High Energy Astrophysics and Neutron Stars
Research Group
High-energy astrophysics deals with the study of some of the most energetic phenomena in our universe, produced by cosmic objects with truly extreme characteristics. Neutron stars and black holes, along with supernova remnants and pulsar wind nebulae—where they form—are the main objects of study in our research.
At the Astronomical Observatory of Cagliari, we specifically focus on:
Research and study of radio pulsars
Pulsars are neutron stars with extremely high magnetic fields that, due to their rapid rotation (up to 800 revolutions per second!), emit beams of radio waves from their magnetic poles. Their emission, like that of a lighthouse, is captured by our radio telescopes as a series of very regular periodic pulses, one for each rotation of the star. The pulsar signal is thus comparable to the ticking of extremely precise cosmic clocks. For this reason, pulsars are used as true probes in our Galaxy to conduct studies of astrophysics and fundamental physics. Their study provides unique information on stellar and binary system evolution, gravity under extreme conditions (neutron stars are essentially failed black holes), the nature of nuclear matter (a pulsar, given its extremely high density, is comparable to a giant atomic nucleus), plasma physics, the distribution of gas and magnetic fields in our Galaxy, and, if studied as a whole, in a so-called Pulsar Timing Array, they can even allow us to detect gravitational waves produced by pairs of supermassive black holes. Our research group is part of some of the most important international collaborations for the study of radio pulsars, including the two Large Survey projects of MeerKAT (TRAPUM and MeerTime), the European and International Timing Array collaborations (EPTA and IPTA), and the pulsar working groups of Lofar and SKAO.
Multifrequency study of neutron stars
Besides appearing as radio pulsars, neutron stars manifest through various other phenomena and in different bands of the electromagnetic spectrum. Since 2007, with the launch of the Agile and Fermi satellites, an increasing number of ‘rotation powered’ pulsars (whose energy source is the star’s rotation) have been discovered and characterized also in the Gamma band, providing new fundamental information to understand their emission mechanism. At high energies (X-rays and gamma), the ‘engine’ of the observable emission from neutron stars can be of different nature: thermal emission (as in the case of Central Compact Objects), magnetospheric (for X-ray Dim Isolated Neutron Stars), deriving from an intense internal magnetic field (Magnetar) or from the accretion of matter from a companion star (X-ray Binaries). The Pulsating Ultraluminous X-ray Sources, in particular, are pulsars up to 500 times more luminous than the Eddington limit. Discovered in 2014, it is unclear how they can produce this luminosity. One possibility is that they have even higher magnetic fields. Through X-ray timing, we can perform various measurements to understand the role of the magnetic field and other physical variables of the system. In general, the study of neutron stars in all their manifestations helps us understand their emission mechanisms and investigate possible evolutionary links between different classes of pulsars.
Development of astronomical time series analysis software
Our group develops various open-source software packages in Python for spectral-temporal analysis and its extension to X-ray polarimetry and other wavelengths. In particular, the Stingray software is currently used worldwide for data analysis of existing missions (IXPE, NICER, XMM-Newton, NuSTAR, Astrosat, …), with an eye on future high-throughput missions like eXTP.
Development of innovative radio observation techniques with large INAF radio telescopes
Complex extended astronomical sources such as Supernova Remnants and Pulsar Wind Nebulae are among the spectacular products of the “explosive” life of many stars, in conjunction with their transformation into compact objects (neutron stars, black holes, white dwarfs, etc.). To study such phenomena at high radio frequencies, “single-dish” observations (using single antennas) are particularly efficient compared to the more widespread interferometric techniques (which use complex networks of radio telescopes). For example, the study of Supernova Remnants through the creation of high-frequency “single-dish” radio images allows us to understand the particle acceleration mechanisms (cosmic rays) in stellar explosion processes and to characterize high-energy emission processes. Through these techniques, our group has obtained for the first time images of very extended Supernova Remnants at frequencies >20 GHz, managing to measure the maximum energy of the produced cosmic rays.
X-ray Binary Sources and Microquasars
These systems are composed of a compact object (a neutron star or a stellar black hole) and a companion star. Multi-frequency observational campaigns allow us to investigate the connection between accretion and ejection processes, trying to better understand the properties, geometry, composition, and changes of the various components of these systems (accretion disk, corona, jets) during their various accretion phases. The Italian radio telescopes (SRT, Medicina, and Noto) allow us to exploit single-dish and VLBI modes, which are very complementary for investigating jets. Single-dish observations allow us to follow the evolution of the flow and the radio spectral index, while VLBI observations offer us the possibility to resolve the jets, determine the speed of the ejecta, and observe structural changes in the jets.
Gamma-Ray Burst
Gamma-Ray Bursts (GRBs) are the signature of cataclysmic stellar-scale events in the Universe, consisting of short and intense pulses of gamma-ray radiation. The burst itself is called prompt emission, detected by dedicated space satellites (X and gamma). The interaction between the matter expelled by the explosion and the surrounding medium generates a long-lasting emission (from days to months) called afterglow, observable at increasingly lower frequencies over time. The study of GRB afterglows is essential to understand emission mechanisms, the microphysics of the relativistic shock, the properties of the surrounding medium, and the jet. GRB radio afterglows, although difficult to observe due to their intrinsic weakness (on the order of sub-mJy), are crucial to fully understand all these aspects. Our research group is involved in the study and modeling of GRB afterglow emission, from high energies to radio frequencies, with related single-dish observations and follow-up with our INAF radio telescopes for the most intense phenomena. These observational campaigns are crucial to study and test the observational capability of our radio telescopes for the weakest signals (on the order of mJy).
Fast Radio Burst
Fast Radio Bursts (FRBs) are intense and very brief (milliseconds) flashes of radio waves of (typically) extragalactic origin. Discovered in 2007 and officially recognized as a new class of astrophysical sources in 2013, they have been the subject of numerous studies in recent years aimed, on one hand, at understanding the nature of their progenitors (probably compact objects—neutron stars or black holes—given the very short duration of their signals) and their emission mechanism, and on the other hand, at exploiting their unique characteristics for cosmology and extragalactic astrophysics studies. At OAC, we have been involved in the research and characterization of FRBs since the beginning, historically through surveys with the Parkes Murriyang telescope (Australia) and in more recent years using Italian radio telescopes (the dishes of Medicina and Noto, the Sardinia Radio Telescope, and the renewed Northern Cross) in the context of multi-frequency observational campaigns. Our group is also the only non-North American partner of the CHORD project, which will lead to the discovery and precise localization of thousands of new FRBs.
Follow-up of Gravitational Wave Bursts and synergies with ET and LISA
The coalescence of compact objects produces genuine explosions of gravitational waves that, since 2015, have been regularly observed by gravitational wave interferometers, LIGO, Virgo, and, in the future, Kagra. When the coalescence involves two neutron stars, a powerful electromagnetic signal, from the gamma band to the radio band, is emitted, and under favorable conditions, it can be observed with ground-based and space-based telescopes. Only one such event has been effectively recorded so far, in 2017, and SRT participated in the worldwide campaign to observe the electromagnetic characteristics of the event. At OAC, on one hand, we plan observations for future favorable events of this type, and on the other hand, we study how radio observations, particularly with SRT, can complement and amplify the data that will be collected by future-generation gravitational wave detectors: LISA (which will be a space-based interferometer) and ET, which is the much more powerful successor to LIGO and Virgo, whose installation in Sardinia may be decided in 2026.
External links
Latest updates
| Date | Description |
| 01/2025 | EPTA pulsars awarded by the Royal Astronomical Society
https://www.media.inaf.it/2025/01/10/un-premio-alleuropean-pulsar-timing-array/ |
| 01/2024 | A mystery object for MeerKat: extremely heavy neutron star, or very light black hole?
https://www.media.inaf.it/2024/01/18/oggetto-mistero-meerkat-buco-nero-stella-neutroni/ |
| 06/2023 | Pulsars reveal the breath of spacetime: evidence of long-period gravitational waves from Pulsar Timing Array experiments
https://www.media.inaf.it/2023/06/29/le-pulsar-ci-svelano-il-respiro-dello-spazio-tempo/ |
| 04/2023 | Ultraluminous sources beyond any limit
https://www.media.inaf.it/2023/04/06/ulx-nustar-limite-eddington/ |