Session K02: Black Holes

The Strong Field Dynamics of Binary Neutron Star

What is the nature of neutron stars? Where are r-process elements formed in the Universe? Multimessenger observations of neutron star mergers might provide us with the key to answer these and other important open questions in theoretical astrophysics. However, multimessenger astronomy also poses new challenges to the theorists who need to develop models for the joint interpretation of all data channels. In this talk, I will review our current theoretical understanding of how neutron star mergers proceed and of how the dynamics is imprinted in their multimessenger emissions. I will present recent simulation results and their implications. Finally, I will discuss future challenges and prospective for this field.   

Small Spins of Primordial Black Holes from Random Geometries

Black hole entropy is a robust prediction of quantum gravity with no established phenomenological consequences to date. We use the Bekenstein-Hawking entropy formula and general-relativistic statistical mechanics to determine the probability distribution of random geometries uniformly sampled in phase space. We show that this statistics (in the limit $\hbar\to 0$) is relevant to large curvature perturbations, resulting in a population of primordial black holes with zero natal spin. In principle, the identification of such a population at LIGO, Virgo, and future gravitational wave observatories could provide the first observational evidence for the statistical nature of black hole entropy.   

Dark Sirens to Resolve the Hubble-Lemaitre Tension

The planned sensitivity upgrades to the LIGO and Virgo facilities could uniquely identify host galaxies of dark sirens---compact binary coalescences without any electromagnetic counterparts---within a redshift of $z=0.1$. This is aided by the higher order spherical harmonic modes present in the gravitational-wave signal, which also improve distance estimation. In conjunction, sensitivity upgrades and higher modes will facilitate an accurate, independent measurement of the host galaxy's redshift in addition to the luminosity distance from the gravitational wave observation to infer the Hubble constant $H_0$ to better than a few percent in five years. A possible Voyager upgrade or third generation facilities would further solidify the role of dark sirens for precision cosmology in the future.   

Black Holes From Atomic Dark Matter

Dissipative dark matter models provide a solution to the dark matter problem with the further intriguing possibility that small dark matter halos can directly collapse into dark black holes with a unique mass spectrum. Prior literature has demonstrated the ability to form such objects using the dark atomic model in the simplest analytic case, analogous to Population III star formation. We present here the next level check of dark black hole formation, tracking the evolution of a simple halo collapse scenario using our extension of the KROME astrochemical software package that includes dark atomic and molecular processes. Our results demonstrate the importance of including molecular processes in these analyses as well as the strong dependence on the molecular properties.   

Modeling black hole ringdown: overtones or mirror modes?

The post-merger signal in a binary black hole merger, described by linear perturbation theory, is, historically, modeled using the dominant positive-frequency (corotating) fundamental mode. Recently, there has been efforts to model the post-merger signal using higher positive-frequency overtones in an attempt to achieve greater accuracy in describing the signal at earlier times. In general, negative-frequency (counterrotating) modes are also excited in a binary black hole merger. In this study, we model the post-merger signal using an overtone model and a mirror (counterrotating) mode model for a set of numerical relativity simulations across mass ratios and (aligned/anti-aligned) spins to identify the sections of the parameter space where an overtone and/or a mirror mode is more important.   

The geometric formulation of the covariant Phase Space with boundaries

In this talk, I will introduce the relative bicomplex framework, a new formalism which is the natural one to deal with the covariant phase space of theories with boundaries. I will show that it provides a formal equivalence between the relative version of a theory with boundary and the non-relative version of the same theory with no boundary. With these tools at hand, we can build over the space of solutions a (pre)symplectic structure canonically associated with the action. I will provide a brief summary of other geometric objects that can be derived, such as symmetries, Noether currents, and charges. Likewise, I will characterize the arbitrariness of these constructions which has been a matter of confusion in the past.