Betelgeuse is the red supergiant star known as the shoulder of Orion, famous for being the brightest red star in the night sky. It was long thought to be a single star, but recent observations have shown it has a companion star. A young yellow star not quite on the main sequence named Siwarha. We can't observe this companion directly, so there has been some debate as to whether the companion truly exists. But new observations look at how the companion disturbs the atmosphere of Betelgeuse.

Betelgeuse is a star near the end of its life. As it struggles to burn the last of its stellar fuel, it has swollen into a large but diffuse star. Though it has a mass only 14 times that of the Sun, its diameter is more than 640 times that of the Sun. Including its atmosphere, the star is wider than the orbit of Mars. But the outer regions of the star are quite diffuse, what we would call a vacuum in a lab on Earth. The companion star Siwarha orbits Betelgeuse very closely.…