NGC 3758

NGC 3758, nicknamed the Owl Galaxy, is an Sb-type spiral galaxy located in the constellation Leo, about 447 million light-years from our Solar System. It spans roughly 70,000 light-years in diameter. Ralph Copeland first spotted it on March 18, 1874, and Edouard Stephan independently found it ten years later.

This galaxy is classified as a Seyfert 1 type and also carries the Markarian designation Mrk 739, meaning its core emits unusually strong ultraviolet light. What makes NGC 3758 especially rare is that it hosts a binary active galactic nucleus—a sign that it is the product of a galaxy merger.

The system consists of two separate galaxies, NGC 3758W and NGC 3758E, each with its own supermassive black hole. These black holes lie just 11,000 light-years apart and are actively feeding on infalling gas, which heats up and radiates energy as it spirals inward. The two galaxies are gravitationally bound, and their orbits will slowly decay until their nuclei merge, a process expected to take a few billion years.

Visually, NGC 3758 resembles a friendly face, with its two bright cores forming the eyes and a swirling, grin-like structure. The binary black holes may also fling stars out of the galaxy at extreme speeds, turning them into hypervelocity stars.

The galaxy contains an extended emission-line region (EELR), first identified through the Galaxy Zoo project. This region could be powered by one or both of the active galactic nuclei. Detailed imaging of oxygen [O III] emission could reveal which AGN is responsible. The European Southern Observatory’s VLT MUSE instrument observed NGC 3758 in 2016, but as of May 2024, no study of the EELR using that data had been published.