A GENERAL RELATIVISTIC NULL HYPOTHESIS TEST with EVENT HORIZON TELESCOPE OBSERVATIONS of the BLACK HOLE SHADOW in Sgr A∗

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Abstract

The half opening angle of a Kerr black hole shadow is always equal to (5 ± 0.2)GM/Dc2, where M is the mass of the black hole and D is its distance from the Earth. Therefore, measuring the size of a shadow and verifying whether it is within this 4% range constitutes a null hypothesis test of general relativity. We show that the black hole in the center of the Milky Way, Sgr A∗, is the optimal target for performing this test with upcoming observations using the Event Horizon Telescope (EHT). We use the results of optical/IR monitoring of stellar orbits to show that the mass-to-distance ratio for Sgr A∗ is already known to an accuracy of ∼4%. We investigate our prior knowledge of the properties of the scattering screen between Sgr A∗ and the Earth, the effects of which will need to be corrected for in order for the black hole shadow to appear sharp against the background emission. Finally, we explore an edge detection scheme for interferometric data and a pattern matching algorithm based on the Hough/Radon transform and demonstrate that the shadow of the black hole at 1.3 mm can be localized, in principle, to within ∼9%. All these results suggest that our prior knowledge of the properties of the black hole, of scattering broadening, and of the accretion flow can only limit this general relativistic null hypothesis test with EHT observations of Sgr A∗ to ≲10%.

Original languageEnglish (US)
Article number115
JournalAstrophysical Journal
Volume814
Issue number2
DOIs
StatePublished - Dec 1 2015

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null hypothesis
event horizon
telescopes
scattering
Radon transform
stellar orbits
accretion
edge detection
monitoring
radon
test
relativity

Keywords

  • accretion, accretion disks
  • black hole physics
  • Galaxy: center
  • scattering
  • techniques: image processing

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

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title = "A GENERAL RELATIVISTIC NULL HYPOTHESIS TEST with EVENT HORIZON TELESCOPE OBSERVATIONS of the BLACK HOLE SHADOW in Sgr A∗",
abstract = "The half opening angle of a Kerr black hole shadow is always equal to (5 ± 0.2)GM/Dc2, where M is the mass of the black hole and D is its distance from the Earth. Therefore, measuring the size of a shadow and verifying whether it is within this 4{\%} range constitutes a null hypothesis test of general relativity. We show that the black hole in the center of the Milky Way, Sgr A∗, is the optimal target for performing this test with upcoming observations using the Event Horizon Telescope (EHT). We use the results of optical/IR monitoring of stellar orbits to show that the mass-to-distance ratio for Sgr A∗ is already known to an accuracy of ∼4{\%}. We investigate our prior knowledge of the properties of the scattering screen between Sgr A∗ and the Earth, the effects of which will need to be corrected for in order for the black hole shadow to appear sharp against the background emission. Finally, we explore an edge detection scheme for interferometric data and a pattern matching algorithm based on the Hough/Radon transform and demonstrate that the shadow of the black hole at 1.3 mm can be localized, in principle, to within ∼9{\%}. All these results suggest that our prior knowledge of the properties of the black hole, of scattering broadening, and of the accretion flow can only limit this general relativistic null hypothesis test with EHT observations of Sgr A∗ to ≲10{\%}.",
keywords = "accretion, accretion disks, black hole physics, Galaxy: center, scattering, techniques: image processing",
author = "Dimitrios Psaltis and Feryal Ozel and Chan, {Chi Kwan} and Marrone, {Daniel P}",
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AU - Psaltis, Dimitrios

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AU - Chan, Chi Kwan

AU - Marrone, Daniel P

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N2 - The half opening angle of a Kerr black hole shadow is always equal to (5 ± 0.2)GM/Dc2, where M is the mass of the black hole and D is its distance from the Earth. Therefore, measuring the size of a shadow and verifying whether it is within this 4% range constitutes a null hypothesis test of general relativity. We show that the black hole in the center of the Milky Way, Sgr A∗, is the optimal target for performing this test with upcoming observations using the Event Horizon Telescope (EHT). We use the results of optical/IR monitoring of stellar orbits to show that the mass-to-distance ratio for Sgr A∗ is already known to an accuracy of ∼4%. We investigate our prior knowledge of the properties of the scattering screen between Sgr A∗ and the Earth, the effects of which will need to be corrected for in order for the black hole shadow to appear sharp against the background emission. Finally, we explore an edge detection scheme for interferometric data and a pattern matching algorithm based on the Hough/Radon transform and demonstrate that the shadow of the black hole at 1.3 mm can be localized, in principle, to within ∼9%. All these results suggest that our prior knowledge of the properties of the black hole, of scattering broadening, and of the accretion flow can only limit this general relativistic null hypothesis test with EHT observations of Sgr A∗ to ≲10%.

AB - The half opening angle of a Kerr black hole shadow is always equal to (5 ± 0.2)GM/Dc2, where M is the mass of the black hole and D is its distance from the Earth. Therefore, measuring the size of a shadow and verifying whether it is within this 4% range constitutes a null hypothesis test of general relativity. We show that the black hole in the center of the Milky Way, Sgr A∗, is the optimal target for performing this test with upcoming observations using the Event Horizon Telescope (EHT). We use the results of optical/IR monitoring of stellar orbits to show that the mass-to-distance ratio for Sgr A∗ is already known to an accuracy of ∼4%. We investigate our prior knowledge of the properties of the scattering screen between Sgr A∗ and the Earth, the effects of which will need to be corrected for in order for the black hole shadow to appear sharp against the background emission. Finally, we explore an edge detection scheme for interferometric data and a pattern matching algorithm based on the Hough/Radon transform and demonstrate that the shadow of the black hole at 1.3 mm can be localized, in principle, to within ∼9%. All these results suggest that our prior knowledge of the properties of the black hole, of scattering broadening, and of the accretion flow can only limit this general relativistic null hypothesis test with EHT observations of Sgr A∗ to ≲10%.

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