I know that stars are formed from dense regions in large gas clouds.
I know that when gravity causes the mass of the clump to get so big that its internal pressure can't sustain it, it collapses and becomes a star.
I know that this threshold is known as the Jeans mass.
What I don't know is exactly what happens during the gravitational collapse of a star and how the hydrogen/helium gas becomes a flaming ball of fire.
How long does the process of gravitational collapse take?
Answer
A star is neither "flaming" nor "fire" in the sense that we use those words about things on Earth. It's just a big, hot ball of ionized gas.
The only thing that happens "to" it is that it gets hotter and denser. At some point the temperature rises high enough to ionize the gas. Later still fusion becomes possible at non-vanishing rates.
The energy for the warming comes from gravity, and how much is well described by the virial theorem.
The proto-star continues to shrink and warm until the power produced by fusion matches that lost to radiation from the surface at which point the system is in equilibrium and stops collapsing.
No comments:
Post a Comment