TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. IV. RELATIVISTICALLY BROADENED IRON LINES

By T. Johannsen, Dimitrios Psaltis. 2012

158 citations recorded by the source corpus.

According to the no-hair theorem, astrophysical black holes are fully characterized by their masses and spins and are described by the Kerr metric. This theorem can be tested observationally by measuring (at least) three different multipole moments of the spacetimes of black holes. In this paper, we calculate the profiles of fluorescent iron lines emitted from the accretion flows around black hole candidates within a framework that allows us to perform the calculation as a function of its mass and spin as well as of a free parameter that measures potential deviations from the Kerr metric. We show that such deviations lead to line profiles that are significantly altered and may exhibit a modified flux ratio of the two peaks in their characteristic double-peaked shape. We also show that the disk inclination can be measured independently of the spin and the deviation parameter at low to intermediate inclination angles, as in the case of Kerr black holes. We estimate the precision that near-future X-ray missions such as Astro-H and ATHENA+ are required to achieve in order to resolve deviations from the Kerr metric in iron line profiles and show that constraints on such deviations will be strongest for rapidly spinning black holes. More generally, we show that measuring the line profile with a precision of ∼5% at disk inclinations of 30° or 60° constrains the deviation parameter to order unity for values of the spin a ≳ 0.5M.

Subfields: Astronomy and Astrophysics, Biomedical Engineering, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/a3a360a2a7aaab5ad53f2a5ca4048eeece4702c7

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Citations in the corpus

TESTING THE NO-HAIR THEOREM WITH EVENT HORIZON TELESCOPE OBSERVATIONS OF SAGITTARIUS A* (2013, background): “…spin, a variety of observations have been brought to bear upon the applicability of the Kerr metric, including relativistically broadened iron lies (Johannsen & Psaltis 2013; Bambi 2013), variability (Johannse & Psaltis 2011b, 2013; Bambi 2012b), continuum accretion disk spectra (Bambi & Barausse…”
Calculating black hole shadows: Review of analytical studies (2021, background): “• photon ring, see Johannsen and Psaltis [46], Johnson et al [24];”
Testing black hole candidates with electromagnetic radiation (2015, methodology): “For instance, Johannsen & Psaltis (2013) showed how iron lines in the JP metric with different a∗ and 3 but the same ISCO radius are very similar, as well as orbital fun- 12 It is worth pointing out that, in this discussion and in what follows, “particle” is used to refer to a parcel of gas.”
Measuring the Kerr spin parameter of regular black holes from their shadow (2013, background): “Other approaches to test the nature of BH candidates are either not yet mature, like the case of quasi-periodic oscillations [32, 33], or it is not clear when astrophysical data will be available, like the case of gravitational waves or observations of a BH binary with a pulsar companion [34–40].”
Hunting for extra dimensions in the shadow of M87* (2019, background): “In particular, knowledge of these three quantities would be enough to uniquely determine the BH quadrupole moment: any deviation from such canonical value would be an indication that new physics is at play [38, 39].”