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Dying star is blasting nearby planet to smithereens

Astronomers learn the fate of planets orbiting a white dwarf, and it's not pretty. 

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Mark A. Garlick/Harvard-Smithsonian Center for Astrophysics/AP
This artist's rendering provided by the Harvard-Smithsonian Center for Astrophysics shows an asteroid slowly disintegrating as it orbits a white dwarf star. On Wednesday, researchers at the Harvard-Smithsonian Center for Astrophysics announced they have discovered a rocky object coming apart in a death spiral around a white dwarf star in the Constellation Virgo. They used NASA's Kepler spacecraft to make the discovery, then followed up with ground observations.

NASA’s Kepler K2 mission has shed some light on what happens to nearby planets when a star dies. And no – this is not the synopsis for a Star Wars movie.

After a star burns through its nuclear fuel and dies, the shriveled stellar corpse, known as a white dwarf, collapses in on itself. The remaining core of the white dwarf emits such a strong gravitational pull, at least 350,000 times the strength of Earth’s gravity, that entire planets can be sucked in. 

Andrew Vanderburg, a graduate student at the Harvard-Smithsonian Center for Astrophysics (CfA), was viewing such a white dwarf star when he saw a planet some 520,000 miles away from the dead star (twice the distance between the Earth and the moon) start to dip and flicker away. Mr. Vanderburg and his colleagues soon realized they were witnessing a dead star eat a planet. 

“The white dwarf was ripping it apart by its extreme gravity and turning it into dust,” Vanderburg told Smithsonian.com.

“This is something no human has seen before,” Vanderburg said in a statement Wednesday. “We’re watching a solar system get destroyed.”

And because the gravitational pull of a white dwarf is so strong, the star’s heavy elements like silicon and iron should be sucked deep into the dwarf’s core. But surprisingly, astronomers say they often see signs of these heavier elements in the white dwarf’s light spectrum.

“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,” CfA co-author John Johnson explains in a statement.

Astronomers have previously predicted that “white dwarfs showing evidence of heavy metals became ‘polluted’ when they consumed rocky planets,” much like the consumption Vanderburg witnessed.

“We now have a ‘smoking gun’ linking white dwarf pollution to the destruction of rocky planets,” says Vanderburg.

Researchers say Earth and Mars can expect the same grim fate, when our sun runs out of energy billions of years from now.

“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,” says CfA’s statement. “This discovery also confirms a long-standing theory behind the source of white dwarf ‘pollution’ by metals.”

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