Teensy star vies for title of smallest known

A teeny-weeny star, with a radius about the size of Saturn’s, is one of the smallest ever found. Known as EBLM J0555-57Ab, the star (illustrated next to Saturn) is significantly smaller than the Jupiter-sized TRAPPIST-1, a peewee star famous for hosting a septet of Earth-sized planets (SN: 3/5/17, p. 6). And the newfound star is comparable in size to a previously reported runt, 2MASS J0523-1403.

Although the newfound star’s girth is similar to Saturn’s, it is much heftier, at almost 300 times Saturn’s mass. Still, that’s only about 8 percent of the sun’s mass, meaning that the star barely meets the qualifications for joining the stellar ranks, scientists report in an upcoming issue of Astronomy & Astrophysics. The star is just at the limit at which nuclear fusion can occur in a stellar core. If the star were less massive, it would instead be a failed star known as a brown dwarf.

The miniature star orbits another, larger star some 600 light-years away. Scientists with the Wide Angle Search for Planets, or WASP, collaboration detected the star with a method typically used to scout out exoplanets: watching it pass in front of its companion and dim the larger star’s light.