On the ``stellar dynamical'' evidences for massive black holes

Junichiro Makino
Department of Astronomy, University of Tokyo, 7-3-1 Hongo,
Bunkyo-ku,Tokyo 113-0033, Japan

Abstract:

We critically examine recent claims that globular clusters M15 and G1 of M31 contains massive central black holes. For both clusters, we performed detailed N-body simulations with realistic effects like the stellar mass loss due to stellar evolution are taken into account. In the case of M15, we found neutron stars and massive white dwarfs concentrate to the center through mass segregation, resulting in a sharp increase in M/L toward the center. While consistent with the presence of a central black hole, the Hubble data can also be explained by this central concentration of neutron stars and massive white dwarfs. In the case of G1, the effect of the mass segregation is not significant, because the relaxation time of G1 is longer than the Hubble time. Even so, we found that our simulation model can perfectly reproduce the observed properties of G1 such as the luminosity profile, velocity dispersion profile, rotation profile and ellipticity profile. Though it's unclear why the existence of the black hole was concluded in the case of G1, simulation models clearly show that black holes are not necessary to explain observations.