Astronomy – Death of a star

When stars like our sun enter very old age, they leave behind their burnt-out cores which we call ‘white dwarfs’. As the white dwarf star dies, its planets tend to suffer the same fate. The evidence of this chaos can be found in and around the dying star’s atmosphere.

Astronomers at UCLA have been studying a nearby white dwarf star named G238-44 in great detail. The star, which lies about 86 light years from us, shows evidence of the star’s cosmic cannibalism. And this could be the ultimate fate of our own sun!

If G238-44 was in the place of our sun, it would have cannibalised all planets, asteroids and comets out to the Kuiper Belt. The inner edge of the Kuiper Belt begins at the orbit of Neptune, about 30 AU from the Sun.

Using data collected from NASA’s retired Far Ultraviolet Spectroscopic Explorer, the Keck Observatory’s High-Resolution Echelle Spectrometer in Hawaii, and the Hubble Space Telescope’s Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph, they found and measured the presence of nitrogen, oxygen, magnesium, silicon and iron, as well as other elements.

The iron would have come from rocky planets like Mercury, Venus, Earth and Mars, and gives us a clue as to the worlds that used to orbit around G238-44. The high amount of nitrogen would indicate that a number of icy bodies such as comets would also have been devoured.

Our own sun is expected to follow the same path in about five billion years’ time. The first stage is when it balloons out into a red giant, where it will swallow up all the inner planets – including Earth. Eventually, it will lose its outer layers which will form a ‘planetary nebula’ of gas and dust. Once this nebula starts drifting away, we are left with the white dwarf.

Due to the immense gravity, the outer planets will be torn apart and the asteroids and comets which aren’t pulled into the star will be pushed out into the cosmos. It is thought that some of these icy bodies are responsible for delivering water to far-flung worlds – sparking the conditions necessary for life.

Perhaps in billions of years, astronomers on a world very far from us will look out at our dying star and spot the remains of Earth in its fading embers.