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Genzel, Reinhard
Genzel, Reinhard
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Eisenhauer, Frank
Eisenhauer, Frank
scientist
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Room: X5 1.2.52
Gillessen, Stefan
Gillessen, Stefan
scientist
Phone: +49 (0)89 30000-3839
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Hämmerle, Hannelore
Hämmerle, Hannelore
press officer
Phone: +49 (0)89 30000-3980
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Room: X5 1.2.20

Original publication

1.
GRAVITY Collaboration
Detection of the Gravitational Redshift in the Orbit of the Star S2 near the Galactic Centre Massive Black Hole

Videos

Gravitational redshift

Artist’s impression of the gravitational redshift of S2 when passing the supermassive black hole at centre of Milky Way.

S2 closest approach

This time-lapse view shows images from the GRAVITY instrument as it tracks the progress of the star S2 during the close passage past the black hole in May 2018.

S2 orbit

Animation of the orbit of the star S2 around the galactic centre black hole

More Information

A team of European astronomers has achieved a crucial milestone for testing Einstein's theory of general relativity with the closest supermassive black hole in the centre of our own galaxy. For the first time, the newly installed GRAVITY instrument has been used together with ESO's Very Large 8m Telescopes to observe a star orbiting the black hole on a period as short as 16 years. Both the target star and a reference star nearby show no signs of being binaries – making future measurements much less complex.

The ideal black hole laboratory

June 21, 2016

A team of European astronomers has achieved a crucial milestone for testing Einstein's theory of general relativity with the closest supermassive black hole in the centre of our own galaxy. For the first time, the newly installed GRAVITY instrument has been used together with ESO's Very Large 8m Telescopes to observe a star orbiting the black hole on a period as short as 16 years. Both the target star and a reference star nearby show no signs of being binaries – making future measurements much less complex.

[more]
Zooming in on black holes is the main mission for the new GRAVITYinstrument, built by a large team of European astronomers and engineers led by the MPE, and now installed at ESO’s Very Large Telescope in Chile. During its first observations, GRAVITY successfully combined starlight using all four Auxiliary Telescopes.

"First Light" for GRAVITY

January 13, 2016

Zooming in on black holes is the main mission for the new GRAVITYinstrument, built by a large team of European astronomers and engineers led by the MPE, and now installed at ESO’s Very Large Telescope in Chile. During its first observations, GRAVITY successfully combined starlight using all four Auxiliary Telescopes. [more]

MPE Press Release

First Successful Test of Einstein’s General Relativity Near Supermassive Black Hole

July 26, 2018

Observations of the Galactic Centre team at the Max Planck Institute for Extraterrestrial Physics (MPE) have for the first time revealed the effects predicted by Einstein’s general relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole in the centre of the Milky Way. This long-sought result represents the climax of a 26-year-long observation campaign using ESO’s telescopes in Chile.

This simulation shows the orbits of stars very close to the supermassive black hole at the heart of the Milky Way. Zoom Image
This simulation shows the orbits of stars very close to the supermassive black hole at the heart of the Milky Way.

Obscured by thick clouds of absorbing dust, the closest supermassive black hole to the Earth lies 26 000 light-years away at the centre of the Milky Way. This gravitational monster, which has a mass four million times that of the Sun, is surrounded by a small group of stars orbiting around it at high speed. This extreme environment — the strongest gravitational field in our galaxy — makes it the perfect place to explore gravitational physics, and particularly to test Einstein’s general theory of relativity.

New infrared observations from the exquisitely sensitive GRAVITY , SINFONI and NACO instruments, developed under the lead of the Max Planck Institute for Extraterrestrial Physics (MPE), have now allowed astronomers to follow one of these stars, called S2, as it passed very close to the black hole during May 2018. At the closest point this star was at a distance of less than 20 billion kilometres from the black hole and moving at a speed in excess of 25 million kilometres per hour — almost three percent of the speed of light.

The S2 orbit around the Black Hole, measured with different instruments. Zoom Image
The S2 orbit around the Black Hole, measured with different instruments.

The team compared the position and velocity measurements from GRAVITY and SINFONI respectively, along with previous observations of S2 using other instruments, with the predictions of Newtonian gravity, general relativity and other theories of gravity. The new results are inconsistent with Newtonian predictions and in excellent agreement with the predictions of general relativity.

These extremely precise measurements were made by an international team led by Reinhard Genzel (MPE) in Garching, Germany, in conjunction with collaborators around the world, at the Paris Observatory–PSL, the Université Grenoble Alpes, CNRS, the Max Planck Institute for Astronomy, the University of Cologne, the Portuguese CENTRA – Centro de Astrofisica e Gravitação and ESO. The observations are the culmination of a 26-year series of ever-more-precise observations of the centre of the Milky Way using ESO instruments.

“This is the second time that we have observed the close passage of S2 around the black hole in our galactic centre. But this time, because of much improved instrumentation, we were able to observe the star with unprecedented resolution,” explains Genzel. “We have been preparing intensely for this event over several years, as we wanted to make the most of this unique opportunity to observe general relativistic effects.”

Artist’s impression of the gravitational redshift of S2 when passing the supermassive black hole at centre of Milky Way. Zoom Image
Artist’s impression of the gravitational redshift of S2 when passing the supermassive black hole at centre of Milky Way. [less]

The new measurements clearly reveal an effect called gravitational redshift. Light from the star is stretched to longer wavelengths by the very strong gravitational field of the black hole. And the change in the wavelength of light from S2 agrees precisely with that predicted by Einstein’s theory of general relativity. This is the first time that this deviation from the predictions of the simpler Newtonian theory of gravity has been observed in the motion of a star around a supermassive black hole.

The team used SINFONI to measure the velocity of S2 towards and away from Earth and the GRAVITY instrument in the VLT Interferometer (VLTI) to make extraordinarily precise measurements of the changing position of S2 in order to define the shape of its orbit. GRAVITY creates such sharp images that it can reveal the motion of the star from night to night as it passes close to the black hole — 26 000 light-years from Earth.

“Our first observations of S2 with GRAVITY, about two years ago, already showed that we would have the ideal black hole laboratory,” adds Frank Eisenhauer (MPE), Principal Investigator of GRAVITY and the SINFONI spectrograph. “During the close passage, we could even detect the faint glow around the black hole on most of the images, which allowed us to precisely follow the star on its orbit, ultimately leading to the detection of the gravitational redshift in the spectrum of S2.”

More than one hundred years after he published his paper setting out the equations of general relativity, Einstein has been proved right once more — in a much more extreme laboratory than he could have possibly imagined!

This diagram shows the motion of the star S2 as it passes close to the supermassive black hole at the centre of the Milky Way. It was compiled from observations with the GRAVITY instrument in the VLT interferometer. At this point the star was travelling at nearly 3% of the speed of light and its shift in position can be seen from night to night. The sizes of the star and the black hole are not to scale. Zoom Image
This diagram shows the motion of the star S2 as it passes close to the supermassive black hole at the centre of the Milky Way. It was compiled from observations with the GRAVITY instrument in the VLT interferometer. At this point the star was travelling at nearly 3% of the speed of light and its shift in position can be seen from night to night.
The sizes of the star and the black hole are not to scale. [less]

“Due to the extremely strong gravitational field we expect to see the effects of general relativity - but only if we can look close enough,” says Stefan Gillessen, “This is why we needed to push the technology. With SINFONI we can measure the radial velocity of stars very accurately and GRAVITY gives us extremely sharp images and accurate positions.”

Continuing observations are expected to reveal another relativistic effect very soon — a small rotation of the star’s orbit, known as Schwarzschild precession — as S2 moves away from the black hole.

Xavier Barcons, ESO’s Director General, concludes: “ESO has worked with Reinhard Genzel and his team and collaborators in the ESO Member States for over a quarter of a century. It was a huge challenge to develop the uniquely powerful instruments needed to make these very delicate measurements and to deploy them at the VLT in Paranal. The discovery announced today is the very exciting result of a remarkable partnership.”

Notes

[1] GRAVITY was developed by a collaboration consisting of the Max Planck Institute for Extraterrestrial Physics (Germany), LESIA of Paris Observatory–PSL / CNRS / Sorbonne Université / Univ. Paris Diderot and IPAG of Université Grenoble Alpes / CNRS (France), the Max Planck Institute for Astronomy (Germany), the University of Cologne (Germany), the CENTRA–Centro de Astrofisica e Gravitação (Portugal) and ESO.

[2] S2 orbits the black hole every 16 years in a highly eccentric orbit that brings it within twenty billion kilometres — 120 times the distance from Earth to the Sun, or about four times the distance from the Sun to Neptune — at its closest approach to the black hole. This distance corresponds to about 1500 times the Schwarzschild radius of the black hole itself.

 

More information

 

The GRAVITY Collaboration team is composed of: R. Abuter (ESO, Garching, Germany), A. Amorim (Universidade de Lisboa, Lisbon, Portugal), N. Anugu (Universidade do Porto, Porto, Portugal), M. Bauböck (Max Planck Institute for Extraterrestrial Physics, Garching, Germany [MPE]), M. Benisty (Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France [IPAG]), J.P. Berger (IPAG; ESO, Garching, Germany), N. Blind (Observatoire de Genève, Université de Genève, Versoix, Switzerland), H. Bonnet (ESO, Garching, Germany), W. Brandner (Max Planck Institute for Astronomy, Heidelberg, Germany [MPIA]), A. Buron (MPE), C. Collin (LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Meudon, France [LESIA]), F. Chapron (LESIA), Y. Clénet (LESIA), V. Coudé du Foresto (LESIA), P. T. de Zeeuw (Sterrewacht Leiden, Leiden University, Leiden, The Netherlands; MPE), C. Deen (MPE), F. Delplancke-Ströbele (ESO, Garching, Germany), R. Dembet (ESO, Garching, Germany; LESIA), J. Dexter (MPE), G. Duvert (IPAG), A. Eckart (University of Cologne, Cologne, Germany; Max Planck Institute for Radio Astronomy, Bonn, Germany), F. Eisenhauer (MPE), G. Finger (ESO, Garching, Germany), N.M. Förster Schreiber (MPE), P. Fédou (LESIA), P. Garcia (Universidade do Porto, Porto, Portugal; Universidade de Lisboa Lisboa, Portugal), R. Garcia Lopez (MPIA), F. Gao (MPE), E. Gendron (LESIA), R. Genzel (MPE; University of California, Berkeley, California, USA), S. Gillessen (MPE), P. Gordo (Universidade de Lisboa, Lisboa, Portugal), M. Habibi (MPE), X. Haubois (ESO, Santiago, Chile), M. Haug (ESO, Garching, Germany), F. Haußmann (MPE), Th. Henning (MPIA), S. Hippler (MPIA), M. Horrobin (University of Cologne, Cologne, Germany), Z. Hubert (LESIA; MPIA), N. Hubin (ESO, Garching, Germany), A. Jimenez Rosales (MPE), L. Jochum (ESO, Garching, Germany), L. Jocou (IPAG), A. Kaufer (ESO, Santiago, Chile), S. Kellner (Max Planck Institute for Radio Astronomy, Bonn, Germany), S. Kendrew (MPIA,ESA), P. Kervella (LESIA; MPIA), Y. Kok (MPE), M. Kulas (MPIA), S. Lacour (LESIA), V. Lapeyrère (LESIA), B. Lazareff (IPAG), J.-B. Le Bouquin (IPAG), P. Léna (LESIA), M. Lippa (MPE), R. Lenzen (MPIA), A. Mérand (ESO, Garching, Germany), E. Müller (ESO, Garching, Germany; MPIA), U. Neumann (MPIA), T. Ott (MPE), L. Palanca (ESO, Santiago, Chile), T. Paumard (LESIA), L. Pasquini (ESO, Garching, Germany), K. Perraut (IPAG), G. Perrin (LESIA), O. Pfuhl (MPE), P.M. Plewa (MPE), S. Rabien (MPE), J. Ramos (MPIA), C. Rau (MPE), G. Rodríguez-Coira (LESIA), R.-R. Rohloff (MPIA), G. Rousset (LESIA), J. Sanchez-Bermudez (ESO, Santiago, Chile; MPIA), S. Scheithauer (MPIA), M. Schöller (ESO, Garching, Germany), N. Schuler (ESO, Santiago, Chile), J. Spyromilio (ESO, Garching, Germany), O. Straub (LESIA), C. Straubmeier (University of Cologne, Cologne, Germany), E. Sturm (MPE), L.J. Tacconi (MPE), K.R.W. Tristram (ESO, Santiago, Chile), F. Vincent (LESIA), S. von Fellenberg (MPE), I. Wank (University of Cologne, Cologne, Germany), I. Waisberg (MPE), F. Widmann (MPE), E. Wieprecht (MPE), M. Wiest (University of Cologne, Cologne, Germany), E. Wiezorrek (MPE), J. Woillez (ESO, Garching, Germany), S. Yazici (MPE; University of Cologne, Cologne, Germany), D. Ziegler (LESIA) and G. Zins (ESO, Santiago, Chile).

 

 
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