Miocchi, Paolo | Search NASA

DOE OSTI2016

INVESTIGATING THE MASS SEGREGATION PROCESS IN GLOBULAR CLUSTERS WITH BLUE STRAGGLER STARS: THE IMPACT OF DARK REMNANTS

We present the results of a set of N -body simulations aimed at exploring how the process of mass segregation (as traced by the spatial distribution of blue straggler stars, BSSs) is affected by the presence of a population of heavy dark remnants (as neutron stars and black holes (BHs)). To this end, clusters characterized by different initial concentrations and different fractions of dark remnants have been modeled. We find that an increasing fraction of stellar-mass BHs significantly delay the mass segregation of BSSs and the visible stellar component. In order to trace the evolution of BSS segregation, we introduce a new parameter ( A {sup +}), which can be easily measured when the cumulative radial distribution of these stars and a reference population are available. Our simulations show that A {sup +} might also be used as an approximate indicator of the time remaining to the core collapse of the visible component.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Dynamical friction in multi-component evolving globular clusters

We use the Chandrasekhar formalism and direct N-body simulations to study the effect of dynamical friction on a test object only slightly more massive than the field stars, orbiting a spherically symmetric background of particles with a mass spectrum. The main goal is to verify whether the dynamical friction time (t {sub DF}) develops a non-monotonic radial dependence that could explain the bimodality of the blue straggler radial distributions observed in globular clusters. In these systems, in fact, relaxation effects lead to a mass and velocity radial segregation of the different mass components, so that mass-spectrum effects on t {sub DF} are expected to be dependent on radius. We find that in spite of the presence of different masses, t {sub DF} is always a monotonic function of radius, at all evolutionary times and independently of the initial concentration of the simulated cluster. This is because the radial dependence of t {sub DF} is largely dominated by the total mass density profile of the background stars (which is monotonically decreasing with radius). Hence, a progressive temporal erosion of the blue straggler star (BSS) population at larger and larger distances from the cluster center remains the simplest and the most likely explanation of the shape of the observed BSS radial distributions, as suggested in previous works. We also confirm the theoretical expectation that approximating a multi-mass globular cluster as made of (averaged) equal-mass stars can lead to significant overestimations of t {sub DF} within the half-mass radius.

79 ASTRONOMY AND ASTROPHYSICS↗