The intense radiation from their stars causes hot Jupiters’ extremely high surface temperatures, and the calculations Hallakoun and her colleagues made about the paired white dwarf-brown dwarf system show just how hot things can get. Analyzing the brightness of the light emitted by the system, they were able to determine the orbiting brown dwarf’s surface temperature in both hemispheres. The dayside, they discovered, has a temperature of between 7,250 and 9,800 Kelvin (about 7,000 and 9,500 Celsius), which is as hot as an A-type star – Sun-like stars that can be twice as massive as the Sun – and hotter than any known giant planet. The temperature of the nightside, on the other hand, is between 1,300 and 3,000 Kelvin (about 1,000 and 2,700 Celsius), resulting in an extreme temperature difference of about 6,000 degrees between the two hemispheres.
A rare glimpse into an unexplored region
Hallakoun says that the system she and her colleagues discovered offers an opportunity to study the effect of extreme ultraviolet radiation on planetary atmospheres. Such radiation plays an important role in a variety of astrophysical environments, from star-forming regions, through primordial gas discs from which planets are formed around stars, to the atmospheres of planets themselves. This intense radiation, which can lead to gas evaporation and the breaking of molecules, can have a significant impact on both stellar and planetary evolution. But that’s not all.
“Merely one million years since the formation of the white dwarf in this system – a minuscule amount of a time on the astronomical scale – we have gotten a rare glimpse into the early days of this kind of compact binary system,” Hallakoun says. She adds that, while the evolution of single stars is fairly well known, the evolution of interacting binary systems is still poorly understood.
“Hot Jupiters are the antithesis of habitable planets – they are dramatically inhospitable places for life,” Hallakoun says. “Future high-resolution spectroscopic observations of this hot Jupiter-like system – ideally made with NASA’s new James Webb Space Telescope – may reveal how hot, highly irradiated conditions impact atmospheric structure, something that could help us understand exoplanets elsewhere in the universe.”