The extragalactic population of neutron stars: the ULX paradigm revolution .

The recent discovery of Ultraluminous X-ray Sources (ULXs) showing fast and rapidly evolving pulsations (PULXs) unambiguously associated these sources to accreting neutron stars (NSs) exceeding up to about 500 times their Eddington luminosity. These sources challenge our understanding of accretion physics and pose a key question about the nature of the ULXs as a class. The possible presence for a high magnetic field component close to the pulsar surface and the possible reason(s) for which a relatively small number of PULXs have been discovered so far is discussed. Furthermore, preliminary results from a search for new PULXs in the UNSEEN XMM-Newton project are shown.