Astrophysics and Gravitation

Research activities in the astrophysics and gravitation group at the University of Guelph cover a broad range of subjects, including high-energy nuclear astrophysics, the physics and astrophysics of black holes and neutron stars, the dynamics of compact binaries, the design of future gravitational-wave detectors, and fundamental aspects of relativistic gravitation. Much of this work is carried out in the context of the emerging area of multi-messenger astronomy, which combines information carried by electromagnetic radiation (in all bands), neutrinos, and gravitational waves. The group enjoys close ties with Perimeter Institute (Siegel and Yang have joint appointments) and with the Canadian Institute for Astrophysics. 

The research activities of Liliana Caballero focus on the role of nuclear reactions, neutrino interactions, and nuclear forces on the synthesis of elements and the evolution and mergers of compact objects (white dwarfs and neutron stars), as well as accretion disks around black holes. These stellar environments exhibit strong gravitational fields and extreme thermodynamic conditions, and constitute a unique extraterrestrial laboratory to probe our understanding of the fundamental forces of nature. Caballero's group provides detailed  predictions of signals emerging from these systems, which will be observed by various telescopes, neutrino detectors, and gravitational-wave observatories. 

A quarter of the surface of last points of scattering for electron neutrinos (outer) and electron antineutrinos (inner) emitted in from matter accreting into a rotating black hole. The color scale represents the local temperature.
A quarter of the surface of last points of scattering for electron neutrinos (outer) and electron antineutrinos (inner) emitted in
from matter accreting into a rotating black hole. The color scale represents the local temperature.

Daniel Siegel's research efforts are devoted to gravitational physics, nuclear astrophysics, high-energy astrophysics, and transient astronomy. Much of this activity aims to unravel the fundamental physics and astrophysics of binary neutron-star mergers. It identifies the physical processes that govern the dynamics of neutron-star mergers and give rise so observable electromagnetic radiation. It elucidates how such mergers and other astrophysical phenomena synthesize heavy elements in the Universe via the rapid neutron capture process. And it reflects on the broader impacts for nuclear physics and astrophysics, and the consequences for cosmology. In order to study these prime targets of multi-messenger astronomy, Siegel's group performs fully general-relativistic magnetohydrodynamic simulations of astrophysical systems on supercomputers, including microphysical equations of state, weak interactions, neutrino radiation transport, and nuclear reaction networks, in combination with analytical and semi-analytical modeling. 

Artist’s impression of a collapsar scenario — the collapse of a rapidly rotating massive star to a black hole.
Artist’s impression of a collapsar scenario — the collapse of a rapidly rotating massive star to a black hole.

Huan Yang's research work is also grounded in the fundamental processes associated with gravitational-wave and multi-band/multi-messenger astronomy. The work focuses on the dynamics and gravitational-wave emission of black-hole and neutron-star systems, with the goal to extract specific predictions that will be verified in observations by ground-based and space-based gravitational-wave detectors. The work also aims to exploit these observations to gather information about the population of black-hole and neutron-star binary systems in the Universe, their formation scenarios, and the fundamental physical processes involved during their mergers. Yang's group initiated and continues to perfect the design of high-frequency gravitational-wave detectors to probe neutron-star physics, in an effort to plan for the construction of third-generation detectors beyond LIGO and Virgo. 

An extreme mass-ratio inspiral system involving a supermassive black hole and a stellar-mass black hole. The orbit of the stellar-mass black hole is perturbed by another stellar-mass black hole nearby.
An extreme mass-ratio inspiral system involving a supermassive black hole and a stellar-mass black hole.
The orbit of the stellar-mass black hole is perturbed by another stellar-mass black hole nearby.

The research efforts of Eric Poisson cover a range of topics in general relativity, including the perturbation theory of black holes and neutron stars, the electromagnetic and gravitational self-force acting on particles moving in a curved spacetime, and the generation and propagation of gravitational waves. The main focus of Poisson's group is on tidal interactions of compact binaries in the context of gravitational-wave astronomy. The tidal interaction affects the orbital motion and the emission of gravitational waves, and the tidal imprint on the waves can thus be measured. Because the tidal deformation of a body is sensitive to the details of internal structure, gravitational-wave observations will eventually reveal intimate details of the physics of a neutron star, in particular the nature of its equation of state.

Binary system involving a black hole (black) and a compact star (yellow). The compact star exerts tidal forces on the black hole, and vice versa.
Binary system involving a black hole (black) and a compact star (yellow).
The compact star exerts tidal forces on the black hole, and vice versa.

Theorists

Liliana Caballero
Eric Poisson
Daniel Siegel
Huan Yang