Astronomy
Using Quasar Absorption Spectra to Probe the Intergalactic Medium
Quick fact
When the light of a bright quasar passes through intergalactic clouds of neutral hydrogen, the atoms absorb specific ultraviolet wavelengths, leaving behind telltale absorption lines in the quasar's spectrum that reveal the gas's presence and properties.
Why this is interesting
What if you could see the invisible gas that fills the space between galaxies? Quasar absorption spectra let astronomers read the hidden story of the universe's structure.