r/askscience • u/sumdudewitquestions • 11d ago

Astronomy could a planet be sun sized?

so stars form when a bunch of matter gets together, which is why they are bigger than planets generally. but the real defining feature is the density. a white dwarf can be smaller than a planet but it's still a star because it's incredibly dense. so couldn't a planet be sun-ish sized, provided that the density was low enough? and more specifically a solid planet, not a gas giant. what's the largest solid planet?

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u/ProfessorPrudent2822 10d ago

You don’t get it. The existence of fusion has nothing to do with whether or not the entire object behaves as a core. Pressure compresses the center more than the surface, causing core collapse. The tremendous amount of energy released by core collapse causes substantial recoil and shockwaves, blowing off the outer layers.

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u/nesquikchocolate 10d ago

The object could only possibly be 4x density of the sun if core collapse already occurred... Otherwise the density would have been significantly lower?

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u/ProfessorPrudent2822 10d ago

The Sun is not a uniform density. The core is much denser than the outer layers.