Dusty Quasars

摘要

Quasars are energetic sources thought to be fueled by matter accreting onto black holes a billion times more massive than the Sun. Some quasars are difficult to detect because of surrounding clouds of gas and dust, so much so that this population of objects has remained elusive. Based on a compilation of x-ray, optical, and mid-infrared data, Treister et al. (p. 660, published online 25 March; see the Perspective by Primack) show that the evolution of quasars across cosmic time occurs during mergers of gas-rich galaxies, with an obscured phase preceding an unobscured state by about 100 million years.