Scientist detect star-forming neutral gas in early universe galaxies

Scientists have found direct evidence of neutral gas inside some of the earliest known galaxies, providing new clues about how stars and galaxies formed in the early Universe. The discovery was made by researchers from Chiba University in Japan using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and data from the James Webb Space Telescope (JWST).

The study focused on star-forming galaxies that existed around 700 to 800 million years after the Big Bang. Scientists have long believed that neutral gas serves as the main fuel for star formation, but directly observing this gas in distant galaxies has been extremely difficult.

Neutral gas is made up of atoms that carry no electrical charge. As large clouds of this gas gather inside galaxies, gravity causes them to collapse into dense regions. Over time, increasing pressure and temperature lead to the formation of stars. As more stars are created, galaxies grow larger and develop more complex structures.

To detect the gas, researchers studied a signal known as the [O I] 145 micrometer emission line, which is produced by neutral oxygen atoms and acts as a direct indicator of neutral gas. They successfully detected this signal in all four galaxies, making it the most distant direct detection of neutral gas in typical star-forming galaxies to date.

The team also examined the [N II] 205 micrometer emission line, which traces ionized gas. They found that this signal was weak or absent, suggesting that most of the detected material was neutral gas rather than ionized gas. By comparing [O I], [C II], and [N II] signals, the researchers were able to better understand the physical conditions inside these galaxies.

Their analysis revealed very dense gas, similar to that found in starburst galaxies known for intense star formation. However, the radiation field was lower than what is typically seen in such galaxies.

The research was led by Yoshinobu Fudamoto and Masamune Oguri from Chiba University, along with researchers Akio K. Inoue, Hanae Inami and Takuya Hashimoto. The team hopes future observations will provide a clearer picture of how galaxies formed and evolved from the early Universe to the present day.