Energetic Explosions from Collisions of Stars at Relativistic Speeds in Galactic Nuclei

Abstract

We consider collisions between stars moving near the speed of light around supermassive black holes (SMBHs), with mass M • 10 8 M , without being tidally disrupted. The overall rate for collisions taking place in the inner ∼ 1 pc of galaxies with M • = 10 8 , 10 9 , 10 10 M are Γ ∼ 5, 0.07, 0.02 yr −1 , respectively. We further calculate the differential collision rate as a function of total energy released, energy released per unit mass lost, and galactocentric radius. The most common collisions will release energies on the order of ∼ 10 49 − 10 51 erg, with the energy distribution peaking at higher energies in galaxies with more massive SMBHs. Depending on the host galaxy mass and the depletion timescale, the overall rate of collisions in a galaxy ranges from a small percentage to several times larger than that of core-collapse supernovae (CCSNe) for the same host galaxy. In addition, we show example light curves for collisions with varying parameters, and find that the peak luminosity could reach or even exceed that of superluminous supernovae (SLSNe), although with light curves with much shorter duration. Weaker events could initially be mistaken for low-luminosity supernovae. In addition, we note that these events will likely create streams of debris that will accrete onto the SMBH and create accretion flares that may resemble tidal disruption events (TDEs).

Collisional Shaping of Nuclear Star Cluster Density Profiles

“…Several theoretical and computational studies have shown that destructive collisions can deplete the supply of stars near the SMBH (e.g., Duncan & Shapiro 1983;David et al 1987aDavid et al , 1987bMurphy et al 1991;Rauch 1999;Freitag & Benz 2002;Rose et al 2023). The frequency and outcomes of direct collisions depend on the distance from the SMBH (e.g., Lai et al 1993;Rauch 1999;Rubin & Loeb 2011;Hu & Loeb 2021;Rose et al 2023). This process may therefore have distinct effects on the stellar density profile (e.g., Rauch 1999;Freitag & Benz 2002).…”