MG15 - Talk detail

Back to previous page

 Participant

Institution

Session

Accepted

Order

Time

Talk

Title

Abstract

Primordial black holes (PBHs) can form in the early Universe from the collapse of cosmological perturbations after cosmological horizon crossing. They are possible candidates for the dark matter component of the Universe as well as for the seeds of supermassive black holes that we observe today in the centres of galaxies. In calculations of spherically symmetric collapse, starting with a non linear curvature perturbation in the super horizon regime, the non linear evolution is simulated using a Lagrangian relativistic hydrodynamical code. If the perturbation is larger than a threshold depending on the equation of state and on the specific shape of the perturbation, a black hole is formed. In this talk I will discuss the dependence of PBH formation from the initial shape of the curvature profile showing the relation between the threshold amplitude and the steepness of the perturbation which is linked to the amplitude of the pressure gradients which arise during the collapse. I will then show how the initial shape can be determined from the power spectrum of cosmological perturbations, using a single field inflation model, calculating the correspondent abundance. The probability of forming PBHs within such scenario is exponentially easier than what previously thought.

Pdf file

Session

Accepted

Order

Time

Talk

Title

Abstract

In calculations of gravitational collapse to form black holes, trapping horizons (foliated by marginally trapped surfaces) make their first appearance either within the collapsing matter or where it joins on to a vacuum exterior. Those which then move outwards with respect to the matter have been proposed for use in defining black holes, replacing the global concept of an “event horizon” which has some serious drawbacks for practical applications. We here present results from a study of the properties of both outgoing and ingoing trapping horizons, assuming strict spherical symmetry throughout. We have investigated their causal nature (i.e. whether they are spacelike, timelike or null), following two different approaches, one using a geometrical quantity related to expansions of null geodesic congruences, and the other using the horizon velocity measured with respect to the collapsing matter. The models treated are simplified, but do include pressure effects in a meaningful way and we analyze how the horizon evolution depends on the initial conditions of energy density and pressure of the collapse. (NOTE: Although the work is not concerning wormholes and its space time properties, some aspects of this work are related. This session seems to me the most adequate to present this work.)

Pdf file

Back to previous page