In the early universe, the gas between stars and galaxies was opaque – energetic starlight could not penetrate it. But 1 billion years after the Big Bang, the gas became completely transparent. New data from NASA’s James Webb Space Telescope has revealed exactly why: The stars of galaxies emit enough light to heat and ionize the gas around them, clearing our collective imagination for hundreds of millions of years.

The results of a research team led by Simon Lilley of ETH Zurich in Switzerland are the latest insights into a time period known as the Re-ionization Age, when the Universe underwent dramatic changes. After the Big Bang, the gas in the universe was incredibly hot and dense. Over hundreds of millions of years, the gas cooled. Then the universe presses again. The gas—probably due to early star formation in galaxies—warmed and ionized again, becoming transparent over millions of years.

Researchers have long sought definitive evidence to explain these transformations. The new results effectively pull back the curtain on the end of this reionization period. “Webb not only clearly showed that these transparent regions are around galaxies, but we also measured their size,” said Daichi Kashino of Nagoya University in Japan, lead author of the team’s first paper. “Thanks to Webb’s data, we can see galaxies reionizing the gas around them.”

These regions of transparent gas are huge compared to galaxies; Imagine a balloon with peas hanging inside it. Webb’s data show that these relatively small galaxies are causing reionization and clearing large regions of space around them. Over the next hundred million years, these transparent “bubbles” continued to grow larger and larger, eventually merging and the entire universe becoming transparent.

Lilly’s team deliberately targeted a time before the end of the reionization period, when the universe was neither completely pure nor transparent, but contained patches of gas in various states. By releasing gas between the quasar and our telescopes, the scientists pointed Webb in the direction of a quasar (an extremely bright, active supermassive black hole that acts like a giant flashlight). (Look for it in the center of this image: it’s small and pink, with six prominent diffraction spikes.)

As the quasar’s light passed to us through various gas particles, it was either absorbed by the opaque gas or was freely moving in the transparent gas. The team’s groundbreaking results were only possible by combining Webb’s data with observations of the central quasar from the WM Keck Observatory in Hawaii and the European Southern Observatory’s Very Large Telescope and the Magellan Telescope at Las Campanas Observatory, both located in Chile. .

“By illuminating the gas in our field of view, the quasar gives us comprehensive information about the composition and state of the gas,” said Anna-Christina Eilers of the Massachusetts Institute of Technology, lead author of another team paper.

The researchers then used Webb to identify galaxies near this line of sight and showed that the galaxies are typically surrounded by open regions with a radius of about 2 million light-years. In other words, Webb witnessed galaxies clearing the space around them at the end of the reionization period. To put that in perspective, the area these galaxies clear is roughly the same distance as the distance between our Milky Way galaxy and our nearest neighbor, Andromeda.

Until now, researchers had no conclusive evidence of what caused the reionization—until Webb wasn’t entirely sure what was responsible.

What do these galaxies look like? “They’re more chaotic than in the neighboring universe,” said Jorit Matti, also from ETH Zürich and lead author of the team’s second paper. Webb shows that they are actively forming stars and possibly initiating many supernovae. They had quite an adventurous youth!”

Along the way, Eulers used Webb’s data to confirm that the black hole in the quasar at the center of this field is the largest known to date in the early universe, weighing 10 billion times the mass of the Sun. “We still can’t explain how quasars got this big so early in the universe’s history,” he shared. “This is another puzzle to be solved!” The excellent images taken by Webb also found no evidence of gravitational lensing of light from the quasar, ensuring mass measurements were precise.

The team will soon dive into exploring galaxies in five additional regions, each anchored by a central quasar. Webb’s initial results were so clear they were eager to share. “We expected to identify a few dozen galaxies that existed during the reionization period, but we were able to easily select 117,” Caschino explained. “Webb exceeded our expectations.”

Lilly’s research group, Emission Line Galaxies and Intergalactic Gas in the Reionization Period (EIGER), demonstrated the unique power of combining conventional images from Webb’s NIRCam (near infrared camera) with wide-field slitless spectroscopy data from the same device. . The mode, which outputs the spectrum of each object in the images, turns Webb into what the team calls “an impressive redshift spectroscopic machine.” Source