WD 0032-317B, a brown dwarf orbiting around the hot, low-mass white dwarf WD 0032-317, is estimated to have a surface temperature of about 8,000 K and a day-to-night temperature difference of about 6,000 K.
“When a planet orbits very close to a star, the strong tidal forces it experiences tend to synchronize its orbital and rotational periods, permanently locking one side of the planet facing the star — the so-called tidal locking,” said Weizmann Institute of Science astronomer Na’ama Hallakoun and colleagues.
“The planet’s ‘day-side’ hemisphere is then continuously exposed to direct radiation.”
“Depending on the heat redistribution on the planet surface, this can lead to extreme temperature differences between the day and night sides of the planet, and to thermal dissociation of the molecules on the planet’s day side.”
“Out of the few dozen ultra-hot giant planets discovered so far, only KELT-9b receives ultraviolet radiation high enough in amount for molecular dissociation, with a day-side temperature of 4,600 K.”
The white dwarf WD 0032-317 was observed in the early 2000s and was considered likely to be part of a double white dwarf system.
In the new study, Dr. Hallakoun and colleagues analyzed follow-up observations of the system from the Ultraviolet and Visual Echelle Spectrograph (UVES) on ESO’s Very Large Telescope.
They found that a brown dwarf, WD 0032-317B, not another white dwarf, likely orbits the main star.
WD 0032-317B has a mass of 75-88 times that of Jupiter and was probably enclosed in a common gas envelope with the white dwarf until around one million years ago.
The white dwarf has a very high surface temperature of around 37,000 K and the companion brown dwarf orbits very closely, receiving an intense amount of ultraviolet radiation and making it over 2,000 K hotter than the Sun.
“WD 0032-317B always shows the same side to the white dwarf,” the astronomers said.
“This means that the brown dwarf…
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