Karl Schwarzschild Medal 2024 for Anton Zensus
The Astronomische Gesellschaft awards the Karl Schwarzschild Medal to Prof. Dr. Anton Zensus, Director at MPIfR in Bonn, recognizing his leading role in the development of radio astronomical observation methods with very high angular resolution and sensitivity. Very Long Baseline Interferometry (VLBI) has developed into a key observation method, particularly due to the influence of Anton Zensus and his research group. The unique images from the Event Horizon Telescope project, which show the supermassive black holes in the elliptical galaxy M87 and in the center of our Milky Way, have caused a worldwide sensation and opened up new avenues for research into active galactic nuclei.
Anton Zensus, Director at the Max Planck Institute for Radio Astronomy (MPIfR) and head of the research department "Radio Astronomy / VLBI" at the MPIfR, has been a leading figure in the development of radio astronomy with extreme angular resolution and sensitivity for decades. Already in the early 1980s, he made significant contributions to the technique of "Very Long Baseline Interferometry" (VLBI) which makes it possible to image the structure of the central regions of active galactic nuclei. At that time, VLBI was optimized for radio waves in the centimetre range and could produce images on the scale of light years. This was sufficient to study details in the jets, but not to fully resolve the central source of the galaxies and identify their driving mechanisms.
To confirm the prediction that the central driving mechanisms consist of supermassive black holes, a much higher resolution was required. This meant extending the VLBI technique to shorter wavelengths in the millimeter range and even including radio telescopes orbiting the Earth.
Anton Zensus and his team at the MPIfR rose to this challenge. They integrated the IRAM telescopes on Pico-Veleta in Spain and on the Plateau de Bure in France into VLBI observations at 1.3 mm wavelength. Subsequently, the VLBI network was extended to transatlantic scales and established in collaboration with international partners as the "Global Millimeter VLBI Array" (GMVA), which provided reliable research data at 3 mm wavelength. The next step was to select telescopes capable of observing at 1.3 mm and even at 0.87 mm wavelength (230 and 345 GHz respectively), including the two IRAM telescopes, APEX and ALMA, and to equip the telescopes with the necessary hardware and software.
Since the late 1970s, it had been known from calculations that the event horizon of a supermassive black hole appears as a dark "shadow" whose size in the sky depends directly on the distance and mass of the object against the distorted background of gas emissions from its surroundings. The small size of the expected shadow, even for the best candidates, the central sources of the galaxy M87 and our Milky Way, made it clear that significant improvements in observational technology and global collaboration were needed to image these objects directly. This gave rise to the "Event Horizon Telescope" (EHT) project, which uses VLBI observations at short wavelengths (1.3 mm). This is done with a large number of telescopes distributed across Europe, North and South America, Oceania and Antarctica to achieve an angular resolution of 20 microarcseconds.
The EHT measurements not only confirmed the masses previously determined by other methods, but also made it possible for the first time to image the shadow of a black hole compared to the relativistic matter orbiting it in close proximity - just a few Schwarzschild radii from the center.
The Schwarzschild radius corresponds to the radius defining the event horizon of a black hole in the Schwarzschild solution of Einstein’s field equations. It is named in honor of the German astronomer Karl Schwarzschild after whom the Karl Schwarzschild medal is named.
This is much closer to the central source than with other methods, and into the region where the effects of general relativity are most clearly visible. Anton Zensus played an important and fundamental role from the very beginning, especially as the founding chairman of the EHT board. He succeeded in promoting and stabilizing the necessary but complex synergies between various initially competing groups in Europe, the USA and Asia, which ultimately made the success of the EHT possible.
"The Karl Schwarzschild Medal of the Astronomical Society is a great honor. It recognizes our achievements in getting closer and closer to the innermost regions and the central driving sources of active galactic nuclei. With the contributions of our global team and the research possibilities of the Max Planck Society, we have succeeded in making black holes directly visible for the first time, namely as a silhouette against the background of the luminous gas surrounding them," Anton Zensus is pleased to say.
The award is in line with a number of earlier Schwarzschild Prize winners investigating the central sources of active galaxies, starting with the discovery of quasars (Maarten Schmidt, KSM 1968), accretion disks around black holes (Bohdan Paczinsky, KSM 1981), the question of whether there are black holes in every galaxy (Martin Rees, KSM 1989) and most recently the investigation of supermassive black holes, in particular Sgr A*, in the centers of galaxies (Reinhard Genzel, KSM 2011).
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Biographical Notes:
Prof. Dr. J. Anton Zensus received his PhD from the University of Münster and worked as a postdoctoral fellow and research associate at the California Institute of Technology and the National Radio Observatory in the United States. Anton Zensus is known for his innovative research and technology program, in particular for his leading contributions to the study of active galactic nuclei (AGN) and their central radio sources and jets using Very Long Baseline Interferometry (VLBI). Together with his collaborators, he has made groundbreaking technological and methodological breakthroughs, including significant improvements in VLBI observations of polarized sources, accurate position measurements from VLBI data, and detailed analysis of the two-dimensional structure of radio emission. Zensus and his team have developed several generations of digital imagers, designed and operated a powerful VLBI correlator capable of processing both space and mm-VLBI data, and provided critical components for the integration of ALMA into the VLBI network. As founding Chairman of the EHT Collaboration Board, Anton Zensus has made important contributions to all aspects of this research program.
Anton Zensus is Director at the Max Planck Institute for Radio Astronomy and Head of the Research Department "Radio Astronomy/VLBI", as well as Honorary Professor at the Institute for Astrophysics, University of Cologne.
Wissenschaftlicher Ansprechpartner:
Prof. Dr. Anton Zensus
Director and Head of Research Department „Radio Astronomy / VLBI“
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49 228 525-378
E-mail: azensus@mpifr-bonn.mpg.de
Prof. Dr. Eduardo Ros
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49 228 525-125
E-mail: ros@mpifr-bonn.mpg.de
Weitere Informationen:
https://www.mpifr-bonn.mpg.de/announcements/2024/5
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