An international team of astronomers has uncovered evidence of a minor planet being torn apart as it spirals around WD 1145+017, a white dwarf located approximately 570 light-years from Earth in the constellation Virgo.
In this artist’s conception, a dwarf planet vaporizes as it orbits a white dwarf star. Image credit: Mark A. Garlick / Harvard-Smithsonian Center for Astrophysics.
The evidence for this strange system came from NASA’s repurposed Kepler telescope, known as the K2 mission.
The data revealed a regular dip every 4.5 hours, which places the object in an orbit about 520,000 miles from WD 1145+017. It is the first planetary object to be seen transiting a white dwarf.
“This is something no human has seen before,” said team member Andrew Vanderburg, a graduate student at the Harvard-Smithsonian Center for Astrophysics.
“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,” added Vanderburg, who is the lead author of a paper published in the journal Nature.
Vanderburg and co-authors from the United States and the UK made additional observations using a number of ground-based telescopes: the 1.2-m and MINERVA telescopes at Whipple Observatory, the MMT, MEarth-South, and Keck.
Combining all the data, the astronomers found signs of several additional chunks of material, all in orbits between 4.5 and 5 hours.
The main transit was particularly prominent, dimming the star by 40%. The transit signal also showed a comet-like pattern.
Both features suggest the presence of an extended cloud of dust surrounding the fragment.
The total amount of material is estimated to be about the mass of Ceres, a dwarf planet and the largest asteroid in our Solar System yet known.
In addition to the strangely shaped transits, the astronomers found signs of heavier elements polluting the atmosphere of the white dwarf star, as predicted by theory.
This image shows the white dwarf star WD 1145+017 (blue object in the center). Image credit: Sloan Digital Sky Survey.
Due to intense gravity, such stars are expected to have chemically pure surfaces, covered only with light elements of helium and hydrogen.
For years, scientists have found evidence that atmospheres of some white dwarfs are polluted with traces of heavier elements such as calcium, silicon, magnesium and iron.
“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,” said co-author Dr John Johnson, also of the Harvard-Smithsonian Center for Astrophysics.
Astronomers have long suspected that the source of this pollution was an asteroid or a minor planet being torn apart by the star’s gravity.
“For the last decade we’ve suspected that white dwarf stars were feeding on the remains of rocky objects, and this result may be the smoking gun we’re looking for. However, there’s still a lot more work to be done figuring out the history of this system,” said Dr Fergal Mullally of SETI and NASA’s Ames Research Center, who was not involved in the study,
“This discovery highlights the power and serendipitous nature of K2. The science community has full access to K2 observations and is using these data to make a wide range of unique discoveries across the full range of astrophysics phenomena,” said Dr Steve Howell, also of NASA’s Ames Research Center.
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Andrew Vanderburg et al. 2015. A disintegrating minor planet transiting a white dwarf. Nature 526, 546-549; doi: 10.1038/nature15527
