What happens when the sun burns out

Science in dialogue

What happens when the sun goes out?

The sun's light and warmth are created by the nuclear fusion that takes place inside. Put simply, hydrogen atoms are fused to form helium atoms, releasing huge amounts of heat and energy.

The fact that the whole "sun ball" does not fly apart is due to the balance of forces. The outward directed force of solar radiation is balanced with the inward directed mass attraction. The nuclear fusion and thus also the sun are stable. This changes dramatically when one - in human dimensions - very distant day the hydrogen inside the sun runs out and the sun's radiation decreases.

Then the gravitational pull will exceed the radiation pressure, the sun will begin to shrink. However, this increases the temperature inside the sun, which makes other merging processes possible. They create heavier elements like carbon and oxygen. The severity of these processes is extremely dependent on the temperature and increases rapidly to higher values. Therefore, there will no longer be a new equilibrium of forces and the layers in which nuclear fusion takes place will shift from the sun's core to the outside. As a result, the sun will inflate and parts of the gas envelope will be repelled. This process of shrinking and expanding can be repeated several times. The sun "flickers" and a white dwarf forms. In the case of the sun, it eventually becomes colder and remains a red dwarf.

So when the sun goes out, the problem for living beings (on earth) will not be that there will be no more light or heat. Much earlier, the sun will expand across the inner planets and raise the temperatures there so much that life will be impossible. Around 4.5 billion years should pass before the beginning of the end of the sun, about as much time as the sun is already shining in a relatively stable manner.

The question was answered by Dr. J├╝rgen Rendtel from the Astrophysical Institute Potsdam.