What is the Circinus Galaxy?

The Circinus Galaxy is a spiral active galaxy that lies only 15 million light-years away, in the constellation Circinus, but went unnoticed until 1975 because it lies just 4° from the plane of the Milky Way and is thus heavily obscured. It is the scene of tumultuous gas motions, most of them concentrated in two rings. One, about 700 light-years from the center, appears to be undergoing tremendous bursts of star formation. An inner ring, only 130 light years from the center, almost certainly encircle a massive black hole.  In the center of the galaxy and within the inner starburst ring is a V-shaped structure of gas. The structure appears whitish-pink in this composite image, made up of four filters. Two filters capture the narrow lines from atomic transitions in oxygen and hydrogen; two wider filters detect green and near-infrared light. In the narrow-band filters, the V-shaped structure is very pronounced. This region, which is the projection of a three-dimensional cone extending from the nucleus to the galaxy’s halo, contains gas that has been heated by radiation emitted by the accreting black hole. A “counter-cone,” believed to be present, is obscured from view by dust in the galaxy’s disk. Ultraviolet radiation emerging from the central source excites nearby gas causing it to glow. The excited gas is beamed into the oppositely directed cones like two giant searchlights.

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