Astronomers at the British University of Cambridge have just discovered the smallest star ever documented.

The small star (artist’s depiction shown in reddish orange) is about the size of Jupiter, and slightly smaller than the ultracool dwarf Trappist-1 (shown in grey). Image: A Boetticher et al., 2017

The star, with the slightly odd name “EBLM J0555-57Ab”, has a mass of only 0.081 our own sun’s mass and the star is only slightly larger than the planet Saturn, the astronomers write in the research report.

It is a Saturn-size low-mass star at the hydrogen-burning limit. Just big enough to allow nuclear fusion to persist. According to the researchers, the newly discovered star is at the exact limit for what a celestial body can be to described as a star.

“Our discovery reveals how small stars can be. Had this star formed with only a slightly lower mass, the fusion reaction of hydrogen in its core could not be sustained, and the star would instead have transformed into a brown dwarf.”

– Cambridge astronomer Alexander von Boetticher

EBLM J0555-57Ab is a binary star system located about 600 light years from our own system.


Alexander von Boetticher, Amaury H.M.J. Triaud, Didier Queloz et al. The EBLM project III. A Saturn-size low-mass star at the hydrogen-burning limit arXiv:1706.08781 [astro-ph.SR]