Professor Dr. Karl Martin Menten
03 October 1957 — 30 December 2024
On December 30, 2024, Professor Dr. Karl Martin Menten, Scientific Member of the Max Planck Society and Director at the Max Planck Institute for Radio Astronomy in Bonn, Germany, died at the age of 67.
Karl Menten's research spanned a wide range of astrophysical topics, from the birth of stars to their end of evolution, and star formation in the Milky Way to the Early Universe. Early on in his career, he discovered a widespread methanol maser transition, the brightest of its kind, that since then has been used as a signpost for the early stages of massive star formation but also as a tool for high precision astrometry.
Karl Menten studied Physics and Astronomy at the Rheinische Friedrich-Wilhelms-Universität in Bonn and earned his doctoral degree in 1987, with a dissertation on “Interstellar Methanol towards Galactic HII Regions”. He worked as a postdoctoral research fellow at the Harvard College Observatory at the Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, MA, USA, later-on as radio astronomer and senior radio astronomer at the Smithsonian Astrophysical Observatory before he was appointed scientific member of the Max Planck Society and Director for Millimeter and Submillimeter Astronomy at the Max Planck Institute for Radio Astronomy in Bonn in 1996.
Menten's groundbreaking career began with two transformative projects during his postdoctoral years. He led the discovery of seven sub-millimeter water vapor maser transitions, including isotopic lines, documented in five landmark papers. These discoveries opened the field of sub-millimeter maser astronomy and advanced the theoretical understanding of radiative transfer in such environments.
His discovery of the 6.7 GHz methanol maser remains one of molecular astronomy’s most significant breakthroughs. Methanol masers, intensely bright and prevalent in high-mass star-forming regions, are critical for identifying massive young stellar objects and performing high-precision astrometry. Menten’s VLBI imaging revealed their pivotal role in probing galactic structure and dynamics.
In 2010, Karl Menten co-founded the Bar and Spiral Structure Legacy (BeSSeL) Survey with Mark Reid, mapping over 150 methanol maser sources with trigonometric parallaxes accurate to ±10 microarcseconds. BeSSeL confirmed the Milky Way’s four-armed spiral structure, refined the Sun’s distance from the Galactic center to 8.15 kpc, and determined the Galaxy’s rotation speed to 236 km/s. This work surpassed Gaia’s capabilities in the Galactic plane and contributed to refining orbital decay measurements of the Hulse-Taylor binary pulsar.
His contributions to the study of the Galactic Centre have been equally transformative. He developed a calibration grid linking radio and infrared images with milliarcsecond precision using radio interferometry. This grid was used in the interpretation of the Nobel Prize-winning observations of stellar orbits around Sgr A* by Genzel and Ghez.
As director of the Max Planck Institute for Radio Astronomy, Karl Menten championed millimeter and submillimeter astronomy, driving the construction of the Atacama Pathfinder Experiment (APEX), which has yielded over 1000 peer-reviewed papers. He also secured European participation in ALMA, revolutionizing studies of molecular and dust emissions in galaxies and shaping our understanding of star formation and galaxy evolution across cosmic time.
He made important contributions to astrochemistry through his observations and initial discoveries of a large number of hydrides, the simplest building blocks of interstellar molecular chemistry. In addition to APEX, he also drove the construction of instruments for these studies at the Herschel Space Observatory and the Stratospheric Observatory for Infrared Astronomy (SOFIA).
He also continued a long Bonn tradition of sky surveys: the observations of cold dust and molecules in the Milky Way with APEX allowed a complete census and characterization of the massive star-forming regions and their surrounding molecular clouds. By combining the Effelsberg radio telescope and the Very Large Array in New Mexico, it was also possible to map the hot gas ionized by newly formed stars in these clouds, as well as the maser emission from protostars.
Menten’s stellar astrophysics contributions include determining the Orion Nebula’s distance and studying red giants with masers near the Galactic center, advancing knowledge of stellar mass loss and interstellar medium enrichment.
By integrating observational, theoretical, and technological advancements, Menten has inspired a generation of scientists and revitalized radio astronomy. His unparalleled achievements made him a towering figure in modern astronomy.
Letters of condolence can be sent to condolence-Karl-Menten@mpifr.de
The Directors at the Max Planck Institute for Radio Astronomy
Michael Kramer
Amélie Saintonge
J. Anton Zensus