Theoretical astrophysics and cosmology
This research sector aims to investigate the physical nature of cosmic structures at different scales, from the stellar to the extragalactic and cosmological ones from an observational, theoretical and statistical point of view. Observational activity covers the entire electromagnetic spectrum from radio to infrared, from optical to the highest energies (X-rays and gamma rays). For this purpose, our group has access to the most modern instrumentation, both from the ground (10m class optical telescopes) and from space (X-band, optical/infrared, radio and microwave satellites. Direct access to a large amount of data, often obtained thanks to observation proposals from our group, supports and stimulates cutting-edge theoretical research, aimed at developing models for the interpretation of observational data and complex numerical simulations.
In particular, the active research lines cover stellar astrophysics (advanced phases of the evolution of low-mass stars), the astrophysics of neutron stars and black holes (properties of ultra-magnetized media, polarization of radiation in general relativity) and cosmology (study of the Universe as a whole, its primordial phases, the CMB and its evolution up to today). The study of gravitational waves is of growing importance from both an observational and theoretical point of view.
Staff
Full Professors: Paola Marigo, Sabino Matarrese, Roberto Turolla
Associate Professors: Nicola Bartolo, Michele Liguori, Alvise Raccanelli
Assistant Professors: Daniele Bertacca, Alessandro Renzi, Roberto Taverna, Michele Trabucchi
Post-doc
Nicola Bellomo, Diego Bossini, Marco Marinucci, Lorenzo Marra, Giada Pastorelli, Andrea Ravenni, Jesus Torrado Cacho, Lorenzo Valbusa Dall’Armi, Elena Vanetti, Ragavendra Honnahalli Venkataramanan, Guglielmo Volpato
PhD students
Ripalta Amoruso, Andrea Begnoni, Bartolomeo Bottazzi Baldi, Silvia Conforti, Jessie Arnoldus De Kruijf, Mohamed Yousry Elkahashab, Yiwen Huang, Ruth Kelly (UCL-DFA), Alina Mierna, Matteo Pegorin, Gabriele Perna, Federico Semenzato, Francesco Spezzati, Eleonora Vanzan
External collaborators
Léo Girardi (INAF), Simone Zaggia (INAF), Sandro Bressan (SISSA), Guglielmo Costa (Université de Lyon), Francesco Addari (SISSA), Kendall Shepherd (SISSA), Alessandro Mazzi (Università di Bologna), Chi Thanh Nguyen (SISSA), Silvia Zane (MSSL-UCL), Angelo Ricciardone (Università di Pisa).
Research activities
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. Building on the results achieved with the STARKEY project (ERC Consolidator Grant, PI P. Marigo), the scientific activities of the stellar evolution group are strongly committed to the development of detailed modeling for the advanced evolutionary phases of low-mass stars (with mass 1- 8 Msun), which play a crucial role in the interpretation of multiple aspects of astrophysics, from the chemical composition of meteorites in the pre-solar nebula to the spectro-photometric properties of high redshift galaxies.
Contacts: Paola Marigo, Michele Trabucchi
Neutron Star Astrophysics
Stars with a mass between about 8 and 25 solar masses end their life in a core-collapse supernova explosion. The density in the contracting core becomes so high 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 at Soft Gamma Repeaters and Anomalous X-ray pulsars, X-ray sources hosting an ultra-magnetized neutron star, a “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 eXTP) 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.
The IXPE mission, launched in December 2021, measured, for the first time ever, a large polarization degree in magnetars, providing further confirmation that these sources host ultra-strong magnetic fields. In addition, IXPE observations revealed that the surface layers of a neutron star can be in a condensed form, again a consequence of the super-strong field, and yield the first evidence of vacuum birefringence.
Contacts: Roberto Turolla, Roberto Taverna
Cosmology
The main research interests of our group lie in the interplay between Cosmology and Fundamental Physics. This involves studies of both the physics of the Early Universe and of the Large-Scale Structure (LSS) of the Universe. Our study of Early Universe Physics revolves around inflationary mechanisms for the generation of primordial cosmological perturbations, considering both theoretical and observational aspects. We devote much effort to the analysis of primordial fluctuations and to their statistics - namely, their deviations from Gaussianity, and to the study of the Gravitational Wave Background (GWB) from inflation and from astrophysical sources. We are heavily involved in the modeling of the evolution of the large-scale structure of the Universe and how to use it to constrain cosmological models.
This work includes theoretical modeling, the analysis of primordial GWB potential signatures in the Cosmic Microwave Background (CMB) polarization B-mode and the characterization for their measurement with interferometers. Regarding low-redshift cosmic acceleration, our interest is centred on the study of Modified Gravity (MG) models on cosmological scales, including predicting and measuring observational signatures of such models in CMB and LSS datasets. These measurements are strongly dependent on the details of the accelerated expansion and can be used to set strong constraints on MG. For both primordial and late-universe astrophysical sources, we focus on the characterization of the backgrounds including also the effects of the propagation of gravitational waves through cosmic inhomogeneities. The group is deeply involved in several important international experimental collaborations, such as the Einstein Telescope, Euclid, LISA, LiteBird, SKA and has been very strongly involved in the Planck mission, for the analysis dedicated to inflation and non-Gaussianity.
A very important area of investigation for our group is the study of the formation and evolution of large-scale cosmic structures, both via analytical tools and numerical simulations, also including General Relativistic effects. We focus on the evolution of LSS, with the aim of providing new tests for dark energy models, tests of gravity and early universe physics. Within this topic, our group is strongly involved in several cosmological surveys, including the ESA satellite Euclid and the international collaboration SKA. Finally, we are at the forefront of the development of joint GW-LSS analyses, in particular for the study of the physics and the origin of black holes and for the study of primordial black holes.
Contacts: Sabino Matarrese, Nicola Bartolo, Michele Liguori, Alvise Raccanelli, Daniele Bertacca
