Introducing EBLM J0555-57Ab, which now has the distinction of being the smallest star ever discovered. In fact, scientists at the University of Cambridge say stars cannot possibly get much smaller and still function as stars, per a release at Phys.org. This one is 600 light-years away from Earth and 2,000 to 3,000 times dimmer than our own star, aka the sun. In terms of size, it's more like a planet than a star—by way of comparison, it's slightly bigger than Saturn but smaller than Jupiter. Scientists spotted it while hunting for exoplanets and figured, based on its size, that it was an exoplanet itself. Their thinking changed, however, when they looked beyond the object's radius and focused on its mass.
As it turns out, 57ab has 85 times the mass of Jupiter, "which makes it just massive enough to fuse hydrogen into helium and become a true star," per Popular Mechanics. If it were any smaller in mass, 57ab wouldn't be able to pull off the feat of nuclear fusion in its core and thus wouldn't qualify as a star. Instead, it would be a measly brown dwarf. "Our discovery reveals how small stars can be," says the lead author of the study in Astronomy and Physics. A co-author tells the CBC he was surprised to find one so small. It "likely represents the smallest natural fusion reactor that we know of," he says. "We're trying to replicate fusion on Earth in labs, but that's basically as small as it gets in nature." (Scientists have identified Lord Byron's famous "star.")