This artist's impression shows the pair of brown dwarfs named CFBDSIR 1458+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.
Credit: ESO
This image of the brown dwarf binary CFBDSIR 1458+10 was obtained using the Laser Guide Star (LGS) Adaptive Optics system on the Keck II Telescope in Hawaii.
Credit: Michael Liu, University of Hawaii.
GARCHING: There is a new candidate for the coldest known star: a brown dwarf in a double system with about the same temperature as a freshly made cup of tea — hot in human terms, but extraordinarily cold for the surface of a star.
Observations with the European Southern Observatory’s (ESO) Very Large Telescope, along with two other telescopes, have shown that this object - identified as CFBDSIR 1458+10B - is cool enough to begin crossing the blurred line dividing small cold stars from big hot planets.
"We were very excited to see that this object had such a low temperature, but we couldn’t have guessed that it would turn out to be a double system and have an even more interesting, even colder component," said co-author Philippe Delorme of the Institut de planétologie et d’astrophysique de Grenoble in southeastern France of the paper published in The Astrophysical Journal.
Coldest brown dwarf has colder twin
Brown dwarfs are essentially failed stars: they lack enough mass for gravity to trigger the nuclear reactions that make stars shine. A double, or binary, system involves two astronomical objects that both satisfy the definition of planet - such as brown dwarfs - whilst being close together enough that they have a significant gravitational effect on each other compared with the effect of the star, or stars, they orbit.
The powerful X-shooter spectrograph on ESO’s Very Large Telescope (VLT) was used to show that the composite object was very cool by brown dwarf standards.
It is the dimmer member of a binary brown dwarf system located just 75 light-years from Earth. The pair seem to be orbiting each other at a separation of about three times the distance between the Earth and the Sun in a period of about thirty years.
Properties similar to an exoplanet's
CFBDSIR 1458+10B, the dimmer of the two dwarfs, has now been found to have a temperature of about 100 degrees Celsius — the boiling point of water, and not much different from the temperature inside a sauna.
“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," said lead author 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."
