THE EVENT HORIZON OF SAGITTARIUS A*

By A. Broderick, Abraham Loeb, Ramesh Narayan. 2009

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Black hole event horizons, causally separating the external universe from compact regions of spacetime, are one of the most exotic predictions of general relativity. Until recently, their compact size has prevented efforts to study them directly. Here we show that recent millimeter and infrared observations of Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, all but require the existence of a horizon. Specifically, we show that these observations limit the luminosity of any putative visible compact emitting region to below 0.4% of Sgr A*'s accretion luminosity. Equivalently, this requires the efficiency of converting the gravitational binding energy liberated during accretion into radiation and kinetic outflows to be greater than 99.6%, considerably larger than those implicated in Sgr A*, and therefore inconsistent with the existence of such a visible region. Finally, since we are able to frame this argument entirely in terms of observable quantities, our results apply to all geometric theories of gravity that admit stationary solutions, including the commonly discussed f(R) class of theories.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f2201b912a45a0dd9eb716b89f382802c77de69e

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Citations in the corpus

Appearance of Keplerian discs orbiting Kerr superspinars (2010, background): “Such a possibility seems to be realistic in the near future for the case of the supermassive object (black hole or superspinar) predicted in the galaxy centre (Sgr A∗) [12, 46].”
Constraining the spin and the deformation parameters from the black hole shadow (2014, background): “The non-observation of electromagnetic radiation emitted by the possible surface of these objects may also be interpreted as an indication for the existence of an event horizon [29, 30] (but see [31, 32]).”
PHOTON RINGS AROUND KERR AND KERR-LIKE BLACK HOLES (2013, methodology): “Using the measurements of the mass and distance of Sgr A* from the monitoring of close stellar orbits (Ghez et al. 2008; Gillessen et al. 2009), Broderick et al. (2009a, 2011a) combined the VLBI observations of Sgr A* with measurements of its spectral energy distribution (Yuan et al. 2004 and…”
Testing black hole candidates with electromagnetic radiation (2015, background): “In the case of SgrA∗, the supermassive BH candidate at the center of the Galaxy, millimeter and infrared observations strongly constrain any possible thermal blackbody component emitted from the surface of this object (Broderick et al., 2009; Broderick & Narayan, 2007).”
Hot Accretion Flows Around Black Holes (2014, methodology): “…been used to argue for the existence of an event horizon in this object (Narayan et al. 1998a, Broderick & Narayan 2006, Narayan & McClintock 2008, Broderick et al. 2009; see also Narayan et al. 1997b, Menou et al. 1999a, Garcia et al. 2001, McClintock et al. 2004 for related arguments in the…”
Shadows of spherically symmetric black holes and naked singularities (2018, background): “A number of tests have been proposed to confirm the presence of event horizons in black hole candidates (Narayan & McClintock 2008; ⋆ E-mail: rajibul.shaikh@tifr.res.in † E-mail: k.prashant@tifr.res.in ‡ E-mail: rnarayan@cfa.harvard.edu § E-mail: psj@tifr.res.in Broderick et al. 2009, 2015).”
Measuring the Kerr spin parameter of regular black holes from their shadow (2013, background): “The non-observation of electromagnetic radiation emitted by the possible surface of these objects may also be interpreted as an indication for the existence of an event horizon [11, 12] (but see [13, 14]).”
TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. II. BLACK HOLE IMAGES (2010, methodology): “The requirement that the spin is not near the maximal Kerr value allows us to apply this method to images of Sgr A∗, for which first, although uncertain estimates from millimeter VLBI observations indicate that the black hole is not spinning rapidly (Broderick et al. 2009).”