Improving constraints on the extended mass distribution in the Galactic center with stellar orbits

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
² Max Planck Institute for Extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁴ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁵ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁶ 1st Institute of Physics, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
⁷ CENTRA – Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
⁸ Universidade de Lisboa – Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
⁹ European Southern Observatory, Casilla 19001, Santiago 19, Chile
¹⁰ Faculdade de Engenharia, Universidade do Porto, rua Dr. Roberto Frias, 4200-465 Porto, Portugal
¹¹ Departments of Physics & Astronomy, Le Conte Hall, University of California, Berkeley, CA 94720, USA
¹² Max Planck Institute for Astrophysics, Karl-Schwarzschild-Straße 1, 85748 Garching, Germany
¹³ Max Planck Institute for Radio Astronomy, auf dem Hügel 69, 53121 Bonn, Germany
¹⁴ Institute of Multidisciplinary Mathematics, Universitat Politècnica de València, València, Spain
¹⁵ Kavli Institute for Astronomy and Astrophysics, Beijing, China
¹⁶ Advanced Concepts Team, ESA, TEC-SF, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹⁷ Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark
¹⁸ ORIGINS Excellence Cluster, Boltzmannstraße 2, 85748 Garching, Germany
¹⁹ Department of Physics, Technical University of Munich, 85748 Garching, Germany
²⁰ Higgs Centre for Theoretical Physics, Edinburgh, UK
²¹ Department of Physics, Sapienza, University of Rome, P.le A. Moro 5, 00185 Rome, Italy
²² School of Physics and Materials Science, Guangzhou University, Guangzhou 510006, PR China
²³ Key Laboratory for Astronomical Observation and Technology of Guangzhou, 510006 Guangzhou, PR China
²⁴ Astronomy Science and Technology Research Laboratory of Department of Education of Guangdong Province, Guangzhou 510006, PR China

^★★ Corresponding author; mbordoni@mpe.mpg.de

Received: 17 September 2024
Accepted: 12 November 2024

Abstract

Studying the orbital motion of stars around Sagittarius A* in the Galactic center provides a unique opportunity to probe the gravitational potential near the supermassive black hole at the heart of our Galaxy. Interferometric data obtained with the GRAVITY instrument at the Very Large Telescope Interferometer (VLTI) since 2016 has allowed us to achieve unprecedented precision in tracking the orbits of these stars. GRAVITY data have been key to detecting the in-plane, prograde Schwarzschild precession of the orbit of the star S2 that is predicted by general relativity. By combining astrometric and spectroscopic data from multiple stars, including S2, S29, S38, and S55 – for which we have data around their time of pericenter passage with GRAVITY – we can now strengthen the significance of this detection to an approximately 10σ confidence level. The prograde precession of S2’s orbit provides valuable insights into the potential presence of an extended mass distribution surrounding Sagittarius A*, which could consist of a dynamically relaxed stellar cusp comprising old stars and stellar remnants, along with a possible dark matter spike. Our analysis, based on two plausible density profiles – a power-law and a Plummer profile – constrains the enclosed mass within the orbit of S2 to be consistent with zero, establishing an upper limit of approximately 1200 M_⊙ with a 1σ confidence level. This significantly improves our constraints on the mass distribution in the Galactic center. Our upper limit is very close to the expected value from numerical simulations for a stellar cusp in the Galactic center, leaving little room for a significant enhancement of dark matter density near Sagittarius A*.