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The Question

(Submitted April 22, 1997)

Are all stars formed from nebulae? If not where do they come from? What happens to a star after they are burned out? Do all stars end up a black hole or supernova? What determines their final destination? Where will our Sun end up when its fuel is spent? What are dwarf stars?

The Answer

Yes, all stars are formed from nebulae (the plural of nebula). Nebula is a term for a cloud of gas, and stars form from gas. Stars more massive than ~ 6 solar masses are expected to supernova, stars less massive than this (like our Sun, of course) become white dwarfs. After a supernova, there may be nothing left, or there could be a remnant: either a neutron star or a blackhole. If the remnant is more massive than around 3 solar masses it will probably end up as a blackhole. Stars are smallest when they are burning hydrogen into helium, which is what stars do during most of their lifetimes. Stars in this stage are sometimes called dwarfs. There are also two other kinds of "dwarfs": white dwarfs are burned-out stars mentioned above (the Learning Center has more info on these), and brown dwarfs are stars which never accumulated enough mass to start burning hydrogen.

Andy Ptak
for the Ask an Astrophysicist Team

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