Ultraluminous X-ray sources (ULXs), the most extreme among binary stars, can aid us to face the following question: how many black holes managed to grow up to 10 billion Solar masses in less than a billion years after the Big Bang? This is one of the relevant mysteries in astrophysics and cosmology.

The AthenaNuggets #44 by Ciro Pinto tells us about the discovery of pulsations and super-Eddington winds in several ULXs using the XMM-Newton telescope and how the unprecedented performance of the Athena X-ray Integral Field Unit (X-IFU) will unveil the physics of these accretion flows in the coming decades.

Read more in Athena X-ray observatory website.