Probing the black hole metric: Black hole shadows and binary black-hole inspirals

Abstract

In general relativity, the spacetimes of black holes have three fundamental properties: (i) they are the same, to the lowest order in spin, as the metrics of stellar objects; (ii) they are independent of mass when expressed in geometric units; and (iii) they are described by the Kerr metric. In this paper, we quantify the upper bounds on potential black-hole metric deviations imposed by observations of black-hole shadows and of binary black-hole inspirals in order to explore the current experimental limits on possible violations of the last two predictions. We find that both types of experiments provide correlated constraints on deviation parameters that are primarily in the tt components of the spacetimes when expressed in areal coordinates. We conclude that, currently, there is no evidence for deviations from the Kerr metric across the 8 orders of magnitude in mass and 16 orders in curvature spanned by the two types of black holes. Moreover, because of the particular masses of black holes in the current sample of gravitational-wave sources, the correlations imposed by the two experiments are aligned and of similar magnitudes when expressed in terms of the far-field, post-Newtonian predictions of the metrics. If a future coalescing blackhole binary with two low-mass (e.g., ∼3 M ⊙ ) components is discovered, the degeneracy between the deviation parameters can be broken by combining the inspiral constraints with those from the black-hole shadow measurements.

Polarimetric signatures of the photon ring of a black hole that is pierced by a cosmic axion string

“…Very large baseline interferometry therefore allows us to test aspects of fundamental physics that affect the structure and properties of the photon ring in the regime close to a black hole. This includes testing gravity, the black hole no hair conjecture and various aspects of particle physics in that regime (works along these lines include [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]). In this work we shall study one new aspect of this sort, namely the impact that certain cosmic strings can have on the black hole photon ring when they pierce the black hole.…”

Understanding Gravitational Entropy of Black Holes: A New Proposal via Curvature Invariants

“…The Cauchy, Killing and apparent horizon(s) [52] coincide and can still be found by solving f (r H ) = 0. This framework allows one to study post-Newtonian effects in astrophysical phenomena [53][54][55][56]. Replacing l a and n a in the null coframe (30) with…”

Light ring images of double photon spheres in black hole and wormhole space-times

“…The Kerr hypothesis has become a common test-bed for our ideas on the gravitational interaction [6]. Since its verification somewhat resembles the Scottish black sheep tale -since it would require to check that every black hole in the universe is actually of Kerr type -, this half of the dilemma can only aspire to perform null-tests, i.e, whether a given observation matches the Kerr expectation, and to what degree of precision [7][8][9].…”