Smallest-ever star discovered

Scientists have discovered the smallest known star in the universe - slightly larger than Saturn in size - which may possibly have Earth-sized planets with liquid water in its orbit.

 

Researchers from University of Cambridge in the UK identified the star located about six hundred light years away, called EBLM J0555-57Ab as it passed in front of its much larger companion.

The star is likely as small as stars can possibly become, as it has just enough mass to enable the fusion of hydrogen nuclei into helium, researchers said.

If it were any smaller, the pressure at the centre of the star would no longer be sufficient to enable this process to take place, they said.

With a size just a sliver larger than that of Saturn, the gravitational pull at its stellar surface is about 300 times stronger than what humans feel on Earth.

The discovery is also the best possible candidates for detecting Earth-sized planets which can have liquid water on their surfaces, such as TRAPPIST-1, an ultracool dwarf surrounded by seven temperate Earth-sized worlds, researchers 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," said Alexander Boetticher, Master's student at University of Cambridge.

The star was identified by WASP, a planet-finding experiment run by several universities.

EBLM J0555-57Ab was detected when it passed in front of, or transited, its larger parent star, forming what is called an eclipsing stellar binary system.

The parent star became dimmer in a periodic fashion, the signature of an orbiting object.

Researchers measured the mass of the star was established via the Doppler, wobble method, using data from the CORALIE spectrograph.

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

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, they said.

"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," Boetticher said.

The star has a mass comparable to the current estimate for TRAPPIST-1, but has a radius that is nearly 30 per cent smaller.

"The smallest stars provide optimal conditions for the discovery of Earth-like planets, and for the remote exploration of their atmospheres," said Amaury Triaud, senior researcher at University of Cambridge.

The study appears in the journal Astronomy and Astrophysics.