Thesis

Shadows and gravitational lensing of Black Holes interacting with fundamental fields

• Call:

  IDPASC Portugal - PHD Programme 2015

• Academic Year:

  2015 / 2016

• Domains:

  General Relativity | Astrophysics

• Supervisor:

  Vitor Cardoso

• Co-Supervisor:

  Carlos Herdeiro

• Institution:

  Instituto Superior Técnico

• Host Institution:

  IST and University of Aveiro

• Abstract:

  There is strong observational evidence that extremely compact and massive objects populate the Universe: black holes (BHs). According to General Relativity, equilibrium BHs are highly constrained objects, described by the Kerr metric and depend solely on two parameters: mass and angular momentum. This is the General Relativity BH paradigm. This idea, partly based on rigorous theorems, but partly conjectured, has been immortalized in the mantra “BHs have no hair”. At present, however, it is unknown if the observed BH candidates are the paradigmatic BHs of General Relativity, BHs described by an alternative model, or even other types of compact objects without an event horizon. The next decade promises to shed light on this issue: we are on the verge of gathering observational evidence that will map the spacetime geometry close to BH candidates. This evidence will come from i) gravitational wave astronomy, in particular with the aLIGO detectors, but potentially also with Pulsar Timing Array techniques; ii) astrometric measurements, using the GRAVITY instrument; iii) large baseline interferometry, using the Event Horizon Telescope - EHT. The latter promises to resolve angular scales of the order of the horizon scale for the supermassive BH at the galactic centre and study the BH shadow - its gravitational lensing and redshift effect on the radiation from surrounding sources. These forthcoming experiments make it timely to explore alternative models to the General Relativity BH paradigm, and their associated phenomenology. The goal of this thesis is to understand the astrophysical phenomenological for alternative BH models, which will both constraint these models and understand the specifities of the Kerr paradigm. In particular we shall consider a recently discovered qualitatively novel family of solutions of “hairy” rotating BHs. These BHs unveiled a new mechanism which allows generalizations thereof to be constructed, wherein different fundamental scalar (or vector) fields can form the BH “hair”. This thesis will address astrophysical observables of these new families of solutions and compare them with those of the standard Kerr case, such as: shadows, orbits of material particles, emission of gravitational radiation from perturbed solutions, efficiency in matter-radiation conversion and other electromagnetic signatures, such as QPOs and properties of accretions disks.