Brown dwarf hotter than the Sun spotted 1,400 light-years away from Earth

The brown dwarf circles its host star so closely that its temperature incredibly exceeds that of our Sun.
Mrigakshi Dixit
Artist’s conception of a brown dwarf.
Artist’s conception of a brown dwarf.


The universe is replete with strange and unusual cosmic objects. Just a few days back, astronomers announced the discovery of the fastest runaway stars in the Milky Way galaxy. 

And now they've discovered a scorching planet-like object that's hotter than our Sun. 

The observations are led by researchers from the Weizmann Institute of Science in Israel.

A super hot brown dwarf 

The object in the spotlight is WD0032-317B, a brown dwarf located around 1,400 light-years from Earth. Brown dwarfs are stellar objects that are between the size of a giant planet like Jupiter and a small star.

Its mass is estimated to be between 75 to 88 Jupiters. 

The brown dwarf circles its host star so closely that its temperature incredibly exceeds that of our Sun. According to Live Science, it has a 2.3-hour orbital period around its host star.

The brown dwarf was found orbiting WD0032-317, a low-mass white dwarf. The star has just 40 percent the mass of our Sun, but it is significantly hotter, with temperatures reaching 37,000 Kelvin. In comparison, the surface of the sun is roughly 5,778 K (5,504 degrees Celsius).

Because of its proximity to the star, the brown dwarf typically burns at 8,000 K (7,727 degrees Celsius), which is substantially higher than the temperature of other known brown dwarfs. That's hot enough to cause any atmospheric molecules to disintegrate into their constituent atoms. 

Tidally locked

The brown dwarf is tidally locked, which means that one side of the object is always facing its star and the other is always facing away.

This results in temperatures varying from 7,250 to 9,800 K (6,976 to 9,526 degrees Celsius) on one side facing the star, while the one away experiences relatively lower temperatures about 1,300 to 3,000 K. 

The authors note that the hot side's temperatures are almost 5,100 K (4,826 degrees Celsius) hotter than any other known large exoplanet. As a result of these extreme temperatures, WD0032-317B is the hottest known brown dwarf to date.

WD0032-317 was discovered in early 2000 using data from the European Southern Observatory's Very Large Telescope. 

The research might assist to shed light on the relationship between blazing stars and their impact on orbiting objects. 

The study has been approved for publication in the journal Nature Astronomy and is now available on the arXiv pre-print service.

Study abstract:

Planets orbiting close to hot stars experience intense extreme-ultraviolet radiation, potentially leading to atmosphere evaporation and to thermal dissociation of molecules. However, this extreme regime remains mainly unexplored due to observational challenges. Only a single known ultra-hot giant planet, KELT-9b, receives enough ultraviolet radiation for molecular dissociation, with a day-side temperature of ~4,600K. An alternative approach uses irradiated brown dwarfs as hot-Jupiter analogues. With atmospheres and radii similar to those of giant planets, brown dwarfs orbiting close to hot Earth-sized white-dwarf stars can be directly detected above the glare of the star. Here we report observations revealing an extremely irradiated low-mass companion to the hot white dwarf WD0032-317. Our analysis indicates a day-side temperature of ~8,000K, and a day-to-night temperature difference of ~6,000K. The amount of extreme-ultraviolet radiation (with wavelengths 100-912Å) received by WD0032-317B is equivalent to that received by planets orbiting close to stars as hot as a late B-type stars, and about 5,600 times higher than that of KELT-9b. With a mass of ~75-88 Jupiter masses, this near-hydrogen-burning-limit object is potentially one of the most massive brown dwarfs known.

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