Located 12,000 light-years from Earth, this colossal star is so bright that it is just about visible even with the naked eye. It is about one million times brighter than the Sun.
HR 5171A, a "yellow hypergiant star," measures more than 1,300 times the diameter of the Sun. It is the largest yellow star known so far.
Tt has a partner, too. “The new observations also showed that this star has a very close binary partner, which was a real surprise,” said Olivier Chesneau of the Observatoire de la Côte d’Azur, Nice, France, who along with her team examined the yellow star. “The two stars are so close that they touch and the whole system resembles a gigantic peanut.”
The companion star that orbits around HR 5171A every 1,300 days is only slightly hotter than HR 5171A’s surface temperature, which is more than 9,000 degrees Fahrenheit. The two stars compose an "eclipsing binary system," in which the smaller companion passes in front and behind the larger one while orbiting.
“The companion we have found is very significant as it can have an influence on the fate of HR 5171 A, for example, stripping off its outer layers and modifying its evolution," Chesneau said.
In addition to being the biggest known yellow star, HR 5171A is one of the top ten biggest known stars. It is 50 percent larger than the red supergiant Betelgeuse located in the Orion constellation.
Scientists examined the star using a technique called interferometry, which combines light collected from several individual telescopes to create a giant virtual telescope measuring up to 460 feet. The star was seen using European Southern Observatory’s Very Large Telescope Interferometer in Chile.
A rare class of stars, yellow hypergiants are at a stage where they are undergoing rapid changes. The most famous among them is the Rho Cassiopeia.
Found in the constellation Cassiopeia, Rho Cassiopeia is located about 8,200 light years from Earth in the constellation Cassiopeia.
"HR 5171 A has been found to be getting bigger over the last 40 years, cooling as it grows, and its evolution has now been caught in action. Only a few stars are caught in this very brief phase, where they undergo a dramatic change in temperature as they rapidly evolve," researchers noted in a press release by the European Southern Laboratory.