Light curves and spectra for stellar collisions between main-sequence stars in galactic nuclei

Abstract

High-velocity stellar collisions in galactic nuclei produce ejecta that generate potentially observable electromagnetic radiation, making them promising nuclear transients. However, the photometric and spectroscopic properties of these collisions, which would more frequently involve main-sequence stars, remain largely unexplored. Here, using 3D hydrodynamics and 1D radiative-transfer simulations, we investigate the properties and observables of the debris produced in high-velocity collisions between terminal-age main-sequence stars, covering a wide range of collision configurations. The ejecta produce bright ultraviolet (UV) flares with bolometric luminosities typically peaking at $\gtrsim 10^{43}$ erg s${}^{-1}$, declining steeply as $t^{-2}-t^{-4}$ to reach $\gtrsim 10^{41}-10^{42}$ erg s${}^{-1}$ at 0.5 d and leveling off on a plateau at $10^{39}-10^{41.5}$ erg s${}^{-1}$ ($M_V$ between $-$10 to $-$15 mag) after a few days. Their spectra evolve considerably during the first few days, morphing from UV- to optical-dominated. The UV range shows numerous resonance transitions from metals like C, N, and O, whereas the optical primarily shows H I Balmer lines. These properties are qualitatively similar to those observed, as well as obtained in models of Type II supernovae. Observables from these events exhibit clear correlations with collision configurations, including impact parameter, relative velocity, and stellar masses. We provide fitting formulae to describe these correlations. Detecting these flares requires sub-day cadence surveys such as ULTRASAT, combined with spectroscopic observations to disentangle degeneracies and infer collision characteristics.

arXiv comment23 page, 20 figures, 2 tables, accepted for publication in A&A. Movies available at https://www.youtube.com/playlist?list=PLxLK3qI02cQequh99QnHHUhOKl0SO3vQB

References in corpus (21)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• E pur si muove: Galiliean-invariant cosmological hydrodynamical simulations on a moving mesh
• Monitoring stellar orbits around the Massive Black Hole in the Galactic Center
• The Galactic Center Massive Black Hole and Nuclear Star Cluster
• Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
• A catalogue of masses, structural parameters and velocity dispersion profiles of 112 Milky Way globular clusters
• The Arepo public code release
• Tidal Disruption Events
• Improving the convergence properties of the moving-mesh code AREPO
• Type II-Plateau supernova radiation: dependencies on progenitor and explosion properties
• Time Dependent Radiative Transfer Calculations for Supernovae
• A comprehensive set of simulations of high-velocity collisions between main sequence stars
• Constructing stable 3D hydrodynamical models of giant stars
• Synthetic line and continuum linear-polarisation signatures of axisymmetric type II supernova ejecta
• On Socially Distant Neighbors: Using Binaries to Constrain the Density of Objects in the Galactic Center
• Stellar Collisions in Galactic Nuclei: Impact on Destructive Events Near a Supermassive Black Hole
• Transient stellar collisions as multimessenger probes: Non-thermal-, gravitational wave emission and the cosmic ladder argument
• The Primary Flare Following a Stellar Collision in a Galactic Nucleus