UGPS 0722-05

Lucas et al, 2010;
UKIDSS GPS, UKIRT

Larger image set.

UGPS 0722-05 is invisible to the unaided
Human eye in Earth's night sky but can be
detected using infrared telescopes (more).

The Brown Dwarf

UGPS 0722-05 is one of the coolest brown dwarfs known as of June 22, 2010 (along with DENIS J081730.0-615520), with a revised temperature estimate of around 207 to 287° Celsius -- 405 to 549° Fahrenheit, or 480 to 560° Kelvin (Ken Croswell, New Scientist, June 24, 2010; Lucas et al, 2010; and Artigau et al, 2010). The object is also the dimmest brown dwarf yet observed, as it is only around 0.000026 percent as luminous as our Sun, Sol. It radiates mostly at infrared rather than visible wavelengths, and so it would take some 3.8 million clones of this object to equal the Sun's radiative power. Although tentatively classified as a "T10," methane brown dwarf, its spectrum exhibits deeper water vapor and methane bands than other T-type dwarfs (plus "an unidentified absorption feature at 1.275 micrometers) and so may eventually be classified as the first example of a new spectral type (e.g., "Y"). In 2011, however, the brown dwarf was reclassified "as the T9 spectral standard" (Cushing et al, 2011). Roughly the size of Jupiter, UGPS 0722-05 is projected to have around 5 to 30 Jupiter-masses based on evolutionary modelling for similar brown dwarfs (Lucas et al, 2010; Ken Croswell, New Scientist, April 9, 2010; and David Matson, Scientific American Blog, April 9, 2010). Useful designations for this object include: UGPS J072227.51-054031.2, USPS J0722-05, and UGPS 0722-05.

Robert Hurt, IPAC, NASA

Larger illustration: Sol; M,L,T dwarfs;
and Jupiter.

At one billion years in age, large brown
dwarfs are reddish like the smallest
M-type stars, but cooler, dimmer T-dwarfs
are more magenta in hue (more).

Brown Dwarfs or Planets?

Extremely dim celestial objects, "... brown dwarfs are substellar objects with masses between those of giant planets like Jupiter and the least massive stars like Proxima Centauri. Some have been found as isolated objects, while others have been detected in orbit around stars or newly formed in star clusters. Since 1995, more than 100 methane brown dwarfs, or type-T dwarfs, have been found with spectra similar to that of the planet Jupiter, with effective surface temperatures between 500 and 1,300° Kelvin [227 to 1,027° Celsius, or 400 to 1,881° Fahrenheit]. The detection of even cooler objects has been eagerly anticipated by astronomiers and may open up a new arena for atmospheric physics and help to determine the formation rate of stars and brown dwarfs in our Galaxy as a function of both mass and of time" (Lucas et al, 2010, page 2).

© American Scientist



Artwork by Linda Huff
(for Martin et al, 1997)
used with permission.

Although brown dwarfs lack sufficient mass (at least 75-80 Jupiters) to ignite core hydrogen fusion, the smallest true stars (red dwarfs) can have such cool atmospheric temperatures (below 4,000° K) that it is difficult to distinguish them from brown dwarfs. While Jupiter-class planets may be much less massive than brown dwarfs, they are about the same diameter and may contain many of the same atmospheric molecules.

When brown dwarfs were just a theoretical concern, astronomers differentiated those hypothetical objects from planets by how they were formed. If a substellar object was formed the way a star does, from a collapsing cloud of interstellar gas and dust, then it would be called a brown dwarf. If it was formed by gradually accumulating gas and dust inside a star's circumstellar disk, however, it was called a planet. Once the first brown dwarf candidates were actually found, however, astronomers realized that it was actually quite difficult to definitely rule on the validity of competing hypotheses about how a substellar object was actually formed without having been there. This problem is particularly difficult to resolve in the case of stellar companions, objects that orbit a star -- or two.

© Anglo-Australian Telescope Board
(Image by Chris Tinney)



Wide field image with satellite trail.



"True-color" image of the brown
dwarf binary DENIS 1228-1547
(more information).

University of California at Berkeley astronomer Ben R. Oppenheimer, who helped to discover the other nearby brown dwarf, Gliese 229 b, is part of a growing group that would like to define a brown dwarf as an substellar object with the mass of 13 to 80 (or so) Jupiters. While these objects cannot fuse "ordinary" hydrogen (a single proton nucleus) like stars, they have enough mass to briefly fuse deuterium (hydrogen with a proton-neutron nucleus). Therefore, stellar companions with less than 13 Jupiter masses would be defined as planets.

Other prominent astronomers, such as San Francisco State University astronomer Geoffrey W. Marcy who also has helped to discover many extrasolar planets, note that there may in fact be many different physical processes that lead to the formation of planets. Similarly, there may also be many different processes that lead to the creation of brown dwarfs, and some of these may also lead to planets. Hence, more observational data may be needed before astronomers can determine how to make justifiable distinctions in the classification of such substellar objects.