Mass segregation

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

Models of mass segregation at the Galactic centre

Abstract: We study the process of mass segregation through 2-body relaxation in galactic nuclei with a central massive black hole (MBH). This study has bearing on a variety of astrophysical questions, from the distribution of X-ray binaries at the Galactic centre, to tidal disruptions of main-sequence and giant stars, to inspirals of compact objects into the MBH, an important category of events for the future space borne gravitational wave interferometer LISA. In relatively small galactic nuclei, typical hosts of MBHs with masses in the range 1e4-1e7 Msun, the relaxation induces the formation of a steep density cusp around the MBH and strong mass segregation. Using a spherical stellar dynamical Monte-Carlo code, we simulate the long-term relaxational evolution of galactic nucleus models with a spectrum of stellar masses. Our focus is the concentration of stellar black holes to the immediate vicinity of the MBH. Special attention is given to models developed to match the conditions in the Milky Way nucleus.

The Birth, Evolution and Death of Star Clusters

Abstract: A dense-enough gas-accumulation evolves, over a few Myr of intensifying star formation, to an embedded cluster If it contains a sufficient amount of mass, O stars form and explosively expel the remaining gas, whereas poorer clusters reduce their embryonic gas content more gradually The sudden expulsion of gas unbinds most of a rich cluster, but a significant fraction of it can condense by two-body interactions to become an open cluster despite a star-formation efficiency as low as 30 per cent Poorer clusters survive their gradual mass loss more easily, but have short, relaxation-limited life-times Pleiades-like clusters may thus form as nuclei of expanding OB associations, by filling their tidal radii and having large (1-2 pc) core-radii A 'main-sequence' of clusters is thus established Ultimately, a cluster dies an explosive death through the ever shortening relaxation time, and leaves a remnant that consists of about 4-10 stars arranged in a highly hierarchical and thus long-lived system Dynamical mass segregation in very young clusters is extremely rapid, and heats a cluster substantially, which is partially off-set by the cooling from the disruption of primordial binaries

Mass segregation in young compact star clusters in the Large Magellanic Cloud: I. Data and Luminosity Functions

Abstract: We have undertaken a detailed analysis of HST/WFPC2 and STIS imaging observations, and of supplementary wide-field ground-based observations obtained with the NTT of two young ~10-25 Myr) compact star clusters in the LMC, NGC 1805 and NGC 1818. The ultimate goal of our work is to improve our understanding of the degree of primordial mass segregation in star clusters. This is crucial for the interpretation of observational luminosity functions (LFs) in terms of the initial mass function (IMF), and for constraining the universality of the IMF. We present evidence for strong luminosity segregation in both clusters. The LF slopes steepen with cluster radius; in both NGC 1805 and NGC 1818 the LF slopes reach a stable level well beyond the clusters' core or half-light radii. In addition, the brightest cluster stars are strongly concentrated within the inner ~4 R_hl. The global cluster LF, although strongly nonlinear, is fairly well approximated by the core or half-light LF; the (annular) LFs at these radii are dominated by the segregated high-luminosity stars, however. We present tentative evidence for the presence of an excess number of bright stars surrounding NGC 1818, for which we argue that they are most likely massive stars that have been collisionally ejected from the cluster core. We therefore suggest that the cores of massive young stars clusters undergo significant dynamical evolution, even on time-scales as short as ~25 Myr.

Gravity or turbulence V: star-forming regions undergoing violent relaxation

Abstract: Using numerical simulations of the formation and evolution of stellar clusters within molecular clouds, we show that the stars in clusters formed within collapsing molecular cloud clumps exhibit a constant velocity dispersion regardless of their mass, as expected in a violent relaxation processes. In contrast, clusters formed in turbulence-dominated environments exhibit an inverse mass segregated velocity dispersion, where massive stars exhibit larger velocity dispersions than low-mass cores, consistent with massive stars formed in massive clumps, which in turn, are formed through strong shocks. We furthermore use Gaia EDR3 to show that the stars in the Orion Nebula Cluster exhibit a constant velocity dispersion as a function of mass, suggesting that it has been formed by collapse within one free-fall time of its parental cloud, rather than in a turbulence-dominated environment during many free-fall times of a supported cloud. Additionally, we have addressed several of the criticisms of models of collapsing star forming regions: namely, the age spread of the ONC, the comparison of the ages of the stars to the free-fall time of the gas that formed it, the star formation efficiency, and the mass densities of clouds vs the mass densities of stellar clusters, showing that observational and numerical data are consistent with clusters forming in clouds undergoing a process of global, hierarchical and chaotic collapse, rather than been supported by turbulence.