon-Pluto orbit in the solar system is considered a binary system, and Charon has $$12\%$$ the mass of Pluto.