Centaurus A

Centaurus A (Cen A) is a nearby active galaxy in the constellation Centaurus. It is the closest such galaxy to our own Milky Way Galaxy and one of the most studied galaxies in the sky. Cen A is a member of the Virgo Cluster, which contains more than 2,000 galaxies. The Virgo Cluster is itself part of an even larger structure known as the Local Supercluster, which includes some 50,000 galaxies spread over 100 million light years.

Cen A is classified as a Seyfert 2 galaxy, meaning that it has a bright nucleus with strong emission lines in its spectrum. Seyfert galaxies are named after Carl Seyfert who first described them in 1943. In addition to its strong emission lines, Cen A also has a high level of radio emission due to its central black hole.

The distance to Cen A is estimated to be about 13 million light years, making it one of the closest active galaxies to us. Despite this relatively close distance, Cen A was not discovered until 1826 when James Dunlop observed it with a small telescope at Parramatta Observatory in Australia.

Since then, Cen A has been studied extensively across the entire electromagnetic spectrum from radio waves to gamma rays. In particular, detailed studies have been made of its jet – a stream of particles moving at near-light speed away from the central black hole along the axis of rotation of the galaxy. The jet extends for over 10 thousand light years and has been studied using radio telescopes all over the world including Australia’s CSIRO Parkes Observatory and America’s VLA (Very Large Array).

In 2010, astronomers using NASA’s Fermi Gamma-ray Space Telescope discovered that Cen A was emitting high-energy gamma rays – invisible photons with energies greater than X-rays on the electromagnetic spectrum. This discovery was surprising because most active galaxies emit their highest energy radiation at optical and ultraviolet wavelengths rather than gamma rays.