When sufficiently large clouds of dust and gas collapse under their own gravity, the temperatures and pressures generated at their hearts are large enough to trigger nuclear fusion. When that happens, a star is born.
However, the original cloud must have a mass greater than a specific threshold for this to happen. When the cloud is too small, the conditions inside never trigger fusion and the star never switches on. These failed stars are called brown dwarfs and they are not as unfamiliar as they might sound.
Brown dwarfs have much in common with the planet Jupiter, which is thought to have about the same size, mass, and composition as these objects. If Jupiter had formed alone in the depths of space, it too would be classified as a failed star.
Brown dwarfs were first discovered in 1995, and since then astronomers have found several hundred others orbiting other stars, orbiting each other or simply wandering alone. No one knows how many there ought to be but the best guestimate is that there may be about a third as many brown dwarfs as there are stars, meaning that most remain undiscovered.
So the news from Philip Lucas at the University of Hertfordshire and a few pals that they have discovered one of these objects nearby is not entirely unexpected. They call this object, somewhat unromantically, UGPSJ0722-05.
Lucas and company say this body has a radius about the same as Jupiter’s and a similar temperature of about 500K. That makes it the coolest brown dwarf ever discovered. Spectroscopic studies of its atmosphere show signs of methane and even water vapor.
This combination of temperature and evidence of water will make UGPSJ0722-05 a fascinating talking point for astrobiologists. Jupiter’s beautiful coloured bands are the result of organic molecules in its atmosphere. So the question of what could be floating around UGPSJ0722-05’s atmosphere will be hotly debated.
Part of this debate will focus on another interesting observation about this body: its atmosphere also contains something that is absorbing radiation at a wavelength of 1.25 micrometres. As yet, nobody is able to explain this mysterious absorption feature but it may mean that UGPSJ0722-05 is an entirely new type of brown dwarf.
Best of all is that fact that this Jupiter-like object is only nine light-years away, making it one of the sun’s 10 nearest neighbors and a candidate for significantly more investigation in the near future.
Expect to hear more about UGPSJ0722-05 from Lucas and others. A decent name would be a good start.
Ref: arxiv.org/abs/1004.0317: Discovery Of A Very Cool Brown Dwarf Amongst The Ten Nearest Stars To The Solar System.