• Moiya McTier

Astronomy Fun Fact #90

You learned in Fun Fact #89 that there's a lower limit for the mass of a star. There's also a theoretical upper limit.


Stars are a careful balance of gravity pushing in and pressure pushing out. The balance is called hydrostatic equilibrium because it means that the material of the star isn't moving in our out.


But if there's enough mass in a gas cloud, which is where stars form, then the force of radiation pressing out would be stronger than the force of gravity pulling in. This mass limit is called the Eddington Limit named after Sir Arthur Eddington. It puts the upper mass limit for stars at a couple hundred times the mass of the Sun.


Of course, this is only a theoretical limit. The most massive star ever observed (this is not the same as the biggest star, mind you) is R136a1, which has a mass about 300 times that of our Sun, or 6x10^32 kg.

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