It used to be simple. Star were the objects that shined. Planets go around stars. But the hunt for ever-colder star-like bodies two years ago led to a a new class of such objects. However, until now no one has known exactly how cool their surfaces really are – some evidence suggested they could be room temperature.
A new study shows that while these brown dwarfs, sometimes called failed stars, are indeed the coldest known free-floating celestial bodies, they are warmer than previously thought with temperatures about 250-350 degrees Fahrenheit. 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.
“If one of these objects was found orbiting a star, there is a good chance that it would be called a planet,” says Trent Dupuy, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics. 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.”
The new data also present new puzzles to astronomers that study cool, planet-like atmospheres.
Planets, stars, orin between? Additional objects discovered in the past two years remain to be studied and will hopefully shed light on some of these outstanding issues.