Introduction to Stars
This is a short summary of the life,birth,and death of stars.
The ``life'' of a star is the time during which it slowly burns up its hydrogen fuel,and evolves only slowly in the process.The star is in force balance between pressure and gravity.It is also in energy balance between production by fusion reactions,transport by photon radiation,and loss from the surface by the (usually) visible radiation by which we can detect the star.
The ``birth'' of a star refers to the process by which it is formed from diffuse clouds of cold gas that are present in its galaxy.A cloud collapses to form a number of stars when it is disturbed so that its gravity overcomes its motion and pressure.
The ``death'' of a star occurs when its fusion fuel,first hydrogen and then heavier nuclei,has run out.This can be very violent if the star is very massive,ending in things like a black hole and/or a supernova,perhaps leaving a neutron star behind.If the star is not very massive,like the Sun or even smaller,it ends by ejecting part of its atmosphere and then settling down to a cold,dense white dwarf.