Artist’s impression of Schwarzschild precession
Orbits of stars around black hole at the heart of the Milky Way
Wide-field view of the centre of the Milky Way
Sagittarius A* in the constellation of Sagittarius
Videos
Artist’s animation of S2’s precession effect
Zooming in on the heart of the Milky Way
The star S2 makes a close approach to the black hole at the centre of the Milky Way
Interview with Reinhard Genzel (in English)
Interview with Reinhard Genzel (in German)
Observations made with ESO’s Very Large
Telescope (VLT) have revealed for the first time that a star orbiting
the supermassive black hole at the centre of the Milky Way moves just as
predicted by Einstein’s general theory of relativity. Its orbit is
shaped like a rosette and not like an ellipse as predicted by Newton's
theory of gravity. This long-sought-after result was made possible by
increasingly precise measurements over nearly 30 years, which have
enabled scientists to unlock the mysteries of the behemoth lurking at
the heart of our galaxy.
Located 26 000 light-years from the Sun, Sagittarius A* and
the dense cluster of stars around it provide a unique laboratory for
testing physics in an otherwise unexplored and extreme regime of
gravity. One of these stars, S2, sweeps in towards the supermassive
black hole to a closest distance less than 20 billion kilometres (one
hundred and twenty times the distance between the Sun and Earth), making
it one of the closest stars ever found in orbit around the massive
giant. At its closest approach to the black hole, S2 is hurtling through
space at almost three percent of the speed of light, completing an orbit once every 16 years. “After
following the star in its orbit for over two and a half decades, our
exquisite measurements robustly detect S2’s Schwarzschild precession in
its path around Sagittarius A*,” says Stefan Gillessen of the MPE, who led the analysis of the measurements published today in the journal Astronomy & Astrophysics.
Most stars and planets have a non-circular orbit and
therefore move closer to and further away from the object they are
rotating around. S2’s orbit precesses, meaning that the location of its
closest point to the supermassive black hole changes with each turn,
such that the next orbit is rotated with regard to the previous one,
creating a rosette shape. General Relativity provides a precise
prediction of how much its orbit changes and the latest measurements
from this research exactly match the theory. This effect, known as
Schwarzschild precession, had never before been measured for a star
around a supermassive black hole.
The study with ESO’s VLT also helps scientists learn more
about the vicinity of the supermassive black hole at the centre of our
galaxy. “Because the S2 measurements follow General Relativity so
well, we can set stringent limits on how much invisible material, such
as distributed dark matter or possible smaller black holes, is present
around Sagittarius A*. This is of great interest for understanding the
formation and evolution of supermassive black holes,” say Guy Perrin and Karine Perraut, the French lead scientists of the project.
This result is the culmination of 27 years of observations
of the S2 star using, for the best part of this time, a fleet of
instruments at ESO’s VLT, located in the Atacama Desert in Chile. The
number of data points marking the star’s position and velocity attests
to the thoroughness and accuracy of the new research: the team made over
330 measurements in total, using the GRAVITY, SINFONI and NACO
instruments. Because S2 takes years to orbit the supermassive black
hole, it was crucial to follow the star for close to three decades, to
unravel the intricacies of its orbital movement.
The research was conducted by an international team led by
Frank Eisenhauer of the MPE with collaborators from France, Portugal,
Germany and ESO. The team make up the GRAVITY collaboration, named after
the instrument they developed for the VLT Interferometer, which
combines the light of all four 8-metre VLT telescopes into a
super-telescope (with a resolution equivalent to that of a telescope 130
metres in diameter). The same team reported in 2018
another effect predicted by General Relativity: they saw the light
received from S2 being stretched to longer wavelengths as the star
passed close to Sagittarius A*. “Our previous result has shown that
the light emitted from the star experiences General Relativity. Now we
have shown that the star itself senses the effects of General Relativity,”
says Paulo Garcia, a researcher at Portugal’s Centre for Astrophysics
and Gravitation and one of the lead scientists of the GRAVITY project.
With ESO’s upcoming Extremely Large Telescope, the team
believes that they would be able to see much fainter stars orbiting even
closer to the supermassive black hole. “If we are lucky, we might capture stars close enough that they actually feel the rotation, the spin, of the black hole,”
says Andreas Eckart from Cologne University, another of the lead
scientists of the project. This would mean astronomers would be able to
measure the two quantities, spin and mass, that characterise Sagittarius
A* and define space and time around it. “That would be again a completely different level of testing relativity," says Eckart.
More Information
This research was presented in the paper “Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole” to appear in Astronomy & Astrophysics (DOI: 10.1051/0004-6361/202037813).
The GRAVITY Collaboration team is composed of R. Abuter (European Southern Observatory, Garching, Germany [ESO]), A. Amorim (Universidade de Lisboa - Faculdade de Ciências, Portugal and Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, Portugal [CENTRA]), M. Bauböck (Max Planck Institute for Extraterrestrial Physics, Garching, Germany [MPE]), J.P. Berger (Univ. Grenoble Alpes, CNRS, Grenoble, France [IPAG] and ESO), H. Bonnet (ESO), W. Brandner (Max Planck Institute for Astronomy, Heidelberg, Germany [MPIA]), V. Cardoso (CENTRA and CERN, Genève, Switzerland), Y. Clénet (Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France [LESIA], P.T. de Zeeuw (Sterrewacht Leiden, Leiden University, The Netherlands and MPE), J. Dexter (Department of Astrophysical & Planetary Sciences, JILA, Duane Physics Bldg.,University of Colorado, Boulder, USA and MPE), A. Eckart (1st Institute of Physics, University of Cologne, Germany [Cologne] and Max Planck Institute for Radio Astronomy, Bonn, Germany), F. Eisenhauer (MPE), N.M. Förster Schreiber (MPE), P. Garcia (Faculdade de Engenharia, Universidade do Porto, Portugal and CENTRA), F. Gao (MPE), E. Gendron (LESIA), R. Genzel (MPE, Departments of Physics and Astronomy, Le Conte Hall, University of California, Berkeley, USA), S. Gillessen (MPE), M. Habibi (MPE), X. Haubois (European Southern Observatory, Santiago, Chile [ESO Chile]), T. Henning (MPIA), S. Hippler (MPIA), M. Horrobin (Cologne), A. Jiménez-Rosales (MPE), L. Jochum (ESO Chile), L. Jocou (IPAG), A. Kaufer (ESO Chile), P. Kervella (LESIA), S. Lacour (LESIA), V. Lapeyrère (LESIA), J.-B. Le Bouquin (IPAG), P. Léna (LESIA), M. Nowak (Institute of Astronomy, Cambridge, UK and LESIA), T. Ott (MPE), T. Paumard (LESIA), K. Perraut (IPAG), G. Perrin (LESIA), O. Pfuhl (ESO, MPE), G. Rodríguez-Coira (LESIA), J. Shangguan (MPE), S. Scheithauer (MPIA), J. Stadler (MPE), O. Straub (MPE), C. Straubmeier (Cologne), E. Sturm (MPE), L.J. Tacconi (MPE), F. Vincent (LESIA), S. von Fellenberg (MPE), I. Waisberg (Department of Particle Physics & Astrophysics, Weizmann Institute of Science, Israel and MPE), F. Widmann (MPE), E. Wieprecht (MPE), E. Wiezorrek (MPE), J. Woillez (ESO), and S. Yazici (MPE, Cologne).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.
Links
- Research paper
- Photos of the VLT
- MPE GRAVITY webpage
- For scientists: got a story? Pitch your research paper
Contacts
Reinhard Genzel
Director, Max Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 89 30000 3280
Email: genzel@mpe.mpg.de
Stefan Gillessen
Max-Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 89 30000 3839
Cell: +49 176 99 66 41 39
Email: ste@mpe.mpg.de
Frank Eisenhauer
Max-Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 89 30000 3563
Cell: +49 162 3105080
Email: eisenhau@mpe.mpg.de
Paulo Garcia
Faculdade de Engenharia, Universidade do Porto and Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, Portugal
Porto, Portugal
Cell: +351 963235785
Email: pgarcia@fe.up.pt
Karine Perraut
IPAG of Université Grenoble Alpes/CNRS
Grenoble, France
Guy Perrin
LESIA – Observatoire de Paris - PSL
Meudon, France
Andreas Eckart
1st Institute of Physics, University of Cologne
Cologne, Germany
Tel: +49 221 470 3546
Email: eckart@ph1.uni-koeln.de
Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: pio@eso.org
Source: ESO/News