Wind-type outflows from black hole X-ray binary MAXI J1820+070: the near infrared view

Black hole X-ray binaries (BHXBs) are stellar systems composed of an accreting black hole and a donor star. These are mostly transient objects, which sample largely different accretion regimes during their weeks-to-months long outbursts. The study of their wind-type outflows is a fundamental part in our understanding of black hole accretion, as winds can carry away significant amounts of mass and angular momentum. BHXB winds are detected in two flavours, the so-called hot and cold winds. Hot winds are revealed via X-ray spectroscopy and they are mostly detected during the soft state of the outburst, whereas cold winds are seen at optical wavelengths during the hard state. In this talk, I will present VLT/X-shooter spectroscopy of the BHXB MAXI J1820+070, showing that an accretion disc wind is detected during both hard and soft states in the near-infrared. This outflow exhibits the same kinetic properties that a hard-state optical wind previously discovered in the system, indicating that cold winds are most likely present during the entire outburst. These results open a new, exciting window to study black hole accretion disc winds in the infrared, which is particularly interesting considering the powerful ground- and space-based facilities coming along over the next years, such as ELT and the James Webb Space Telescope.