when a protostar stops contraction

shirin

It is written that when the gas of the protostar is completely ionized, it stops contraction and it gets into hydrostatic equilibrium. I don't understand why?

ibysaiyan

It doesn't as far as my knowledge on stellar evolution goes.When the star reaches "main sequence" stage and produces enough outward radiation pressure through nuclear fusion to counter inward pull of gravity,it's at this stage when hydrostatic equilibrium is achieved.
P.S: does it mention that the star is shrinking ? or just attains equilibrium ? I think ions as the no. of ions increases they tend to absorb heat than radiating away.That might be the reason?

-ibysaiyan

qraal

Ionization means the object is no longer transparent to heat/light and so the rate of contraction slows down to match the loss of heat via radiation from the object's photosphere. It can only contract if it can lose heat, else it remains inflated. Fusion energy provides a source of internal heat, keeping stars puffed up else they'd contract to white dwarf size via gravitational collapse because their cores are degenerate matter.

shirin

why the ionization means the object is no longer transparent to heat/light? I can understand it for nuclea but what about free electrons? what has happened to them by now? because they can tranfer heat/light!