Recently, astronomers detected one of the largest known brown dwarfs, an object with a mass between 75 and 90 times that of Jupiter and a temperature of 8,000 K (about 7.725° Celsius).
For comparison, the surface of the Sun only has a temperature of 5,772 K (about 5500° Celsius). Astronomers observed a very hot, extremely large brown dwarf using the European Southern Observatory’s Very Large Telescope in 2019 and 2020. Their findings were recently published in the journal Nature Astronomy.
What is a brown dwarf?
Brown dwarfs occupy an odd position between planets and stars. These objects, though larger than gas giants like Jupiter, are smaller than small stars. Brown dwarfs are also sometimes referred to as failed stars, as they do not have the mass necessary for stars to burn hydrogen for nuclear fusion.
The latest research team takes a more respectful approach, calling the object (WD 0032-317B) “irradiated Jupiter-like.” The brown dwarf orbits a white dwarf star 1,406 light-years from Earth. The team suggests that the brown dwarf was in a gas envelope with its partner, the white dwarf, until about a million years ago.
Brown dwarfs’ high temperature is particularly noteworthy, as they are usually the coldest, dimmest objects in the Hertzsprung-Russell diagram of stars’ luminosities and effective temperatures.
The brown dwarf is tidally locked with its white dwarf neighbor, meaning the scorching day side always faces the white dwarf with a surface temperature of about 37,000 K (about 36725° Celsius). The night-side temperature of the brown dwarf is much cooler than the star-facing side, around 2,000 K (about 1725° Celsius).
Comparing brown dwarfs with hot Jupiters, gas giant exoplanets orbiting their host stars, making them very hot is not a new phenomenon. This analogy has proven more pertinent than previously realized, as astronomers found evidence of polar storms and stripes similar to those seen in brown dwarfs on Jupiter in 2021. But dwarfs can also be colder than the boiling point of water. The coldest known brown dwarf has a cold temperature of -23° Celsius, which by some definitions means it is not a brown dwarf but an unusual exoplanet.
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