How does a star live long?

Answer 1

It is estimated that a star like the Sun may last about 15 to 20 billion years, although less than half of that in its current active form. About halfway through its lifespan, a typical yellow star will begin to expand into a red giant. Ultimately, it will form a dwarf star.

Stars last anywhere from about a million years to several trillion years. It depends on the star's mass; higher-mass stars live for less time. Once a star becomes a white dwarf, or a neutron star, it no longer supports fusion. But it will remain at a very high temperature (thousands of kelvins) for many billions of years.