Jets

Active galactic nuclei: Observations indicate that many galaxies most likely harbour extremely massive rotating black holes (with masses of a million to several billion times the mass of the sun) in their centers. The black hole swallows interstellar gas and stars, if they enter the sphere of influence of the black hole's gravitational field. Before being swallowed the stars are torn apart by tidal forces. In a still not fully understood process, the energy liberated during this process is used to eject a very small part of the sucked in gas in form of two collimated gas streams, called jets, along the rotation axis of the black hole.

According to Einstein's theory of General Relativity, a distribution of mass which collapses to a radius smaller than its gravitational (Schwarzschild) radius decouples from its surroundings and forms a black hole. Nothing, not even light, can leave the black hole, and reach the outside world. For the Sun the Schwarzschild radius is about three kilometers. Observations indicate that many galaxies most likely harbour extremly massive rotating black holes (with masses of a million to several billions times the mass of the sun) in their centers. Black holes with masses of several times the mass of the sun are supposed to be one of the components of a number of X-ray binaries observed in the Milky Way.

Shock waves or shock fronts are discontinuities in gas or fluid flows where the density, pressure and velocity jump abruptly. Shock fronts can be created by objects that move supersonically through a medium, for example in the earth atmosphere by a plane flying faster than the speed of sound. The bow shocks of astrophysical jets propagate with up to 10 000 times the speed of sound and with up to 99,99 percent of the speed of light through interstellar and intergalactic space.

Shock waves or shock fronts are discontinuities in gas or fluid flows where the density, pressure and velocity jump abruptly. Shock fronts can be created by objects that move supersonically through a medium, for example in the earth atmosphere by a plane flying faster than the speed of sound. The bow shocks of astrophysical jets propagate with up to 10 000 times the speed of sound and with up to 99,99 percent of the speed of light through interstellar and intergalactic space.

Shock waves or shock fronts are discontinuities in gas or fluid flows where the density, pressure and velocity jump abruptly. Shock fronts can be created by objects that move supersonically through a medium, for example in the earth atmosphere by a plane flying faster than the speed of sound. The bow shocks of astrophysical jets propagate with up to 10 000 times the speed of sound and with up to 99,99 percent of the speed of light through interstellar and intergalactic space.

Many galaxies, like 3C219 shown here, have an active galactic nucleus with a massive black hole in the center. The black hole swallows gas and stars in its neigbourhood. Two collimated gas streams form, which can propagate at a velocity very close to the speed of light. These jets extend, perpendicular to the plane of the galaxy, several hundred thousand light years into intergalactic space, visible by their intensive radio emission. The propagation of astrophysical jets is studied at the MPA by means of computer simulations. Gas enters through a nozzle the computational domain, which is homogeneously filled with a denser gas. The velocity of the injected gas is six times the speed of sound. Because of the supersonic propagation of the jet a bow shock forms. Some gas in the beam is deflected sideways at the head of the jet and accumulates in the turbulent coccoon, which encloses the beam. Shock waves and expansion waves within the beam are the cause for the remarkable collimation of the jet.