The birth of galaxies
The only direct evidence of the Big Bang itself is a faint glow in space. Spacecraft and telescopes on balloons see this as a patchy pattern of slightly warmer and cooler gas all around us. These ripples also show where the hydrogen clouds were slightly denser.
As millions of years passed, the dense areas pulled in material because they had more gravity. Finally, about 100 million years after the Big Bang, the gas became hot and dense enough for the first stars to form.
New stars were being born at a rate 10 times higher than in the present-day Universe. Large clusters of stars soon became the first galaxies.
Last update: 20 December 2004