A Giant Planet Candidate Transiting a White Dwarf

Kavli Affiliate: Saul A. Rappaport

| First 5 Authors: Andrew Vanderburg, Saul A. Rappaport, Siyi Xu, Ian Crossfield, Juliette C. Becker

| Summary:

Astronomers have discovered thousands of planets outside the solar system,
most of which orbit stars that will eventually evolve into red giants and then
into white dwarfs. During the red giant phase, any close-orbiting planets will
be engulfed by the star, but more distant planets can survive this phase and
remain in orbit around the white dwarf. Some white dwarfs show evidence for
rocky material floating in their atmospheres, in warm debris disks, or orbiting
very closely, which has been interpreted as the debris of rocky planets that
were scattered inward and tidally disrupted. Recently, the discovery of a
gaseous debris disk with a composition similar to ice giant planets
demonstrated that massive planets might also find their way into tight orbits
around white dwarfs, but it is unclear whether the planets can survive the
journey. So far, the detection of intact planets in close orbits around white
dwarfs has remained elusive. Here, we report the discovery of a giant planet
candidate transiting the white dwarf WD 1856+534 (TIC 267574918) every 1.4
days. The planet candidate is roughly the same size as Jupiter and is no more
than 14 times as massive (with 95% confidence). Other cases of white dwarfs
with close brown dwarf or stellar companions are explained as the consequence
of common-envelope evolution, wherein the original orbit is enveloped during
the red-giant phase and shrinks due to friction. In this case, though, the low
mass and relatively long orbital period of the planet candidate make
common-envelope evolution less likely. Instead, the WD 1856+534 system seems to
demonstrate that giant planets can be scattered into tight orbits without being
tidally disrupted, and motivates searches for smaller transiting planets around
white dwarfs.

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