Transcript

NARRATOR 1:

What happens to a star during the rest of its life depends on how massive it is at its birth.

NARRATOR 2:

A star like the sun is in a delicate balance between gravity, which wants to make the star collapse in on itself, and the pressure that pushes outwards that comes from the energy that’s being produced and these fusion reactions happening at its core. However, at some point in the future, the hydrogen runs out. And at that point, the core of the star will start to collapse in on itself under its own weight. It gets denser. It gets hotter, until a point where you can actually start to use the helium atoms themselves as the fuel for the fusion, pushing helium atoms together and making carbon and oxygen the next heavier elements in the periodic table.

NARRATOR 1:

As the star begins to fuse helium it creates more energy, and that causes the outer layers of the star to expand. One day our sun will grow so large it will swallow up the inner planets of the solar system out as far as the Earth. It will become a red giant. For the sun, this will be the beginning of the end.

NARRATOR 2:

What happens is that the outer layers of the star get farther and farther from the middle. The force of gravity that they feel is getting weaker and weaker. And actually, the star loses hold of its outer atmosphere. Its outer atmosphere drifts off out into space. It expands out to become a planetary nebula, and they’re some of the most beautiful objects in the universe.

NARRATOR 1:

Once the outer layers have drifted away, all that is left of the star is its core.

NARRATOR 2:

A white dwarf star is the dead remnant core of a star like the sun at the end of its life. What’s left behind is something that might weigh as much as half the mass of the sun, but it’s only about the size of the Earth. So it’s an incredibly dense object. It’s dead. There's no nuclear fusion going on there anymore. It’s incredibly hot. But then, over millions of years, it will gradually cool down to become a black dwarf.