This is the smallest star discovered to date: the size of Saturn and 300 times more gravity than Earth
It is more than likely that the name Stephenson 2-18 does not tell you anything, but if we tell you that it is the largest star discovered to date the thing changes. It is so large that it has a radius of 2,150 solar radii. Come on, its volume is 10,000 million times greater than the Sun. It is a huge star, so huge that if we put it in the center of the Solar System would reach the orbit of Saturn.
And now that we know the largest one discovered today, it is time to talk about its counterpart, the smallest. She doesn’t have such a cool name, so we have to settle for calling her EBLM J0555-57Ab. It is 600 light years from Earth and, despite being the smallest, it is larger than Saturn.
Why this star is so interesting
EBLM J0555-57Ab was discovered in 2017 thanks to the WASP (Wide Angle Search for Planets) consortium. Getting it was a milestone, since it is very weak. According to astronomers, between 2,000 and 3,000 times weaker than the Sun. Being part of a binary system (orbiting a larger star), finding it was like “trying to look at a candle next to a lighthouse.”
As the researchers explain, was identified when passing in front of her partner, much larger. As it passed in front of its parent star, it periodically became dimmer, which is an indication that there is an orbiting object. This method, curiously, is often used to identify planets, not stars.
EBLM J0555-57 From it something bigger than saturn and its gravity is 300 times higher than what we experience on Earth. And why is it interesting? Because, in the words of the astronomer Alexander Boetticher (University of Cambridge):
“Our discovery reveals how small stars can get. If this star were formed with a slightly lower mass, the hydrogen fusion reaction in its core could not be sustained, and the star would have transformed into a brown dwarf.”
Despite being a very small star, it is large enough that hydrogen nuclei can fuse into helium. If it were smaller, the pressure in the center of the star would not be enough and the star would have become a brown dwarf (aka failed star).
Interestingly, the researchers assure that these stars (those with sizes and masses less than 20% of the Sun) are the most numerous in the Universe, but they are difficult to detect due to their size and low brightness.