NGC 818

Lore & Background

NGC 818 was discovered by German-British astronomer William Herschel on 18 October 1786. It is a member of the galaxy group [CHM2007] LDC 148, which also includes NGC 834 and several other galaxies. The galaxy's velocity relative to the cosmic microwave background yields a Hubble distance of 59.14 ± 4.15 Mpc, while 14 non-redshift measurements give a closer mean distance of 51.700 ± 2.565 Mpc, indicating some uncertainty in its exact distance.

The galaxy has a possible active galactic nucleus, meaning a compact central region emits significant energy across the electromagnetic spectrum, with characteristics suggesting the luminosity is not produced by stars. Based on near-infrared K-band luminosity measurements of its bulge, NGC 818 hosts a supermassive black hole with a mass of 13 million solar masses. One supernova, SN 1992az (Type II, magnitude 18), was observed in the galaxy, discovered by Christian Pollas on 27 September 1992.

Reader's Guide

NGC 818's significance lies in its dual distance measurements and the presence of a possible active galactic nucleus, which marks it as a galaxy with energetic central activity beyond ordinary stellar processes. The supermassive black hole at its core, with a mass of 13 million solar masses, places it among galaxies where black hole demographics can be studied. The supernova SN 1992az, a Type II event, adds to the record of stellar explosions in this system. As a member of the [CHM2007] LDC 148 group, NGC 818 contributes to understanding galaxy interactions and group dynamics. The discrepancy between its Hubble distance and closer non-redshift measurements highlights the challenges in determining extragalactic distances, making it a useful object for calibrating distance indicators. Its discovery by William Herschel in 1786 connects it to the early cataloging of deep-sky objects, and its continued observation helps refine models of galaxy evolution and black hole growth.