Fountain-shaped sources of matter are observed in astronomical systems at different speeds, ranging from fast to slow. Jets of matter flowing at different speeds, from fast to slow, are commonly observed in astronomical systems. The fastest jets are relative and can reach speeds close to the speed of light. Although this phenomenon is widely observed, the origin and many characteristics of these jets remain a mystery.

For a long time, experts were stunned by the bi-mode speed distribution of jet aircraft, some incredibly fast and others incredibly slow, and a noticeable lack of speed in between. However, researchers at Bar-Ilan University have looked at the data and seem to have finally solved this puzzling riddle.

In many different galactic and extragalactic systems, matter emission is usually observed in the form of jets. The pace at which this show takes place varies greatly. Besides the relatively slow jets associated with neutron stars or binary star systems, there are also very fast relativistic jets whose velocities are very close to the speed of light. The fastest known jets are associated with a phenomenon known as gamma-ray bursts.

This phenomenon is characterized by the first gamma-ray burst lasting a few seconds, during which strong gamma-ray emission can be seen. Then comes the “final redness”, which lasts much longer—hours, days, or even months. During this period the radiation gradually weakens and is observed at lower wavelengths, as X-rays, ultraviolet, optical, infrared and, very late, radio frequencies.

Aside from the question of why the jets from these objects are so fast, it remains a seemingly unrelated mystery as to what happens during the intervening period of hundreds to thousands of seconds when the radiation either dies or remains constant. In some cases, after a few tens of seconds, X-ray emission is significantly reduced, as would be expected from a relative explosion colliding with matter and radiation in the interstellar space of the galaxy.

However, in about 60% of observed cases, visible radiation does not disappear, it remains constant. This observation has long been a source of confusion for researchers, and no convincing explanation has been found since the phenomenon was discovered nearly 18 years ago.

Researchers in the Department of Physics at Bar-Ilan University have now shown that this apparent continuous emission is a natural consequence of a jet velocity that is much lower than previously thought and bridges the gap between velocities measured from different sources. In other words, the lower initial velocity of the jet could explain the lack of distortion and the more visible and persistent emission. The researchers showed that previous results of high velocities in these objects are invalid in these cases. They also changed the paradigm and proved that jets occur in nature at any speed.