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International Research Team Detects Kink in Plasma Flow

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In the center of a black background, a blue-white round light source can be seen, from which an equally blue-white beam emanates. Around the light source are individual bright dots. © Peter Jurik​/​Adobe Stock
Artist’s impression of a black hole with a jet.

An international team has been able to gain an unprecedented view of the processes that occur in an active galactic nucleus. With the help of data collected by telescopes around the world, they were able to corroborate a process taking place in the plasma jet of the active galactic nucleus BL Lacertae that had long been assumed. The evidence is so spectacular that the work has made it into the current issue of the prestigious scientific journal Nature. Associate professor Dr. Dominik Elsässer from the Department of Physics at TU Dortmund University was also involved in the observations. To collect the data, he worked with school students from Würzburg.

Active galactic nuclei are among the most luminous objects in the Universe. They are extremely bright core regions of galaxies that can be observed from great distances. Their brightness usually results from the processes taking place around a black hole, toward which matter from the surrounding area rushes. Plasma flows of charged particles, known as jets, sometimes form in the process. Astrophysicists are studying active galactic nuclei and their jets because they suspect that these particles can accelerate at an enormous rate and in the process reach far higher energies than the largest particle accelerators on Earth.

Kink in plasma flow causes fluctuations in brightness

“Blazars” are a subclass of active galactic nuclei, and a well-known one is “BL Lacertae”: This galaxy, about 900 million light years away, hosts a black hole with a mass 170 million times greater than that of our Sun. When analyzing data from a particular outburst of BL Lacertae in 2020, astronomers noticed that the brightness fluctuated at an unusually regular rate. The researchers were able to explain these quasi-periodic oscillations with a change in the jet’s plasma, known as kink instability, which influences the magnetic field. The visible fluctuations in brightness occur because the high-energy particles in the jet move through precisely this kink.

“Kink instability is very important for the study of plasmas. The discovery in the jet of BL Lacertae now permits entirely new insights into this cosmic particle accelerator,” says Dr. Dominik Elsässer. This is the reason why the work was selected for publication by the prestigious scientific journal Nature. The article was compiled within the Whole Earth Blazar Telescope project, an international consortium of astronomers who are monitoring above all blazars.

School students monitor the brightness of active galactic nuclei

Some of the data that led to the current publication in Nature originate from a collaborative project between Friedrich-Koenig-Gymnasium, a high school in Würzburg, the Chair for Astronomy at the University of Würzburg and the Department of Physics at TU Dortmund University. The school students have monitored the brightness of active galactic nuclei in their laboratory for ten years. They carry out the measurements independently on over 100 nights each year and also evaluate the data themselves. Professor Karl Mannheim from the University of Würzburg and Dr. Dominik Elsässer from TU Dortmund University are the project’s scientific directors.

Several students standing around a telescope in an observatory. © Naturwissenschaftliches Labor für Schüler am FKG e.V.
School students around a telescope in the observatory.

To the publication in Nature

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PD Dr. Dominik Elsässer
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