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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.
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Location & approach
The campus of TU Dortmund University is located close to interstate junction Dortmund West, where the Sauerlandlinie A 45 (Frankfurt-Dortmund) crosses the Ruhrschnellweg B 1 / A 40. The best interstate exit to take from A 45 is “Dortmund-Eichlinghofen” (closer to South Campus), and from B 1 / A 40 “Dortmund-Dorstfeld” (closer to North Campus). Signs for the university are located at both exits. Also, there is a new exit before you pass over the B 1-bridge leading into Dortmund.
To get from North Campus to South Campus by car, there is the connection via Vogelpothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at North Campus and use the H-Bahn (suspended monorail system), which conveniently connects the two campuses.
TU Dortmund University has its own train station (“Dortmund Universität”). From there, suburban trains (S-Bahn) leave for Dortmund main station (“Dortmund Hauptbahnhof”) and Düsseldorf main station via the “Düsseldorf Airport Train Station” (take S-Bahn number 1, which leaves every 15 or 30 minutes). The university is easily reached from Bochum, Essen, Mülheim an der Ruhr and Duisburg.
You can also take the bus or subway train from Dortmund city to the university: From Dortmund main station, you can take any train bound for the Station “Stadtgarten”, usually lines U41, U45, U 47 and U49. At “Stadtgarten” you switch trains and get on line U42 towards “Hombruch”. Look out for the Station “An der Palmweide”. From the bus stop just across the road, busses bound for TU Dortmund University leave every ten minutes (445, 447 and 462). Another option is to take the subway routes U41, U45, U47 and U49 from Dortmund main station to the stop “Dortmund Kampstraße”. From there, take U43 or U44 to the stop “Dortmund Wittener Straße”. Switch to bus line 447 and get off at “Dortmund Universität S”.
The AirportExpress is a fast and convenient means of transport from Dortmund Airport (DTM) to Dortmund Central Station, taking you there in little more than 20 minutes. From Dortmund Central Station, you can continue to the university campus by interurban railway (S-Bahn). A larger range of international flight connections is offered at Düsseldorf Airport (DUS), which is about 60 kilometres away and can be directly reached by S-Bahn from the university station.
The H-Bahn is one of the hallmarks of TU Dortmund University. There are two stations on North Campus. One (“Dortmund Universität S”) is directly located at the suburban train stop, which connects the university directly with the city of Dortmund and the rest of the Ruhr Area. Also from this station, there are connections to the “Technologiepark” and (via South Campus) Eichlinghofen. The other station is located at the dining hall at North Campus and offers a direct connection to South Campus every five minutes.
The facilities of TU Dortmund University are spread over two campuses, the larger Campus North and the smaller Campus South. Additionally, some areas of the university are located in the adjacent “Technologiepark”.