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Exoplanets: Giant planet candidate orbiting a white dwarf


September 17, 2020

Evidence of a Jupiter-sized planet orbiting a white dwarf is reported in a study in this week’s Nature. The findings support the theory that massive planets can migrate into a close orbit and survive during the creation of a white dwarf.

A white dwarf is the collapsed core of a Sun-like star, left over after shedding its atmosphere. They are typically the size of Earth, with masses about half that of our Sun. Most exoplanets discovered so far orbit stars that will eventually form white dwarfs. As these stars use up their reserves of hydrogen, they first evolve into red giants, expanding and then engulfing any planets in a close orbit, making it unlikely that any close planets could remain to orbit the star in its white dwarf phase. Although some white dwarfs show evidence that planets might be found in their orbit, no intact planets have previously been detected.

Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission, Andrew Vanderburg and colleagues report the discovery of a giant planet candidate (designated WD 1586 b) transiting the white dwarf WD 1856+534 every 1.4 days. The authors estimate that WD 1586 b is no more than 14 times the mass of Jupiter.

The authors assume that to avoid destruction when the progenitor star of WD 1856+534 evolved into a red giant, WD 1586 b must have been more than 1 astronomical unit (the distance between Earth and the Sun) away from the host star. However, it is unclear how it arrived in the close orbit observed, estimated to be 4 solar radii from the white dwarf (or roughly 20 times closer to the white dwarf than Mercury is to the Sun). On the basis of their simulations, the authors suggest that when the star evolved into a white dwarf, WD 1586 b was thrown into a close orbit due to interactions with other planets in the remnant planetary system.

doi: 10.1038/s41586-020-2713-y

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