Ellen Phiddian
Cosmos science journalist
Astronomers have solved a nearly 30-year-old mystery about a brown dwarf. It is, in fact, brown dwarfs: there are 2 of them.
Brown dwarfs are astronomical objects that are bigger than planets, but smaller than stars – they’re massive enough to emit faint light.
The brown dwarf Gliese 229B was discovered in 1995, and has since been used in a bevy of astronomical work.
But it kept throwing up strange measurements: given its apparent mass, it should be much brighter than it was.
A paper published in Nature explains the anomaly: it’s actually 2 brown dwarfs, 38 and 34 times the mass of Jupiter, circling each other every 12 days.
“Gliese 229B was considered the poster-child brown dwarf,” says lead author Jerry Xuan, a graduate student at the California Institute of Technology (Caltech), USA.
“And now we know we were wrong all along about the nature of the object. It’s not one but two. We just weren’t able to probe separations this close until now.”
The team has dubbed the two new brown dwarfs Gliese 229Ba and Gliese 229Bb.
They were observed with 2 instruments at the Very Large Telescope in Chile, which is run by the European Southern Observatory.
“This discovery that Gliese 229B is binary not only resolves the recent tension observed between its mass and luminosity but also significantly deepens our understanding of brown dwarfs, which straddle the line between stars and giant planets,” says co-author Professor Dmitri Mawet, also at Caltech.
“These two worlds whipping around each other are actually smaller in radius than Jupiter. They’d look quite strange in our night sky if we had something like them in our own solar system,” says co-author Professor Rebecca Oppenheimer, who was part of the team that first observed Gliese 229B in 1995.
“This is the most exciting and fascinating discovery in substellar astrophysics in decades.”
