How Much Longer Will the Sun Survive?

Question posed by max jon.

The lifetime of a star is determined by its mass. The more mass a star has - and this sometimes feels like it goes against intuition - the shorter its life will be.

The most massive stars in the universe, called hypergiants, have many tens of times the mass of our Sun, are in the region of a few hundred thousand times as luminous, and last for only a few million years. The largest star we know of, VY Canis Majoris (VY CMa to its mates), has somewhere between 30 and 40 times the mass of our sun, and burns 450,000 times as bright. In terms of size, if it occupied the position currently inhabited by our own Sun, its surface would be well beyond the orbit of Mars, with some astronomers calculating it to be large enough to reach as far out as Saturn's orbit. It's expected to go hypernova some time in the next 100,000 years.

It can be difficult to imagine how breathtakingly massive these things are, so this video might help:

At the other end of the scale, the smallest stars that we know of, red dwarfs, have less than half the mass of our Sun, and can burn for hundreds of billions of years- some estimates even suggest that they can last for trillions of years. There are no red dwarf stars coming to the end of their life span anywhere in the universe: there simply hasn't been enough time.

Somewhere between these two extremes is our Sun. With its 2,000,000,000,000,000,000,000,000,000,000 (that's 2 nonillion) kg of fuel packed into a volume of space 1 million km across, it is unofficially known as a yellow dwarf* star (its official classification is 'G2V', but that's less catchy) and as such has an expected life span of around 10 billion years. It's been going strong now for something like 4.5 billion years, so it's got a good 5 billion left in it yet.

If you'd like to know what'll happen to the Sun (and the Earth) when it dies, this post would be a good place to start.

* Why's it green, then?


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