Discovery of a star sensitive to the spin of Sagittarius A*
- K. Abd El Dayem
- R. Abuter
- N. Aimar
- P. Amaro-Seoane
- A. Berdeu
- J.-P. Berger
- G. Bourdarot
- W. Brandner
- A. Burkert
- D. Caldéron
- C. Correia
- J. Cuadra
- R. Davies
- D. Defrère
- L. Delit
- A. Drescher
- F. Eisenhauer
- L. Esteras Otal
- M. Fabricius
- H. Feuchtgruber
- S. Flesch
- N. M. Förster Schreiber
- A. Foschi
- Q. Fournier
- P. Garcia
- R. Garcia Lopez
- A. Generozov
- R. Genzel
- S. Gillessen
- F. Gonté
- X. Haubois
- S. F. Hönig
- M. Houllé
- S. Joharle
- A. Kaufer
- J. Kammerer
- P. Kervella
- J. Kolb
- L. Kreidberg
- L. Labadie
- S. Lacour
- O. Lai
- R. Laugier
- J.-B. Le Bouquin
- J. Leftley
- R. Li
- B. Lopez
- D. Lutz
- F. Mang
- A. Mérand
2026-08-19
Residing in the centre of the Milky Way, Sagittarius A* (Sgr A*) is the closest massive black hole 1 (MBH). Its vicinity has allowed measuring individual stellar orbits around it 2–4 . The stars act as test particles and probe the gravitational potential around the 4.3 × 10 6 M ⊙ MBH. These observations have determined the central mass to sub-per-cent precision 5 , and the mildly relativistic motions of stars have given access to the dominant relativistic corrections, the gravitational redshift 6,7 , the transverse Doppler effect and the prograde precession imposed by the Schwarzschild metric nature of the potential 8 . These effects are of order β 2 = ( v / c ) 2 (for velocity v and speed of light c ). The Kerr metric for a rotating black hole leads to corrections of order β 3 . Here, we report the discovery of a faint main-sequence star ( m K = 19.3), S301, on an 8.7-year orbit and with small enough a pericentre distance, such that the peak velocity of the star reaches 25,000 km s −1 . Within the measurement abilities of current near-infrared interferometry and future spectroscopy on an extremely large telescope, the motion of S301 is directly sensitive to the spin of Sgr A*. The high eccentricity of S301 suggests that it is the captured component of a binary that was torn apart by the Hills mechanism.