Distant Cloud

When astronomers look deep into space, they also look far back in time, probing the universe as it looked long ago. Recently, for example, they measured the composition of a gas cloud that existed less than a billion years after the Big Bang. The discovery provides new insight into the conditions that prevailed during the ancient universe.

The cloud itself is invisible. But it absorbs the light of a quasar that’s behind it. That imprints the chemical fingerprint of the cloud in the quasar’s light.

The Big Bang occurred about 13.8 billion years ago. It produced only hydrogen, helium, and a little bit of lithium. These elements formed giant clouds that collapsed to give birth to the first stars. The stars then created heavier elements, such as the oxygen we breathe and the iron that flows through our veins.

The cloud is almost 13 billion light-years from Earth. That means we see it as it appeared about 800 million years after the Big Bang. The cloud seems pristine — it’s made of eleme