Astronomers Find the Smallest Star Yet

The faint orb is just a smidgen bigger than Saturn and around 2,000 to 3,000 times dimmer than our own sun

Small Star
Amanda Smith

Stars don't seem particularly hard to find—a whole array of these glimmers of light can be seen overhead every night. But not all stars are easy to see. Around 600 light years from Earth, reports Nicole Mortillaro at CBC News, lurks star EBLM J0555-57Ab (57Ab for short). This star is so dim, astronomers think that it's likely the smallest they've ever—or will ever—find.

Planet-hunting researchers from the University of Cambridge’s Institute of Astronomy spotted 57Ab while searching for exoplanets as part of the Wide Angle Search for Planets program. Researchers spot these distant worlds when they pass infront of the star they orbit, causing the light from the flaming body to dip—ever so slightly.

When the scientists first spotted 57Ab, they thought it was a planet, Mortillaro reports. But by studying its mass, they determined that 57Ab is actually a dim star that is part of what's known as a binary star system, where two stars orbit each other.

The faintly glowing orb is just slightly larger than our planet Saturn, but has 85 times the mass of Jupiter and 300 times the gravity of Earth. Mortillero reports that the star is 2,000 to 3,000 times fainter than our sun. The research appears in the journal Astronomy & Astrophysics.

According to a press release, this dim, low-mass star may be as small as the fiery orbs can get. "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,”  says Alexander Boetticher, researcher at  the Institute of Astronomy and lead author of the study, in the release.

Brown dwarfs are objects larger than planets—but not massive enough for gravity and high pressure to keep their fusion reaction going. According to a recent study, there may be up to 100 billion of these failed stars in our galaxy alone.

Tiny 57Ab  is more than just a curiosity. According to the press release, these dim, ultra-cool stars, some of which are cooler than some large gas-giant exoplanets, are the most common stars in the universe and are the best places to look for potentially habitable planets. John Wenz at Popular Mechanics reports that the Trappist-1 system found earlier this year, which has seven planets, also orbits an ultra-cool star.

Finding those types of stars to study, however, is a big challenge. “It is a little ironic that those small stars are the most common stars in the cosmos, but because they are faint, we don't know as much about them as we wish,” co-author Amaury Triaud tells Wenz. “This is why, in parallel to our investigations into planets orbiting ultra-cool stars, we are also investigating the stars themselves.”

According to Mortillaro, the researchers hope to figure out how much light 57Ab emits, though its partner stars make that akin to “trying to look at a candle beside a lighthouse.” The astronomers also hope to figure out how such different stars can form so close to one another.

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