Spectral evolution of the ultra-luminous X-ray source NGC 55 ULX-1

By Francesco Barra, a recent graduate student of the University of Palermo and an INAF associate

Ultra-luminous X-ray sources (ULX) are the most extreme among accreting binary systems. Here, the compact object, a neutron star or a black hole, rips matter from a companion star at a high speed. This matter spirals onto the compact object forming an accretion disk that emits radiation at all wavelengths due to the strong viscosity. This radiation peaks in the canonical X-ray band (0.3-10 keV), exceeds the theoretical limit known as Eddington Luminosity, and pushes away much of the matter into a strong wind that inflates huge cavities into the interstellar medium. Despite two decades of dedicated studies, these objects are still mysterious and many questions still remain unanswered. In this seminar Francesco Barra will discuss his research project aimed at understanding the nature of ULXs through X-ray spectroscopy. The results obtained with observations of ESA’s XMM-Newton satellite show a complex structure of the accretion disk of matter, altered by strong winds, and favour a black hole as a compact object.