The cause of the radical transformation of the universe millions of years after its creation

2023-06-13 13:45:38

There was a time when the universe was opaque, like a city in a thick fog. The starlight could not be seen.

But about a billion years after the Big Bang (the “explosion” with which the universe was born), the gas had become completely transparent. Because? Research based on observations by the James Webb Space Telescope has discovered why: the stars in the newly formed galaxies gave off enough light to heat and ionize the gas around them, clearing the sky and leaving the cosmic landscape visible throughout a process that took a few hundred million years.

The study was carried out by a team consisting of, among others, Simon Lilly of the Swiss Federal Institute of Technology in Zurich (ETH) and Daichi Kashino of Nagoya University in Japan.

The results of the study provide new and revealing data about a period of time known as the Reionization Era, when the universe underwent drastic changes that led to the transparency of space. After the Big Bang, the gas in the universe was incredibly hot and dense. Over hundreds of millions of years, the gas cooled. The gas then became heated and ionized again (due to the formation of the first stars in galaxies) and, over millions of years, became transparent.

The scientific community has long sought definitive evidence of the nature of these transformations. The new results finally draw the curtain and show the final part of this reionization period. By scrutinizing the universe at a great enough distance, it can be seen as it was at that time, as many years ago as light-years separate us from the observed sector.

The Webb Space Telescope not only clearly shows that these transparent regions are found around the most distant galaxies (and therefore more distant in time), but has also made it possible to measure their size. Using the Webb data, Lilly and Kashino’s team have been able to see how these early galaxies reionize the gas around them.

These regions of transparent gas are gigantic compared to galaxies. The Webb data show that these relatively tiny galaxies drove the reionization of the cosmos, clearing up massive regions of space around them. Over the next hundreds of millions of years, these transparent “bubbles” kept growing larger and larger, eventually merging with each other and causing the entire sky to become transparent.

The four main stages by which the universe went from being opaque to being transparent:

1: Birth of the first stars and formation of the first galaxies. The universe is opaque, like a city in a thick fog. (Illustration: NASA/ESA/CSA/Joyce Kang (STScI))

2: Galaxies begin to disturb the gas around them, creating bubbles of transparency. (Illustration: NASA/ESA/CSA/Joyce Kang (STScI))

3: Those transparent bubbles of altered gas expand. (Illustration: NASA/ESA/CSA/Joyce Kang (STScI))

4: The expansion of the altered gas bubbles encompasses the entire sky of the universe, which becomes transparent, as we see it today. (Illustration: NASA/ESA/CSA/Joyce Kang (STScI))

Lilly and Kashino’s team intentionally peered into a sector of the cosmos dating from just before the end of the Reionization Era, when the sky was neither entirely transparent nor entirely opaque. At that time, it contained a mosaic of gas clouds in various states. The scientists pointed Webb in the direction of a quasar (an active supermassive black hole whose immediate vicinity is extremely bright), which acted like a huge flashlight, illuminating the gas between the quasar and the telescope.

As the light from the quasar traveled toward us through different patches of gas, it was either absorbed by the opaque gas or moved freely through the transparent gas. This revealed the location and extent of the transparent and opaque areas.

The groundbreaking results obtained by the research team would not have been possible if the Webb data had not been combined with observations of the quasar made by the WM Keck Observatory in Hawaii, the VLT (Very Large Telescope) of the European Southern Observatory (ESO) in Chile and the Magellan Telescope at the Las Campanas Observatory in Chile.

The researchers then used Webb to identify galaxies close to this line of sight and showed that, in general, galaxies in that area and time of the universe are surrounded by transparent regions about 2 million light-years in radius. In other words, the Webb has managed to witness the action of galaxies clearing the space around it at the end of the Reionization Era. (Fountain: NCYT de Amazings)