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Cited by 281Astrophysical Phenomena and ObservationsAstrophysics and Cosmic PhenomenaGalaxies: Formation, Evolution, Phenomena

Variable Infrared Emission from the Supermassive Black Hole at the Center of the Milky Way

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Ghez, A. M., Wright, S. A., Matthews, K., Thompson, D., Le Mignant, D., Tanner, A., Hornstein, S. D., Morris, M. +2 more·2004·The Astrophysical Journal
DOI 10.1086/382024
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Abstract

We report the detection of a variable point source, imaged at L ' (3.8 μm) with the Keck II 10 m telescope's adaptive optics system, that is coincident to within 18 mas (1 σ) of the Galaxy's central supermassive black hole and the unique radio source Sgr A*. While in 2002 this source (Sgr A* IR) was confused with the stellar source S0-2, in 2003 these two sources are separated by 87 mas, allowing the new source's properties to be determined directly. On four separate nights, its observed L ' magnitude ranges from 12.2 to 13.8, which corresponds to a dereddened flux density of 4-17 mJy; no other source in this region shows such large variations in flux density—a factor of 4 over a week and a factor of 2 over 40 minutes. In addition, it has a K - L ' color greater than 2.1, which is at least 1 mag redder than any other source detected at L ' in its vicinity. Based on this source's coincidence with the Galaxy's dynamical center, its lack of motion, its variability, and its red color, we conclude that it is associated with the central supermassive black hole. The short timescale for the 3.8 μm flux density variations implies that the emission arises quite close to the black hole, within 5 AU, or 80 R s . We suggest that both the variable 3.8 μm emission and the X-ray flares arise from the same underlying physical process, possibly the acceleration of a small population of electrons to ultrarelativistic energies. In contrast to the X-ray flares, which are only detectable ~2% of the time, the 3.8 μm emission provides a new, constantly accessible window into the physical conditions of the plasma in close proximity to the central black hole.

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  • Sgr A* exhibits broadband variability on timescales of minutes to hours.

    “Sgr A * exhibits broadband variability on timescales of minutes to hours”

    From First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass (2022) · cites this paper as Ghez et al. 2004

    The Results report Sgr A* IR flux changes within 40 minutes, and the Introduction describes X-ray flares lasting about an hour. These passages support rapid variability in the infrared and X-ray bands, but this paper does not establish minutes-to-hours variability broadly across wavelengths; its Introduction describes radio variations on much longer timescales. (LLM, conf=0.82)

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Research works printed but not linked: 2

  1. Cle ´net, Y., et al. 2003, A&A, in press (astro-ph/0312108) · arXiv
  2. Ghez, A. M., Salim, S., Hornstein, S. D., Tanner, A., Morris, M., Becklin, E. E., & Duche ˆne, G. 2003b, ApJ, submitted (astro-ph/0306130) · arXiv

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Authors
Ghez, A. M., Wright, S. A., Matthews, K., Thompson, D., Le Mignant, D., Tanner, A., Hornstein, S. D., Morris, M., Becklin, E. E., & Soifer, B. T.
Affiliations
  • University of California, Los Angeles (US)
  • California Institute of Technology (US)
ORCID
Venue
The Astrophysical Journal
Publisher
American Astronomical Society
Published
2004-01-27
Volume
601
Issue
2
Pages
L159-L162
ISSN
  • 0004-637X (ISSN-L)
  • 1538-4357
DOI
10.1086/382024
OpenAlex
W2047891905
Cited by
281
References
37
Citations by year
2026: 8 · 2025: 5 · 2024: 6 · 2023: 11 · 2022: 7 · 2021: 5 · 2020: 10 · 2019: 10 · 2018: 5 · 2017: 7 · 2016: 17 · 2015: 9 · 2014: 15 · 2013: 6 · 2012: 11
FWCI
17.50
Type
journal article
Language
en
Open access
Locations
  • The Astrophysical Journal (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • National Science Foundation (9988397)
  • National Aeronautics and Space Administration
  • W. M. Keck Foundation
  • California Institute of Technology
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysical Phenomena and Observations
  • Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › Astrophysics and Cosmic Phenomena
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
Keywords
Sgr A*, supermassive black holes, infrared variability, Galactic Center, X-ray flares, electron acceleration, relativistic electrons, accretion disks, adaptive optics imaging

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