Centaurus A(redirected from Caldwell 77)
Centaurus AAn intense radio and X-ray source in the southern constellation Centaurus and a source also of infrared radiation and gamma rays. It is identified with the galaxy NGC 5128 lying at a distance of only 5 megaparsecs from the Solar System, making it the nearest active galaxy. It is an elliptical galaxy, 100 kpc in diameter, cut across by broad belts of gas and dust. A complex elongated radio structure emerges from the center of the gas and dust belts, approximately along their axis of rotation and extending about 400 kpc in each direction. The radio structure consists broadly of two large lobes more or less symmetrically disposed about a central nucleus, from which a jet extends toward one of the lobes. The jet is broken up into a number of knots. This huge radio galaxy, stretching over 9° of the sky, has a flux density at 86 megahertz of 8700 jansky, believed to be synchrotron emission.
Centaurus A is also one of the brightest hard X-ray sources, its spectrum being measured to about 200 kiloelectronvolts. It is also variable on timescales down to a few days, suggesting that most of the X-ray emission arises in the nucleus. An Einstein Observatory image showed not only the bright nucleus but in addition a line of sources, i.e. an X-ray jet, significantly along the axis of the radio lobes. The X-ray emission follows closely the radio jet but extends beyond it into the radio lobe.