Our Sun is massive. Really, it's the most massive thing we have daily experience with. On the scale of the Universe, it's not really that big, and in fact it's downright tiny in comparison to other stars out there. The European Space Agency’s Very Large Telescope has spotted a yellow star so huge that it’s size is 1,300 times bigger than our Sun. This star, HR 5171 A, currently sits at the top spot for largest yellow star ever seen, and gets a place in the top 10 of the largest stars we've ever known.
Astronomers used the Very Large Telescope to discover HR 5171 A using an interferometer which takes light from multiple telescopes and combines it to create one massive virtual telescope. After discovering HR 5171 A, the astronomers then looked at over 60 years’ of studies of that particular area of space and confirmed the yellow star’s existence. A yellow star (our Sun is a yellow dwarf, but it's actually white if you look at it from outside the atmosphere) occurs when a star is at a part of its life cycle that makes it unstable. This instability creates a stellar object that is in constant change. Because of that, the star throws off a lot of light as its atmosphere expands. Finding a star during its yellow state is rare, but HR 5171 A is now so bright that a trained naked eye may see it from Earth. That’s impressive when you consider that the star is nearly 12,000 light-years away from us. As HR 5171 A grows bigger, astronomers hope to understand this small phase of the star life cycle and the changes it undergoes during it, perhaps teaching us more about stars and their evolution.
There's another thing that's remarkable about HR 5171 A: it’s part of a binary star system, and has a smaller sibling orbiting it. Because HR 5171 A is so massive, though, the two stars are actually touching, making them appear like a peanut shape in the night sky. Astronomers are studying this system carefully, waiting to see if the smaller star’s closeness will affect HR 5171 A.