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Found: The Smallest Star Ever Observed

It’s about as small as a star can be.

The newly discovered star (right) compared to the size of Saturn.
The newly discovered star (right) compared to the size of Saturn. Amanda Smith

Some 600 light-years away, two stars, one very large, one very small, orbit each other. Recently, from the perspective of Earth, the smaller one passed in front of the larger one, a transit that allowed scientists to see the smaller one for the first time.

That smaller one is, in fact, the smallest star ever observed—about the size of Saturn—and, scientists say, about as small as stars can get. Any smaller, they believe, and there probably wouldn’t be enough pressure on the stellar core to create the hydrogen fusion reaction that powers many stars, including the Sun.

The discovery was announced Wednesday by the University of Cambridge. The scientists who found the star were actually looking for planets, which are often found by the same method of waiting for them to pass in front of stars—where they dim stellar brightness ever-so-slightly.

“While a fascinating feature of stellar physics, it is often harder to measure the size of such dim low-mass stars than for many of the larger planets,” Alexander Boetticher, the lead author of a study published in Astronomy & Astrophysics, explained in the announcement. “Thankfully, we can find these small stars with planet-hunting equipment, when they orbit a larger host star in a binary system. It might sound incredible, but finding a star can at times be harder than finding a planet.”

The star has been christened EBLM J0555-57Ab and, according to scientists, shares a lot of features with stars such as Trappist-1, which was recently found to be surrounded by seven temperate planets (one of which may, perhaps, possibly, be conducive to life). But EBLM J0555-57Ab has no planets—just a parent star that it orbits in a lonely dance that will likely continue for tens of thousands of years.