A strange 鈥渇ailed star鈥� has shed its outer layers 鈥� an event that astronomers had never seen before. The celestial body appears to be surrounded by a bubble of gas that was mostly blasted off by an immense pulse of heat.
at the National Radio Astronomy Observatory in Virginia and her colleagues were looking for the early signs of planets forming when they spotted what seemed to be a bubble of carbon monoxide. 鈥淲hen I found this object it was so different I thought maybe I did something wrong,鈥� says Ru铆z-Rodr铆guez. 鈥淚t was completely unexpected.鈥�
Further observations revealed that it was a brown dwarf a little more than 50 times the mass of Jupiter, about 150 light years away. Brown dwarfs are somewhere between gas giant planets and stars, far larger than Jupiter but not quite large enough to fuse hydrogen atoms into helium in their cores. The veil of carbon monoxide surrounding this brown dwarf was unusual, though, as was its anomalous brightness.
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鈥淭he only way that we could explain what we鈥檙e observing is to compare it with other objects where we observe events like that, and in this case it would be older objects like giant stars,鈥� says Ru铆z-Rodr铆guez. When some stars begin to fuse helium, they undergo a huge burst of energy called a thermal pulse that travels outwards through the star like an expanding fireball and blows off its outer layers. Something similar may be going on here.
鈥淚t鈥檚 like a brown dwarf with some personality problems,鈥� says Ru铆z-Rodr铆guez. 鈥淪ometimes it behaves like a planet, sometimes it behaves like a star, and in this case it鈥檚 behaving more like a star.鈥�
The researchers鈥� models showed that the most likely explanation is that the brown dwarf began to fuse deuterium 鈥� a heavy form of hydrogen 鈥� at its centre, creating a similar thermal pulse. While brown dwarfs aren鈥檛 massive enough to fuse regular hydrogen, deuterium is easier to ignite and young brown dwarfs are expected to do so briefly.
This process is poorly understood, particularly as this is the first report of a gas bubble like this around a brown dwarf. Ru铆z-Rodr铆guez searched through archival data on about 1000 other brown dwarfs and only found two objects that appeared to match this one, so these types of brown dwarfs are probably extremely uncommon, she says. She and her colleagues plan to follow up on those objects in hopes of learning more about the inner workings of brown dwarfs and what causes them to blow their tops.
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