Astroboffins stunned by biggest brown dwarf ever seen – just a hop and a skip away (750 ly)

Yeah, we're talking hundreds of light years

Brown dwarf
Artist's impression of brown dwarf (Credit: Chuck Carter / Gregg Hallinan / Caltech)

Pic Astronomers claim to have identified the largest and purest brown dwarf ever seen, measuring in at a record-breaking 90 times the mass of Jupiter. And it's hovering fairly nearby in the Milky Way.

Brown dwarves are failed stars that did not grow large enough to start the hydrogen fusing process like main-sequence stars such as the Sun. They aren't completely dull; some brown dwarves can burn deuterium and lithium, and even emit bright flares sometimes.

Sitting in the constellation of Pisces 750 light years away, the star known as SDSS J010448.46+153501.8 is a ball of gas made up of more than 99.9 per cent hydrogen, and is 250 times more pure than the Sun. It is in the "halo brown dwarf transition zone" – where the stars have a surface temperature of approximately 1,200°K (926°C / 1,700°F).

Using measurements taken from the European Southern Observatory's Very Large Telescope, a paper published in the Monthly Notices of the Royal Astronomical Society estimates the star is roughly 11-13 Gigayears (10^9) old. With a mass 90 times larger than Jupiter, it is the biggest brown dwarf ever found.

It was previously classified as an M-type star, but the paper has boosted it to an L‑type star, after discovering it had lower metallicity levels and a dimmer surface than expected.

Dr ZengHua Zhang, lead author of the paper and researcher at the Institute of Astrophysics in the Canary Islands, said: "We really didn't expect to see brown dwarfs that are this pure. Having found one though often suggests a much larger hitherto undiscovered population – I'd be very surprised if there aren't many more similar objects out there waiting to be found." ®

PS: The Royal Astronomical Society described this star as being on "the outermost reaches" of the galaxy. True, the star is in a halo in the Milky Way – but it's the brown dwarf transition halo, not an outer halo. We are happy to clarify this point.

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