Star-UBB Seminar Series:- Stability analysis of spin evolution in compact binaries with black hole, neutron star, gravastar, or boson star components
The speaker will discuss the spin dynamics and stability of precessing compact binaries on eccentric orbit with gravastar, black hole, neutron star, or boson star components. This is based on a closed system of first-order differential equations characterising the secular evolution to second post-Newtonian–order, with leading-order spin-orbit, spin-spin, and mass quadrupole-monopole contributions included.
Among the interesting effects are
i) new, quadrupole-induced spin flip-flops occurring when the neutron star with dominant spin has a quadrupolar parameter ≈ 3 and
ii) a swinging-type azimuthal evolution in the case of equal mass binaries with the black hole companion being either a gravastar or another black hole (the spins of the components periodically overpassing each other), as opposed to their conserved sequence, when the companion is a boson star.
Both the aligned and more generic coplanar configurations of the spins and orbital angular momentum have fixed points. The speaker and his team mapped the parameter regions with stable fixed points of the spins. They include the binary configurations with both spins aligned to the orbital angular momentum (with the exception of certain quadrupolar parameter ranges of neutron stars and boson stars), both spins antialigned, also the extremal mass ratio. For equal masses, the configurations of one of the spins aligned and the other antialigned is stable for gravastar binaries, for neutron star binaries in the high quadrupolar parameter range, and for boson star binaries. The speaker and his team identified a new transitional instability regime during the inspiral of certain gravastar, neutron star, or boson star binaries with opposing spins. For coplanar configurations instabilities occur only for the gravastar – gravastar, boson star – boson star and black hole – boson star binaries.
In summary, both the spin dynamics and the stability of fixed points heavily depend on the nature of the binary components.
講者：Prof. Laszlo Arpad Gergely (Institute of Physics, University of Szeged, Szeged, Hungary)
Scientific and Technological Advanced Research- Babeș-Bolyai University(Star-UBB) Seminar Series in Gravitation, Cosmology and Astrophysics
Presently a period of rapid and intense change are being witnessed in our understanding of the gravitational force, at a rate that is quickly increasing since the important observational discoveries of the late 1990s. With the advent of new observational techniques, the emergence of important cosmological and astrophysical paradigms can be seen that lead to a deep change in our understanding of the Universe. Astronomical observations strongly suggest that at large scales the force of gravity may not behave according to standard general relativity, and that a generalization of the gravitational action, either at the geometric level, or at the matter level, may be required for a full understanding of the gravitational interaction.
The goal of the present seminar is to bring Theoretical Gravitational Physics closer to the observations and experiments, and to discuss current topics in general relativity, high-energy physics, astrophysics and cosmology.