Using the James Webb Space Telescope (JWST), astronomers have demonstrated that faint miniature galaxies cleared the blurred fog of atomic hydrogen in the early universe, allowing starlight to pass through the universe for the first time.
The study, published today in the journal Nature 1, provides evidence that dwarf galaxies, about 100 times smaller than the Milky Way, triggered a process known as reionization, which changed the course of cosmic history. "The universe has become transparent," said Hakeem Artek, an astrophysicist at the Institut de Astrophysics in Paris and lead author of the study. "It is because of reionization that we can see galaxies far away. ”
Rise from the Cosmic Dark Ages.
For about 380,000 years after the universe was large, the universe was a hot, dense furnace of subatomic particles. When the universe cools, free electrons and protons combine to form a gas made up of neutral hydrogen atoms.
What followed was a dull dark period. This continued until the gas collapsed in some places and merged to form the first stars, producing ultraviolet light. However, the remaining gases that permeate the universe either absorb or disperse this light. Thus, the universe resembles a foggy forest, dotted with dim flickering fireflies, and the light source can only be seen at short distances.
Astronomers detected light from the first star in the universe.
To make space transparent, it is necessary to bombard this gas with powerful "ionizing" radiation, which can convert neutral hydrogen atoms into charged hydrogen particles or ions. The three candidates are high-energy jets of light known as quasars, powered by supermassive black holes; Massive galaxies about the same size as the Milky Way; Finally, there are the "little fish" – dwarf galaxies.
Claudia Scarrata, an astrophysicist at the University of Minnesota in Minneapolis, said massive galaxies absorb large amounts of their own ultraviolet light. And maybe there are too few quasars to coordinate the whole process. However, dwarf galaxies are small enough to easily escape the ultraviolet light they produce.
Observations of young dwarf galaxies closer to Earth have shown that they can emit ionizing radiation. James Rhoads, an astrophysicist at NASA Goddard Space Flight Center in Greenbelt, Maryland, said that still, "nothing corroborates this better than actually getting data from early galaxies." However, dwarf galaxies in the reionization era are too small and faint to detect – even JWST.
The story of two telescopes.
To overcome this, the authors made use of "natural telescopes": a cluster of galaxies about 1.2 million parsecs from Earth. This star cluster is so large that it distorts the light passing through it, thus magnifying any light sources that are behind the lens as observed from Earth.
The authors used this lens to observe eight dwarf galaxies in the reionization era, when the age of the universe was less than 1 billion years. These galaxies were the faintest objects observed at the time.
Astronomers are delighted to see a lonely black hole for the first time.
Using the data collected by JWST, astronomers analyzed the ultraviolet wavelengths of these galaxies. This allowed the team to estimate that even these tiny small galaxies could easily remove the surrounding hydrogen. The researchers also estimate that even if 5% of ionizing radiation escapes into intergalactic space, the number of dwarf galaxies would be enough to ionize the entire universe 1 billion years after the universe is large.
Small galaxies are the first galaxies to form in the universe, which "may make it easier to start the [reionization] process earlier in the history of the universe," Rhoads said. As each galaxy emits radiation, it effectively blows out a transparent bubble that expands into neutral gas. Eventually, all the bubbles from all galaxies overlapped to complete the transformation.
Dwarf galaxies blow bubbles smaller than those produced by quasars and massive galaxies, and such small bubbles may ensure that reionization proceeds evenly throughout the universe. This, in turn, has an impact on the structure of the universe today, Atek said.