FEBRUARY 19, 2020
UGC 12591: The Fastest Rotating Galaxy Known
EXPLANATION
Why does this galaxy spin so fast? To start, even identifying which type of galaxy UGC 12591 is difficult—featured on the lower left, it has dark dust lanes like a spiral galaxy but a large diffuse bulge of stars like a lenticular. Surprisingly 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. Progenitor scenarios for UGC 12591 include slow growth by accreting ambient matter, or rapid growth through a recent galaxy collision or collisions—future observations may tell. The light we see today from UGC 12591 left about 400 million years ago, when trees were first developing on Earth.
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