JWST Unveils Mysterious Glow in the Early Universe; What Do Lyman-Alpha Lines Say About the Cosmos?

During its early stage, the universe used to be a very dark place, packed with light-blocking hydrogen. It was only during the Epoch of Reionization when the first stars began illuminating their surroundings with UV radiation.

But before the cosmos became well-lit, there was a mysterious type of light, called the Lyman-alpha emissions, which pierced the darkness. Despite the early universe being too dark for light to travel through the opaque gas that dominated it, scientists have still detected some Lyman-lines prior to the coming of lights in the Epoch of Reionization. Its origin has been a puzzle that continues to mystery experts.

Inexplicable Light Emission

Lyman-alpha emissions refer to the wavelength of light which occurs in the ultraviolet range. They come from hydrogen atoms when their electrons undergo transition to a specific energy state. They are detected in the form of Lyman-alpha spectral lines which are part of what experts call the Lyman-alpha forest.

This forest is a series of absorption lines that stem from the hydrogen in distant astronomical objects. As their light crosses the gas clouds with various redshifts, it leads to the formation of the forest of Lyman-alpha lines.

In a new study, a team of researchers led by Cambridge University researcher Callum Witten tried to provide an explanation for the surprising detection of Lyman-alpha in the early galaxies. Their findings are discussed in the paper "Deciphering Lyman-α emission deep into the epoch of reionization."

Deciphering the Great Escape

Many hypotheses have been previously proposed to explain the inexplicable hydrogen emission. In the latest investigation, scientists use data gathered by James Webb Space Telescope, a device designed to peer back into the early days of the universe.

JWST has the ability to sense the photons released by stellar objects in the first galaxies. It has both the sensitivity and the angular resolution to follow ancient light back to its original source. This capability has opened a new window into the young universe and provides answers to long-standing astronomical questions.

The research team observed Lyman-alpha emitter LAE EGSY8p68 using JWST which revealed more detail than the Hubble Space Telescope. Webb's resolving power reveals a clump of dimmer galaxies around the bright galaxies in LAE EGSY8p68 which Hubble failed to see. This region is much busier and more crowded with lots of active stellar formation.

To interpret the collected data, the team used a galactic merger simulation called Azahar to produce a mock JWST image. The simulation shows what happened as the stellar mass gathered and as stars formed in the early galaxies.

It was found that the early galaxies were star producers and used to be a rich source of Lyman-alpha emissions. Most of these emissions were blocked by the primordial neutral hydrogen which filled the space between galaxies.

According to the researchers, this implies that galactic mergers and their abundant star formation are responsible for Lyman-alpha emissions. These mergers and interactions created a path for them out of the dense, opaque neutral hydrogen which dominated the young universe.