Reionization of the Intergalactic Medium

Understand

After recombination the cosmic gas was left in a cold and neutral state.

• However, as the first stars and black holes formed within early galactic systems, their UV and X-ray radiation induced a gradual phase transition of the intergalactic gas into the warm and ionized state we currently observe.
• This process is known as cosmic reionization.
• Understanding how the energy deposition connected with galaxy and star formation shaped the properties of the intergalactic gas is one of the primary goals of present-day cosmology.