The Coolest Dwarf

The infrared deep-sky survey now being carried out by the United Kingdom Infrared Telescope is only 5% done, but already astronomers looking at its data have found the coolest solitary brown dwarf ever seen.

The object, named ULAS J0034–00, is located in Cetus. A followup analysis by the Gemini Observatory of steam and methane features in its infrared spectrum pegs its temperature at just 600 to 700 kelvins (330° to 430°C, or 620° to 800°F). This puts it at the very bottom of spectral class T — or perhaps in the still-cooler proposed spectral class Y, for which no other object has yet been found.

Estimated to be 50 light-years away, ULAS J0034–00 has a near-infrared magnitude of about 18.5 and a likely mass of 15 to 30 Jupiters. Like all brown dwarfs, it should have just about Jupiter’s diameter.
This image is from the infrared survey. Paradoxically, T dwarfs appear blue in composite-color infrared images; the molecular absorption bands in their spectra block the longer (“redder”) infrared wavelengths.

All comments must follow the Sky & Telescope Terms of Use and will be moderated prior to posting. Please be civil in your comments. Sky & Telescope reserves the right to use the comments we receive, in whole or in part, and to use the commenter’s username, in any medium. See also the Terms of Use and Privacy Policy.


This site uses Akismet to reduce spam. Learn how your comment data is processed.