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?
Dave - Very good question Jim.
There are lots of different types of stars and what happens depends upon how big the star is to start with.
If you've got a very small star - for instance what's called a Brown Dwarf, which is 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 nuclear 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, and you get stars in which the gas collapses, they heat up and start burning (fusing) 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 again.
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 mass stars, like the Sun, burn their hydrogen away but then they've got enough mass to collapse down further and begin burning their helium to form carbon; then that will burn away. As it does so, 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's got a very small core with a great big kind of diffuse, warmish red star outside it.
This core is not massive enough to burn the carbon to form anything else. So, the core can make an explosion, it blows away the gas to leave a cold, carbon core.
Some of these, as they cool down, can crystallize and form diamond-type things.
If you get a bit bigger than this white dwarf, that's got enough mass to collapse and form a neutron star, that explodes and forms a huge supernova. If you get even bigger than that, it's so massive that the neutron star will collapse to form a black hole from which nothing even light can escape.