Cosmic `Death Star` espied `wrecking` planet

Washington DC: A large, rocky object disintegrating in its death spiral around a distant white dwarf star has been spotted, hinting at 'Star Wars'-like cosmic Death Star effect.

The discovery also confirms a long-standing theory behind the source of white dwarf "pollution" by metals.

"This is something no human has seen before," says lead author Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics (CfA). "We're watching a solar system get destroyed."

The evidence for this unique system came from NASA's Kepler K2 mission, which monitors stars for a dip in brightness that occurs when an orbiting body crosses the star. 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 (about twice the distance from the Earth to the Moon). It is the first planetary object to be seen transiting a white dwarf.

The white dwarf star is located about 570 light-years from Earth in the constellation Virgo. 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.

Questions remain about the origin of these rocky objects. The most likely scenario is that an existing planet's orbit became unstable and it was kicked inward.

What is certain is that the remaining objects will not last forever. They are being vaporized 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.