Largest Yellow Hypergiant Star

ESO’s Very Large Telescope Interferometer has revealed the largest yellow star — and one of the ten largest stars found so far. This hypergiant has been found to measure more than 1300 times the diameter of the Sun. Artist’s impression of the yellow hypergiant star HR 5171. Image © ESO

Top image: HR 5171, the brightest star just below the centre of this wide-field image. Image © ESO

The yellow hypergiant star HR 5171 is part of a double star system, with the second component so close that it is in contact with the main star. Observations spanning over sixty years, some from amateur observers, also indicate that this rare and remarkable object is changing very rapidly and has been caught during a very brief phase of its life.

Using ESO’s Very Large Telescope Interferometer (VLTI), Olivier Chesneau (Observatoire de la Côte d’Azur, Nice, France) and an international team of collaborators have found that the yellow hypergiant star HR 5171 A is absolutely huge — 1300 times the diameter of the Sun and much bigger than was expected. This makes it the largest yellow star known. It is also in the top ten of the largest stars known — 50% larger than the famous red supergiant Betelgeuse — and about one million times brighter than the Sun.

“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.”

The astronomers made use of a technique called interferometry to combine the light collected from multiple individual telescopes, effectively creating a giant telescope up to 140 metres in size. The new results prompted the team to thoroughly investigate older observations of the star spanning more than sixty years, to see how it had behaved in the past.

This artist’s animation shows the yellow hypergiant star HR 5171. This is a very rare type of star and only a dozen are known in our galaxy. Its size is over 1300 times that of the Sun — one of the ten biggest stars found so far. Observations with ESO’s Very Large Telescope Interferometer have shown that it is actually a double star, with the companion in contact with the main star.

VLT Spots Largest Yellow Hypergiant Star | Mix of new and old observations reveals exotic binary system.

ESO’s Very Large Telescope Interferometer has revealed the largest yellow star — and one of the ten largest stars found so far. This hypergiant has been found to measure more than 1300 times the diameter of the Sun, and to be part of a double star system, with the second component so close that it is in contact with the main star. Observations spanning over sixty years, some from amateur observers, also indicate that this rare and remarkable object is changing very rapidly and has been caught during a very brief phase of its life.