A team of astronomers recently discovered the largest yellow star revealed to this date utilizing the European Southern Observatory's Very Large Telescope Interferometer. As we learned in class, interferometry allows one to combine numerous telescopes spaced apart into one large telescope with a smaller diffraction limit (theta is inversely proportional to d, the distance between the telescopes).
The yellow hypergiant, named HD 5171 A, is located 12,000 ly from Earth, is 13,000 times the size of our sun, and is twice the size of Betelgeuse! Additionally, it is one of the ten largest stars currently known. Because of this, it is not terribly surprising that HD 5171 A is slightly visible to the naked eye. Yellow hypergiants are also very rare, with only 12 being located in the Milky Way.
Perhaps even more surprising than finding this rare, giant star was finding its binary partner. Specifically, HD 5171 A is part of an eclipsing binary system, which was determined by measuring the varying brightness of the star with time. The data also yielded a period of 1300 days for the companion star. What is really interesting, though, is that orbiting partner is close enough to HD 5171 A that they are in contact with each other (illustrated below). This is important since it can alter the evolution process of the yellow hypergiant.
The video below is also a cool animation of the star in space!
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