Abstract

The detection of “fully-grown” supermassive black holes powering active galactic nuclei at high redshift, when the Universe was young, challenges the theories of black holes growth, requiring long periods of high accretion, most likely above the Eddington limit. This is a focus of the next generation large missions, but cannot be done with the current instrumentation due to the large distances. Therefore, we need to study objects accreting at high rates in the nearby Universe. Most ultraluminous X-ray sources (ULXs, luminosities > 3·10^39 erg/s) show X-ray spectra that are consistent with stellar mass black holes or neutron stars accreting at or above Eddington and provide the best workbench to study super-Eddington accretion and fast growth rates. A few, exceptionally bright, ULXs are good candidates for hosting intermediate mass black holes (e.g. 1000 solar masses), which are thought to be necessary seeds for the formation of supermassive black holes. In this talk I will discuss some very recent, groundbreaking, discoveries that shook this research field in support for super-Eddington accretion such as the detection of extremely fast winds and pulsations.