UGC 12591
UGC 12591 is a spiral galaxy located about 400 million light years away from the Earth in the constellation Pegasus. Also, it is the spiral galaxy with the highest known rotational speed of about 500 km/s, almost twice the rotational speed of our galaxy, the Milky Way. The high rotational speed means the galaxy must be very massive at the center; the galaxy has a mass estimated at 4 times that of the Milky Way, making it the third most massive known spiral galaxy after ISOHDFS 27 and J2345-0449.