UGC 12591 is a spiral galaxy in the constellation Pegasus. Its velocity with respect to the cosmic microwave background is , which corresponds to a Hubble distance of . However, five non-redshift measurements give a farther mean distance of . The first known reference to this galaxy comes from Part 2 of the Morphological Catalogue of Galaxies, published in 1964, where it is listed as MCG +05-55-015.
UGC 12591 is the spiral galaxy with the highest known rotational speed of about , almost twice that of the Milky Way galaxy. 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.
UGC 12591 is relatively isolated; the nearest galaxy to it, WISEA J232529.77+283021.3, is 3.55 million light-years (1.09 Mpc) away. However, its morphology suggests a merger or accretion event in its past: it is somewhat lenticular-like, with a central bulge and dust lanes reminiscent of the Sombrero Galaxy.