High-Velocity Outflows (HVOs) seen as absorption in X-ray spectra were first reported in 2002. Soon after the first reports other studies challenged the existence of these HVOs suggesting other interpretations to the data. After 15 years of studies we can try to assess the existence and the importance of HVOs: Are HVOs really exist or other interpretations can explain the data? Are HVOs a variable phenomenon and thus what is its real influence on the AGN environment? What are the evidences of HVOs in high-resolution spectra? What studies need to be done to shed more light on the phenomenon?
// by Adi