When did scientists discover that the Sun has a life cycle and that it is going to die? I have been researching the history of scientific studies about the the Sun. However I have been unable to find out much information about how the scientific consensus started forming around stars' life cycles.
I know that it has been known since Galileo that some star have sudden changes in luminosity during their life. But I was unable to find out when scientists actually discovered that stars are born and die, and especially how this influenced the view on the future of the Solar System.
I suppose this happened somewhere at the start of the 20th century, when more information and research about supernovae was being found, but I couldn't find more precise information about it.
Any more precise information about this is greatly appreciated.
Although various astronomers have speculated that the Sun was a star (some were imprisoned or even burnt alive for such heresy), this was not known definitively until 1838 when Friedrich Bessel used parallax to calculated the distance to 61 Cygni.
In the late 19th century, Lord Kelvin provided rather small (less than 100 million years) for the ages of the Sun and of the Earth. He did not know about fusion. The nature of what powers the Sun was not known until the 1920s based on observations of the mass of a proton versus that of a helium-4 nucleus. The exact mechanism wasn't known until 1938 when Hans Bethe developed models by which hydrogen fuses to form helium.
This model provided the basis for knowing that the Sun will eventually die as it will eventually run out of fuel. Working from this, a number of scientists developed models of what happens inside stars of various masses based on the growing knowledge of stellar nucleosynthesis.