14 DAY TRIAL // Astronomers operating an interferometer instrument on the European Southern Observatory's (ESO) Very Large Telescope (VLT) at Cerro Paranal, in Chile, were recently able to identify the largest yellow hypergiant star ever discovered. The object is so large that it immediately jumped in the top 10 largest stars ever observed in the Cosmos.
The star has been designated HR 5171 A and was found in the constellation of Centaurus (The Centaur). In terms of size, this thing is absolutely massive, at least 1,300 times the diameter of the Sun. The VLT Interferometer (VLTI) instrument also determined that the object was in a binary system.
A second star, significantly smaller than the hypergiant, has been discovered orbiting this celestial body. The object is so close to its massive companion that astronomers believe their surfaces touch. Based on this, experts say that HR 5171 A is now being observed during a very brief stage in its life.
The investigation was led by astronomer Olivier Chesneau, who is based at the Observatoire de la Côte d’Azur in Nice, France. He and his team determined that HR 5171 A is around 1 million times brighter than the Sun and roughly 50 percent larger than the more famous red supergiant Betelgeuse.
“The new observations also showed that this star has a very close binary partner, which was a real surprise. The two stars are so close that they touch and the whole system resembles a gigantic peanut,” Chesneau explains. The expert and his team combined light from multiple telescopes via a technique called optical interferometry to capture such exquisite views of the star.
Additional data collected by other observatories over the past 60 years was also included in this research. This effort enabled astronomers to discover another member of the very rare yellow hypergiant class of stars. Around 12 such objects have been found in the Milky Way to date.
The VLTI investigation revealed that the companion star passes in front of HR 5171 A once every 1,300 days, and that it boasts a temperature of roughly 5,000 degrees Celsius (9,000ºF). “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 explains.
The binary system lies around 12,000 light-years from Earth, which made VLT observations easier to conduct. This installation features four large observational and four small tracking telescopes, which together form the most advanced optical observatory in the world today.