Science Questions

What is the ultimate fate of a star?

I’ve recently developed an interest in astronomy and I hope you can clear up what appears to be some contradictory explanations concerning the final phase in the life cycle of stars. Different astronomers and astrophysicist that I’ve listened to have stated that stars end up as white horse, neutron stars, pulsars, quasars, black holes, and in fact one scientist even mentioned that some stars eventually contract into large diamonds. So, that’s quite a range of possibilities. So, my question is - what does the final stage of the stars life look like? Are all of these possibilities or is there one final state that all stars eventually reach? And if so, what is that state? Jim Geeting, Dallas

Dave -   Very good question Jim.  There’s basically lots of different type of stars and basically depends on how big the star was to start with.

If you got a very small star, if you’ve got what’s called a Brown Dwarf – that’s a minute star maybe 8 percent of the mass of the sun.  It collapses, forms something like a big Jupiter.  It starts to warm up, but it doesn’t even warm enough to start fusion.  It doesn’t fuse any hydrogen.  It just sit there and slowly cools down and ends up as a very cold planet.

Slightly bigger, you get stars which the gas in them collapses.  They heat up to start burning hydrogen.  These are small stars, less than about half of the mass of the sun.  They burn all the hydrogen, but they never get hot enough or dense enough to start burning helium so they then cool down.  A star is basically just hot gas, the only thing that is supporting it under gravity is its temperature.  So, it slowly cools down and shrinks and shrinks and shrinks and forms this very big lump of helium as sort of helium White Dwarf.

Normal stars like the sun.  They burn the hydrogen away, but then they’ve got enough mass to collapse down and they start burning their helium to form carbon then it will burn away.  As it does that the core of the star collapses.  It gets very, very hot and blows the outer layers of the star out to form a red giant.  It got a very small core with a great big kind of diffuse sort of warmish red star outside it.  This core is not massive enough to burn the carbon from anything else.  So, the core can make an explosion, it blow away the gas at last another cold , carbon core.  Some of these as they cool down they can crystallize and form diamond-type things.

If you get a bit bigger than this white dwarf that it got enough mass to collapse and form a neutron star as I was talking about earlier, that explodes and forms a huge  supernova.   If you get even bigger than that, it so massive that  the neutron star will collapse to form a black hole from which nothing even light can escape from.

June 2009