To reach such low surface temperatures after cooling for billions of years means that these objects can only have about 5 to 20 times the mass of Jupiter.
Unlike the Sun, these objects' only source of energy is from their gravitational contraction, which depends directly on their mass.
Trent Dupuy, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics, said that if one of these objects was found orbiting a star, there will be a good chance that it would be called a planet.
But because they probably formed on their own and not in a proto-planetary disk, astronomers still call these objects brown dwarfs even if they are 'planetary mass.'
Characterizing these cold brown dwarfs is challenging because they emit most of their light at infrared wavelengths, and they are very faint due to their small size and low temperature.
The study has been published in the Science Express online.
--ANI (Posted on 06-09-2013)