3C 120

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3C 120, also known as Markarian 1506, is a lenticular galaxy in the constellation Taurus about 420 million light-years away. Its center hosts an active nucleus that makes it a type I Seyfert galaxy and a bright broad-line radio galaxy, notable for its energetic jet.

A supermassive black hole sits at the core, with mass estimates around several tens of millions of solar masses. The X-ray emission from the nucleus is highly variable and shows features typical of material swirling around the black hole and its corona, including a Fe K-alpha line. The variability seen in X-rays often matches changes in other wavelengths, indicating a close connection between the accretion disk and the surrounding regions.

3C 120 has a one-sided, relativistic jet that shines in radio and X-rays. The jet contains bright knots that appear to move very fast, sometimes seeming to travel faster than light in projection. New knots are commonly observed after dips in X-ray light, suggesting that material from the inner accretion disk feeds the jet. The jet is tilted only a little relative to our line of sight, roughly 10–20 degrees, and spans a large area with several distinct features along its length.

The galaxy is a strong emitter across the spectrum, including gamma rays up to about 10 GeV, with the gamma-ray brightness changing over time. This makes 3C 120 one of the clearest examples of a link between the central engine and the jet’s activity.

3C 120’s host shows signs of past interactions, including shell structures and tidal features that point to a merger. It forms stars at a modest rate and has extensive regions of ionized gas around the nucleus, highlighting the active environment shaped by its central black hole.

Discovered as a variable object in optical light in 1940, 3C 120’s radio emission was later cataloged in the Third Cambridge Catalogue, marking it as an important target for studies of active galaxies and their jets.