Shadow Shapes Around the Black Hole in the Galactic Centre

Nucita, A. A.; Paolis, F. De; Ingrosso, G.

doi:10.1007/3-540-26373-x_7

Cited by 12 publications

(16 citation statements)

References 46 publications

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“…[31] discussed a possibility to detect retro-images of the Sun by a Schwarzschild black hole and the formation of mirages near rapidly rotating Kerr black hole horizons. They proposed a procedure to measure masses and rotation parameters through analysis of the form of the mirages.…”

Section: Introductionmentioning

confidence: 99%

Kerr-Sen dilaton-axion black hole lensing in the strong deflection limit

2007

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In the present work we study numerically quasi-equatorial lensing by the charged, stationary, axially-symmetric Kerr-Sen dilaton-axion black hole in the strong deflection limit. In this approximation we compute the magnification and the positions of the relativistic images. The most outstanding effect is that the Kerr-Sen black hole caustics drift away from the optical axis and shift in clockwise direction with respect to the Kerr caustics. The intersections of the critical curves on the equatorial plane as a function of the black hole angular momentum are found, and it is shown that they decrease with the increase of the parameter Q 2 /M . All of the lensing quantities are compared to particular cases as Schwarzschild, Kerr and Gibbons-Maeda black holes. I. INTRODUCTIONOne of the consequences of Einstein's General Theory of Relativity is that light rays are deflected by gravity. Although this discovery was made in the last century, the possibility that there could be such a deflection had been suspected much earlier, by Newton and Laplace, for the first time. The phenomena resulting from the deflection of electromagnetic radiation in a gravitational field are referred to as gravitational lensing (GL) and an object causing a detectable deflection is known as a gravitational lens. Nowadays, gravitational lensing is a rapidly developing area of research, and it has found applications ranging from the search of extrasolar planets and compact dark matter to the estimation of the values of the cosmological parameters [10]. In most of these cases it is possible to assume that the gravitational field is weak, hence the angle of deflection of the light in the field of a spherically symmetric body with mass M can be approximated by: that the present lens model could be able to distinguish observationally a black hole from naked singularity.The study of the gravitational lensing when light passes very close to a massive body, such as a black hole (a process also known as gravitational lensing in the strong deflection

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Section: Introductionmentioning

confidence: 99%

Kerr-Sen dilaton-axion black hole lensing in the strong deflection limit

2007

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“…Numerical calculations confirm also that the width Eq. (138) decreases with the increase of b [property (4)]. The asymmetry (5) of the spectrum is a generic property of the broadening of the sharp spectral lines for the emitters moving near black holes.…”

Section: Resultsmentioning

confidence: 99%

“…One of the most useful methods is to use iron Kα lines as probes of the black hole vicinity (see, e.g., [2][3][4][5] and references therein). This line of iron has an energy that depends on the state of the ionization of the atom and is in the range of 6.40-6.97 keV.…”

Section: Introductionmentioning

confidence: 99%

Radiation from an emitter revolving around a magnetized nonrotating black hole

2014

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One of the methods of study of black holes in astrophysics is based on broadening of the spectrum of radiation of ionized iron atoms. The line Kα associated with iron emission at 6.4 keV is very narrow. If such an ion is revolving around a black hole, this line is effectively broadened as a result of the Doppler and gravitational redshift effects. The profile of the broadened spectrum contains information about the gravitational field of the black hole. In the presence of a regular magnetic field in the vicinity of a black hole, the characteristics of the motion of charged ions are modified. In particular, their innermost stable circular orbits become closer to the horizon. The purpose of this work is to study how this effect modifies the spectrum broadening of lines emitted by such an ion. Our final goal is to analyze whether the change of the spectrum profiles can give us information about the magnetic field in the black hole vicinity.

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“…A possibility to observe mirages (shadows) around black holes using space based interferometers (like Radioastron space radio telescope) was discussed in paper [81].…”

Section: Discussionmentioning

confidence: 99%

The iron Kα-line as a tool for an evaluation of black hole parameters

Zakharov

2004

AIP Conference Proceedings

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Abstract. Recent X-ray observations of microquasars and Seyfert galaxies reveal broad emission lines in their spectra, which can arise in the innermost parts of accretion disks. Simulations indicate that at low inclination angle the line is measured by a distant observer as characteristic two-peak profile. However, at high inclination angles (> 85 0 ) two additional peaks arise. This phenomenon was discovered by using the Schwarzschild black hole metric to analyze such effect. They assumed that the effect is applicable to a Kerr metric far beyond the range of parameters that they exploited. We check and confirm their hypothesis about such a structure of the spectral line shape for the Kerr metric case. We use no astrophysical assumptions about the physical structure of the emission region except the assumption that the region should be narrow enough. Positions and heights of these extra peaks drastically depend on both the radial coordinate of the emitting region (annuli) and the inclination angle. It was found that these extra peaks arise due to gravitational lens effect in the strong gravitational field, namely they are formed by photons with some number of revolutions around black hole. This conclusion is based only on relativistic calculations without any assumption about physical parameters of the accretion disc like X-ray surface emissivity etc. We discuss how analysis of the iron spectral line shapes could give an information about an upper limit of magnetic field near black hole horizon.

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Shadow Shapes Around the Black Hole in the Galactic Centre

Cited by 12 publications

References 46 publications

Kerr-Sen dilaton-axion black hole lensing in the strong deflection limit

Kerr-Sen dilaton-axion black hole lensing in the strong deflection limit

Radiation from an emitter revolving around a magnetized nonrotating black hole

The iron Kα-line as a tool for an evaluation of black hole parameters

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