Astronomy Picture of the Day (Unofficial)

Astronomy Picture of the Day for 2020-02-19 12:30:02.356061

Astronomy Picture of the Day (Unofficial) at

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2020 February 19
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UGC 12591: The Fastest Rotating Galaxy Known
Image Credit: NASA, ESA, Hubble; Processing & Copyright: Leo Shatz

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.

Tomorrow's picture: open space