Mark Gieles

Mark Gieles

Universitat de Barcelona

Experimental Sciences & Mathematics

Mark Gieles obtained his PhD in 2006 from Utrecht University in the Netherlands under the supervision of Prof Henny Lamers and Prof Simon Portegies Zwart. He then moved to the European Southern Observatory (ESO) in Chile as a research fellow and support astronomer on the Very Large Telescope (VLT) at Cerro Paranal in the Atacama desert. In 2009 he won a Royal Society University Research Fellowship (URF) which he took up at the Institute of Astronomy of the University of Cambridge and in 2013 he moved it to the University of Surrey, where he started a new astrophysics research group. From 2013 to 2019 he was PI of a Starting Grant of the European Research Council (ERC) and since 2017 he is a member of the editorial board of Monthly Notices of the Royal Astronomical Society (MNRAS), one of the leading peer-reviewed journals in astronomy and astrophysics.

Research interests

I am interested in the formation and dynamical evolution of globular clusters to shed light on the stellar initial mass function, black holes, gravitational waves and the dark matter distribution in galaxies. The Milky Way contains 150 globular clusters, for which we have exquisite observations, including kinematics and chemistry. To understand these, I use both star-by-star N-body simulations and dynamical mass models. I developed a new family of mass models (limepy) to search for black holes in star clusters and to probe dark matter in the Milky Way using data from the ESA-Gaia satellite and related surveys. I am also interested in the abundance problem of globular clusters. I proposed a globular cluster formation model in which a supermassive star forms via stellar collisions and pollutes the cluster with hot hydrogen-burning products in the first few million years.

Selected publications

– Antonini F, Gieles M & Gualandris A 2019, ‘Black hole growth through hierarchical black hole mergers in dense star clusters: implications for gravitational wave detections’, Monthly Notices Of The Royal Astronomical Society, 486, 4, 5008 – 5021.

– de Boer TJL, Gieles M, Balbinot E, Henault-Brunet V, Sollima A, Watkins LL & Claydon I 2019, ‘Globular cluster number density profiles using Gaia DR2’, Monthly Notices Of The Royal Astronomical Society, 485, 4, 4906 – 4935.

– Hénault-Brunet V, Gieles M, Sollima A, Watkins LL, Zocchi A, Claydon I, Pancino E, & Baumgardt H 2019, `Mass modelling globular clusters in the Gaia era: a method comparison using mock data from an N-body simulation of M4′, MNRAS, vol. 483, pp 1400-1425

Selected research activities

In 2019 my ERC starting grant CLUSTERS came to an end. CLUSTERS developed new dynamical models for globular clusters (GCs) (limepy) and compared them to state-of-the art observations. The CLUSTERS team found that several GCs contain a large population of stellar-mass BHs and that these give rise to similar observational signatures as the sought-after intermediate-mass BH. To understand the evolution of BH populations in GCs, a fast model for the evolution of GCs with BHs was developed (clusterbh). This new model was used to make predictions for dynamically produced BH binary mergers that can now be observed with gravitational wave observatories. The team also proposed a new formation mechanism for GCs, in which a supermassive star forms together with the cluster to explain the anomalous abundances that are ubiquities in GCs today.

The most important conclusions of CLUSTERS are that:

  • 1. stellar-mass BHs are common in GCs;
  • 2. supermassive stars may have existed in all GCs;
  • 3. there is no convincing evidence for intermediate-mass BHs in GCs;
  • 4. the reported signatures of dark matter in GCs can be explained by Galactic tides.