We’ve said it before and we’ll say it again: astronomy advances through the back and force development of both better computers and better telescopes. 

For the past several decades we’ve all held up the same illustration, that on one piece of paper went from the Cosmic Microwave background light from the moment the universe became visible, and then in cartoon ways, on an 8.5×11 inch piece of paper, evolved from that light to the Swiss cheese structure of galaxy clusters and voids that we have in our modern universe. With surveys like the Sloan Digital Sky Survey and Dark Energy Survey, astronomers have been able to map out the distribution of galaxies at different periods of time and see how they match this diagram to a point. 

While we can see the Cosmic Microwave Background, and we can see the distribution of galaxies changing over time, there is a period early in the universe that we know almost nothing about. Depicted in old diagrams as a lot of glowy gas and called the age of reionization, this is the period when the universe went from a lot of neutral gas to starting to form galaxies and stars; and this is a period of time that we haven’t been able to survey, yet.

With the JWST so far seeming like it is going to work, we are starting to feel like maybe we will finally be able to survey that part of time and fill in more details. With these observations in (we hope) the near-ish future, modelers have been working to define the details of those early days.

And they are getting really cool results. The early universe saw more of an evolution of state than of structure. While the gas and dark matter density did change over time, the biggest changes seen in the models were in the amount of gas that was ionized, and thus transparent, and the overall temperature of the gas when it heated up as the first stars turned on.

If JWST lives up to its potential, we will be able to start seeing these pockets of visible and transparent gas around galaxies. Just as star-forming regions are wild structures with material that is forming stars and reveals pockets of these stars in the gas, young galaxies are pockets – really, really big pockets – of stars in the early universe.

And we will get to see this, not just in these computer models, but in the universe, if JWST works. There are a lot of hopes in that one spacecraft — a lot of hopes and dreams for science.

More Information

CfA Harvard | Smithsonian press release

“The THESAN project: Lyman-α emission and transmission during the Epoch of Reionization,” A Smith et al., 2022 March 24, Monthly Notices of the Royal Astronomical Society