Community Research and Development Information Service - CORDIS


CLUSTERS Report Summary

Project ID: 335936
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Mid-Term Report Summary - CLUSTERS (Galaxy formation through the eyes of globular clusters)

Globular clusters (GCs) are among the first stars to form in the Universe and they witnessed the earliest phases of galaxy formation. Despite their ubiquity and importance for our understanding of astrophysics, their origin is shrouded in mystery. We want to understand how GCs formed, because it gives us insight in the conditions of the early Universe. The stars in GCs have evolved during their long life, both as the result of internal evolution on a nuclear fusion time-scale and dynamical interactions with other stars, because two-body interactions in GCs are frequent. To wind the clock back, we have to unravel the effect of GC evolution on their pristine properties. We do this by following GCs within models of the evolution a large chunk of the Universe in which our Milky Way forms. By coupling this to fast computer models to evolve GCs, we can explore all the possible initial properties of GCs and find the ones that can explain the properties of GCs today. The ESA-Gaia satellite is soon providing us with a goldmine of data on kinematics of stars. In anticipation of that, we developed tools that allow us to study the properties of of GCs now. Needless to say, the detailed properties of GCs now carries vital information about their formation. In most case, only a fraction of the GCs members are visible for our telescope. About half of the mass of GCs sits in dark stellar remnants such as white dwarfs, neutron stars, and black holes and low-mass (faint) stars. Their presence has a measurable effect on the visible stars and we developed models that allow us to make the invisible visible. We found from the distribution of stars in one particular GC that it contains a large number of black holes. These black holes form at the end of the life of massive stars, and until recently they were thought to be removed from clusters by a kick they receive during the supernova explosion in which they form, and the few remaining were believed to be ejected by dynamical sling shots. Our result shows that the supernova kicks could not have been very high, and that the cluster itself must have formed with a low density. As a consequence, we also learned that the conditions in the galaxy where this cluster formed, must have been favourable for survival. Finally, these GCs with black holes could be the cradle of black hole mergers and associated gravitational wave emission, which have recently been discovered.

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United Kingdom
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