Q942187

NGC 4151 is an intermediate spiral Seyfert galaxy with weak inner ring structure located 15.8 megaparsecs (52 million light-years) from Earth in the constellation Canes Venatici. The galaxy was first mentioned by William Herschel on March 17, 1787. It was one of the six galaxies described in Carl Seyfert's original paper which defined such systems. It is one of the nearest galaxies to Earth to contain an actively growing supermassive black hole. The black hole would have a mass on the order of 2.5 million to 30 million solar masses. It was speculated that the nucleus may host a binary black hole, with about 40 million and about 10 million solar masses respectively, orbiting with a 15.8-year period. This is, however, still a matter of active debate.

Some astronomers nickname it the "Eye of Sauron" from its appearance.