"On their way to Earth, the X-rays from a distant quasar dim as they pass
through a cloud of the intergalactic gas. By measuring the amount of dimming
due to oxygen and other elements in the cloud, astronomers were able to
estimate the temperature, density and mass of the absorbing gas." My question
regards the presence of oxygen in the gas. Where did it come from? It seems
that the gas is primordial and, therefore, should only contain hydrogen
and trace amounts of helium. What am I missing? Oxygen is only produced
inside of stars, and is spread only through supernova explosions. This gas
hasn't been through this process?
The primordial gas was enriched with oxygen and other elements by stars
that formed when the universe was only few hundred million years to a
few billion years old. A important by-product of the research on the
intergalactic clouds is to set limits on the amount of oxygen, etc.
produced in the early universe. At present this is poorly determined,
but is thought to be about 10% of the present concentration of oxygen in