It would seem sensible to seek the source of these in the universe's most conspicuous energy factories: quasars and gamma-ray bursts billions of light-years away from Earth.
The extension of astronomy from visible light to radio waves to x-rays and gamma rays never failed to lead to the discovery of unusual objects such as radio galaxies, quasars, and pulsars.
从可见光扩展到无线电波，再到 X 射线和伽马射线，天文学总是会发现不寻常的物体，如射电星系、类星体和脉冲星。
3
The black holes in question are at the centres of quasars.