High-resolution X-ray spectroscopy: The coming-of-age.

Since the launch of Chandra and XMM-Newton, high-resolution X-ray spectra of cosmic sources of all kinds have become available. These spectra have resulted in major scientific breakthroughs. However, because of the techniques used, in general, high-quality spectra can be obtained only for the brightest few sources of each class. Moreover, except for the most compact extended sources, such as cool core clusters, grating spectra are limited to point sources. Hitomi made another major step forward, providing for the first time a high-quality spectrum of an extended source and improved spectral sensitivity in the Fe-K band. For point sources with the proposed Arcus mission, and for all sources with the launch of Athena, X-ray spectroscopy will become mature. It will allow us to extend the investigations from the few handful of brightest sources of each category to a large number of sources far away in space and time, or to get high time resolution and high spectral resolution spectra of bright time-variable sources. [ABSTRACT FROM AUTHOR]