Astronomers have found the smallest star yet

Courtesy of Earth Sky News

ON July 12 a team of astronomers, led by University of Cambridge, announced it has discovered the smallest star yet.

SMALLEST STAR: Artist’s concept of newly-measured smallest star, called EBLM J0555-57Ab, in contrast to planets Jupiter and Saturn and to the small, cool star Trappist-1, known to be home to at least 7 planets. Image via the University of Cambridge.

This star is smaller than Jupiter, our solar system’s largest planet. It’s slightly larger than Saturn, second-largest planet in our solar system. But it’s a star, not a planet, and therefore much more massive than Jupiter or Saturn. More mass translates to stronger gravity; the pull of gravity of this very small star is some 300 times stronger than Earth’s (Jupiter’s gravity is about 2.5 times that of Earth).

The newly-measured star, known to astronomers as EBLM J0555-57Ab, is located about 600 light-years away. Details about it will be published in the peer-reviewed journal Astronomy & Astrophysics.

Can stars get any smaller than this one? Astronomers say it’s unlikely because – in order to create the thermonuclear fusion reactions needed for stars to shine – stars need a minimum mass.

Alexander Boetticher, the lead author of the study, commented:

Our discovery reveals how small stars can be. 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.

EBLM J0555-57Ab is part of a double star system. It was identified as it passed in front of its much larger companion star by the same technique – called the transit technique – used to identify many exoplanets.

And speaking of exoplanets … astronomers say that small, dim stars like EBLM J0555-57Ab are the best possible candidates for detecting Earth-sized exoplanets that might have liquid water on their surfaces.

In fact, EBLM J0555-57Ab is being compared to TRAPPIST-1, an ultracool dwarf star, recently discovered to be surrounded by at least seven temperate Earth-sized worlds. The newly-measured star has a mass comparable to the current estimate for TRAPPIST-1 but has a radius nearly 30% smaller.

Boetticher said:

[EBLM J0555-57Ab] is smaller, and likely colder, than many of the gas giant exoplanets that have so far been identified. 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. 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.

Bottom line: Astronomers have measured a size and mass for the star EBLM J0555-57Ab and determined it’s the smallest star yet discovered.

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