What will happen at the end of our sun's life? You may have heard that stars typically explode in a gigantic supernova when they reach their final days, but that will only happen to stars a fair bit bigger than our sun (typically about eight times more massive). Stars about the size of our sun have a less violent, but nonetheless exciting fate.
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The first thing that will happen, is that the Sun will expand many times larger than it is today, and become what's known as a red giant. These are old stars who are running out of hydrogen to burn in their cores and are starting to burn helium. When our sun reaches this stage, it will swell up and likely swallow Mercury, Venus and likely Earth as well - luckily this is about 5 billion years from now, so we have time to boil a cup of tea.
As time goes on, it will start thermally pulsating and become unstable, losing material in huge amounts while rapidly changing in temperature and brightness. It is at this stage that our sun will have become a type of star known as a Mira variable, a brilliant type of object that is named after the star Mira. Mira variables are very important objects to study, particularly as they shine a window into what the sun will be like when it gets older.
Mira variables are fascinating objects, both to learn about and do astronomy with. These stars vary in brightness over the course of a year, with some changing in brightness by more than 1000 times. In fact, they are the most popular objects for amateur astronomers with a backyard telescope to study.
In the US, a group known as the American Association of Variable Star Observers (AAVSO) have collected over 35 million observations of stars such as these, more than a million a year. These observations are invaluable to professional astronomers who study these stars, such as myself, as we can look at these changes in brightness and reverse engineer how the star works inside.
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Mira, in particular, is one of my favourite objects to study, as it is not just one star but two. The other star is much smaller and fainter than its big sibling; some think it may even be a white dwarf, which is the final fate of a star like the sun once it has finished burning material in its core and lost most of its gas.
This companion star is starting to receive most of the material that's shedding off of Mira, and forming into a disc surrounding it - a disc that may even be forming planets.
I recommend that if you have a telescope at home, maybe try doing your own astronomical observations by finding one of these stars, for example Mira (visible later in the year around October and November), R Hya or R Car (visible now) and measuring its brightness by taking a picture of it and looking at it on a computer (maybe have a search on the internet how to do this).
You can then come back a few weeks or months later and see whether it has changed significantly in brightness - and just like that you are doing valuable astronomical research. Magical.
- Jonah Hansen is a PhD student specialising in space interferometry and Mira variables at Mount Stromlo Observatory, at the Australian National University.
