Abstract Details
| Name: Seshadri Sridhar Affiliation: RRI, Bengaluru Conference ID: ASI2019_574 Title : Stalling of Globular Cluster Orbits in Dwarf Galaxies Authors and Co-Authors : S. Sridhar, Raman Research Institute, Bengaluru Abstract Type : Invited Abstract Category : Plenary Abstract : A globular cluster orbiting a dwarf galaxy is expected to in-spiral to the centre of the galaxy within the age of the Universe, according to the Chandrasekhar dynamical friction formula. But globular clusters are found well away from the centres of some dwarf galaxies, arousing concerns about the applicability of the formula in the cores of dwarf galaxies. The manner of its failure has been investigated by numerical simulations but a dynamical explanation has been absent. Karamveer Kaur and I used the Tremaine-Weinberg theory of dynamical friction to solve this problem. The retarding torque (`drag’) on the cluster is exerted by stars whose orbital frequencies are in resonance with the globular cluster’s orbit, and given as a sum over the infinitely many resonances by the Lynden-Bell—Kalnajs (LBK) formula. We classified core resonances as a function of the cluster’s orbital radius, and found that there is a progressive loss of strong resonances at smaller radii. Hence the LBK torque is highly suppressed, by factors of 100 to 10,000, when compared with the Chandrasekhar torque. Therefore an in-spiralling globular cluster would appear to stall outside of a characteristic `filtering’ radius of about 220 pc. |