Caught in the Act: White Dwarf is Killing a Planet

Like any crime scene, there's forensic evidence that can be used to work out who committed the deed and how it was done. This goes for "crimes" on a cosmic scale too; particularly when a planet is being ripped to shreds by its host star.

During observations of the white dwarf WD 1145+017, astronomers headed by Andrew Vanderburg, of the Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, Mass., noticed the presence of several planetary pieces in orbit. They were detected by the Kepler space telescope (that is currently in its "K2" mission phase) and the total mass of debris is thought to be around the size of giant asteroid Ceres that is located inside our solar system's main asteroid belt.

These small planetary husks, all having orbits of between 4.5 to 4.9 hours, are too small to be seen by themselves; but their presence became known when the researchers detected huge dust clouds trailing them in their orbits. Follow-up observations by ground-based observatories were used to decipher what elements are inside the debris.

These dusty trails are accompanied by a debris disk surrounding WD 1145+017 and the dust contains magnesium, aluminium and silicon. And it's these elements that form the evidence for the white dwarf's "planetary murder" -- they are the ingredients for a small rocky planet, a planet that is being ripped apart and pounded to dust. This is the first time a white dwarf has been "caught in the act" of destroying its planetary system.

"This is something no human has seen before," said Vanderburg in a CfA news release. "We're watching a solar system get destroyed."

A white dwarf forms after a main sequence star, like our sun, runs out of fuel. The star puffs up into a red giant and then violently sheds its outer layers as powerful stellar winds. The resulting planetary nebula leaves a small white dwarf star in its wake.

For any surviving planets, life around a white dwarf star is harsh. If a planet or asteroid drifts too close, the star's intense tides can rip any rocky body to pieces, creating a dusty envelope of destruction.

Heavy elements like the ones found around WD 1145+017 should fall into the star pretty quickly -- they have short "settling times" according to astronomers -- so the fact that these elements are still in orbit suggests they were deposited there fairly recently (within the past million years), a sign that a rocky planetary body (or bodies) is being pulverized to dust by the star's tidal forces right now.

Dusty white dwarfs have been studied before, and there has been circumstantial evidence that this dust has come from pulverized planets, but this is the first time a planetary body has been seen in orbit around a white dwarf while being destroyed.

"We now have a 'smoking gun' linking white dwarf pollution to the destruction of rocky planets," added Vanderburg.

Read more at Discovery News