Abstract

Invited Talk - Plenary

Tuesday, 10 September 2024, 09:15   (Aula 1&2 / virtual plenum)

Imaging Black Holes - A Very Long Baseline Interferometry Success Story

Anton Zensus
Max-Planck-Institut für Radioastronomie

The development of the Very Long Baseline Interferometry (VLBI) technique led to the groundbreaking achievement of capturing the first images of black holes, including those at the centers of the elliptical galaxy M87 and our own Milky Way. Since the 1970s, model computations have consistently shown that the signature of a black hole embedded in a luminous plasma, such as an accretion disk, would appear as a dark silhouette with an angular size proportional to the black hole’s mass and inversely proportional to its distance. However, even for the most promising candidates, it was clear early on that reaching the necessary angular resolution, sensitivity, and image quality would require significant advancements far beyond the capabilities of 1990s arrays.
Two primary approaches to overcome these challenges were pursued: extending interferometric baselines beyond Earth using space-based elements (Space VLBI) and observing at the shortest radio wavelengths accessible from the ground (mm-VLBI). The quest to image black holes ultimately succeeded thanks to the development of large new instruments, such as the Atacama Large Millimeter/submillimeter Array (ALMA), which were combined with mm-wavelength telescopes across Europe, the Americas, Antarctica, and Oceania. This effort also required enhancing the sensitivity and bandwidth of existing mm-receivers and devising new methods for processing vast amounts of data. In this lecture, I address the scientific motivation of these development, the technical and organisational challenges and the opportunities for this field going forward.