'We're watching a solar system get destroyed'
22.10.2015 22:00
A real-life Death Star is pulverising a planet in a system far, far away.
Astronomers have discovered a large rocky object disintegrating as it spirals towards a distant white dwarf star while being ripped apart by gravity.
White dwarfs are the hot remnants of sun-like stars at the end of their lives that have swollen up and discarded their outer layers.
Lead scientist Andrew Vanderburg, from the Harvard-Smithsonian Centre for Astrophysics, said: 'This is something no human has seen before. We're watching a solar system get destroyed.'
The white dwarf acting out the role of the Death Star in the film Star Wars is about 570 light-years from Earth in the constellation Virgo.
Using Nasa's Kepler space telescope, scientists spotted the doomed planetary object from the dip in brightness caused when an orbiting body crosses in front of a star.
It was the first such object to be seen 'transiting' a white dwarf, they reported in the journal Nature.
The data revealed a regular dip every 4.5 hours, which places the object in an orbit about 520,000 miles from the white dwarf.
Evidence suggests the planetoid has about the same mass as Ceres, the largest body in the asteroid belt of our solar system.
Combining all the data, they found signs of several additional chunks of material, all in orbits between 4.5 and 5 hours.
This indicates the presence of a debris disc and the white dwarf's 'pollution' by heavy metals consumed from its rocky victim.
'We now have a 'smoking gun' linking white dwarf pollution to the destruction of rocky planets,' said PhD student Mr Vanderburg.
When a sun-like star reaches the end of its life, it swells into a red giant and sloughs off its outer layers.
The hot, Earth-sized core that remains is a white dwarf star, and generally consists of carbon and oxygen with a thin hydrogen or helium shell.
Sometimes, though, astronomers find a white dwarf that shows signs of heavier elements like silicon and iron in its light spectrum.
This is a mystery because a white dwarf's strong gravity should quickly submerge these metals.
'It's like panning for gold - the heavy stuff sinks to the bottom. These metals should sink into the white dwarf's interior where we can't see them,' explains Harvard co-author John Johnson (CfA).
Theorists speculated that white dwarfs showing evidence of heavy metals became 'polluted' when they consumed rocky planets or asteroids.
However, the evidence was often circumstantial. A fraction of polluted white dwarfs showed signs of surrounding debris disks, but the origin of the disks was uncertain.
This system shows all three: a polluted white dwarf, a surrounding debris disk, and at least one compact, rocky object.
What is certain is that the remaining objects will not last forever.
They are being vapourised by the intense heat of the white dwarf. They also are orbiting very close to the tidal radius, or distance at which gravitational tides from the white dwarf can rip apart a rocky body.
Within the next million years or so, all that will remain of these asteroidal bits is a thin metal dusting on top of an innocent-looking white dwarf star.
(dailymail.co.uk)
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