demarcation points for star categories?

Sort of a follow-on to the previous thread about brown dwarves vs. main
sequence stars. What are the currently accepted minimum masses that
demarcate a brown dwarf from a planet, and a main sequence star from a
brown dwarf? I heard that the smallest main sequence stars can be only
0.08 solar masses. How many solar masses for a brown dwarf?

Secondly, if the Sun can last for 10 billion years, how many years can
the smallest main sequence star last? 100's of billions of years,
trillions, etc? Also since brown dwarves are even smaller than those
stars, does that mean they'll last even longer? Or does the fact that a
brown dwarf can only fuse with the rarer deuterium nucleii, mean that
its burning lifespan is smaller?

Yousuf Khan

Yousuf Khan wrote:
Sort of a follow-on to the previous thread about brown dwarves vs. main
sequence stars. What are the currently accepted minimum masses that
demarcate a brown dwarf from a planet, and a main sequence star from a
brown dwarf? I heard that the smallest main sequence stars can be only
0.08 solar masses. How many solar masses for a brown dwarf?

Secondly, if the Sun can last for 10 billion years, how many years can
the smallest main sequence star last? 100's of billions of years,
trillions, etc? Also since brown dwarves are even smaller than those
stars, does that mean they'll last even longer? Or does the fact that a
brown dwarf can only fuse with the rarer deuterium nucleii, mean that
its burning lifespan is smaller?

Yousuf Khan


Main sequence stars are those that have sustained hydrogen burning
occurring in their cores.

Estimate of main sequence lifetime

t/t_sun = (m/m_sun)^-2.5

where t is time on the main sequence and m is star mass.

See: http://www.astronomynotes.com/ evolutn/s1.htm
http://www.eclipse.net/~cmmill er/BH/blkmain.html
http://www.edu-observatory.org/eo/white_dwarfs.html
http://www.edu-observatory.org/eo/black_holes.html