X-ray binaries

X-ray binaries, which are systems where a compact object accretes from a close low-mass or high-mass stellar companion. Dr. Enrico Bozzo and Dr. Carlo Ferrigno are active in this field.

Research in the field of low-mass X-ray binaries mainly focuses on the interaction between the compact object and the accretion disk produced by the material inflowing from the donor star, while for high-mass X-ray binaries the interest is more directed toward the investigation of the geometry of the strong magnetic field of the compact object or the interaction between this field and the material flowing from the donor star in the form of a fast and dense wind. This wind can be probed indirectly by the compact object.

The extreme gravitational and magnetic environments around X-ray binaries make these perfect laboratories to study unique physical processes producing light in a variety of energy domains, ranging from radio to gamma-rays. X-ray binaries are also often bright and wildly variable sources, displaying many different accretion regimes, each characterized by different observable emission properties and variability timescales.

The richness of observational and theoretical challenges posed by the incredibly vast zoo of X-ray binary sub-classes makes these objects very well suited to build international collaborations, featuring scientists from different fields, including stellar experts, fundamental physicists, as well as experts working on facilities across the entire electromagnetic spectrum. These research topics are also extremely relevant for the emerging field of multi-messenger astronomy, especially gravitational-wave sources. The INTEGRAL mission, which was led by Dr Ferrigno, discovered the electromagnetic counterpart of the first binary neutron star merger detected by gravitational wave antennas.