jet

History

The first jets were noticed in galaxy M87 in 1918, but their nature was not understood for a long time. In the 1970s, with the development of radio astronomy, it became clear that they are associated with black holes.

How it works

Around a black hole, a disk of gas (accretion disk) rotates. Due to strong magnetic fields and rotation, some of this gas does not fall into the hole but is ejected outward along the rotation axis, like spinning pizza dough — it flies apart.

History

The first jets were noticed in galaxy M87 in 1918, but their nature was not understood for a long time. In the 1970s, with the development of radio astronomy, it became clear that they are associated with black holes.

How it works

Around a black hole, a disk of gas (accretion disk) rotates. Due to strong magnetic fields and rotation, some of this gas does not fall into the hole but is ejected outward along the rotation axis, like spinning pizza dough — it flies apart.

History

An extended stream in galaxy M87 was first described by Heber Curtis in 1918. For a long time, jets were considered rare, but with the development of radio interferometry in the 1970s, they were discovered in many active galactic nuclei and quasars. Theoretical understanding advanced thanks to the work of Roger Blandford and Roman Znajek (the Blandford-Znajek mechanism for extracting energy from a rotating black hole) and John Wheeler, who coined the term 'black hole' and promoted recognition of their astrophysical role. Space observatories (Hubble, Chandra, Event Horizon Telescope) have allowed observation of jets at high resolution.

How it works

Gas falling onto a compact object forms a rotating accretion disk. The frozen-in magnetic field of the disk is amplified by differential rotation. Part of the rotational energy is transferred to the plasma via magnetic stresses, and it is ejected as two oppositely directed streams. For black holes, an additional mechanism is possible: the rotating hole interacts with the magnetic field, inducing an electric potential and accelerating charges along the axis — the Blandford-Znajek process. Conservation of angular momentum plays a key role.

Open problems & fun facts

The collimation mechanism is not fully understood: why do jets remain so narrow over enormous distances?; Composition problem: the relative contribution of electron-positron plasma compared to ordinary electron-ion plasma is not precisely known.; Formation of extremely powerful jets from quasars at limited accretion rates.

💡 Some jets rotate around their axis, displaying a spiral structure of the magnetic field twisted like a donut — this phenomenon is called a 'magnetic rope'.