arXiv subjects

Sean Fortuna

Publications and source records attributed to Sean Fortuna.

3 recordsLinked to original sources

arXiv2025

Imprints of a galactic environment on TDEs: Suppressed peaks, shallower decays and late-time rebrightening episodes

Classic models of tidal disruption events (TDEs), employing a purely Keplerian description of stellar debris dynamics, have proven remarkably successful in describing the observed early-time emission of these transients. By construction, however, this picture treats the disruption as an isolated star-black hole encounter, leaving the gravitational influence of the surrounding galaxy absent from the dynamics. We relax this assumption by embedding the debris within the gravitational field of a spherically symmetric mass distribution representing either the host galaxy or a dark matter halo, while deliberately retaining a minimal Newtonian framework so that the environmental contribution remains transparent and straightforward to interpret. Within this extended model, we find that the host potential can imprint clear signatures on the light curve that lie outside the predictive scope of traditional models, such as a suppressed initial accretion peak, phases of shallow decay and rebrightening episodes. For TDEs in ordinary galaxies, however, the latter signatures turns on far too late to be captured by current observations, explaining why simple Keplerian models have proven so effective despite neglecting the galactic environment. Only at much longer times does the broader galactic structure begin to reshape the fallback dynamics, gradually steering the system away from the canonical $t^{-5/3}$ decay. This provides an exciting opportunity for next-generation time-domain surveys to capture the long-term evolution of TDEs, enabling searches for delayed signals that encode information about the surrounding galactic mass.

astro-ph.HE↗

arXiv2022

Electromagnetic quasinormal modes of Schwarzschild-anti-de Sitter black holes: Bifurcations, spectral similarity, and exact solutions in the large black hole limit

We revisit the peculiar electromagnetic quasinormal mode spectrum of an asymptotically anti-de Sitter Schwarzschild black hole. Recent numerical calculations have shown that some quasinormal mode frequencies become purely overdamped at some critical black hole sizes, where the spectrum also bifurcates. In this paper, we shed light on unnoticed and unexplained properties of this spectrum by exploiting some novel analytic results for the large black hole limit. We demonstrate, both numerically and analytically, that the quasinormal mode spectra of large black holes become approximately isospectral, and refer to this new symmetry property as spectral similarity. We take advantage of this spectral similarity to derive a precise analytic expression for the locations of the bifurcations, in which a surprising Feigenbaum-like constant appears. We derive an exact solution for its spectrum and eigenfunctions, and find that large black holes cannot be made to vibrate with electromagnetic perturbations, independently of the boundary conditions imposed at spatial infinity. Finally, we characterize the insensitivity of the spectrum to different boundary conditions by analyzing the expansion of the quasinormal mode spectrum around the large black hole limit.

gr-qc↗

arXiv2020

Bernstein spectral method for quasinormal modes and other eigenvalue problems

Spectral methods are now common in the solution of ordinary differential eigenvalue problems in a wide variety of fields, such as in the computation of black hole quasinormal modes. Most of these spectral codes are based on standard Chebyshev, Fourier, or some other orthogonal basis functions. In this work we highlight the usefulness of a relatively unknown set of non-orthogonal basis functions, known as Bernstein polynomials, and their advantages for handling boundary conditions in ordinary differential eigenvalue problems. We also report on a new user-friendly package, called \texttt{SpectralBP}, that implements Berstein-polynomial-based pseudospectral routines for eigenvalue problems. We demonstrate the functionalities of the package by applying it to a number of model problems in quantum mechanics and to the problem of computing scalar and gravitational quasinormal modes in a Schwarzschild background. We validate our code against some known results and achieve excellent agreement. Compared to continued-fraction or series methods, global approximation methods are particularly well-suited for computing purely imaginary modes such as the algebraically special modes for Schwarzschild gravitational perturbations.

gr-qc↗