Speaker
Description
Most stars in galaxies reside in binary systems, many of which are interacting and powered by matter transfer onto a compact object. The brightest and most extreme among these systems are ultraluminous X-ray sources (ULXs). Reaching luminosities well above $10^{41}$ erg/s, ULXs routinely breach the classical Eddington limit of stellar-mass objects, making them the "enchanted kingdom" of high-energy astrophysics. The discovery of coherent pulsations, powerful winds, and ultra-soft spectra suggests that the majority of these sources are powered by neutron stars and stellar-mass black holes undergoing supercritical accretion. Their extreme nature is mirrored in relativistic winds — detected via blueshifted X-ray absorption lines up to 0.3$c$ — which carry enough kinetic power to inflate 100-pc superbubbles and self-regulate the accretion process. Yet, many secrets of this kingdom remain unsolved, from the physics of spectral transitions to the exact population demographics and wind structures. In this talk, I will provide a comprehensive overview of the ULX landscape, highlight recent breakthroughs, and discuss how upcoming flagship missions — most notably NewAthena — will revolutionise our understanding of these cosmic behemoths.