Testing the rotational nature of the supermassive object M87* from the circularity and size of its first image

By Cosimo Bambi, K. Freese, S. Vagnozzi, Luca Visinelli. Physical Review D, 2019

289 citations recorded by the source corpus.

The Event Horizon Telescope (EHT) collaboration has recently released the first image of a black hole (BH), opening a new window onto tests of general relativity in the strong field regime. In this paper, we derive constraints on the nature of M87* (the supermassive object at the centre of the galaxy M87), exploiting the fact that its shadow appears to be highly circular, and using measurements of its angular size. We first consider the simple case where M87* is assumed to be a Kerr BH. We find that the inferred circularity of M87* excludes Kerr BHs with observation angle $\theta_{\rm obs} \gtrsim 45^{\circ}$ for dimensionless rotational parameter $0.95 \lesssim a_* \leq 1$ whereas the observation angle is unbounded for $a_* \lesssim 0.9$. We then consider the possibility that M87* might be a superspinar, i.e. an object described by the Kerr solution and spinning so fast that it violates the Kerr bound by having $|a_*| > 1$. We find that, within certain regions of parameter space, the inferred circularity and size of the shadow of M87* do not exclude the possibility that this object might be a superspinar.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/2637cd0864de0a2d7093d8dd75b3ec014f2abc1b

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In Astronomy and Astrophysics

1. D. Mota
2. A. Allahyari
3. Mohsen Khodadi
4. S. Vagnozzi
5. M. Jamil
6. Qiang Wu
7. Indrani Banerjee
8. Tao Zhu

Citations in the corpus

• Shadows and deflection angle of charged and slowly rotating black holes in Einstein-Æther theory (2019, background): “[1] K. Akiyama et al. [Event Horizon Telescope Collaboration], “First M87 Event Horizon Telescope Results.”
• Silhouette of M87*: A new window to peek into the world of hidden dimensions (2019, background): “Thus deviation of the shadow from circularity ∆C is another primary observable which can be defined as (see [53]),”
• Magnetically charged black holes from non-linear electrodynamics and the Event Horizon Telescope (2019, methodology): “1 in [41]).”
• Black holes with scalar hair in light of the Event Horizon Telescope (2020, background): “For an incomplete list of works in this direction, see for instance [115–167].”