Ultrafaint dwarf galaxy spotted just 480 million years after the Big Bang | Ski.News

Located behind a supercluster of galaxies called Abell 2744, the galaxy JD1 is gravitationally lensed and displays three images.

A projected image of the galaxy JD1 (inset), which lies behind the Abell 2744 galaxy cluster. Image credit: Guido Roberts-Borsani, UCLA / NASA / ESA / CSA / Swinburne University of Technology / University of Pittsburgh / STScI.

A projected image of the galaxy JD1 (inset), which lies behind the Abell 2744 galaxy cluster. Image credit: Guido Roberts-Borsani, UCLA / NASA / ESA / CSA / Swinburne University of Technology / University of Pittsburgh / STScI.

The first billion years of life of the Universe were a crucial period in its evolution.

After the Big Bang about 13.8 billion years ago, the early Universe expanded and cooled sufficiently 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 went dark 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. This, in turn, allowed photons to travel through space, making the Universe transparent.

Determining the types of galaxies that dominated that era – dubbed the epoch of reionization – is a major goal of astronomy today, but until the development of the NASA/ESA/CSA James Webb Space Telescope, astronomers lacked the sensitive infrared instruments needed to study the first generation of galaxies.

Most of the galaxies found so far with Webb are bright, rare galaxies and not thought to be particularly representative of the young galaxies that populated the early Universe, said Dr. Guido Roberts-Borsani, a postdoctoral researcher at the University of California, Los Angeles. Angeles.

As such, while important, they are not thought to be the main agents that burned off all that hydrogen mist.

Ultra-faint galaxies like JD1, on the other hand, are much more numerous, which is why we believe they are more representative of galaxies that have conducted the process of reionization, allowing ultraviolet light to travel unhindered through space and time. .

First discovered in 2014, JD1 lies behind the massive galaxy cluster Abell 2744.

Abell 2744 is about 4 billion light-years away, about 350 million light-years in diameter, and has a mass equivalent to more than 4 trillion solar masses.

The cluster combined with gravitational pull bends and amplifies the light from JD1, making the faint galaxy appear larger and 13 times brighter than it otherwise would be.

Dr. Roberts-Borsani and colleagues used the Webbs Near Infrared Spectrograph (NIRSpec) to obtain the infrared spectrum of JD1, allowing them to determine its precise age and distance from Earth, as well as the number of stars and the amount of dust and heavy elements that has formed in its relatively short life.

Because light takes time to reach Earth, JD1 is seen as it was about 13.3 billion years ago, when the Universe was only about 4 percent of its current age, they explained.

The combination of gravitational magnification of the galaxy and new images from the Webbs Near-Infrared Camera (NIRCam) also allowed the team to study the galaxy’s structure in unprecedented detail and resolution, revealing three major elongated clusters of dust and gas that are forming stars. .

The authors 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.

Before Webb lit up just a year ago, we couldn’t even dream of confirming such a faint galaxy, said Professor Tommaso Treu, an astronomer at the University of California, Los Angeles.

The combination of Webb and the magnifying power of gravitational lenses is a revolution.

We are rewriting the book on how galaxies formed and evolved immediately after the Big Bang.

The results were published in the journal Nature.


G. Roberts-Borsani et al. The nature of an ultra-faint galaxy in the cosmic dark ages as seen with JWST. Nature, published online May 17, 2023; doi: 10.1038/s41586-023-05994-w

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