Séminaire de Physique ThéoriqueImaging a boson star at the center of the Galaxy
Frédéric Vincent (CNRS - Observatoire de Paris/LESIA)
Thursday 19 May 2016 14:00 - Tours - Salle 1180 (Bât E2)
The center of our Galaxy harbors a supermassive compact object that closely resembles a black hole : Sagittarius A* (Sgr A*). However, for the time being, it is not possible to unambiguously demonstrate that Sgr A* is indeed a black hole. Alternative compact objects lead to rather similar observables, and current observations do not allow to differentiate various compact objects. It is the goal of a near-future instrument, the Event Horizon Telescope (EHT, ~2020), to image the surroundings of Sgr A* with an exquisite resolution. These observations might allow to differentiate for the first time the observables associated to different compact objects. One of the most fascinating goal of the EHT is to test the presence of an event horizon at Sgr A* by imaging the black hole shadow, this dark region on the observer's sky that is due to background photons being captured by the black hole. The clear detection of an event horizon would be a direct proof that Sgr A* is indeed a black hole. The goal of my talk will be to present the first simulations of an accretion flow at Sgr A* assuming that this compact object is no longer a black hole, but a boson star. Such an object is a long-studied alternative to black holes, which does not possess any event horizon, nor any central singularity. I will show images of an accretion torus surrounding a boson star at Sgr A*, and discuss the specific observational properties of rotating boson stars as opposed to the classical black holes of general relativity (Kerr black holes). I will focus in particular on the (im)possibility to demonstrate the existence of an event horizon from imaging the close surroundings of Sgr A*.