Theoretical Astrophysics and Cosmology

Theoretical Astrophysics and Cosmology

Staff

Nicola Bartolo, Daniele Bertacca, Michele Liguori, Paola Marigo, Sabino Matarrese, Giuseppe Tormen, Roberto Turolla

Postdocs

Bernhard Aringer, Yang Chen, Dionysios Karagiannis, Purnendu Karmakar, Andrei Lazanu, Josefina Montalban, Ambra Nanni, Angelo Ricciardone, Stefano Rubele, Roberto Taverna, Michele Trabucchi

PhD students

Giampaolo Benevento, Alexander Ganz, Denis Gonzalez Canjulef, Filippo Oppizzi, Giorgio Orlando, Giada Pastorelli, Andrea Ravenni, Elena Sarpa

Theoretical Astrophysics

Stellar Structure and Evolution

This research line has a recognized leading position in the international context. It is based on the fruitful collaboration between researchers at the Department of Physics and Astronomy (DFA) in Padua, the National Institute of Astrophysics (INAF) in Padua, and the International School for Advanced Studies (SISSA) in Trieste. The theoretical investigation deals with several aspects of stellar physics, in particular: the equation state and the opacity of atomic and molecular gas, the analysis of stellar oscillations (asteroseismology), the computation of static and dynamic atmospheres of cool stars, the equation of radiative transport across circumstellar dusty envelopes,  mixing processes and nucleosynthesis in the stellar interiors. These physical ingredients are then used to compute large grids of stellar evolutionary tracks and isochrones as a function of age and initial chemical composition.  All "stellar deliverables" are made publicly available through dedicated web interfaces of widespread use. Another active line of research is the stellar population synthesis. We can simulate in detail the stellar populations in galaxies and their evolutionary properties in all photometric bands of the major astronomical telescopes and surveys. In relation to stellar nucleosyntesis we mention the collaboration with the National Institute of Physics Nucleare (INFN), in the framework of LUNA and LUNA-MV projects, and the participation in the European ECOST Action CheTEC. The ongoing scientific activities of the stellar evolution group are strongly committed to the development of the STARKEY project (ERC Consolidator Grant, PI P. Marigo). It focuses on the advanced evolutionary phases of low mass stars (1-8 Msun ) that play a critical role in the interpretation of various aspects of astrophysics, from the chemical composition of meteorites belonging to the pre-solar nebula to the spectro-photometric properties of high-redshift galaxies.


Neutron Star Astrophysics

Stars with a mass in between about 8 and 25 solar masses ends their life in a core-collapse supernova explosion. The density in the contracting core becomes so high (> 107 g/cm3) to make the formation of neutrons through electron capture by protons energetically favourable. The enormous pressure exerted by degenerate neutrons finally halts the collapse and a neutron star is born. With radius 10-15 km and mass 1-2 solar masses, neutron stars are the densest objects and the strongest magnets known in the present universe. The combination of extreme density, gravity and magnetic field makes neutron stars ideal cosmic laboratories where to test fundamental physical theories, from quantum electro-and chromo-dynamics to general relativity in the strong field limit.
Our team has a strong track record and a leading international role in neutron star astrophysics with particular regard to the theoretical and observational  investigation of high-energy (through space observatories like Chandra, XMM, Swift and INTEGRAL) and optical (with VLT and HST) emission from isolated neutron stars. A major research effort is aimed to Soft Gamma Repeaters and Anomalous X-ray pulsars, X-ray sources hosting an ultra-magnetized neutron star, or “magnetar”, with a magnetic field exceeding the quantum critical limit. Our team is actively involved in the development of new X-ray polarimetric missions (IXPE and XIPE) which offer an unique opportunity to directly observe QED effects, like the magnetized vacuum birefringence, predicted more than 80 years ago and never tested in the lab.


Cosmology and Fundamental Physics

Our group has a strong interest in research focusing on the interplay between Cosmology and Fundamental Physics. This involves studies of the Early Universe, on one side, and of the present day cosmic acceleration, on the other.
Our study of Early Universe Physics revolves around inflationary mechanisms for the generation of primordial cosmological perturbations, considering both theoretical and observational aspects. We pay particular attention to the analysis of the statistics of primordial fluctuations - namely, their deviations from Gaussianity -  and to the study of the Primordial Gravitational Wave (PGW) background from inflation, , including its theoretical modeling, the actual analysis of PGW potential signatures in the Cosmic Microwave Background (CMB) polarization B-mode and the combination of CMB data with direct interferometer measurements.
Regarding low-redshift cosmic acceleration, our interest is centered on the study of Modified Gravity (MG) models on cosmological scales, including predicting and measuring observational signatures of such models in CMB and Large Scale Structure datasets. These measurements are strongly dependent on the details of the accelerated expansion and can be used to set strong constraints on MG.
The group is very strongly involved, at international level, in several important experimental collaborations, such as Planck, Euclid, SKA, eLISA.


Evolution of Cosmic Structures and Dark Matter

Another important area of work is the study of formation and evolution of cosmic structures, via numerical N-body simulations, focusing on a detailed analysis of the properties of Dark Matter (DM) halos. We pay particular attention to the following scientific issues: 1) The link between the properties of the initial density field and the final structure of halos, 2) The description and properties of substructures. This research, besides its obvious interest in a purely cosmological framework, also bears profound implications for studies of the nature of Dark Matter, from a Particle Physics perspective. Along similar lines, another area of interest for the group consists in the search for DM decay and annihilation signals in the diffuse gamma-ray background.