Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Edward Macharia on 15/07/2008 10:04:02

Title: Does a bigger star trap more light inside itself than a smaller star?
Post by: Edward Macharia on 15/07/2008 10:04:02

Edward Macharia asked the Naked Scientists:

Hello,
I’m writing from Nairobi Kenya.

If the light in our sun takes about a million years to get out of the sun, would it take two or three million to get out of a massive star that can go super-nova?  And when it does; will a million years worth of light be released in less than ten minutes? And what is the effect of having a million years worth of photonic pressure inside a star?

Best Regards,
Edward Macharia

What do you think?

Title: Re: Does a bigger star trap more light inside itself than a smaller star?
Post by: lyner on 15/07/2008 10:54:48

Good questions.
Yes, it takes proportionally longer for the light to 'get out'.
But it won't all come out at once. It is constantly being produced throughout the body of the star and emerges at a constant rate.
The photonic pressure is one of the balanced forces which determine its radius. It's a battle between gravity and pressure and the radius stays the same for most of the star's life. When the energy production changes and more heavy elements are formed, the situation changes and the star swells up into a Red Giant with a new 'stable' radius. When energy production ceases, the Star collapses - heating up first, then cooling to nothing. (At least that's for most normal sized stars)