A team of French and American astronomers led by Michael Liu of the University of Hawaii has measured the temperature of a nearby brown dwarf star, CFBDS J1458+10B. Surprisingly, that brown dwarf is only about 100 degrees Celcius. That’s the boiling point of water, an amazingly low temperature even for a failed star like a brown dwarf.
Brown dwarfs are celestial objects that fall somewhere in size between large gas giant planets and small stars. They are too small to sustain the hydrogen fusion reactions that give ‘normal’ stars their glow. Because of this, they have been hard to find, let alone study. Over the past few decades, however, newer telescopes and technologies have facilitated the discovery of hundreds of brown dwarfs, including CFBDS J1458+10B.
CFBDS J1458+10B is actually one of a binary pair of brown dwarfs 75 light-years from Earth. The system, CFBDS J1458+10, is the coolest binary pair found to date, and the smaller, dimmer partner, 10B, is barely hotter than a steaming cup of coffee.
According to Liu:
At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets -- it could even have water clouds in its atmosphere.
To put things in perspective, our sun is about 5500 degrees Celcius, and it’s far from the hottest thing in the sky. The hottest blue supergiant stars can reach over 40,000 degrees Celcius!
This artist’s impression shows the pair of brown dwarfs named CFBDS J1458+10. Observations with ESO’s Very Large Telescope and two other telescopes have shown that this pair is the coolest pair of brown dwarfs found so far. The colder of the two components (shown in the background) is a candidate for the brown dwarf with the lowest temperature ever found. The two components are both about the same size as the planet Jupiter.Credit: ESO/L. Calçada.