To look through space is to look through time, so getting a glimpse of the early days of the universe is a matter of peering deeper and deeper into space. Now, astronomers from MIT and Arizona State University have peered right back to the “Cosmic Dawn” – the time when the first stars were beginning to fire up – by picking up an extremely faint radio signal that marks the earliest evidence of hydrogen, just 180 million years after the Big Bang.

In the early years, the Universe was a very dark, very cold place. Light basically didn’t exist, and the hydrogen gas that made up the majority of the interstellar medium was virtually indistinguishable from the cosmic background radiation, left over from the Big Bang.

But over time pockets of matter clumped together, grew larger and eventually exerted such high pressure that nuclear fusion kicked into gear. This resulted in the first stars flickering on across the Universe, and the UV radiation they emitted interacted with the surrounding hydrogen gas. The hydrogen atoms absorbed the background radiation, and it’s this change that the new study was able to detect as radio waves.

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