Telescope in Chile reveals largest yellow star ever seen

Discovery of giant star more than a thousands times the size of the Sun could help us understand the evolutionary process of hypergiants.

Visible to the keen-sighted from earth, the star recently revealed to be one of the biggest of its kind ever detected by mankind has long lingered on the edge of astronomers’ understanding but its full size and shape remained a mystery — until now.

Using European Southern Observatory’s (ESO) Very Large Telescope (VLT), an international team based in Chile was able to unlock the secrets of HR 5171 A,  revealing it to be the largest yellow star ever detected and one of the ten biggest stars ever seen. The hypergiant measures a whopping 112 billion-odd miles across — more than 1300 times the diameter of the Sun. HR 5171 A is also 50 percent larger than the famous red supergiant Betelgeuse and about one million times brighter than the Sun — surely enough to earn it a catchier name in the near future?

Leading the project was Olivier Chesneau (Observatoire de la Côte d’Azur, Nice, France) who, alongside a team of collaborators from a range of nations, used a technique called interferometry to combine the light collected from multiple individual telescopes, effectively creating a giant telescope up to 450 feet in size.

Using this method, the team was able to reveal the true size of the star that had long been known to experts but was estimated to be much smaller. Also shown was that the hypergiant is, in fact, part of a double star system so close that it is in contact with the main star.

“The new observations also showed that this star has a very close binary partner, which was a real surprise,” Chesneau said. “The two stars are so close that they touch and the whole system resembles a gigantic peanut.”

Following the revelation of the star’s true, record-breaking size, experts returned to the work of older observations —those of both amateurs and professionals — to study the hyper giants’ behavior over time. Typically unstable, yellow giants often change quickly and HR 5171 is no exception — The gigantium star appears to be expanding and cooling as it does so. Astronomers say the opportunity to watch the star change over time could be a helpful clue to furthering our understanding of the behavior of hyper giants.

Due to its almost non-existent humidity and clear skies, the Atacama is the world’s premier location for astronomy. Chile is home to almost half the world’s telescope infrastructure, and this is set to increase to over two thirds in the next decade.