Quasars are super-luminous galaxy cores whose light has typically been traveling for billions of years across space before reaching our telescopes. As extremely distant sources of light, they make ideal guinea pigs for the detection of intervening junk.

Quasars are super-luminous
galaxy cores whose light has typically been traveling for billions of years across
space before reaching our telescopes. As extremely distant sources of light, they
make ideal guinea pigs for the detection of intervening junk.