[astroseminar at Sapienza] Two Gravity theory webinars next week

[Paolo Pani]

Dear All,

next week there will be two gravity-theory webinars:

*1) **Nico Sanchis-Gual (IST, Lisbon):* "*Light in the dark: GW190521 as a
Proca star merger"*
*Mon* (*Nov 30**th @ noon*)

The detections of gravitational waves are opening a new window to the
Universe. The nature of black holes and neutron stars may now be unveiled,
but gravitational radiation may also lead to exciting discoveries of new
exotic compact objects, oblivious to electromagnetic waves. In particular,
Advanced LIGO-Virgo recently reported a short gravitational-wave signal
(GW190521) interpreted as a quasi-circular merger of black holes, one at
least populating the pair-instability supernova gap. We found that GW190521
is also consistent with numerically simulated signals from head-on
collisions of two (equal mass and spin) horizonless vector boson stars (aka
Proca stars). This provides the first demonstration of close degeneracy
between these two theoretical models, for a real gravitational-wave event.

*2) Horng Sheng Chia (Princeton, US): "Tidal Deformation and Dissipation of
Rotating Black Holes"*
*Wed (Dec, 2nd @ 3pm) *

Black holes are never isolated in realistic astrophysical environments;
instead, they are often perturbed by complicated external tidal fields. How
does a black hole respond to these tidal perturbations? In this talk, I
will discuss both the conservative and dissipative responses of the Kerr
black hole to a weak and adiabatic gravitational field. The former
describes how the black hole would change its shape due to these tidal
interactions, and is quantified by the so-called “Love numbers”. On the
other hand, the latter describes how energy and angular momentum are
exchanged between the black hole and its tidal environment due to the
absorptive nature of the event horizon. I will show that the Love numbers
of the Kerr black hole vanish identically — in other words, you cannot
stretch a black hole. I will also describe how the Kerr black hole's
dissipative response implies that energy and angular momentum can either be
lost to or extracted from the black hole, with the latter process commonly
known as the black hole superradiance. I will end by discussing how these
tidal responses leave distinct imprints on the gravitational waves emitted
by binary black holes. Time permitting, I will also argue that the
ambiguity issue of Love numbers in General Relativity can be resolved
through a careful consideration of the boundary condition at asymptotic
infinity.


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

Calendar of the future gravity theory seminars:
https://calendar.google.com/calendar/u/1?cid=Y191MGo3bG9pYzE1bjBxdGFhN3A4MTlzNDg2Y0Bncm91cC5jYWxlbmRhci5nb29nbGUuY29t

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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