Astronomers announced today (October 21) that they have spotted a large, rocky object disintegrating in its death spiral around a distant white dwarf star. The discovery, which appears in the October 22 issue of the journal Nature, supports a long-held theory that white dwarfs are capable of cannibalizing possible remnant planets that have survived within its solar system.
Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics (CfA) is the lead author of the paper. Vanderburg said:
This is something no human has seen before. We’re watching a solar system being destroyed.
We are for the first time witnessing a miniature “planet” ripped apart by intense gravity, being vaporized by starlight and raining rocky material onto its star.
The white dwarf star is located about 570 light-years from Earth in the constellation Virgo. As stars like our sun age, they puff up into red giants and then gradually lose about half their mass, shrinking down to 1/100th of their original size to roughly the size of Earth. This dead, dense star remnant is called a white dwarf.
The devastated planetesimal – a kind of “mini-planet” formed from dust, rock, and other materials – is estimated to be the size of a large asteroid, and is the first planetary object to be confirmed transiting a white dwarf.
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), extremely close to the white dwarf and its searing heat and shearing gravitational force.
A research team found an unusual, but vaguely familiar pattern in the data. While there was a prominent dip in brightness occurring every 4.5 hours, blocking up to 40 percent of the white dwarf’s light, the transit signal of the tiny planet did not exhibit the typical symmetric U-shaped pattern. It showed an asymmetric elongated slope pattern that would indicate the presence of a comet-like tail. Together these features indicated a ring of dusty debris circling the white dwarf, and what could be the signature of a small planet being vaporized. Vandenburg said:
The eureka moment of discovery came on the last night of observation with a sudden realization of what was going around the white dwarf. The shape and changing depth of the transit were undeniable signatures.
In addition to the strangely shaped transits, Vanderburg and his team found signs of heavier elements polluting the atmosphere of WD 1145+017, as predicted by theory.
Due to intense gravity, white dwarfs are expected to have chemically pure surfaces, covered only with light elements of helium and hydrogen. For years, researchers have found evidence that some white dwarf atmospheres are polluted with traces of heavier elements such as calcium, silicon, magnesium and iron. Scientists have long suspected that the source of this pollution was an asteroid or a small planet being torn apart by the white dwarf’s intense gravity.
Bottom line: Astronomers have spotted a “mini-planet” disintegrating around a distant white dwarf star. The discovery supports a long-held theory that white dwarfs are capable of cannibalizing remnant planets that have survived within its solar system. The paper appears in the October 22, 2015 issue of Nature