Despite it’s just about the smallest star physics allows, EBLM J0555-57Ab is also one the densest active stellar objects. While Jupiter has a gravitational pull equivalent to 2.5 times of Earth, this tiny star has a gravity some 300 times strong than of our planet. The smallest theoretical mass for a star is between 0.07 to 0.08 solar masses and EBLM J0555-57Ab just nails it slightly above the limit with 0.081 solar masses. We might find an even smaller active star but given the rarity, it ought to take a while.
“Our discovery reveals how small stars can be,” said Alexander Boetticher, the lead author of the study, and a Master’s student at Cambridge’s Cavendish Laboratory and Institute of Astronomy. “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.”
The star is likely colder than many of the gas giant exoplanets that have so far been identified. Stars in the same class as EBLM J0555-57Ab are considered prime hunting ground for finding Earth-like alien planets. For instance, the greatly hyped Trappist-1 system is comprised of a white dwarf that’s about 2,000 times dimmer than the Sun but also seven Earth-like planets, three of which are supposed to be in the habitable zone — not too cold, not too hot, but just right for liquid water to plausibly form on the rocky surface of these alien worlds. The newly-measured star has a mass comparable to the current estimate for TRAPPIST-1, but has a radius nearly 30% smaller. Details about it will be published in the peer-reviewed journal Astronomy & Astrophysics (for now you can find it in preprint).