What I would like to tell an anonymous student

Being an astrophysicist is a little bit like being an investigator. Our job is about finding connections between facts which others failed to see. Other people may have similar or even better data than you have, other people may have similar or even better simulations than you have, but what really makes the difference is if you are able to making connections that passed unnoticed before. On top of everything, never give up..if you feel you are on the right track, just stick to it.

PhD projects

Simulating the nursery of stars in the era of Gaia

Understanding the formation of star clusters (SCs) is one of the most pressing challenges of contemporary astrophysics. In the local Universe, most stars (~70-90 per cent) are believed to form in SCs. Despite the importance and ubiquity of SCs, their formation is still an enigma. Ongoing optical and near-infrared ground-based surveys (e.g. the Gaia-ESO Survey and the Vista Magellanic Cloud Survey) and the Gaia mission are about to provide a wealth of new data about young SCs in the local Universe. Thus, theoretical models must be ready to meet the challenge posed by the new observations. The aim of this thesis is to investigate the formation and evolution of young SCs by means of innovative hydro-dynamical simulations. The student will compare the results of the simulations with the data from the Gaia ESO Survey and other ongoing surveys. We will make predictions for the Gaia mission. The simulations will adopt a completely new methodology, to account for stellar dynamics, for stellar evolution, and for the hydro-dynamics of the parent molecular gas.

The impact of the environment on the formation of blue straggler stars

Blue straggler stars (BSS) are one of the most fascinating enigmas of stellar evolution and dynamics. They lie above and blue-wards the turn-off in the color magnitude diagram of a star cluster (SC). Thus, BSS are H-burning stars with a puzzling high mass. The nature of BSS is still an open issue: are BSS the result of a collision between 2 stars or the product of mass transfer? Does their formation pathway depend on the environment (e.g. on metallicity)? The student will perform innovative N-body+stellar evolution simulations to investigate the formation of BSS in different environments (from dense metal-rich young SCs to old metal-poor globular clusters). This will revolutionize our knowledge of BSS, since self-consistent metallicity-dependent N-body models of BSS in different environments have never been performed. This is now possible thanks to the huge advance of software and hardware facilities (GPUs) in computational astronomy, combined with the outstanding experience of our group in the study of BSS.

The enigma of the young massive stars in the Galactic centre

At a distance of 8 kpc from us, the Galactic centre (GC) is a unique laboratory to study the extreme processes that occur in the vicinity of a supermassive black hole (SMBH). Despite the tidal shear exerted by the SMBH, >100 young massive stars (YMSs) have been observed in the central parsec. Their formation is an enigma: several scenarios have been proposed, but none of them is completely satisfactory. The goal of this Thesis is to investigate the formation of the YMSs in the GC, by means of innovative simulations, which will make use of a direct-summation N-body code, combined with an hydrodynamical code. The student will simulate the disruption of a molecular cloud, leading to the formation of a dense gas disc around the SMBH. Then, the student will investigate whether stars can form in this disc, and how they evolve in the GC potential. This project will shed light on the formation and on the dynamical evolution of stars in the vicinity of a SMBH, thanks to a novel computational approach.

Planets around the Monster

Recent theoretical models by our group and recent radio observations indicate that protoplanetary discs exist in the central parsec of our Galaxy. Such protoplanetary discs are exposed to intense ultra-violet radiation from the massive stars in the Galactic centre and can be affected by super-massive black hole tidal shear. The student will perform hydrodynamical simulations of protoplanetary discs, to understand whether they can survive and lead to the formation of planets in the Galactic centre. Moreover, the student will perform N-body simulations and analytical calculations, to estimate the probability that such planets are captured and disrupted by the supermassive black hole. These results will give important predictions for future X-ray missions (ATHENA) and for the 30m class telescopes (e.g. E-ELT).

The properties of gas in galactic nuclei

Recent sub-millimeter and radio observations (with ALMA, SMA and JVLA) of the gas in the central parsecs of the Milky Way show a variety of interesting gas features (e.g. inflows of dense molecular gas). A model is missing that fully describes the thermo-dynamical state of gas in the central parsec around a quiescent or active super-massive black hole. The student will perform hydro-dynamical simulations of molecular gas around super-massive black holes. The simulations will include an accurate treatment of non-equilibrium chemistry. The final goal is make predictions for future ALMA and SKA observations of nearby galactic nuclei.

Shedding light on massive stellar black holes: from X-ray sources to gravitational waves

Stellar black holes (BHs) form from the collapse of massive stars. BHs power a plethora of astrophysical processes, from X-ray sources to emission of gravitational waves. Despite the importance of BHs for astrophysics, their mass range is very uncertain: most BHs are currently thought to be in the 3-20 solar mass (Msun) range, but recent theoretical models by our group, and recent observations indicate the existence of several stellar BHs with mass >20 Msun. Dynamical processes and stellar metallicity are two key ingredients to shape the mass spectrum of BHs. Dynamical interactions influence the mass of BHs, as they trigger mass transfer and mergers between stars and between stars and BHs. The metallicity of the progenitor star strongly influences the mass of the remnant, as metal-poor stars lose less mass by stellar winds than metal-rich stars. The aim of this project is to study the mass spectrum of stellar BHs by means of dynamical+stellar evolution simulations. The student will develop software for N-body simulations, optimized for graphic processing units (GPUs), including recipes for stellar and binary evolution. The results of such simulations will be employed to study the evolution of BHs, the population of X-ray binaries and the population of BH-BH binaries. This goal is essential to make predictions for forthcoming science runs by second-generation ground-based gravitational-wave interferometers, Advanced LIGO and Virgo.