What happens to a star after ten billion years?

Answer 1

It depends on the star. A moderate, yellow type G star like the sun will run out of fuel after 10 billion years. We are halfway to that point now. In another 5 billion years or so, our sun will begin to run out of fuel and so it will begin to contract in on itself, causing the remaining hydrogen in the core to fuse rapidly into helium. This will generate more heat and will drive the outer atmosphere of the sun outward, where it will form a red giant star and engulf all of the terrestrial planets out to Mars.

When the core becomes unstable, it will puff out this outer atmosphere in a planetary nebula, leaving behind a white dwarf core. This white dwarf star will continue to burn hot and white until there is less hydrogen to burn, in which case it will gradually pass through all of the other colors of the visible spectrum until, after billions of years, it will no longer shine. Then it will be a black dwarf (NOT a black hole!), meaning it will have all of its gravity but will emit no light or other radiation.

Stars with several times more mass than our sun will not last 10 billion years. They burn hot and fast and will go supernova long before that. After this huge explosion, the core will be left behind as either a neutron star or a black hole depending on the mass of the core.

Red dwarf stars last far longer than 10 billion years. They burn cool and red for much longer, and eventually they too run out of fuel and will become a small white dwarf that will fade relatively quickly because of the small mass and far less fuel available.

Answer 2

After about ten billion years, a star like the Sun will exhaust its nuclear fuel and enter the red giant phase. It will expand and become much larger and cooler, eventually shedding its outer layers into space as a planetary nebula. The remaining core will eventually cool down and become a white dwarf.