In March 2013 I completed my undergraduate degree in Astronomy at the University of Padua. Not really knowing what to do with myself, I decided to embark on a big overseas adventure. So I started a PhD in Astrophysics at Swinburne University of Technology in Melbourne, which I obtained in October 2017.

My research focusses on Galactic Dynamics in general (how galaxies form and evolve), compact stellar systems in particular (how stars from and evolve within galaxies). Telescope images show us that the great majority of stars don’t form in isolation, but they are born with other stars within giant clouds of gas. A famous example of a star-forming region is the Orion Nebula. We suspect that even our Sun was born with brothers and sisters and some scientists are currently looking for them.

The Orion Nebula, a stellar nursery.  (Credit: ESO/H. Drass et al.)

The Orion Nebula, a stellar nursery. (Credit: ESO/H. Drass et al.)

These groups of stars are known as STAR CLUSTERS. The smaller clusters (called “open clusters“) count from a dozen to a few hundreds members, while the bigger ones (called “globular clusters”) can be composed of hundreds of thousands, or even millions of stars.

Open Cluster M45, a.k.a. the Pleiades. ( Credit :  NASA, ESA, AURA/Caltech, Palomar Observatory)

Open Cluster M45, a.k.a. the Pleiades. (Credit: NASA, ESA, AURA/Caltech, Palomar Observatory)

Globular Cluster 47 Tuc. Each bright dot in the image is a star. ( Credit: NASA/Hubble Space Telescope)

Globular Cluster 47 Tuc. Each bright dot in the image is a star. (Credit: NASA/Hubble Space Telescope)

Globular clusters are particularly interesting because they are very old and they are found in pretty much every galaxy. In fact, some of them are as old as 12.5 - 13 billion years. As a comparison, the estimated age of the Universe itself is about 13.5 billion years, so pretty close…relatively speaking…. Essentially they are cosmic fossils and by studying them we can infer information on the life of galaxies though cosmic time.

One ”problem” with star clusters is that they “evaporate“. Several astrophysical processes contribute to the loss of stars from the clusters, often until complete dissolution, and the escaping stars end up orbiting somewhere in the host galaxy. For example, there are about 150 known globular clusters orbiting in our own Milky Way, but we suspect that the initial number would have been much higher.

The core of my research is dedicated to understand the life of these collections of stars. Not using telescopes, but powerful supercomputers. Essentially we came up with a theoretical model (a bunch of equations) describing the behaviour of these clusters. Such mathematical model is far too complicated to be solved with just pen and paper. That’s why we implemented it in a big computer code. This state-of-the-art software has been developed and constantly updated and improved since the seventies and can simulate the life of the single stars (from birth until death), the gravitational interaction between all the cluster members and even the formation of exotic objects such as black holes, white dwarfs, neutron stars and supernovae. Most of the simulations we run finish within a few days, but some of them can take weeks or months, or even years before they are completed.

It’s pretty interesting and humbling stuff really. If you want to know more here is a list of my first author peer reviewed publications. Please feel free to drop me an email as well in case!

  • Reconstructing the initial mass function of disc-bulge Galactic globular clusters from N-body simulations, Rossi, L. J., Hurley, J. R., 2015MNRAS.446.3389R, 2015/02

  • Proper motions and kinematics of selected bulge globular clusters, Rossi, L.J. et al., 2015MNRAS.450.3270R, 2015/07

  • NIGO: A Numerical Integrator of Galactic Orbits, Rossi, L. J., J2015A&C....12...11R, 2015/09

  • Estimating the impact of the Galactic bar on the evolution of Galactic star cluster from N-body simulations, Rossi, L. J., 2015MNRAS.454.1453R,2015/12

  • Evolution of star cluster systems in isolated galaxies: first results from direct N-body simulations, 2016MNRAS.462.2861R, Rossi, L. J., Bekki, K., Hurley, J. R., 2016/11

  • Long-term evolution of initially unvirialized, clumpy, mass-segregated star cluster in tidal fields, Rossi, L. J., 2017MNRAS.468.4441R, 2017/07

  • The impact of an evolving bar on the kinematics of a primordial hot population of star clusters in the bulge, Rossi, L. J. et al, 2018MNRAS.480.1912R, 2018/10