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Stellar Evolution
The whole process takes about 10 millions years.
• If a protostar forms with a mass less than 0.08
solar masses, its internal temperature never
reaches a value high enough for thermonuclear
fusion to begin.
• This failed star is called a brown dwarf, halfway
between a planet (like Jupiter) and a star.
• Brown dwarfs still
emit energy, mostly in
the IR, due to the
potential energy of
collapse converted
into kinetic energy.
• Brown dwarfs
eventual fade and cool
to become black
dwarfs.
• The helium ash builds up,
• energy generation stops in the core.
• The fusion process moves outward into a shell
surrounding the hot helium core.
• Helium can also undergo fusion but, since it is a
larger atom, it requires over a 100 million degrees
of temperature.
• For small stars, this temperature is never reached
and the helium core remains inert.