Astronomers have found a star so small that even some planets are larger. It is the smallest one ever discovered and it teaches scientists more about the little stars around which potentially habitable planets form throughout the universe.
The star, called EBLM J0555-57Ab, is just a little bit larger than Saturn, the ringed gas giant in the outer solar system, according to a study in Astronomy & Astrophysics. But in such a small space, it contains a mass similar to other small stars. Being so compact, it is one of the densest stars out there, which means its gravitational pull is intense: about 300 times stronger than the pull of Earth’s gravity on this planet’s surface.
“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,” the University of Cambridge explained in a statement on the research, referring to the same process that takes place within the sun and generates the energy we enjoy on Earth. “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.”
In that case, it would have been a brown dwarf, an object that is kind of a halfway point between a planet and a star. Typically, these objects are bigger than Jupiter — the biggest planet in our solar system — but smaller than the smallest stars. Authorities like NASA have previously classified brown dwarfs as being between 15 times the mass of Jupiter and 75 times the mass of Jupiter.
EBLM J0555-57Ab surpasses that mass and thus fits the bill of a small star on that front. Where it bends the rules is in its diameter, which is similar to that of Saturn, the second largest planet in the solar system.
“Our discovery reveals how small stars can be,” lead study author Alexander von Boetticher said in the Cambridge statement. “This star is smaller, and likely colder than many of the gas giant exoplanets that have so far been identified.”