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: Nicola Bartolo, Roberto Turolla
Associate Professors: Daniele Bertacca, Michele Liguori, Alvise Raccanelli
Assistant Professors: Diego Bossini, Guglielmo Costa, Alessandro Renzi, Roberto Taverna, Michele Trabucchi
Post-doc
Michele Catone, Silvia Conforti, Ruth Kelly (UCL-DFA), Rosa Laura Lechuga Solis, Manuela Mattiussi, Alina Mierna, Ragavendra HV,
PhD students
Ripalta Amoruso, Chaima Baztami, Andrea Begnoni, Bartolomeo Bottazzi Baldi, Silvia Conforti, Jessie Arnoldus De Kruijf, Yiwen Huang, Ruth Kelly (UCL-DFA), Alina Mierna, Matteo Pegorin, Gabriele Perna, Federico Semenzato.
External collaborators
Léo Girardi (INAF), Simone Zaggia (INAF), Sandro Bressan (SISSA), Kendall Shepherd (SISSA), Alessandro Mazzi (Università di Bologna), Chi Thanh Nguyen (SISSA), Silvia Zane (MSSL-UCL), Angelo Ricciardone (Università di Pisa), Giada Pastorelli (INAF), Guglielmo Volpato (Université libre de Bruxelles)
Research activities
Stellar Structure and Evolution
This research line holds a leading position in the international scientific landscape. It is based on collaboration among researchers from the Department of Physics and Astronomy (DFA) at the University of Padua, the National Institute for Astrophysics (INAF) in Padua, and the International School for Advanced Studies (SISSA) in Trieste. The theoretical research addresses multiple aspects of stellar physics, particularly: the equation of state and opacity of atomic and molecular gas (using the AESOPUS code, recently updated thanks to the PRIN 2022NEXMP8_001 project “Radiative Opacities for Astrophysical Applications,” PI P. Marigo), mixing and nucleosynthesis processes in stellar interiors, stellar rotation, mass loss through stellar winds, and the modeling of stellar pulsations and oscillations (stellar variability and asteroseismology).
In the field of stellar nucleosynthesis, the group collaborates with the National Institute for Nuclear Physics (INFN) on the LUNA and LUNA-MV projects to evaluate the astrophysical impact of new nuclear reaction rates and to link laboratory measurements with stellar models. These physical inputs are integrated into the evolutionary codes PARSEC and COLIBRI to compute state-of-the-art stellar models.
Building on the results of the STARKEY project (ERC Consolidator Grant, PI P. Marigo), the stellar evolution group focuses on developing detailed models for the advanced evolutionary stages of low- and intermediate-mass stars (using the COLIBRI code). These stars play a crucial role in interpreting multiple astrophysical phenomena, from the chemical composition of presolar nebula meteorites to the spectrophotometric properties of high-redshift galaxies.
Recently, the group has also extended its research to massive and very massive stars, primordial composition stars, binary systems, and rapidly rotating stars, mainly using the PARSEC evolutionary code. The goal is to provide the scientific community with updated and consistent models across the full range of stellar masses and conditions.
Active research projects include the study of variability and mass loss in the final evolutionary stages of low- and intermediate-mass stars (CONVERGENCE project, funded by the European Union “Next Generation EU” and the University of Padua through the Starting Grant STARS@UniPd 2023, PI M. Trabucchi), and the formation of primordial stars (FIRES project, funded by the European Union “Next Generation EU,” PNNR, Mission 4 Component 2 “Young Researchers Seal of Excellence,” PI G. Costa).
The products of the group include extensive grids of evolutionary tracks (covering masses from 0.1 to 2000 M☉ and chemical compositions from primordial – Big Bang nucleosynthesis – to super-solar), corresponding isochrones with ages from a few million years to tens of billions, tables of opacities and equations of state, predictions of stellar variability, and tools for asteroseismic interpretation. The research line also includes the development of simulations of galactic and extragalactic stellar populations across the photometric bands of current and future major telescopes and surveys. All stellar research products are made available through publications and widely used web interfaces, which are regularly updated and accessible athttps://stev.oapd.inaf.it.
This expertise is employed by the group in the planning and scientific support of some of the most important recent and future surveys and missions, including Gaia, Rubin/LSST, PLATO, Ariel, 4MOST, major JWST programs, and the Roman mission, with active participation in the corresponding scientific consortia, as well as involvement in European-level initiatives (e.g., ECOST CheTEC).
Contacts: Michele Trabucchi, Guglielmo Costa, Diego Bossini
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
