Star clusters, their evolution and their stars

Advisor: Pavel Kroupa (AI MFF CUNI and University of Bonn)

Funding: Top-up funding may be available.

Website: https://astro.uni-bonn.de/~pavel/

Advisor: Pavel Kroupa (AI MFF CUNI and University of Bonn), together with Frantisek Dinnbier, Ladislav Subr, Jaroslav Haas in Prague and Tereza Jerabkova at ESA.

Stars from in sub-pc groups which contain from a few binaries to many millions of stars. As these are embedded in a molecular cloud core, which collapses under its own self-gravity, these groups are called embedded clusters.

This project aims to study how the embedded clusters expel their gas, consequentially expanding, revirialising and then evolving until they die with their stars becoming members of the hosting galaxy. The particular problems to be addressed include computations of the violent stellar-dynamical events in the cluster cores and the ejections of very massive stars with large velocities, the transformation of the stellar population remaining in the cluster as the stars which the cluster looses are subject to the energy-equipartition process and stellar encounters and mergers, the astrophysical evolution of the binary-star population which was born in the embedded cluster, the properties of the tidal tails and how these evolve to become the galactic field population. The methods involve high-end Nbody codes and data analysis. The work will be in consultation with Sverre Aarseth in Cambridge and ESA in the Netherlands and will invoke Gaia data releases to test various aspects of the models. Special sub-projects on the Galactic centre including the super-massive black hole, on the formation of super-massive black holes and on globular star clusters in the far reaches of the Galaxy are possible.

Description of the figure: A Pleiades-like star cluster 200 Myr after its birth is seen looking down onto the Galaxy with the Sun being shown as the filled yellow circle. The cluster formed and expelled two-third of its mass in the form of gas. A thick cloud of stars expanded and is now seen as the density-dependent green coloured contours. After revirialisation, the cluster evolves through the energy-equipartition process and evaporates its stars with a very small velocity relative to the cluster forming the classical tidal tails seen in red. With time, these become longer and develop Kuepper epicyclic overdensities. The calculation was performed with the Aarseth-Nbody6 code by Frantisek Dinnbier in Prague.

References:

Dinnbier & Kroupa 2020
Kroupa et al. 2020
Subr et al. 2019
Subr & Haas 2016