Reinhard Genzel
German astrophysicist who co-discovered the Milky Way's central supermassive black hole.
Reinhard Genzel is a German astrophysicist born on 24 March 1952 in Bad Homburg vor der Höhe. His father, Ludwig Genzel, was a professor of solid state physics. Genzel studied physics at the University of Freiburg and the University of Bonn, earning his PhD in radioastronomy in 1978 from the Max Planck Institute for Radio Astronomy. He then worked at the Center for Astrophysics at Harvard & Smithsonian in Cambridge, Massachusetts, and was a Miller Fellow from 1980 to 1982. During this period, he also became an associate and later a full professor in the Department of Physics at the University of California, Berkeley, starting in 1981. In 1986, he left Berkeley to become a director at the Max Planck Institute for Extraterrestrial Physics in Garching and a Scientific Member of the Max-Planck-Gesellschaft. He has been an honorary professor at LMU Munich since 1988 and held a part-time joint appointment as a full professor at UC Berkeley from 1999 to 2016. Genzel’s research focuses on infrared and submillimetre astronomy, and he and his group develop ground- and space-based instruments. They tracked the motions of stars at the centre of the Milky Way around Sagittarius A*, demonstrating that these stars orbited a very massive object, now identified as a black hole. In July 2018, Genzel and colleagues reported that the star S2, during its pericentre approach in May 2018, reached a speed of 7,650 km/s, or 2.55% the speed of light, at about 120 AU from Sgr A*. This observation allowed them to test the redshift predicted by general relativity at relativistic velocities, providing additional confirmation of the theory. Genzel also studies the formation and evolution of galaxies. He was awarded a quarter-share of the 2020 Nobel Prize in Physics, shared with Andrea Ghez and Roger Penrose, for the discovery of a supermassive compact object at the centre of our galaxy.
- field
- Astrophysics
- nationality
- German
- known_for
- Discovery of a supermassive compact object at the centre of the Milky Way
- awards
- Nobel Prize in Physics (2020)
Verified Timeline
Lore & Background
Reinhard Genzel led an international team at the Max Planck Institute for Extraterrestrial Physics that, on October 16, 2002, reported the observation of the motion of the star S2 near Sagittarius A* throughout a period of ten years. According to the team's analysis, the data ruled out the possibility that Sgr A* contains a cluster of dark stellar objects or a mass of degenerate fermions, strengthening the evidence for a massive black hole. The observations used near-infrared interferometry in the Ks-band (2.1 μm) because of reduced interstellar extinction in that band. SiO masers were used to align NIR images with radio observations. From examining the Keplerian orbit of S2, they determined the mass of Sagittarius A* to be 4.1±0.6 million solar masses, confined in a volume with a radius no more than 17 light-hours (120 AU). Later observations of the star S14 showed the mass to be about 4.1 million solar masses within a volume with radius no larger than 6.25 light-hours (45 AU). Genzel's team also determined the distance from Earth to the Galactic Center as 8,000 ± 600 parsecs (30,000 ± 2,000 light-years). In 1994, infrared and sub-millimetre spectroscopy studies by a Berkeley team involving Nobel Laureate Charles H. Townes and future Nobel Prize Winner Reinhard Genzel showed that the mass of Sgr A* was tightly concentrated and on the order of 3 million Suns. After monitoring stellar orbits around Sagittarius A* for 16 years, Gillessen et al. (with Genzel as team leader) estimated the object's mass at 4.31±0.38 million solar masses, announced in 2008 and published in 2009. Genzel said the study delivered 'what is now considered to be the best empirical evidence that supermassive black holes do really exist. The stellar orbits in the Galactic Center show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt.'
Reader's Guide
Reinhard Genzel's key contribution is the observational proof that Sagittarius A* is a supermassive black hole at the centre of the Milky Way. Using infrared and submillimetre spectroscopy, his team tracked the orbits of stars like S2 and S14 around Sgr A* over many years. The Keplerian orbit of S2 gave a mass of 4.1±0.6 million solar masses within a radius of 17 light-hours, and later S14 refined that to 4.1 million solar masses within 6.25 light-hours. These measurements ruled out alternative explanations such as a cluster of dark stellar objects or degenerate fermions. Genzel's work, alongside Andrea Ghez's, earned them each a quarter-share of the 2020 Nobel Prize in Physics, with Sir Roger Penrose receiving the other half. The discovery confirmed that the only explanation for the compact object at the Galactic Center is a black hole, fundamentally changing our understanding of the Milky Way's structure and the role of supermassive black holes in galaxies.
Did You Know?
- Reinhard Genzel was awarded a quarter-share of the 2020 Nobel Prize in Physics for his discovery that Sagittarius A* is a supermassive compact object, for which a black hole was the only explanation.
- In 1994, Genzel was part of a Berkeley team (including Nobel Laureate Charles H. Townes) that showed the mass of Sgr A* was tightly concentrated and on the order of 3 million Suns.
- On October 16, 2002, Genzel's team reported that observations of star S2 ruled out the possibility that Sgr A* contains a cluster of dark stellar objects or a mass of degenerate fermions.
- Genzel's team determined the distance from Earth to the Galactic Center as 8,000 ± 600 parsecs (30,000 ± 2,000 light-years).
- After 16 years of monitoring stellar orbits, Genzel's team estimated the mass of Sgr A* at 4.31±0.38 million solar masses, announced in 2008.
Frequently Asked Questions
Who is Reinhard Genzel?
Reinhard Genzel is a German astrophysicist born on 24 March 1952 who currently serves as co-director of the Max Planck Institute for Extraterrestrial Physics. He is most celebrated for his pioneering research into the heart of the Milky Way.
What discovery made Reinhard Genzel famous?
Genzel headed a team that provided compelling evidence for a supermassive compact object sitting at the center of our galaxy, now widely recognized as a supermassive black hole. That finding reshaped how astronomers think about galactic cores.
What major award did Reinhard Genzel receive?
In 2020 he was granted the Nobel Prize in Physics for identifying that supermassive compact object at the Milky Way's center. The honor was shared with fellow astrophysicist Andrea Ghez and theorist Roger Penrose.
Where does Reinhard Genzel work?
He holds the co-directorship at the Max Planck Institute for Extraterrestrial Physics in Germany. Much of his landmark work on galactic nuclei was carried out in that setting.
Who shared the 2020 Nobel Prize in Physics with Reinhard Genzel?
Andrea Ghez received half the prize for independently confirming the Milky Way's central black hole, while Roger Penrose was recognized for his theoretical contributions to understanding black hole formation. Genzel split the other half with Ghez.
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