Science Questions

What is the ultimate fate of a star?

Sun, 14th Jun 2009

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Jim Geeting, Dallas asked:

Iíve 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 Iíve 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, thatís 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.  Thereís 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 youíve got whatís called a Brown Dwarf Ė thatís 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 doesnít even warm enough to start fusion.  It doesnít 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 theyíve 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.


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Jim Geeting asked the Naked Scientists: I've recently developed an interest in astronomy.† Hope you can clear up some contradictory explanations about the final phase in the life of a star. Different astronomers and astrophysicists have stated stars end up as: †† †- white dwarfs †† †- pulsars †† †- quasars †† †- black holes And lastly, one scientist claimed stars eventually contract into large diamonds. † How confusing.† I'm sure beginning mass or size of the object may have something to do with this range of explanations. † So, what does the final stage of life for a star look like? Jim in Dallas What do you think? Jim Geeting , Sun, 14th Jun 2009

You have correctly recognised that the central factor in the evolution of a star is its mass. Here is a grossly simplified summary.

Stars less than about twice the mass of the sun will pass through a red giant phase, then collapse to a white dwarf and eventually fade to a black dwarf.

Stars of greater mass will also go through a giant phase, then go supernova. Those less than twenty five times the mass of the sun will become neutron stars and those greater will become black holes. (Pulsars are rapidly spinning neutron stars.)

Stars do not become quasars.

For more information Google (or Bing) stellar evolution. This is a good article to start with. Ophiolite, Sun, 14th Jun 2009

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