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We won鈥檛 be there to see it. But when our sun reaches the end of its life, it will produce a massive and expanding burst of light called a planetary nebula that astronomers have until now considered unlikely for our sun.

That鈥檚 because as stars go, ours has been considered too small to make it happen. Now, a new model of how our star will evolve has challenged this, showing that it is probably just massive enough after all to generate a planetary nebula that will last 10,000 years.

When stars die, they first balloon and brighten, becoming a stellar object called a red giant. In around 5 billion years, our sun is expected expand out to where Venus orbits now. 鈥淚t will be curtains for the Earth at that point,鈥� says at the University of Manchester in the UK, and a member of the team re-analysing the sun鈥檚 evolutionary course.

Pushing the limit

If the cores of dying stars heat up fast enough 鈥� typically within around 10,000 years 鈥� they can provide enough heat to begin ionising gas in the dispersing cloud of debris that is blown away from the core before all the material is lost to outer space. This is what produces the light in a planetary nebula.

But until now, it had been assumed that cores of dying stars only produce enough heat to do this if they are large, and that our own sun would heat up too slowly to produce a nebula. 鈥淭he assumption has been that all the interstellar dust and gas would be gone by the time it became hot enough to ionise it,鈥� says Zijlstra.

But more recent work on the fates of cores in dying stars suggest that they heat up three times faster than previously thought. Zijlstra and his colleagues included these revised trajectories in their model. It predicted that after all, our sun would heat up just fast enough to produce a planetary nebula. 鈥淲e鈥檙e right at the limit, and if our sun was a fraction less massive, it wouldn鈥檛 happen,鈥� he says.

Blaze of glory

Besides revealing that our own sun will go out in an unexpected blaze of glory, the model applied by Zijlstra and his colleagues helps resolve what he says is a clash between theory and observation of planetary nebulae in distant galaxies.

Elliptical galaxies are among the oldest in the universe, with all their largest stars already burnt out and only small, old stars remaining. According to existing theory, these should be too small to generate planetary nebulae, yet astronomers see them.

The new model resolves this by showing that like our sun, these older, smaller stars do produce heat fast enough to generate planetary nebulae. 鈥淥ur findings agree with you seeing them in old galaxies, and we explain the brightness very well,鈥� says Zijlstra.

Read more: Hiding in plain sight: The mystery of the sun鈥檚 missing matter