Quasar J0100+2802 (NIRCam Image)

There are more than 20,000 galaxies in this field. This James Webb Space Telescope view is found between the Pisces and Andromeda constellations.

Researchers using Webb anchored their observations on quasar J0100+2802, an active supermassive black hole that acts like a beacon. It is at the center of the image above, and appears tiny and pink with six prominent diffraction spikes.

The quasar is so luminous that it acts like a flashlight, illuminating the gas between it and the telescope. The team analyzed 117 galaxies that all existed approximately 900 million years after the big bang – focusing on 59 that lie in front of the quasar. The researchers could study not only the galaxies themselves, but also the illuminated gas surrounding them.   

These galaxies existed just before the end of the Era of Reionization, when the universe contained a patchwork of gas – some opaque and some transparent (or ionized). “As we look back into the teeth of reionization, we see a very distinct change,” explained Simon Lilly of ETH Zürich in Switzerland, who leads this team of researchers. “Galaxies, which are made up of billions of stars, are ionizing the gas around them, effectively transforming it into transparent gas.”

Researchers have long sought evidence to explain what happened during this period, when the universe experienced dramatic changes. After the big bang, gas in the universe was incredibly hot and dense. Over hundreds of millions of years, the gas cooled. Then, the universe hit “repeat.” The gas again became hot and ionized – and transparent.

The team’s results more concretely define the conditions at this specific “stop” in the universe’s history. “Not only does Webb clearly show that these transparent regions exist around galaxies, we’ve also measured how large they are,” explained Daichi Kashino of Nagoya University in Japan and the lead author of the team’s first paper. Think of the transparent regions of gas like hot air balloons, with galaxies the size of peas clearing that space.

Webb showed that galaxies have fully ionized the gas within a 2 million light-year radius. That’s approximately the same distance as the space between our Milky Way galaxy and our nearest neighbor, Andromeda. Over the next hundred million years, the bubbles went on to grow larger and larger, eventually merging and causing the entire universe to become transparent.

These results were announced by members of the Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) team. The team will eventually have images and data from six fields, each centered on a quasar, but Webb’s first image from NIRCam (Near-Infrared Camera) and data known as spectra are so detailed that they could easily make definitive conclusions without waiting for additional observations.