This Hubble Space Telescope image shows the massive spiral galaxy UGC 12591. It resides about 400 million light-years away from Earth, in the westernmost region of the Pisces-Perseus Supercluster, a long chain of galaxy clusters that stretches out for 250 million light-years -- one of the largest known structures in the cosmos. The galaxy and its halo together contain several hundred billion times the mass of the Sun, and four times the mass of the Milky Way. It whirls around extremely quickly, rotating at speeds of up to 1.8 million kilometers per hour!