The First Measurement of Spectral Lines in a Short-Period Star Bound to the Galaxy’s Central Black Hole: A Paradox of Youth

By A. Ghez, G. Duchêne, K. Matthews, S. Hornstein, A. Tanner, J. Larkin, Mark R. Morris, E. Becklin, S. Salim, Ted Kremenek and 4 more. 2003

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We have obtained the first detection of spectral absorption lines in one of the high-velocity stars in the vicinity of the Galaxy's central supermassive black hole. Both Brγ (2.1661 μm) and He I (2.1126 μm) are seen in absorption in S0-2 with equivalent widths (2.8 ± 0.3 and 1.7 ± 0.4 Å) and an inferred stellar rotational velocity (220 ± 40 km s-1) that are consistent with that of an O8-B0 dwarf, which suggests that it is a massive (~15 M☉) young (less than 10 Myr) main-sequence star. This presents a major challenge to star formation theories, given the strong tidal forces that prevail over all distances reached by S0-2 in its current orbit (130-1900 AU) and the difficulty in migrating this star inward during its lifetime from farther out where tidal forces should no longer preclude star formation. The radial velocity measurements ( = -510 ± 40 km s-1) and our reported proper motions for S0-2 strongly constrain its orbit, providing a direct measure of the black hole mass of 4.1(±0.6) × 106 3 M☉. The Keplerian orbit parameters have uncertainties that are reduced by a factor of 2-3 compared to previously reported values and include, for the first time, an independent solution for the dynamical center; this location, while consistent with the nominal infrared position of Sgr A*, is localized to a factor of 5 more precisely (±2 mas). Furthermore, the ambiguity in the inclination of the orbit is resolved with the addition of the radial velocity measurement, indicating that the star is behind the black hole at the time of closest approach and counterrevolving against the Galaxy. With further radial velocity measurements in the next few years, the orbit of S0-2 will provide the most robust estimate of the distance to the Galactic center.

Subfields: Astronomy and Astrophysics, Biomedical Engineering

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Citations in the corpus

Stellar Dynamics in the Central Arcsecond of Our Galaxy (2003, background): “We found that six stars in our sample (S1, S2, S8, S12, S13, and S14) show clear signs of nonlinear proper motion, three of which are well-known candidates, i.e., S1, S2, and S8 (Ghez et al. 2000; Eckart et al. 2002; Schödel et al. 2002).”
The Proper Motion of Sagittarius A*. II. The Mass of Sagittarius A* (2004, background): “Statistical estimators applied to proper motions give central masses toward the lower end of this range, while fits to stellar orbits favor the higher end of the range (Schödel et al. 2003; Ghez et al. 2003).”
Stellar and wind properties of massive stars in the central parsec of the Galaxy (2006, background): “Previously, Ghez et al. (2003) and Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20066688 Eisenhauer et al. (2005) had shown that the group of stars located in the central arcsecond of the Galaxy and orbiting very close to the black…”
First simultaneous NIR/X-ray detection of a flare from Sgr A (2004, background): “Especially in the case of the center of our Galaxy, progress could be made through the investigation of the dynamics of stars (Eckart & Genzel 1996, Genzel et al. 1997, 2000, Ghez et al. 1998, 2000, 2003a, 2003b, Eckart et l. 2002, Schödel et al. 2002, 2003).”
A Medium Resolution Near-Infrared Spectral Atlas of O and Early-B Stars (2005, background): “…for a variety of applications, including studies of very young star-forming regions (Bik et al. 2003) and the Galactic center region (Najarro et al. 1997, 2004; Ghez et al. 2003) as well as distant massive clusters throughout the Galaxy (Hanson et al. 1997; Blum et al. 1999; Figer et al. 2005).”
A Universal Stellar Initial Mass Function? A critical look at variations in extreme environments (2010, background): “2.4.2 Galactic center The central region of the Galaxy is a rather unique place as the dynamics are heavily influenced by the presence of a massive black hole, MBH ∼ 3 × 10 6M⊙ (e.g. Ghez et al. 2003; Schödel et al. 2003).”
Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole (2018, methodology): “…were taken with the AO-assisted integral field spectrometer SINFONI at the VLT (Eisenhauer et al. 2003a; Bonnet et al. 2004), with five additional 2000-2003 slit-spectra from the AO imagers and spectrometers NIRC2 at Keck (see Ghez et al. 2003; Chu et al. 2018) and NACO (Eisenhauer et al. 2003b).”
Nuclear star clusters (2009, background): “In addition to the old stars, there is a population of about 200 massive and young Wolf-Rayet and O- and B-type stars that are confined to the central 0.5 pc (Allen et al. 1990; Krabbe et al. 1991; Ghez et al. 2003; Bartko et al. 2010; Pfuhl et al. 2011; Feldmeier-Krause et al. 2015).”
HST STIS Spectroscopy of the Triple Nucleus of M31: Two Nested Disks in Keplerian Rotation around a Supermassive Black Hole (2005, background): “Similar considerations make it difficult to understand young stars near the Galactic center BH (e.g., Morris 1993; Genzel et al. 2003, Ghez et al. 2003, 2005).”
The most massive stars in the Arches cluster (2007, background): “Some of them are approaching the black hole at distances of only a few light hours (Ghez et al. 2003; Eisenhauer et al. 2005).”
MONITORING STELLAR ORBITS AROUND THE MASSIVE BLACK HOLE IN THE GALACTIC CENTER (2008, methodology): “This addresses for example the so-called ’paradox of youth’ for the stars in the central arcsecond (Ghez et al. 2003) or the puzzling existence of a large number of O-stars and Wolf-Rayet stars in the GC (Paumard et al. 2006).”
An Update on Monitoring Stellar Orbits in the Galactic Center (2016, background): “The first orbit determination dates back to 2002 (Schödel et al. 2002; Ghez et al. 2003).”
Massive Black Hole Binary Evolution (2004, background): “This process might explain the puzzling presence of early-type stars [66, 68] deep inside the sphere of influence of the SBH at the Galactic center ([84], but see [99]).”
SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month (2005, methodology): “This constitutes a ‘‘paradox of youth’’ (Ghez et al. 2003).”
The nuclear star cluster of the Milky Way: proper motions and mass (2009, background): “The measurements of stellar orbits have provided, so far, the best evidence for its nature (e.g., Schödel et al. 2003; Ghez et al. 2003).”
Supermassive black hole demography: the match between the local and accreted mass functions (2004, background): “…is no direct evidence that all MDOs are black holes (BHs), the evidence for a singularity is actually very tight in the Galaxy (Schödel et al. 2002; Ghez et al. 2003) and alternative explanations are severely constrained in NGC 4258 (Miyoshi et al. 1995; see also, for example, Kormendy 2004).”
The Low End of the Supermassive Black Hole Mass Function: Constraining the Mass of a Nuclear Black Hole in NGC 205 via Stellar Kinematics (2005, background): “Below 107M only twomeasurements exist: in theMilky Way (MBH ¼ 4 ; 106 M ; Ghez et al. 2003; Schödel et al. 2003) and in M32 (MBH ¼ 2:5 ; 106 M ; Verolme et al. 2002; van der Marel et al. 1998).”
Stellar Disk in the Galactic Center: A Remnant of a Dense Accretion Disk? (2003, background): “INTRODUCTION The dusty center of our Galaxy harbors a compact massive object, Sgr A*, most likely a black hole (Genzel et al. 1997; Ghez et al. 1998, 2003; Scho¨del et al. 2002).”