Astronomers Have Discovered The Smallest Star Yet

A comparison between Jupiter, Saturn, EBLM J0555-57Ab, and TRAPPIST-1. University of Cambridge

An international team of astronomers has discovered the smallest star yet, which is just slightly larger than Saturn and about 8 percent the mass of the Sun.

The newly discovered object, called EBLM J0555-57Ab, is located 600 light-years away and it orbits a much bigger star. As reported in Astronomy & Astrophysics, the object is touching the limit on how small a star can be. Scientists discovered that figure is about 70 times the mass of Jupiter – less than that, it's a failed star, more than that, it becomes a star – and EBLM J0555-57Ab is about 85 times the gas giant.

“Our discovery reveals how small stars can be,” lead author Alexander von Boetticher, a Master’s student at Cambridge’s Cavendish Laboratory and Institute of Astronomy, said in a statement. “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.”

Stars shine due to nuclear fusion at their core. That happens due to the extreme pressures and temperature that hydrogen gas experiences there. The smaller the star, the cooler is going to be. So red dwarfs like EBLM J0555-57Ab tend to be very dim.

“This star is smaller, and likely colder than many of the gas giant exoplanets that have so far been identified,” said von Boetticher. “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.”

The discovery was part of WASP (wide-angle search for planets), a collaborative research project that has discovered a large number of exoplanets. It’s interesting that these can be used to find red dwarfs as well, and hopefully learn more about these stars. The discovery of Earth-sized planets around red dwarfs like TRAPPIST-1 and Proxima Centauri has ignited an interest in these poorly understood stars.

“The smallest stars provide optimal conditions for the discovery of Earth-like planets, and for the remote exploration of their atmospheres,” said co-author Amaury Triaud, senior researcher at Cambridge’s Institute of Astronomy. “However, before we can study planets, we absolutely need to understand their star; this is fundamental.”

Stars that are less than 20 percent the size and mass of our Sun are the most common in the universe and new ways to spot them might help us to finally crack their mysteries.


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