NASA’s Kepler space telescope has brought in new evidence of a tiny, rocky ‘planet’ being destroyed as it is swallowed by a white dwarf star, recreating cannibalism of the dead stars in the solar syste, said researchers.
It means the stars like our Sun, when aged, are burnt out and lose thier gravity before vaporising into smaller sizes. “We are for the first time witnessing a miniature planet ripped apart by intense gravity, being vaporised by starlight and raining rocky material onto its star,” said researcher Andrew Vanderburg of Harvard-Smithsonian Centre for Astrophysics.
Aged stars puff up into red giants and then gradually lose about half their mass down to 1/100th of their original size to roughly the size of Earth, becoming a white dwarf.
The devastated planetesimal, or cosmic object formed from dust, rock, and other materials, is estimated to be the size of a large asteroid and it orbits its white dwarf, WD 1145+017, once every 4.5 hours. This orbital period places it extremely close to the white dwarf and its searing heat and shearing gravitational force.
During its first observing campaign from May 30 to Aug. 21, 2014, K2 trained its gaze on a patch of sky in the constellation Virgo, measuring the minuscule change in brightness of the distant white dwarf. When an object transits, or passes in front of a star from the vantage point of the space telescope, a dip in starlight is recorded. The periodic dimming of starlight indicates the presence of an object in orbit about the star.
Vanderburg 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.
“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,” said Vanderburg.
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.
Analysis of the star’s atmospheric composition was conducted using observations made by the University of Arizona’s MMT Observatory near Tucson.