Cool brown dwarf could have water-based clouds

Posted by Kate Taylor

We normally think of stars as hot - but scientists using ESO's Very large telescope say they've found a pair of cool brown dwarfs, one of which is no hotter than a sauna or a cup of tea.

Indeed, says the team, it may be so cool that it actually has water-based clouds.

In fact, brown dwarfs are essentially failed stars, in that they lack enough mass for gravity to trigger nuclear reactions.

The newly discovered CFBDSIR 1458+10B is part of a binary brown dwarf system located just 75 light-years from Earth, and is the coolest yet discovered. Its temperature was determined using the VLT's X-shooter spectrograph.

"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," says Michael Liu of the University of Hawaii's Institute for Astronomy.

"In fact, once we start taking images of gas-giant planets around Sun-like stars in the near future, I expect that many of them will look like CFBDSIR 1458+10B."

But CFBDSIR 1458+10B may have some competition as the coolest known star. The Spitzer Space Telescope recently identified two other very faint objects as possible contenders - although their temperatures have not been measured so precisely.

Future observations should settle the matter. Liu and his colleagues are planning to observe CFBDSIR 1458+10B again to better determine its properties and to begin mapping the binary's orbit, which, after about a decade of monitoring, should allow astronomers to determine its mass.