Nuclear Interaction Gamma-Ray Lines from the Galactic Center Region

TL;DR

This paper predicts stationary gamma-ray lines from nuclear interactions caused by subrelativistic ions generated during star disruptions near the Milky Way's central black hole, with potential for future detection to reveal high-energy processes.

Contribution

It models the energy and spatial distribution of particles from star disruptions and predicts gamma-ray line emissions, providing new insights into black hole-induced high-energy phenomena.

Findings

Gamma-ray lines are emitted within a 5° region around the Galactic center.

Total flux below 8 MeV is approximately 10^{-4} photons cm^{-2} s^{-1}.

Detection with current instruments like INTEGRAL is unlikely, but future telescopes may observe these lines.

Abstract

Aims. The accretion of stars onto the central supermassive black hole at the center of the Milky Way is predicted to generate large fluxes of subrelativistic ions in the Galactic center region. We analyze the intensity, shape and spatial distribution of de-excitation gamma-ray lines produced by nuclear interactions of these energetic particles with the ambient medium. Methods. We first estimate the amount and mean kinetic energy of particles released from the central black hole during star disruption. We then calculate from a kinetic equation the energy and spatial distributions of these particles in the Galactic center region. These particle distributions are then used to derive the characteristics of the main nuclear interaction gamma-ray lines. Results. Because the time period of star capture by the supermassive black hole is expected to be shorter than the lifetime of the ejected fast particles against Coulomb losses, the gamma-ray emission is predicted to be stationary. We find that the nuclear de-excitation lines should be emitted from a region of maximum 5$^\circ$ angular radius. The total gamma-ray line flux below 8 MeV is calculated to be $\approx10^{-4}$ photons cm$^{-2}$ s$^{-1}$. The most promising lines for detection are those at 4.44 and $\sim$6.2 MeV, with a predicted flux in each line of $\approx$$10^{-5}$ photons cm$^{-2}$ s$^{-1}$. Unfortunately, it is unlikely that this emission can be detected with the INTEGRAL observatory. But the predicted line intensities appear to be within reach of future gamma-ray space instruments. A future detection of de-excitation gamma-ray lines from the Galactic center region would provide unique information on the high-energy processes induced by the central supermassive black hole and the physical conditions of the emitting region.