The Hubble images were taken in the light of neutral hydrogen.

During this time, the majority of matter in the universe is neutral hydrogen.

The neutral hydrogen is detected as far as 6 kpc (7.5') from the center.

The total mass of the neutral hydrogen is estimated at 370-450 million Solar masses.

No light could beam through the omnipresent neutral hydrogen.

The second phase change occurred once objects started to form in the early universe energetic enough to ionize neutral hydrogen.

The Cornell team was searching for neutral hydrogen inside other known galaxies.

At this point the only radiation emitted is the 21 cm spin line of neutral hydrogen.

Streams of neutral hydrogen connect them to the Milky Way and to each other.

With the formation of neutral hydrogen, the cosmic microwave background was emitted.