Webb confirms the faintest galaxy, 13.3 billion light-years away

June 1 () –

An international research team led by UCLA astrophysicists has confirmed the existence of the faintest galaxy ever seen in the early universe, 13.3 billion light-years away.

The galaxy, called JD1, is one of the most distant identified to date, and is typical of the type of galaxies that burned through the haze of hydrogen atoms left over from the Big Bang, letting the light shine through the universe and shaping what exists today.

The discovery was made with the NASA/ESA/CSA James Webb Space Telescope (JWST) and the findings are published in the journal Nature.

The first billion years of the universe’s life were a crucial period in its evolution. After the Big Bang, about 13.8 billion years ago, the universe expanded and cooled enough for hydrogen atoms to form. Hydrogen atoms absorb ultraviolet photons from young stars; However, until the birth of the first stars and galaxies, the universe darkened and entered a period known as the cosmic dark ages. The appearance of the first stars and galaxies, a few hundred million years later, bathed the universe in energetic ultraviolet light that began to burn, or ionize, the hydrogen mist. That, in turn, allowed the photons to travel through space, rendering the universe transparent.

Determining the types of galaxies that dominated that era, called the Epoch of Reionization, is an important goal in astronomy today, but until the development of the Webb telescope, scientists lacked the sensitive infrared instruments needed to study the first generation of galaxies.

“Most of the galaxies found with JWST so far are bright galaxies that are rare and are not thought to be particularly representative of the young galaxies that populated the early universe,” he said. it’s a statement Guido Roberts-Borsani, a UCLA postdoctoral researcher and the study’s first author. “As such, while they are important, they are not thought to be the main agents that burned up all that hydrogen mist.

“Ultra-faint galaxies like JD1, on the other hand, are much more numerous, so we think they are more representative of the galaxies that underwent the reionization process, allowing ultraviolet light to travel unimpeded through space and time.”

JD1 is so faint and so far away that it is challenging to study it without a powerful telescope and a helping hand from nature. JD1 lies behind a large cluster of nearby galaxies, called Abell 2744, whose combined gravitational force bends and amplifies light from JD1, making it appear larger and 13 times brighter than it would otherwise. The effect, known as gravitational lensing, is similar to how a magnifying glass distorts and amplifies light within its field of view; without gravitational lensing, JD1 would probably have been lost.

The researchers used the Webb Telescope’s near-infrared spectrograph instrument, NIRSpec, to obtain a spectrum of infrared light from the galaxy, allowing them to determine its precise age and distance from Earth, as well as the number of stars and how many of dust and heavy element particles that it formed in its relatively short lifetime.

The combination of the galaxy’s gravitational magnification and new images from another of the Webb Telescope’s near-infrared instruments, NIRCam, also made it possible for the team to study the galaxy’s structure with unprecedented resolution and detail, revealing three elongated main clumps of dust and gas that are forming stars. The team used the new data to trace the light from JD1 back to its original source and shape, revealing a compact galaxy only a fraction of the size of older galaxies like the Milky Way. which is 13.6 billion years old.

Because it takes light to travel to Earth, JD1 looks like it did about 13.3 billion years ago, when the universe was only about 4% of its current age.

“Before the Webb telescope was turned on, just a year ago, we couldn’t even dream of confirming such a faint galaxy,” said Tommaso Treu, a UCLA professor of physics and astronomy and second author of the study. “The combination of JWST and the magnifying power of gravitational lensing is a revolution. We are rewriting the book on how galaxies formed and evolved immediately after the Big Bang.”