Far out cosmology: early tiny galaxies clear fog (Introduction)

by David Turell , Thursday, February 29, 2024, 19:36 (266 days ago) @ David Turell

They removed hydrogen atoms:

https://www.nature.com/articles/d41586-024-00594-8?utm_source=Live+Audience&utm_cam...

"The research, published today in Nature1, provides evidence that dwarf galaxies roughly 100 times smaller than the Milky Way triggered the process known as reionization, which changed the course of cosmic history. “The Universe became transparent,” says Hakim Atek, an astrophysicist at the Paris Institute of Astrophysics and lead author of the study. “It’s because of reionization that we are able to see distant galaxies.”

"For around 380,000 years after the Big Bang, the Universe was a hot, dense furnace of subatomic particles. As the cosmos cooled, the free electrons and protons combined to form a gas of neutral hydrogen atoms.

"What followed was a dreary period of darkness. This lasted until the gas collapsed in places to fuse and form the first stars, which produced ultraviolet (UV) light. However, the remaining gas permeating the Universe either absorbed or scattered this light. As a result, the Universe resembled a foggy forest speckled with dim, flickering fireflies, and light sources were visible only for short distances.

"To render space transparent, something needed to bombard this gas with powerful ‘ionizing’ radiation, which could transform the neutral hydrogen atoms into charged particles, or ions, of hydrogen. The three candidates were energetic light jets called quasars, which are powered by supermassive black holes; massive galaxies roughly the same size as the Milky Way; and, finally, the ‘minnows’ — dwarf galaxies.

***

"Using data gathered by the JWST, the astronomers analysed the wavelengths of UV light from these galaxies. This allowed the team to estimate that even these faint, small galaxies could have expunged hydrogen gas around them easily. The researchers also estimate that dwarf galaxies were abundant enough up to one billion years after the Big Bang to have ionized the entire Universe, even if 5% of their ionizing radiation escaped into intergalactic space.

"Small galaxies were the first to form in the Universe, which “probably makes it easier to start the [reionization] process early” in the history of the cosmos, Rhoads says. As each galaxy emitted radiation, it effectively blew a bubble of transparency that expanded into neutral gas. Eventually, all the bubbles from all the galaxies overlapped to complete the transformation.

"Dwarf galaxies would have blown bubbles smaller than those produced by quasars and massive galaxies, and such small bubbles might have ensured that reionization proceeded homogeneously across the Universe. This, in turn, had implications for the architecture of the present-day Universe, Atek says."

Comment: this helps to explain the early times after the Big Bang.