Astronomers foresee end of our solar system
White dwarf contains an apocalyptic warning
Astronomers have captured a vision of the cataclysmic fate which awaits our solar system in about five billion years' time. Observation of a star system some 450m light years from Earth has revealed all that remains of a planetary system located around a star that was once eight times the size of our Sun.
Scientists have discovered a lonely dwarf star orbited by a small ring of metallic gas. The white dwarf is now a hundred times smaller than our Sun, burning with a surface temperature 22,000C.
"It's giving a glimpse of our future," said Tom Marsh, a physicist at the University of Warwick, writing today in Science.
The same fate awaits our Sun. As its hydrogen fuel runs out the Sun will eventually swell to 200 times its present size into a red giant.
At this stage it will destroy the inner planets, Mercury and Venus, and push the remaining planets and asteroids further out. Eventually the red giant will contract into the smaller, more dense, white dwarf.
The findings led Professor Marsh's team to speculate that the white dwarf system was a snapshot of how our own solar system would evolve. In five to eight billion years' time, when our Sun becomes a white dwarf, there will be no inner planets left and the space around the Sun will be left much emptier than it is now.
Asteroids, however, could be knocked towards the star by the large planets, such as Jupiter, that will survive much further away.
Unless humans manage to leave our planet, however, no one will be alive to see the rare rings of metal around our white dwarf Sun.
"The Earth would be extremely singed - the oceans will boil dry and we'll be left with a rather unpleasant rock," said Prof Marsh.
"If it doesn't manage to escape the red giant, it would go inside the envelope and be evaporated in the star itself."
White dwarfs often exist by themselves in the galaxy and are often orbited by clouds of gas. What makes the new discovery rare is that its disc of gas contains no hydrogen or helium, the two gases that make up more than 99% of the universe. The only elements scientists spotted were calcium, iron and magnesium - which imply the ring was not simply a cloud of interstellar gas.
Prof Marsh said the disc was likely to be the remains of a passing asteroid. In addition, astronomers were surprised at how close the ring of metallic gas was to the white dwarf; usually, nothing gets so close to such massive objects.
He said the evidence all pointed to a large, unseen planet lurking further out in the star system of the white dwarf.