Red giant stellar collisions in the Galactic Centre

James. E. Dale1, Melvyn B. Davies1, Ross P. Church1,2, Marc Freitag3

1 Lund Observatory, Box 43, SE-221 00, Lund, Sweden 2 School of Mathematical Sciences, Monash University, Victoria 3800, Australia, 3Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK

Paper: MNRAS, 2008, in press

EPrint Server: 0811.3111


We show that collisions with stellar-mass black holes can partially explain the absence of bright giant stars in the Galactic Centre, first noted by Genzel et al, 1996. We show that the missing objects are low-mass giants and AGB stars in the range 1-3 M_o. Using detailed stellar evolution calculations, we find that to prevent these objects from evolving to become visible in the depleted K bands, we require that they suffer collisions on the red giant branch, and we calculate the fractional envelope mass losses required. Using a combination of Smoothed Particle Hydrodynamic calculations, restricted three-body analysis and Monte Carlo simulations, we compute the expected collision rates between giants and black holes, and between giants and main-sequence stars in the Galactic Centre. We show that collisions can plausibly explain the missing giants in the 10.5

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