Analysis by Ian O’Neill
Wed Apr 7, 2010 04:02 PM ET
Brown dwarf-hunting astronomers have reported the discovery of a "failed star" located within 10 light-years from Earth. This makes it the nearest brown dwarf and one of ten nearest stellar objects to our solar system. Although its location isn’t entirely unexpected (it is thought that the galaxy is stuffed full of these objects), the chemical composition of its atmosphere is a bit of a conundrum.
UGPSJ0722-05 is all by itself, floating through interstellar space, possibly having formed there on its lonesome, or kicked out of its host star system by an ancient gravitational game of stellar pinball. How it got there may not ever be known, but its close proximity allows astronomers to carry out detailed analysis of the object.
And what they found was a surprise.
Philip Lucas at the University of Hertfordshire, UK, and his international team are part of the UKIDSS Galactic Plane Survey, a program that uses the UK Infrared Telescope (UKIRT) in Hawaii to hunt for objects that glow in infrared.
Brown dwarfs are too small to initiate nuclear fusion in their cores for long periods (so they’re not stars), but they are distinct from planets too. Their interior has a convective motion of material, ensuring it is constantly being mixed up, preventing chemicals from settling — chemical differentiation is a planetary trait. Therefore, brown dwarfs are often considered to be the “bridge” between the most massive planets (Jupiter-like gas giants) and the smallest stars.
As brown dwarfs are technically “failed stars,” they are naturally very dim in visible wavelengths, but they do emit in infrared, radiation the UKIDSS survey is sensitive to.
The UKIRT has already detected many cool brown dwarfs, but UGPSJ0722-05 appears to be the coolest ever discovered. It could have a surface temperature as low as 400 Kelvin, even cooler than the team’s previous record of slightly below 500 K.
Using the Gemini Observatory, follow-up spectroscopic analysis has detected methane and water vapor in its atmosphere. As pointed out by the arXiv blog, the presence of organic compounds will surely get astrobiologists talking.
Oddly, when looking at the spectrum from UGPSJ0722-05, there is an anomalous absorption line (i.e. a particular wavelength in the electromagnetic spectrum that is missing) that cannot be explained by our current understanding of brown dwarfs. Perhaps the UKIRT has discovered a new breed of brown dwarf; a very cool object with some chemical in its atmosphere that absorbs infrared radiation at a wavelength of 1.25 micrometers.
This is definitely one brown dwarf to keep a close eye on.
Image: Artist impression of a brown dwarf (Douglas Pierce-Price, Joint Astronomy Centre, Hawaii).
Source: “Discovery of a very cool brown dwarf amongst the ten nearest stars to the Solar System,” Lucas et al., 2010, arXiv:1004.0317v1 [astro-ph.SR] via arXiv blog.