The first brown dwarf ever found was the strangest – now we know why

The first “failed star” ever discovered has been a weird outlier since it was found nearly 30 years ago. New observations show that it is unusually massive because it isn’t a single star after all

By Karmela Padavic-Callaghan

16 October 2024

Congratulations, it’s twins

K. Miller, R. Hurt/Caltech/IPAC

An odd star that has confused researchers for decades now makes sense – it turns out not to be a single star but two companions.

“It used to be that this brown dwarf didn’t make any sense. We worried that we were doing something horribly wrong, or that our models were horribly wrong. But, no, everything’s fine. It just has a friend,” says Timothy Brandt at the Space Telescope Science Institute in Maryland.

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Now, two research teams have used instruments at the W. M. Keck Observatory in Hawaii and the Very Large Telescope in Chile to unravel the mystery of the first brown dwarf.

Brown dwarfs are “failed stars” in that they have too little matter and are too cool to sustain nuclear fusion. They become faint in the night sky, similar to planets, instead of burning bright for millennia. The first brown dwarf, called Gliese 229B, was discovered in 1995, but its mass was inexplicably large, says Jerry Xuan at the California Institute of Technology, who worked on one of the studies.

Gliese 229B was estimated to be about 71 times as massive as Jupiter, and a star born at that size would have not cooled down to be as dim as we see it even if it was as old as the universe, says Brandt, who was part of one of the research teams. This led some researchers to suggest that Gliese 22B is a pair of very faint stars, but until now they had no definitive evidence.