NASA's Webb telescope reveals how galaxies cleared haze of early Universe

In the early universe, the gas between stars and galaxies was opaque, preventing energetic starlight from penetrating it. However, new data from NASA's James Webb Space Telescope has shed light on why the gas became transparent about 1 billion years after the Big Bang. The research, led by Simon Lilly of ETH Zürich in Switzerland, provides valuable insights into a crucial period known as the Era of Reionization when the universe underwent significant changes.

Following the Big Bang, the gas in the universe was incredibly hot and dense. Over hundreds of millions of years, it gradually cooled down. However, the gas later became hot and ionized again, possibly due to the formation of early stars in galaxies. This ionization process eventually led to the gas becoming transparent over millions of years.

The new results offer a breakthrough in understanding the Era of Reionization.

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 had become completely transparent. Why? New data from @NASAWebb has pinpointed the reason: https://t.co/WlhVDrvjUW pic.twitter.com/Wl2R804EeZ

— NASA (@NASA) June 12, 2023

Daichi Kashino of Nagoya University in Japan, the lead author of the research team's first paper, stated, "Not only does Webb clearly show that these transparent regions are found around galaxies, we've also measured how large they are. With Webb's data, we are seeing galaxies reionize the gas around them."

The regions of transparent gas, compared to the galaxies themselves, are enormous. Webb's observations demonstrated that these relatively small galaxies played a crucial role in driving reionization by clearing massive regions of space around them. Over time, these transparent "bubbles" expanded and merged, eventually resulting in the entire universe becoming transparent.

The researchers focused on a specific period - just before the end of the Era of Reionization when the universe was neither fully clear nor entirely opaque. They observed a quasar, an extremely luminous active supermassive black hole acting as a massive flashlight, to study the gas between the quasar and their telescopes.

"As the quasar's light travelled toward us through different patches of gas, it was either absorbed by gas that was opaque or moved freely through transparent gas," the researchers said.

This observation was made possible by combining Webb's data with observations from the W. M. Keck Observatory in Hawaii and the European Southern Observatory's Very Large Telescope and the Magellan Telescope in Chile.

Using Webb's data, the researchers identified galaxies near the line of sight and discovered that these galaxies were surrounded by transparent regions spanning approximately 2 million light-years in radius. This finding indicated that the galaxies were actively clearing the space around them at the end of the Era of Reionization. To put it into perspective, the cleared area is roughly equivalent to the distance between our Milky Way galaxy and its nearest neighbour, Andromeda.

The researchers also discovered that the black hole at the center of the observed quasar was the most massive currently known in the early universe, weighing 10 billion times the mass of the Sun.

The team now plans to continue their research, focusing on galaxies in five additional fields, each anchored by a central quasar. Webb's initial results have already exceeded expectations, revealing 117 galaxies from the Era of Reionization, far surpassing the anticipated number.

The research team, known as the Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER), have shown the powerful capabilities of Webb's Near-Infrared Camera (NIRCam) and its wide-field slitless spectroscopy mode, which turns the telescope into a "spectacular spectroscopic redshift machine."