How did the Chandra X-ray Observatory help explain the cosmic X-ray background?
Shown are apparently normal, solitary galaxies (left), colliding galaxies (centre), and merging galaxies (right).
The Chandra X-ray Observatory played a pivotal role in resolving the mystery of the cosmic X-ray background, a uniform glow of radiation that had puzzled astronomers since its discovery in 1962.
While earlier missions like the Einstein Observatory suggested that this background might consist of a superposition of unresolved point sources, such as quasars, they could not definitively confirm this due to limited resolution. Chandra’s superior high-angular-resolution capability finally allowed astronomers to resolve the diffuse radiation into individual, discrete sources.
Research using Chandra revealed that approximately 75 percent of the X-ray background is produced by roughly 70 million distinct sources spread uniformly across the sky. Many of these sources are distant galaxies containing massive black holes at their centers. As these black holes accrete surrounding gas, the material heats up and emits X-rays. Chandra’s ability to detect these faint, distant objects provided the necessary evidence to explain the origin of the cosmic X-ray background.12