Stars Of Early Galaxies Emitted Enough Light To Ionise Surrounding Gas And Make It Transparent, Webb Proves

Several theories have emerged over the years, but Webb proves that the light from stars in the early galaxies caused the gas between them to become reionised, making the universe transparent.

The gas between stars and galaxies in the early universe was opaque, but one billion years after the Big Bang, these stars emitted enough light to heat and ionise the gas around them. This caused the gas to become completely transparent, marking the end of "reionization", and resulting in a clear universe. The Epoch of Reionization was an era which occurred more than 13 billion years ago, when the gas between galaxies, which was opaque to energetic light, was ionised and cleared, making it possible to observe young galaxies. 

James Webb Space Telescope (Webb) has proved that the light emitted by stars in young galaxies heated and ionised the gas between them, and cleared the view for the world. The Epoch of Reionization lasted for about 600 million years. 

Webb's findings appear in three papers in The Astrophysical Journal. 

What does Webb prove?

The studies, conducted by a research team led by Simon Lilly of ETH Zürich, a public university in Switzerland, provide new insights into the Epoch of Reionization, an era when the universe underwent dramatic changes. The gas in the universe was incredibly hot and dense, but over hundreds of millions of years, the gas cooled. However, the gas became hot and ionised again, due to the formation of early stars in galaxies, and as a result, the universe became transparent. 

Several theories have emerged over the years, but Webb proves that the light from stars in the early galaxies caused the gas to become reionised. 

In a NASA statement, Daichi Kashino, the lead author on the team's first paper, said not only does Webb clearly show that these transparent regions are found around galaxies, but with the help of the telescope's data, the galaxies can be seen re-ionizing the gas around them, and the sizes of the regions can be measured. 

The transparent regions containing gas are much larger than the galaxies. Compared to galaxies, the transparent regions are how large a hot air balloon is, compared to a pea suspended inside the balloon. Webb has shown that the relatively tiny galaxies drove reionisation by clearing massive regions of space around them, and that over the next 100 million years, the transparent bubbles continued to grow larger and larger, eventually merging together. The merging of the transparent bubbles caused the entire universe to become transparent.

According to an infographic shared by NASA, after the Big Bang, stars formed and galaxies assembled, and during the Epoch of Reionization, the galaxies began to change the gas around them, areas of transformed gas expanded, and the universe became clear, marking the end of reionization. 

Why did the team choose a time just before the end of the Epoch of Reionization?

The researchers intentionally chose a time just before the end of the Epoch of Reionization because at that time, the universe was not quite clear and not quite opaque, and contained a patchwork of gas in various states. Webb has been aimed in the direction of a quasar, which is an extremely luminous active supermassive black hole that acts like an enormous flashlight, in order to highlight the gas between the quasar and the telescope.

According to NASA, light from the quasar travelled toward Earth through different patches of gas, and during its journey, it was either absorbed by gas that was opaque or moved freely through transparent gas. 

Data obtained from observations of the central quasar using the WM Keck Observatory in Hawaii, the European Southern Observatory's Very Large Telescope, and the Magellan Telescope at Las Campanas Observatory made it possible for the team to conduct this groundbreaking research. 

In the statement, Anna-Christina Eilers, the lead author on the third paper, said by illuminating gas along the astronomers' line of sight, the quasar gives them extensive information about the composition and state of the gas.

Using Webb, the team identified galaxies near the line of sight, and showed that the galaxies are generally surrounded by transparent regions about two million light-years in radius. This means that Webb witnessed galaxies in the process of clearing the space around them at the end of the Epoch of Reionization. 

According to NASA, the distance up to which the galaxies cleared regions is approximately equal to that between the Milky Way and its nearest neighbour, Andromeda. 

The results are important because until now, researchers did not have definitive evidence of what caused reionization, but Webb proved that the light from the stars in early galaxies is what cleared vast regions. 

These galaxies are more chaotic than those in the nearby universe, according to Jorryt Matthee, the lead author on the second paper. 

Matthee said that Webb shows the galaxies were actively forming stars and must have been shooting off many supernovae. 

Interesting findings

The galaxies studied as part of this research existed when the universe was only 900 million years old, and are clumpy, elongated and actively forming stars. 

Webb confirmed that the black hole in the quasar is the most massive currently known in the universe, and weighs 10 billion times the mass of the Sun. 

Webb's images have revealed no evidence that the light from the quasar had been gravitationally lensed. This means that the mass measurements made by the team are definitive. 

The studies were conducted as part of the Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) survey. The results demonstrate the power of Webb's Near-Infrared Camera (NIRCam), and represent evidence that the local ionising radiation from galaxies is responsible for producing the last traces of transmission of the intergalactic medium, at least along the line of sight. 

According to the second paper, the main implication of the results is that the abundant strong emission lines from galaxies in the early universe make NIRCam observations a highly efficient mode to trace the distribution of galaxies from the peak of star formation to the Epoch of Reionization.