Galaxies tend to be strong emitters of Lyman a photons (from the n = 2 to n = 1 transition in atomic hydrogen). But the intergalactic medium—the very thin gas between the galaxies—tends to absorb Lyman a photons. What can you infer from these observations about the temperature in these two environments? Explain.

Galaxies tend to be strong emitters of Lyman a photons (from the n = 2 to n = 1 transition in atomic hydrogen). But the intergalactic medium—the very thin gas between the galaxies—tends to absorb Lyman a photons. What can you infer from these observations about the temperature in these two environments? Explain.