What makes scientists postulate that dark energy is what keeps a star from collapsing under its own gravity?

I mean, isn't the fact that it's a constant explosion enough to push out on its matter? I don't understand why Einstein needed a cosmological constant to counteract the effects of gravity on a large scale. After a star burns out, it collapses anyway. So wouldn't the heat keep the star at such a... show more I mean, isn't the fact that it's a constant explosion enough to push out on its matter? I don't understand why Einstein needed a cosmological constant to counteract the effects of gravity on a large scale. After a star burns out, it collapses anyway. So wouldn't the heat keep the star at such a light density?
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