Among unusual worlds in the Milky Way, planets orbiting white dwarf stars stand out as especially intriguing. White dwarfs represent the dense cores left after Sun-like stars exhaust their fuel, expand into red giants, shed outer layers, and collapse. This fate awaits the Sun in roughly five billion years, making such planets valuable for understanding the Solar System’s future.
Astronomers using the James Webb Space Telescope obtained the first atmospheric data for the giant planet WD 1856b circling a white dwarf. The results, reported in Nature, revealed temperatures much higher than anticipated.
“The instant we saw WD 1856b’s spectrum, which shows a colossal drop in the effective size of the planet at longer infrared wavelengths, we were like ‘Wow! What the heck is going on here?'” said astronomer Ryan MacDonald of the University of St Andrews.
White dwarfs form when stars up to eight solar masses leave the main sequence. The core collapses under gravity after fusion ceases, creating an object with up to 1.4 solar masses compressed to Earth-like size. In our system, the Sun’s red giant phase may reach Mars’ orbit. Mercury and Venus would be engulfed, Earth’s survival remains uncertain, and outer planets would likely persist before shifting outward due to reduced stellar mass.
Many planets have been detected around white dwarfs, prompting questions about their survival through stellar death. Studying their atmospheres via transits is challenging here because WD 1856b, 82 light-years distant, is seven times larger than its host. The transit covers 56 percent depth and lasts only eight minutes, requiring new analysis methods.
Researchers expected temperatures near -113 degrees Celsius, comparable to Jupiter. Instead, readings reached about 126 degrees Celsius.
