The ESO’s Very Large Telescope in Chile has revealed the largest yellow star ever found. Hypergiant star HR 5171 A is massive — 1300 times the diameter of the Sun. In fact, the star is 50% larger than the famous red supergiant Betelgeuse — and about one million times brighter than the Sun. New surprising observations have also shown that this star has a very close binary partner. The two stars are so close that they touch!
Yellow hypergiants are very rare, with only a dozen or so known in our galaxy — the best-known example being Rho Cassiopeiae. They are among the biggest and brightest stars known and are at a stage of their lives when they are unstable and changing rapidly. Due to this instability, yellow hypergiants also expel material outwards, forming a large, extended atmosphere around the star.
Despite its great distance of nearly 12,000 light-years from Earth, the object can just about be seen with the naked eye. 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. #science #astronomy #cosmos