Scientists predict how much longer Sun will shine
What will happen when our Sun dies (photo: Freepik)
The Sun is the source of life on Earth, but like everything in the Universe, it has its life cycle. Now our sun is in a stable phase - a yellow dwarf - and scientists can already predict what will happen to the Sun in billions of years when it exhausts its hydrogen reserves.
RBC-Ukraine tells about how long our Sun will continue to shine, and what will happen when it starts to fade, with reference to Space, a news site about space exploration, innovation, and astronomy.
What happens when Sun dies?
The sun will start dying in about 5 billion years when it runs out of hydrogen. The sun will end its life as a white dwarf. It will be a dead star that has exhausted all the nuclear fuel it can burn.
As a white dwarf, it will slowly cool and fade to ever lower temperatures. This is the end state of low-mass stars, including the Sun.
Although the volume of the Sun is a million times that of the Earth, a white dwarf is about the same size as our Earth. The majority of a white dwarf will consist of a special superdense state of matter called electronically degenerate matter. This is a state in which all electrons are in the lowest possible energy states.
Our sun, as a white dwarf, will have a core composed mainly of carbon and oxygen, which are the remnants of helium burning. Around this core, there will be a thin layer of helium, which will be the residue of helium burning.
The outer layer will contain a thin layer of hydrogen that has not been burned. Some white dwarfs do not have this outer hydrogen layer because the thermonuclear combustion of hydrogen has been completed in their evolution.
What will happen to Earth when Sun dies?
The Earth will probably even exist when the Sun dies. It is slowly expanding. In about 5 billion years, the sun will enter the red giant phase. During this phase, it switches from burning hydrogen in the core to burning hydrogen around the core, which has been converted to helium by burning hydrogen.
The energy production increases dramatically and forces the star to expand more than 200 times to reach a new state of equilibrium.
Theoretical modeling and observations, supported by distance measurements from the Gaia spacecraft, indicate that the Sun may well swallow the Earth when it reaches its maximum size.
At some point, when the Sun reaches the top of the AGB [asymptotic giant branch], helium burning will begin. In a star like the Sun, helium burning occurs through thermal pulses. In each pulse, the Sun will experience a significant mass loss.
However, the Sun experiences mass loss throughout its lifetime. This mass loss rate is quite low for the Sun and is confirmed by the solar wind.
Even now, the Earth is losing water. Interactions with the ultraviolet radiation field and solar wind particles reaching the Earth dissociate water in our upper atmosphere. Light hydrogen, in particular, can escape the Earth's gravitational pull.
Observations from previous space missions and the Hubble Space Telescope show a broad hydrogen cloud (exosphere) around the Earth. Estimates suggest that the Earth will lose most of its water in a billion years and will look like Mars.
Even if the Sun does not consume the Earth, the increased luminosity and strong stellar winds in the later stages of its evolution will vaporize or boil away any remaining atmosphere or ocean. If the Earth survived, it would be a rocky slag orbiting a white dwarf.
