[astroseminar at Sapienza] Gravity theory webinar: Monday July 5th @noon: Pedro Cunha (Aveiro University) - Constraining ultralight scalar fields around the M87 black hole using the EHT shadow

[Paolo Pani]

Announcement of the next gravity-theory webinar:

Speaker: *Pedro Cunha (Aveiro University)*
Title: *Constraining ultralight scalar fields around the M87 black hole
using the EHT shadow*
Date:* Monday, July 5th @ noon CEST*

Abstract:
*Hypothetical ultralight bosonic fields will spontaneously form macroscopic
bosonic halos around Kerr black holes, via superradiance, transferring part
of the mass and angular momentum of the black hole into the halo. Such a
process, however, is only efficient if resonant: when the Compton
wavelength of the field approximately matches the gravitational scale of
the black hole. For a complex-valued field, the process can form a
stationary, bosonic field-black hole equilibrium state - a black hole with
synchronised hair. For sufficiently massive black holes, such as the one at
the centre of the M87 supergiant elliptical galaxy, the hairy black hole
can be robust against its own superradiant instabilities, within a Hubble
time. Studying the shadows of such scalar hairy black holes, we can
constrain the amount of hair which is compatible with the Event Horizon
Telescope (EHT) observations of the M87 supermassive black hole, assuming
the hair is a condensate of ultralight scalar particles of mass ∼1E−20 eV,
as to be dynamically viable. We show the EHT observations set a weak
constraint, in the sense that typical hairy black holes that could develop
their hair dynamically, are compatible with the observations, when taking
into account the EHT error bars and the black hole mass/distance
uncertainty.  We will also discuss a recent theorem establishing that an
equilibrium Black Hole must admit, under generic conditions, at least one
circular Light Ring orbit outside the horizon. The proof relies on a
topological argument and makes virtually no assumptions on the matter
content or gravity model.*


Zoom link:
https://uniroma1.zoom.us/j/81283707469?pwd=SzkyMk5jRm0xcEN3WE5MYVh1RVFtQT09
ID meeting: 812 8370 7469
Passcode: 915450

Cheers,
Paolo



-- 
Paolo Pani
Associate Professor
ERC StG Fellow, DarkGRA project
Junior Fellow, Scuola Superiore di Studi Avanzati Sapienza

Physics Department (Marconi Building), 3rd floor, room 334
Sapienza University of Rome
Piazzale Aldo Moro 5 - 00185 Rome (Italy)
+39 06 4991 4472 (int 24472)

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