Space Snapshots

摘要

Astronomers from the Netherlands Institute for Space Research (SRON) Ioanna Psaradaki, Elisa Cos-tantini, and Missagh Mehdipour, together with Maria Diaz Trigo from ESO, have made an interesting discovery on the structure of accretion disks in X-ray binaries. They used the eclipse events from the companion star in the binary system EXO 0748-676 in order to study the atmosphere of the accretion disk. They discovered strong X-ray emission lines during the eclipses (see figure above) indicating the presence of hot disk gas above the surface of the accretion disk. This suggests a vertical extension of the disk atmosphere that is higher than predicted by standard theoretical models of accretion. Moreover, they distinguished two different gas components. The hot diffuse plasma is located above the whole disk while a colder, dense component is instead believed to be part of the impact region between the accreted stream from the companion and the accretion disk.