Mass segregation

About: Mass segregation is a research topic. Over the lifetime, 1024 publications have been published within this topic receiving 57729 citations.

Mergers and ejections of black holes in globular clusters

Abstract: We report on results of fully consistent N-body simulations of globular cluster models with N = 100 000 members containing neutron stars and black holes. Using the improved `algorithmic regularization' method of Hellstrom and Mikkola for compact subsystems, the new code NBODY7 enables for the first time general relativistic coalescence to be achieved for post-Newtonian terms and realistic parameters. Following an early stage of mass segregation, a few black holes form a small dense core which usually leads to the formation of one dominant binary. The subsequent evolution by dynamical shrinkage involves the competing processes of ejection and mergers by radiation energy loss. Unless the binary is ejected, long-lived triple systems often exhibit Kozai cycles with extremely high inner eccentricity (e > 0.999) which may terminate in coalescence at a few Schwarzschild radii. A characteristic feature is that ordinary stars as well as black holes and even BH binaries are ejected with high velocities. On the basis of the models studied so far, the results suggest a limited growth of a few remaining stellar mass black holes in globular clusters.

A Gaia EDR3 search for tidal tails in disintegrating open clusters

Abstract: We carry out a search for tidal tails in a sample of open clusters with known relatively elongated morphology. We identify the member stars of these clusters from the precise astrometric and deep photometric data from Gaia Early Data Release 3 using the robust membership determination algorithm, ML-MOC. We identify 46 open clusters having a stellar corona beyond the tidal radius, 20 of which exhibit extended tails aligned with the cluster orbit direction in galactocentric coordinates. Notably we find NGC 6940 (at a distance of ∼1 kpc) is the furthest open cluster exhibiting tidal tails that are ∼50 pc from its center, while also identifying ∼40 pc long tidal tails for the nearby Pleiades. Using the minimum spanning tree length for the most massive stars relative to all cluster members, we obtain the mass segregation ratio ($\rm \lambda _{MSR}$) profiles as a function of the number of massive stars in each cluster. From these profiles, we can classify the open clusters into four classes based on the degree of mass segregation experienced by the clusters. We find that clusters in the most mass segregated classes are the oldest on average and have the flattest mass function slope. Of the 46 open clusters studied in this work, 41 exhibit some degree of mass segregation. Furthermore, we estimate the initial masses (M$\rm _{i}$) of these open clusters finding that some of them, having M$\rm _{i}\gtrsim 10^{4} M_{\odot }$, could be the dissolving remnants of Young Massive Clusters.

Dynamics of embedded proto star clusters in clouds

Abstract: The dynamics of clumps and proto stars in a young proto cluster system embedded in its parent molecular cloud are studied here through numerical simulations. It is found that the presence of massive clumps and their dynamics strongly affects the motion of the lower mass protostars. Mass segregation of clumps due to dynamical drag by the interclump gas results in the formation of a dense central region, and the lower mass proto stars are preferentially ejected out of the cloud via gravitational encounters. The protostellar cluster is found to expand gradually with time, forming a more extended system than the clumps. Thus, embedded proto star clusters are probably dynamically evolved systems with large haloes of low-mass protostars. This explains observations of T Tauri stars, which appear to be isolated from active star-forming sites and are in regions devoid of dense gas. Since multiple star formation sites in clouds are common, outer members are subject to velocity perturbations due to massive clumps and other clusters, possibly leading to a faster removal of objects.

The frequency and mass-ratio distribution of binaries in clusters I: description of the method and application to M67

Abstract: We present a new method for probabilistic generative modelling of stellar colour-magnitude diagrams (CMDs) to infer the frequency of binary stars and their mass-ratio distribution. The method invokes a mixture model to account for overlapping populations of single stars, binaries and outliers in the CMD. We apply the model to Gaia observations of the old open cluster, M67, and find a frequency fB(q > 0.5) = 0.258 ± 0.019 for binary stars with mass ratio greater than 0.5. The form of the mass-ratio distribution function rises towards higher mass ratios for q > 0.3.