Karl-Heinz Mack, a German radio astronomer who spent most of his career in Italy and became a cornerstone of the country's astrophysics community, has died. Colleagues and former students remember him as a generous mentor, a dedicated scientist, and a key figure in bridging the German and Italian astronomical traditions.
Mack's academic journey began at the University of Bonn, where he completed his entire education, earning a PhD in 1996. His doctoral research focused on extragalactic radio sources, and even then his work connected German and Italian facilities: he used the Effelsberg radio telescope in Germany alongside early observational campaigns at the Medicina telescope near Bologna, Italy.
After a postdoctoral year in Bonn, Mack moved to Dwingeloo in the Netherlands in 1997 to work at the Dutch radio astronomy institute Astron. The turning point came in 1999 when he won a Marie Curie fellowship that brought him to Bologna. He quickly integrated into the research environment at what was then the CNR Institute of Radio Astronomy, now part of the National Institute for Astrophysics (INAF). In 2001 he won a permanent researcher position, and in 2010 he became a senior researcher. Bologna became his home and scientific base for the rest of his career.
At the Bologna institute, Mack carried out influential research on radio galaxies, relativistic jets, and hot spots in radio galaxies. He also took on a crucial role in protecting Italy's radio telescopes from technological threats. He led complex projects for frequency defense and interference mitigation, safeguarding the invisible sky observed by the antennas at Medicina, Noto, and the Sardinia Radio Telescope. He promoted common operational approaches for single-dish radio telescopes across Italy.
Throughout his career, Mack placed great importance on teaching and public outreach. He was among the promoters of the Marcello Ceccarelli Visitor Center at the Medicina telescope site, which helps the public understand radio astronomy.
Former students and colleagues have shared memories that highlight Mack's humanity and dedication. Alice Pasetto, a former master's student, recalled entering his office and being struck by his warmth. She said Mack encouraged her to pursue radio astronomy, spent long hours discussing science and life with her, and supported her through the difficulties of studying far from home. He convinced her to travel to Bonn for observations with the Effelsberg telescope, an experience she described as one of the most important of her life. She credited him with helping her become the radio astronomer she is today.
Another former student, who called Mack «Doktorvater» — a German term for a doctoral advisor — thanked him for his immense generosity and for introducing him to the world of radio astronomy. He remembered Mack teaching him about single-dish telescopes and taking him to Effelsberg for the first time. The student said Mack gave him the freedom to pursue his own proposals and manage his own work, which built his confidence and helped him grow as an astronomer. He also recalled Mack's personal kindness: when the student arrived in Bologna, Mack had already arranged housing for him. He remembered their lunches at the institute canteen and Mack's habit of drinking lemon juice with water for vitamins.
Mack's death marks the loss of a scientist who not only advanced the study of radio galaxies and relativistic jets but also built lasting bridges between the German and Italian astronomical communities. His legacy lives on in the students he trained, the telescopes he protected, and the collaborative spirit he fostered.
