Why does this galaxy spin so fast? To start, even identifying which type of galaxy UGC 12591 is difficult — it has dark dust lanes like a spiral galaxy but a large diffuse bulge of stars like a lenticular. Observations show that UGC 12591 spins at about 480 km/sec, almost twice as fast as our Milky Way, and the fastest rotation rate yet measured. The mass needed to hold together a galaxy spinning this fast is several times the mass of our Milky Way Galaxy. The light we see today from UGC 12591 left about 400 million years ago, when trees were first developing on Earth.