Winds in ultraluminous X-ray sources: new challenges

TL;DR

This paper reviews the properties and significance of winds in ultraluminous X-ray sources, emphasizing their role in accretion processes, feedback mechanisms, and implications for black hole growth, while highlighting future observational prospects.

Contribution

It provides a comprehensive overview of ULX winds, recent discoveries, and discusses how upcoming missions will enhance understanding of these phenomena.

Findings

ULX winds reach relativistic speeds of 0.1-0.3 c.

ULX winds significantly influence surrounding medium and feedback processes.

Future missions will improve detection and analysis of ULX winds.

Abstract

Ultraluminous X-ray sources (ULXs) are extreme X-ray binaries shining above 10^39 erg/s, in most cases as a consequence of super-Eddington accretion onto neutron stars and stellar-mass black holes accreting above their Eddington limit. This was understood after the discovery of coherent pulsations, cyclotron lines and powerful winds. The latter was possible thanks to the high-resolution X-ray spectrometers aboard XMM-Newton. ULX winds carry a huge amount of power owing to their relativistic speeds (0.1-0.3 c) and are able to significantly affect the surrounding medium, likely producing the observed 100 pc ULX superbubbles, and limit the amount of matter that can reach the central accretor. The study of ULX winds is therefore quintessential to understand 1) how much and how fast can matter be accreted by compact objects and 2) how strong is their feedback onto the surrounding medium. This is also relevant to understand supermassive black holes growth. Here we provide an overview on this phenomenology, highlight some recent, exciting results and show how future missions such as XRISM, eXTP and ATHENA will improve our understanding.