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Is there something else hidden in the center of the Milky Way?

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center of the Milky Way

Seen in this image are stars in close orbit around the supermassive black hole lurking at the center of the Milky Way known as Sagittarius A* (Sgr A*). Image credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/(Spaceengine), Credits: M. Zamani (NSFs NOIRLab)[2]Precise insights into the supermassive black hole at the heart of the Milky Way

Astronomers are using the Gemini Observatory and an international telescope collaboration to shed light on Sagittarius A*

With the help of the Gemini North telescope, astronomers have made the most accurate measurements yet of the movements of stars around the supermassive one[{” attribute=””>black hole at the center of the

More accurately than ever, astronomers have measured the positions and velocities of four stars in close proximity to Sagittarius A* (Sgr A*),[1] the supermassive black hole lurking at the center of the Milky Way. The motions of these stars – dubbed S2, S29, S38 and S55 – have been found to follow paths showing that the bulk at the center of the Milky Way is almost entirely due to the black hole Sgr A*, leaving very little room for it something remains.

The research team used a variety of state-of-the-art astronomical facilities for this research. To measure the stars’ velocities, they used spectroscopy from the Gemini Near Infrared Spectrograph (GNIRS) at Gemini North near the summit of Maunakea, Hawaii, part of the Gemini International Observatory, a program of NSF’s NOIRLab, and the SINFONI instrument the European Southern Observatory[{” attribute=””>Sehr großes Teleskop. Das GRAVITY-Instrument am VLTI wurde verwendet, um die Positionen der Sterne zu messen.



Schwarzes Loch Schütze A

Abbildung des Schwarzen Lochs Sagittarius A* im Zentrum der Milchstraße. Bildnachweis: Internationales Gemini-Observatorium/NOIRLab/NSF/AURA/J. da Silva/(Spaceengine), Danksagung: M. Zamani (NSFs NOIRLab)

„Wir sind dem Gemini Observatory sehr dankbar, dessen GNIRS-Instrument uns die entscheidenden Informationen lieferte, die wir brauchten“, sagte Reinhard Genzel, Direktor des Max-Planck-Instituts für extraterrestrische Physik und Mitempfänger des Nobelpreises 2020 für Physik. „Diese Studie zeigt die weltweite Zusammenarbeit von ihrer besten Seite.“

Das galaktische Zentrum der Milchstraße, etwa 27.000 Lichtjahre von der Sonne entfernt, enthält die kompakte Radioquelle Sgr A*, die Astronomen als supermassereiches Schwarzes Loch mit 4,3 Millionen Sonnenmassen identifiziert haben. Trotz jahrzehntelanger sorgfältiger Beobachtungen – und des Nobelpreises für die Entdeckung der Identität von Sgr A*[3] – It has been difficult to prove conclusively that most of this mass belongs only to the supermassive black hole and does not also include a large amount of matter such as stars, smaller black holes, interstellar dust and gas, or dark matter.

ESO VLTI images of stars at the center of the Milky Way

These annotated images, taken between March and July 2021 by the GRAVITY instrument on ESO’s Very Large Telescope Interferometer (VLTI), show stars orbiting very closely Sagittarius A*, the supermassive black hole at the heart of the Milky Way. One of these stars, named S29, was observed coming as close as 13 billion kilometers from the black hole, just 90 times the distance between the Sun and Earth. Another star, named S300, has been spotted for the first time in new VLTI observations reported by ESO.
Using the Gemini International Observatory’s Gemini North, a program of NSF’s NOIRLab and ESO’s VLT, astronomers have measured the position and velocity of these stars S29 and S55 (and stars S2 and S38) more accurately than ever before and found that they are moving in a way that shows the mass at the center of the Milky Way is almost entirely due to the black hole Sagittarius A*, leaving very little room for anything else. Photo credit: Collaboration between ESO and GRAVITY

“Now, with the 2020 Nobel Prize in Physics for confirming that Sgr A* is indeed a black hole, we want to go even further. We want to understand whether there is something else hidden at the center of the Milky Way and whether general relativity is actually the correct theory of gravity in this extreme laboratory,” explains Stefan Gillessen, one of the astronomers involved in this work. “The easiest way to answer this question is to closely track the orbits of stars passing near Sgr A*.”

Einstein’s general theory of relativity predicts that the orbits of stars around a supermassive compact object differ slightly from those predicted by classical Newtonian physics. In particular, general relativity predicts that stars’ orbits will trace an elegant rosette shape – an effect known as Schwarzschild precession. To actually see stars tracing this rosette, the team tracked the position and velocity of four stars in close proximity to Sgr A* – dubbed S2, S29, S38 and S55. The team’s observations of the extent to which these stars were precessing allowed them to infer the mass distribution within Sgr A*. They discovered that any extended mass within the orbit of the S2 star is at most 0.1% of the mass of the supermassive black hole.


Animated sequence of[{” attribute=””>ESO’s Very Large Telescope Interferometer (VLTI) images of stars around the Milky Way’s central black hole. This animation shows the orbits of the stars S29 and S55 as they move close to Sagittarius A* (center), the supermassive black hole at the heart of the Milky Way. As we follow the stars along in their orbits, we see real images of the region obtained with the GRAVITY instrument on the VLTI in March, May, June and July 2021. In addition to S29 and S55, the images also show two fainter stars, S62 and S300. S300 was detected for the first time in new VLTI observations reported by ESO.

Measuring the minute variations in the orbits of distant stars around our galaxy’s supermassive black hole is incredibly challenging. To make further discoveries, astronomers will have to push the boundaries not only of science but also of engineering. Upcoming extremely large telescopes (ELTs) such as the

“We will improve our sensitivity even further in future, allowing us to track even fainter objects,” concluded Gillessen. “We hope to detect more than we see now, giving us a unique and unambiguous way to measure the rotation of the black hole.”


Zoom into the heart of the Milky Way to see stars as observed by the European Southern Observatory’s Very Large Telescope (last observation was in 2019). Zooming in further reveals stars even closer to the black hole observed in mid-2021 with the GRAVITY instrument on ESO’s Very Large Telescope Interferometry.

“The Gemini observatories continue to provide new insights into the nature of our galaxy and the massive black hole at its center,” said Martin Still, Gemini program officer at the National Science Foundation. “Further instrument development over the next decade, destined for widespread use, will maintain NOIRLab’s leadership in characterizing the universe around us.”

For more on this research, see Watch stars race around the Milky Way’s supermassive black hole.

Remarks

  1. Sagittarius A* is pronounced “Sagittarius A Star”.
  2. ESO’s VLT consists of four individually arrayed 8.2-metre telescopes that can combine light through a network of mirrors and underground tunnels using a technique known as interferometry to form the VLTI. GRAVITY uses this technique to measure the position of objects in the night sky with high brightness[{” attribute=””>accuracy — equivalent to picking out a quarter-dollar coin on the surface of the Moon.
  3. The 2020 Nobel Prize in Physics was awarded in part to Reinhard Genzel and Andrea Ghez “for the discovery of a supermassive compact object at the center of our galaxy.”

This research is presented in the paper “The mass distribution in the Galactic Centre from interferometric astrometry of multiple stellar orbits” which is published in Astronomy & Astrophysics. A companion paper “Deep Images of the Galactic Center with GRAVITY” has also been published in Astronomy & Astrophysics.

References:

“Mass distribution in the Galactic Center based on interferometric astrometry of multiple stellar orbits” by GRAVITY Collaboration: R. Abuter, N. Aimar, A. Amorim, J. Ball, M. Bauböck, J. P. Berger, H. Bonnet, G. Bourdarot, W. Brandner, V. Cardoso, Y. Clénet, Y. Dallilar, R. Davies, P. T. de Zeeuw, J. Dexter, A. Drescher, F. Eisenhauer, N. M. Förster Schreiber, A. Foschi, P. Garcia, F. Gao, E. Gendron, R. Genzel, S. Gillessen, M. Habibi, X. Haubois, G. Heißel,??, T. Henning, S. Hippler, M. Horrobin, L. Jochum, L. Jocou, A. Kaufer, P. Kervella, S. Lacour, V. Lapeyrère, J.-B. Le Bouquin, P. Léna, D. Lutz, T. Ott, T. Paumard, K. Perraut, G. Perrin, O. Pfuhl, S. Rabien, J. Shangguan, T. Shimizu, S. Scheithauer, J. Stadler, A.W. Stephens, O. Straub, C. Straubmeier, E. Sturm, L. J. Tacconi, K. R. W. Tristram, F. Vincent, S. von Fellenberg, F. Widmann, E. Wieprecht, E. Wiezorrek, J. Woillez, S. Yazici and A. Young, 19 January 2022, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202142465

“Deep images of the Galactic center with GRAVITY” by GRAVITY Collaboration: R. Abuter, N. Aimar, A. Amorim, P. Arras, M. Bauböck, J. P. Berger, H. Bonnet, W. Brandner, G. Bourdarot, V. Cardoso, Y. Clénet, R. Davies, P. T. de Zeeuw, J. Dexter, Y. Dallilar, A. Drescher, F. Eisenhauer, T. Enßlin, N. M. Förster Schreiber, P. Garcia, F. Gao, E. Gendron, R. Genzel, S. Gillessen, M. Habibi, X. Haubois, G. Heißel, T. Henning, S. Hippler, M. Horrobin, A. Jiménez-Rosales, L. Jochum, L. Jocou, A. Kaufer, P. Kervella, S. Lacour, V. Lapeyrère, J.-B. Le Bouquin, P. Léna, D. Lutz, F. Mang, M. Nowak, T. Ott, T. Paumard, K. Perraut, G. Perrin, O. Pfuhl, S. Rabien, J. Shangguan, T. Shimizu, S. Scheithauer, J. Stadler, O. Straub, C. Straubmeier, E. Sturm, L. J. Tacconi, K. R. W. Tristram, F. Vincent, S. von Fellenberg, I. Waisberg, F. Widmann, E. Wieprecht, E. Wiezorrek, J. Woillez, S. Yazici, A. Young and G. Zins, 19 January 2022, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202142459

More information

The team behind this result is composed of The GRAVITY Collaboration, R. Abuter (European Southern Observatory), A. Amorim (Universidade de Lisboa and CENTRA – Centro de Astrofísica e Gravitação), M. Bauböck (Max Planck Institute for Extraterrestrial Physics and University of Illinois), J. P. Berger (University Grenoble Alpes and European Southern Observatory), H. Bonnet (European Southern Observatory), G. Bourdarot (University Grenoble Alpes and Max Planck Institute for Extraterrestrial Physics), V. Cardoso (CENTRA – Centro de Astrofísica e Gravitação and