The Big Bang saw the creation and ionisation of the Universe. The ionisation of a particle is when the particle becomes charged, essentially meaning it is “ready” to react with other particles. The initial “ionisation” of the Universe was when neutral hydrogen gas (a proton and an electron) becomes ionised (the electrons are stripped, leaving a positively charged proton). This ionised gas went from smoothly distributed to slowly collapsing in different areas to become the highly structured galaxies and clusters of galaxies we have today.
Astrophysicists classify the initial blanket of gas as a “smooth universe”, compared to what we now live in as the “clumpy” Universe. Imagine that the layer of gas is a pillowcase, and when you add marbles (stars) into it becomes clumpy and more rigid the more you add. This is similar to what happened in our Universe, but only the very fabric of the pillowcase became the marbles themselves.
In the beginning, only a few stars began to form at a very slow rate, but there was a tipping point – where these stars gave way to a rapid spur of supernova all over the Universe, which is what we call the Epoch of Reionisation.
So how did astrophysicists discover this? Well, as the Universe expands, the stars move away from us and the light that they give off appears to “shift” to the red end of the electromagnetic spectrum. Red Shift acts similarly to the sound of an ambulance that changes in frequency as it speeds past you, but in this case, it’s the light from the star. So by probing (measuring) the distance between to Red Shifted points over time, scientists can understand almost everything about the stars; including the origin. But it’s not just stars that can be measured by this technique. It’s also pulsars (magnetized neutron stars) or even entire galaxies!
Paul Geil, the animator/developer of the 3D data cube, further explains the concept of Red Shift:
“We can look at an object’s spectrum and work out how much that light has elongated due to the expansion of the Universe.”