Hercules A

Hercules A is a bright astronomical radio source in the constellation Hercules corresponding to the galaxy 3C 348.

Observation
During a survey of bright radio sources in the mid-20th century, astronomers found a very bright radio source in the constellation Hercules. The radio source is strongest in the middle range frequency and emits synchrotron radiation, suggesting the source of radio emission may be gravitational interaction. In 1959, astronomers from the Radio Astronomy Group (later the Cavendish Astrophysics Group) detected the radio source using the Cambridge Interferometer of the Cavendish Observatory in Cambridge University in the United Kingdom, including it in the Third Cambridge Catalogue of Radio Sources (3C) as 3C 348, the 348th object detected by the survey.

Galaxy
The galaxy, 3C 348, is a supergiant elliptical galaxy. It is located inside a poor galaxy cluster with an X-ray luminosity of Lbol = 4.8 × 1037 W. 3C 348 is classified as type E3 to E4 of the updated Hubble–de Vaucouleurs extended galaxy morphological classification scheme. It has a companion galaxy, shown appearing as a secondary nucleus, indicating it is merging.

3C 348, the galaxy located in the center of the image, appears to be a relatively normal elliptical galaxy in visible light. When imaged in radio waves, however, plasma jets over one million light years long appear. Detailed analyses indicate that the galaxy is actually over 1,000 times more massive (approx. 10$15$ solar masses) than our Milky Way Galaxy, and the central black hole is nearly 1,000 times more massive (approx. 4 billion solar masses) than the black hole at our Milky Way's center, one of the largest known. The physics that creates the jets are poorly understood, with a likely energy source being matter ejected perpendicular to the accretion disc of the central black hole which has grown more times than 1.7×108 Msolar, enough to produce a shock front in the cluster's interstellar medium.

Radio Source
The radio source in 3C 348 is considered powerful. It is double-lobed with striking bizarre features such as a double optical core and radio intensity rings clustered together inside one of the host galaxy's two radio lobes. Despite not being a Fanaroff-Riley Class II neither an FR I source, it instead shows similarities to both types.