In Andromeda's stellar stream, a long ribbon of stars ripped from a small galaxy during a collision with a larger one, astronomers spotted a star that outshines all its neighbors. It pulsates, swelling and contracting every 89 days, like a heart beating in rhythm. Such stars are called Type II Cepheids, and this one is the brightest known.
Around the star swirls a dusty disk, like Saturn's ring, but made of hot dust. The disk betrays the presence of a companion: it sweeps up material like a chef gathering dough into a ball. The star's spectrum shows an excess of heavy elements: these are produced in stellar interiors and ejected during mergers.
How did such a massive star end up in a stream where stars are usually old and light? Scientists propose a three-star scenario. Two of them merged into one, like two raindrops on a window. The merger gave the star a kick, and then it evolved into a bright pulsating star with a disk. So galaxy collisions not only scatter stars but also create new, unusual ones.
This star's pulsations last 89 days — during that time it swells and contracts, changing its brightness by tens of percent.
In Stanislaw Lem's novel "Solaris," the planet's ocean pulsates like a living heart — somewhat akin to the rhythmic breathing of this distant star.