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With the help of the MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes on La Palma in the Canary Islands, researchers from TU Dortmund University have detected very-high-energy gamma rays from a recurrent nova in the Milky Way. It is the first nova in which such high-energy rays have been evidenced. The event could deliver new insights into this type of explosion and the possible role they play in generating the mysterious high-energy cosmic rays that permeate our Milky Way. The researchers’ findings were published recently in the prestigious journal Nature Astronomy.
When a star dies, it first expands into a red giant star and then collapses into a stellar corpse, a white dwarf. This is composed of a very dense material: A teaspoon of it would weigh about a ton. Under certain circumstances, these stellar corpses can trigger enormous explosions a second time: If the white dwarf has a companion star that for its part passes into the red giant phase, the hydrogen from the giant’s expanded outer layers can succumb to the tremendous gravitational pull of the dense dwarf and accumulate on its surface. In the process, the “dead” star extracts gas from the active star and is therefore also known as a “vampire star”. In isolated cases, even nuclear explosions on the surface can occur in such systems, catapulting a large proportion of the hydrogen and the fusion products into space. As the explosion is extremely bright, the process is also referred to as “stella nova” (new star, in short “nova”). In some cases, the gas transfer repeats and thus also the nova outburst. The term for this is “recurrent nova”.
Very-high-energy gamma rays
One of these recurrent novae is RS Ophiuchi in our Milky Way, for which the next outburst had been expected last year. On 8 August 2021, telescopes were then indeed able to detect the light of an explosion. One day later, astronomers from the MAGIC consortium, an international alliance of around 160 researchers, aimed their telescopes at the eruption taking place. The telescopes are an array of two Imaging Atmospheric Cherenkov Telescopes (IACT) with a diameter of 17 meters. Thanks to the good observation conditions on La Palma and the unique sensitivity of the MAGIC array, it was possible to detect very-high-energy gamma rays during the nova, which could be traced back to proton acceleration. “The observation of celestial objects in the presence of such great energies opens unique windows into the extreme Universe. It allows us to study in detail the processes where particles in the Universe are accelerated to energies significantly higher than in terrestrial experiments,” explains Dr. Dominik Elsässer from the Department of Physics and member of the MAGIC collaboration’s executive board.
Taken in isolation, nova outbursts are less energetic than their sisters – supernovae, in which a whole star is torn apart in an explosion – but they occur much more often. The results suggest that although most of the high-energy cosmic rays that permeate the Milky Way probably emanate from other sources, novae are apparently surprisingly efficient at generating local regions with an overdensity of cosmic rays in their surrounding environment. To fully understand such explosive events, further observations are needed. The research groups at TU Dortmund University are involved here, in particular with detector simulations and the development of intelligent analysis software. In addition, since January 2022 researchers from TU Dortmund University, Ruhr-Universität Bochum (RUB) and the University of Wuppertal have dedicated themselves, in the framework of Collaborative Research Center (CRC) 1491, to understanding the processes taking place in the cosmic interaction of various forms of matter. “It’s above all interdisciplinary cooperation between particle physics, astrophysics, plasma physics and data science that first makes fundamental breakthroughs possible,” says Professor Wolfgang Rhode, professor for astroparticle physics at TU Dortmund University and co-spokesperson of CRC 1491.
Full journal reference: https://www.nature.com/articles/s41550-022-01640-z
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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”.