According to the usual understanding of stellar astrophysics, some white dwarf stars appear to be many times older than the universe. How can that be? Well, the lives of stars in the galaxy, like those in Hollywood, can be complicated. Here is the research paper, “Birth of the ELMs: a ZTF survey for evolved cataclysmic variables turning into extremely low-mass white dwarfs”.
It seems nobody talks about it, but I wonder - since the sun is fusing hydrogen fuel into helium at a prodigious rate - how long until the amount of heat it puts out begins to decrease. It seems likely the Earth will at some point cool noticeably when this happens. Could be that ‘global warming’, if it is occurring, might be beneficial in such a scenario?
As the hydrogen is fused, the sun will shift to helium burning, which will increase temperature and the radius will increase. Over the next 1 to 10 million years it will expand to roughly the orbit of Earth as it blows mass away.
Current models aren’t sure whether Earth will be inside the radius of the sun, but it’ll be toasty.
Edited to add a useful link: https://www.scientificamerican.com/article/the-sun-will-eventually-engulf-earth-maybe/
You clearly know a lot more about this than I do. I am surprised that the time span you mention is in the millions and not the billions of years; that makes this far more immediate in thinking about humanity’s survival.Allow me to refine my question. While the process you describe is taking place but before the Sun’s diameter increases, is there ever likely to be some time span when the Sun’s output will diminish for a substantial period (insofar as humanity is concerned)?
It is amazing how much data is available on the web.
Anton Petrov states that the paper authors used data availble by
Zwicky Transient Facility https://www.ztf.caltech.edu/
and that website reference the following article for available data
I believe that star models suggest hotter first, then eventually a white dwarf. I don’t believe that any astrophysical model has more detail than that.
Following the solar cycle, it does seem to be a lower-than-recent output: Solar Update September, 2021 – Watts Up With That?
The Sun is a non-convective main sequence star. Such stars accumulate helium from nuclear fusion in their cores and burn hydrogen in layers outside the core, gradually becoming brighter over their entire time on the main sequence. The Sun is increasing in brightness by around 10% every 1.1 billion years. This will continue until the Sun leaves the main sequence around 5.4 billion years in the future, when it will swell into a red giant that may engulf the Earth.
Thus, despite depletion of the Sun’s supply of hydrogen, the nature of the fusion reactions in the Sun will cause it to continue to brighten in the future.
A puzzle is the “faint young Sun”. Based upon our current understanding of astrophysics, at the time life originated on Earth, the Sun would have been 25% dimmer than at present. Why wasn’t the Earth an ice ball? There are various theories, but nobody really knows.