An international team of astronomers has spotted the largest yellow star ever discovered, ranking among the ten largest stars found so far.
"Surprisingly large" was the term Olivier Chesneau and his international team used to describe HR 5171 A, a hypergiant star more than 1300 times the diameter of the Sun. Using the European Southern Observatory's Very Large Telescope Interferometer, the astronomers determined that the yellow star is about a million times brighter than the Sun and 50% larger than the famous red supergiant, Betelguese.
This makes HR 5171 A the largest yellow star ever found, and one of the ten largest stars. But that's not all the team discovered -- they also found that HR 5171 A is not alone in the universe. Forming a binary system, it has a low-mass companion star in such close proximity that it is embedded within its dense wind.
"The new observations also showed that this star has a very close binary partner, which was a real surprise," says Chesneau. "The two stars are so close that they touch and the whole system resembles a gigantic peanut."
Only a dozen or so yellow hypergiants have been observed within our galaxy, making them a rarity. On the stellar evolution path to becoming red giants, yellow hypergiants are among the biggest and brightest stars known, and are at a stage in their lives when they are unstable and changing rapidly.
HR 5171 A can be seen by the naked eye, if your eyesight is good enough.