NGC 4725 — Galaxy in Coma Berenices

NGC 4725 is a striking one-armed barred spiral in Coma Berenices about 40 million light-years away. The galaxy has a strong central bar, a prominent inner ring of star formation, and a single dominant outer spiral arm wrapping nearly all the way around the disk while a counterpart arm is much weaker. This asymmetry — common in classification but rarely so dramatic — gives NGC 4725 a uniquely lopsided appearance compared with most barred spirals. It is also a Seyfert galaxy with a low-luminosity active nucleus.

A fine telescope target. A 4-inch at moderate power shows an elongated bright glow with a small concentrated nucleus. An 8-inch at 150-200x reveals the bar as a clear linear axis through the bulge, with hints of the inner ring as a brightening around it. A 12-inch begins to suggest the asymmetric outer arms, although photographs are needed to fully appreciate the one-armed character. Star-hop from Alpha Comae Berenices (Diadem) about 6 degrees east. Best observed March through June.

Discovered by William Herschel on 6 April 1785. NGC 4725 has been a recurring target in studies of bar-driven gas inflow because its inner-ring structure is one of the cleanest examples of a 'resonance ring' fed by a stellar bar. The Seyfert classification of its nucleus was established in the 1960s.