Reinhard Genzel

Reinhard Genzel is a German astrophysicist whose infrared observations of stars near the Milky Way’s center helped establish that a supermassive black hole lies there.

Sagittarius A*: The compact radio source at the Milky Way’s center, associated with its supermassive black hole. The object whose mass Genzel’s team inferred from nearby stars’ orbits.
Infrared astronomy: The study of celestial objects through infrared radiation. Infrared wavelengths penetrate dust that obscures the Milky Way’s central region in visible light.
Andrea Ghez: An American astronomer whose observations of stars near the Milky Way’s center independently supported a central supermassive black hole. Ghez led the other team that shared the 2020 Nobel Prize with Genzel.
Black hole: A region of spacetime whose gravity prevents anything, including light, from escaping beyond its event horizon. Genzel’s measurements established strong evidence for one at the Milky Way’s center.
S2 (star): A star that completes a highly eccentric orbit around Sagittarius A* in about 16 years. Its observed orbit provided a precise probe of the central object’s mass and compactness.
Adaptive optics: A technique that corrects telescope-image distortions caused by Earth’s atmosphere in real time. It sharpened images enough to distinguish stars in the crowded Galactic center.
Reinhard Genzel's research group: The team at the Max Planck Institute for Extraterrestrial Physics that developed long-term Galactic-center observations. Its coordinated measurements tracked stellar motions across decades.
Supermassive black hole: A black hole with a mass from hundreds of thousands to billions of solar masses. The inferred central mass places Sagittarius A* in this class.
Galactic Center: The central region of the Milky Way, containing a dense star cluster and Sagittarius A*. The crowded region where Genzel’s group tracked stellar motions.
Stellar orbit: The path followed by a star under the gravitational influence of other masses. Orbit shapes and periods reveal the mass and location of the central gravitating object.

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