Scientists say our Sun has been shining for about the last 4.6 billion years.
They also say the Sun is expected to have enough hydrogen to fuel nuclear fusion in its core to allow it to continue shining as it has for about another 5 billion years.
Along with creating solar energy, the Sun’s hydrogen nuclear fusion process also produces helium.
When the supply of hydrogen diminishes in the core the Sun it will begin transforming from a “normal” main-sequence star into a red giant star.
The drop in the hydrogen supply will cause an initial collapse of the core.
“But, a shell around the core will quickly heat up and start fusing hydrogen of its own which is the beginning of the red giant phase,” says Michael S. Kirk, a Research Scientist at NASA’s Goddard Space Flight Center and Catholic University in an email to Science World.
“As this phase progresses, the core will continue to heat and eventually begin to fuse helium into carbon producing a significant amount of heat and puffing up the outer layers even more,” he explains.
Scientific research suggests the red giant will continue to expand and grow larger until it engulfs Mercury, Venus and some scientists speculate possibly Earth will be consumed by the Sun. Others say Earth could very well survive the encroachment of the red giant Sun.
Kirk says the entire process that includes the initial collapse, hydrogen shell burning, and the fusion of the helium core (red giant phase) will take between 1 and 1.5 billion years.
“After the sun has exhausted its available fuel (hydrogen and helium) in its core and in a shell around the core, it will collapse in on itself. The outer layers will “bounce” off of the denser core and expand into a planetary nebula,” says Kirk.
A new study, published in the journal Nature Astronomy, suggests this planetary nebula will become brightly illuminated for about 10,000 years, by what would then be the Sun’s remaining tiny compacted core, known as a white dwarf.
According to Michael S. Kirk – “This white dwarf will contain about half the mass of the sun but its surface will be about 20 times hotter than the current sun and will slowly cool for hundreds of billions of years (longer than the current age of the universe).”
As the white dwarf cools, its light will fade, die and become a black dwarf.
However, stars with much more mass than our Sun don’t get to die such a quiet death.
Instead, at the end of their red supergiant phase, they explode as a supernova.
Scientists say this supernova explosion lasts for only a short time, about 100 seconds.
Afterward, stars with a core mass between 1.4 to 3 times that of our Sun will shrink and become neutron stars.
A star with more than 3 times the core mass of our Sun will collapse into a black hole.