A false-color NIRCam image of the Abell 2744 cluster

Early universe galaxy seen by James Webb Telescope

Image credit: Nature (2023)

Astronomers have used the powerful telescope to confirm the existence of the faintest galaxy ever seen in the early universe.

The distant galaxy JD1 was formed from hydrogen left over from the Big Bang and has been confirmed as one of the most distant galaxies identified to date.  

Astrophysicists from the University of California, Los Angeles (UCLA) have been able to confirm the existence of this galaxy using the James Webb Space Telescope (JWST), the largest and most powerful space science telescope ever launched.

JD1 is approximately 13.3 billion years old, and it shows a picture of when the universe was only about 4 per cent of its present age.

The faraway galaxy is located behind a large cluster of nearby galaxies, called Abell 2744. This cluster was key to the identification of JD1, as the combined gravitational strength of Abell 2744's galaxies amplifies the light from JD1, making it appear larger and 13 times brighter than it otherwise would.

The effect, known as gravitational lensing, is similar to how a magnifying glass distorts and amplifies light within its field of view. 

A projected image of the galaxy JD1 (inset), which is located behind a bright cluster galaxy called Abell2744.

A projected image of the galaxy JD1 (inset), which is located behind a bright cluster galaxy called Abell2744. / Guido Roberts-Borsani/UCLA

Image credit: Guido Roberts-Borsani/UCLA); original images: NASA, ESA, CSA, Swinburne University of Technology, University of Pittsburgh, STScI

The gravitational lensing effect would not have been enough to allow scientists to identify JD1 without the capabilities of JWST. 

The $9bn (£8.4bn) James Webb Telescope was launched on Christmas Day 2021. It was designed to give scientists a more detailed look at the start of the universe, the birth of stars, and possibly the origins of life.

In this study, the UCLA researchers used the JWST’s near-infrared spectrograph instrument, NIRSpec, to obtain an infrared light spectrum of the galaxy. Using this technology, they were able to determine its precise age and its distance from Earth, as well as the number of stars and amount of dust and heavy elements that it formed in its relatively short lifetime.

A false-colour NIRCam image of the Abell 2744 cluster.

A false-colour NIRCam image of the Abell 2744 cluster. / Guido Roberts-Borsani/UCLA

Image credit: Nature (2023)

The team also relied on new images from another one of the JWST’s near-infrared instruments, NIRCam, to study the galaxy’s structure in unprecedented detail and resolution, revealing three main elongated clumps of dust and gas that are forming stars.

The team used the new data to trace JD1’s light back to its original source and shape, revealing a compact galaxy just a fraction of the size of older galaxies like the Milky Way, which is 13.6 billion years old.

“Before the Webb telescope switched on, just a year ago, we could not even dream of confirming such a faint galaxy,” said Tommaso Treu, a UCLA physics and astronomy professor, and the study’s second author. “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 in the immediate aftermath of the Big Bang.”

James Webb Space Telescope

James Webb Space Telescope /Nasa

Image credit: Nasa

The discovery of JD1 is expected to help scientists understand the end of the cosmic ages, the period following the Big Bang when the universe expanded and cooled sufficiently for hydrogen atoms to form.

It is after this period that the first stars and galaxies appeared and began burning away the hydrogen fog left over from the Big Bang with energetic ultraviolet light, which rendered the universe transparent like it is today.

Until the development of the Webb telescope, scientists lacked the sensitive infrared instruments required to study the first generation of galaxies.

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

"Ultra-faint galaxies such as JD1, on the other hand, are far more numerous, which is why we believe they are more representative of the galaxies that conducted the reionisation process, allowing ultraviolet light to travel unimpeded through space and time."

JWST’s light-gathering ability is more than twice that of Hubble and its size is bigger than two double-decker buses. Since the telescope instruments need to be cooled to -267°C, JWST orbits the Earth on the other side of the Moon, cloaked in its shadow, and protected from the Sun. 

The telescope has already allowed scientists to take unprecedented images, such as those of Jupiter’s storms and what has been considered the “deepest view of the universe” to date.  

The new images and findings were published in the journal Nature

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