The tiniest star, similar in size to Saturn, has been discovered as part of an eclipsing binary system by a group of astronomers.
Codenamed EBLM J0555-57Ab, researchers believe the star is teetering on the edge of how small a star can possibly be. It has a mass (0.081M☉) and radius (0.084R☉) less than a tenth of our Sun’s mass and radius. Main sequence stars, like the Sun, must have a mass large enough to kickstart the hydrogen-burning process.
Alexander von Boetticher, a Master’s student at the University of Cambridge and lead author of a paper discussing the mini-star, to be published in the journal Astronomy & Astrophysics, said: “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.”
The new star is located about 600 light years away and was detected using the transit method – a technique more commonly used to hunt for exoplanets. Since the star is the smaller companion in its eclipsing binary system, when it passes its larger sister star, the brightness drops.
This varying level of luminosity changes periodically, and is a telltale sign of an orbiting object around a star.
Although teeny stars with masses and sizes less than a fifth of that of the Sun are the most common group of stars sprinkled around in space, they can be hard to find. Their small size and dim brightness make them difficult to detect.
But it’s an important task, said Amaury Triaud, co-author of the study and senior researcher at the University of Cambridge.
“The smallest stars provide optimal conditions for the discovery of Earth-like planets, and for the remote exploration of their atmospheres,” added Triaud. “However, before we can study planets, we absolutely need to understand their star; this is fundamental.” ®