Hotter Than Stars: Record-Breaking Brown Dwarf Discovered

An international team of astronomers has announced the discovery of a previously unknown brown dwarf named WD0032-317B. What makes this finding interesting is that its surface temperature exceeds the temperature of most stars.
A system of white and brown dwarfs as imagined by an artist. Credit: NOIRLab/NSF/AURA/M. Garlick

Brown dwarfs are often referred to as failed stars. They have a significantly greater mass than the largest planets, but still not enough to sustain continuous hydrogen fusion reactions (although deuterium and lithium fusion reactions can occur in their cores).

The newly discovered brown dwarf is a companion to a white dwarf located 1,400 light-years away from Earth. Its mass is 2.5 times smaller than that of the Sun, and its surface temperature is approximately 37,000°C.

Back in the early 2000s, astronomers noticed something “pulling” the white dwarf. Initially, the presence of a stellar companion was suspected. However, during new observations, it was revealed that it was actually a brown dwarf with a mass ranging from 75 to 88 times that of Jupiter.

The brown dwarf orbits at a very close distance to the white dwarf. It completes one revolution around it in just 2.3 hours and is in a tidal capture. Due to this proximity, the temperature of the illuminated hemisphere of the brown dwarf ranges from 7,000 to 9,500°C, while the temperature of the nighttime hemisphere ranges from 1,000 to 2,700°C. For comparison, the temperature of the Sun’s surface is 6,000°C. Currently, WD0032-317B is the hottest known brown dwarf among astronomers.

It is worth noting that recently astronomers discovered a white dwarf whose core began transforming into diamond.