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

In this illustration, stars are seen as orbiting in close orbit around the supermassive black hole that lies at the center of the Milky Way, known as Sagittarius A* (Sgr A*). Credit: Gemini International Observatory/NOIRLab/NSF/AURA/J. da Silva/(Spaceengine), Acknowledgments: M. Zamani (NSF’s NOIRLab)[2]Accurate insights into the supermassive black hole at the heart of the Milky Way

Astronomers use the Gemini Observatory and a joint international telescope to highlight Sagittarius A*

Obtained with the help of the Gemini North telescope, astronomers have made the most accurate measurements to date of the movement of stars around the supermass[{” attribute=””>black hole at the center of the Milky Way. These results show that 99.9% of the mass contained at the very center of the galaxy is due to the black hole, and only 0.1% could include stars, smaller black holes, interstellar dust, and gas, or dark matter.

Astronomers have measured more accurately than ever the position and speed of the four stars in the immediate vicinity of Sagittarius A* (Sgr A*),^[1] The supermassive black hole that lurks at the center of the Milky Way. The motions of these stars – named S2, S29, S38 and S55 – have been found to follow paths that show that the mass in the center of the Milky Way is almost entirely due to Sgr A * The black hole, which leaves very little room for anything else.

The research team used a variety of advanced astronomical facilities in this research. To measure the stars’ velocities, they used spectroscopy from the Gemini Near Infrared Spectrograph (GNIRS) in Gemini North near Maunakea summit in Hawaii, part of the Gemini International Observatory, the NSF NOIRLab program, and the SINFONI instrument on the European Southern Observatory.[{” attribute=””>تلسكوب كبير جدا. تم استخدام أداة GRAVITY في VLTI لقياس مواضع النجوم.

رسم توضيحي للثقب الأسود القوس A * في وسط مجرة درب التبانة. الائتمان: مرصد الجوزاء الدولي / NOIRLab / NSF / AURA / J. دا سيلفا / (Spaceengine) ، شكر وتقدير: M. Zamani (NSF’s NOIRLab)

قال راينهارد جينزل ، مدير معهد ماكس بلانك للفيزياء خارج كوكب الأرض والمشترك في الحصول على جائزة نوبل في الفيزياء لعام 2020: “نحن ممتنون جدًا لمرصد الجوزاء ، الذي أعطتنا أداة GNIRS الخاصة به المعلومات الهامة التي نحتاجها”. “يُظهر هذا البحث التعاون العالمي في أفضل حالاته.”

يحتوي مركز المجرة التابع لمجرة درب التبانة ، الذي يقع على بعد حوالي 27000 سنة ضوئية من الشمس ، على مصدر الراديو المضغوط Sgr A * الذي حدده علماء الفلك على أنه ثقب أسود فائق الكتلة يبلغ 4.3 مليون مرة كتلة الشمس. على الرغم من عقود من الملاحظات المضنية – وتم منح جائزة نوبل لاكتشاف هوية Sgr A ^[3] – It has been difficult to prove definitively that the majority of this mass belongs only to the supermassive black hole and does not also include a huge amount of matter such as stars, which are smaller black holesor interstellar dust and gas, or dark matter.

These annotated images, acquired with the GRAVITY instrument on ESO’s Very Large Telescope Interferometer (VLTI) between March and July 2021, show stars orbiting near Sagittarius A, the supermassive black hole at the heart of the Milky Way. One of these stars, called S29, was observed as it approached the black hole at its closest at a distance of 13 billion km, 90 times the distance between the Sun and Earth. Another star, called S300, was first discovered in new VLTI observations reported by ESO.
Using Gemini North of the Gemini International Observatory, a program from NSF’s NOIRLab and ESO’s VLT, astronomers have measured more accurately than ever the position and speed of these stars S29 and S55 (as well as the stars S2 and S38), and found them moving in a way that shows that the mass in The center of the Milky Way is almost entirely due to the black hole Sagittarius A, leaving very little room for anything else. Credit: ESO/GRAVITY Collaboration

“With the 2020 Nobel Prize in Physics awarded to confirm that Sgr A is indeed a black hole, we now want to move forward. We would like to understand if there is anything else hidden in the center of the Milky Way, and whether general relativity is indeed the correct theory “The most direct way to answer this question is to closely follow the orbits of stars passing near Sgr A,” explained Stefan Gelsen, one of the astronomers involved in this work.

Einstein’s general theory of relativity predicts that the orbits of stars around a compact, supermassive object are slightly different from those predicted by classical Newtonian physics. In particular, general relativity predicts that the orbits of stars will map out an elegant rosette – an effect known as Proactive Schwarzschild. To actually see the stars tracking this rose, the team tracked the position and velocity of four stars in the immediate vicinity of Sgr A – called S2, S29, S38 and S55. The team’s observations of how far these stars have gone allowed to infer the mass distribution within Sgr A. They discovered that any mass extending within the orbit of S2 contributes at most 0.1% of the mass of the supermassive black hole.

animated sequence for[{” 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 Giant Magellan Telescope and the Thirty Meter Telescope (both part of the US-ELT Program) will allow astronomers to measure even fainter stars with even greater precision.

“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 from 2019). Zooming in further reveals stars closer to the black hole, observed using the GRAVITY instrument on ESO’s Very Large Telescope interferometer in mid-2021.

“The Gemini observatories continue to provide new insight into the nature of our galaxy and the supermassive black hole at its center,” said Martin Steele, Gemini Program Officer at the National Science Foundation. “Further development of instruments over the next decade intended for widespread use will maintain NOIRLab’s leadership in characterizing the universe around us.”

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

Notes

Sagittarius A* is pronounced “Sagittarius star”.
ESO’s VLT consists of four single-site telescopes with a diameter of 8.2 meters that can collect light through a network of mirrors and underground tunnels using a technique known as interferometry, to form the VLTI. GRAVITY uses this technology to measure the position of night sky objects by altitude[{” attribute=””>accuracy — equivalent to picking out a quarter-dollar coin on the surface of the Moon.
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 CERN), Y. Clénet (LESIA, Observatoire de Paris), Y. Dallilar (Max Planck Institute for Extraterrestrial Physics), R. Davies (Max Planck Institute for Extraterrestrial Physics), P. T. de Zeeuw (Leiden University and Max Planck Institute for Extraterrestrial Physics), J. Dexter (University of Colorado, Boulder), A. Drescher (Max Planck Institute for Extraterrestrial Physics), A. Eckart (University of Cologne and Max Planck Institute for Radio Astronomy), F. Eisenhauer (Max Planck Institute for Extraterrestrial Physics), N. M. Förster Schreiber (Max Planck Institute for Extraterrestrial Physics), P. Garcia (Universidade do Porto and CENTRA – Centro de Astrofísica e Gravitação), F. Gao (Universität Hamburg and Max Planck Institute for Extraterrestrial Physics), E. Gendron (LESIA, Observatoire de Paris), R. Genzel (Max Planck Institute for Extraterrestrial Physics and University of California, Berkeley), S. Gillessen (Max Planck Institute for Extraterrestrial Physics), M. Habibi (Max Planck Institute for Extraterrestrial Physics), X. Haubois (European Southern Observatory), G. Heißel (LESIA, Observatoire de Paris), T. Henning (Max Planck Institute for Astronomy), S. Hippler (Max Planck Institute for Astronomy), M. Horrobin (University of Cologne), L. Jochum (European Southern Observatory), L. Jocou (University Grenoble Alpes), A. Kaufer (European Southern Observatory), P. Kervella (LESIA, Observatoire de Paris), S. Lacour (LESIA, Observatoire de Paris), V. Lapeyrère (LESIA, Observatoire de Paris), J.-B. Le Bouquin (University Grenoble Alpes), P. Léna (LESIA, Observatoire de Paris), D. Lutz (Max Planck Institute for Extraterrestrial Physics), T. Ott (Max Planck Institute for Extraterrestrial Physics), T. Paumard (LESIA, Observatoire de Paris), K. Perraut (University Grenoble Alpes), G. Perrin (LESIA, Observatoire de Paris), O. Pfuhl (European Southern Observatory and Max Planck Institute for Extraterrestrial Physics), S. Rabien (Max Planck Institute for Extraterrestrial Physics), G. Rodríguez-Coira (LESIA, Observatoire de Paris), J. Shangguan (Max Planck Institute for Extraterrestrial Physics), T. Shimizu (Max Planck Institute for Extraterrestrial Physics), S. Scheithauer (Max Planck Institute for Astronomy), J. Stadler (Max Planck Institute for Extraterrestrial Physics), O. Straub (Max Planck Institute for Extraterrestrial Physics), C. Straubmeier (University of Cologne), E. Sturm (Max Planck Institute for Extraterrestrial Physics), L. J. Tacconi (Max Planck Institute for Extraterrestrial Physics), K. R. W. Tristram (European Southern Observatory), F. Vincent (LESIA, Observatoire de Paris), S. von Fellenberg (Max Planck Institute for Extraterrestrial Physics), F. Widmann (Max Planck Institute for Extraterrestrial Physics), E. Wieprecht (Max Planck Institute for Extraterrestrial Physics), E. Wiezorrek (Max Planck Institute for Extraterrestrial Physics), J. Woillez (European Southern Observatory), S. Yazici (Max Planck Institute for Extraterrestrial Physics and the University of Cologne), and A. Young (Max Planck Institute for Extraterrestrial Physics).