Astronomers find the Galaxy’s Smallest Star

Astronomers have discovered what is now the smallest known star in the galaxy, in a system roughly 600 light-years from Earth. Part of a trinary star system, the smaller of the pair, EBLM J0555-57Ab, is estimated to only be 8 percent of the mass of our own Sun, in a compact package no bigger than Saturn.

This itty-bitty sun may represent the smallest size that a star can be: to sustain the hydrogen fusion process that provides a star’s energy, the gases within must be brought to a high pressure and temperature, meaning that there needs to be enough mass present in the star to provide these conditions.

"Our discovery reveals how small stars can be," explains study lead Alexander Boetticher, of the University of 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."

To put EBLM J0555-57Ab’s size in perspective, it’s diameter is only one-twelfth of the diameter of the Sun, or a mere eleven times the Earth’s diameter — a little over 4/5ths of Jupiter’s diameter. Compared to the red dwarf at the center of the recently-discovered miniature system TRAPPIST-1, EBLM J0555-57Ab is a similar mass, but is compacted into a sphere 30 percent smaller than TRAPPIST-1’s size.