Astronomers have discovered a brown dwarf that is more than 99 % hydrogen and helium.
Artist’s impression shows BD+01 2920B in the foreground, on the right hand side, with its host star in the background. The color and banded atmosphere of the brown dwarf result from atmospheric gases and turbulence (J. Pinfield / RoPACS network / University of Hertfordshire)
This brown dwarf, described in the Monthly Notices of the Royal Astronomical Society, is ultra-cool, having a temperature of just 400 degrees Celsius. Its discovery could be a key step forward in helping astronomers distinguish between brown dwarfs and giant planets.
Brown dwarfs are star-like objects with insufficient mass to ignite hydrogen fusion in their cores. Over time they cool to temperatures of just a few hundred degrees. Formed like stars from the collapse of a giant molecular cloud a few hundred light years across, brown dwarfs in binary systems such as this have the same atmospheric chemistry as their host star.
In contrast, giant planets form with a more diverse chemistry. Those in our own Solar system first formed as large solid cores, which then accreted gas from the disk around them. This led to a different chemistry in their outer layers. For example, when the Galileo spacecraft entered Jupiter’s atmosphere in 1995, it found the proportion of heavier elements to be three times higher than in the Sun. Such differences allow astronomers to discriminate between planets and brown dwarfs and reveal their formation mechanisms.
The astronomers led by Dr. David Pinfield of the University of Hertfordshire detected the brown dwarf using data from the Wide-field Infrared Explorer (WISE) satellite, the UK Infrared Telescope (UKIRT) in Hawaii and the Visible and Infrared Survey Telescope for Astronomy (VISTA) in Chile.
The newly discovered object, known as BD+01 2920B, is about 35 times more massive than Jupiter. It orbits its host star at a distance of 390 billion km or about 2600 times the average distance from the Earth to the Sun.
“The new work has been made possible by combining data from ground- and space-based surveys,” Dr. Pinfield explained. “Surveys from telescopes like VISTA and UKIRT and orbiting observatories like WISE are giving us an unprecedented view of ‘ultra-cool’ bodies in our neighborhood.”
“By finding these rare objects in orbit around nearby stars, we get a handle on the bigger picture, that we live in a galaxy where both giant planets and brown dwarfs are commonplace,” the astronomer concluded.
