Astronomers confirm the faintest galaxy ever seen as we look back toward the Cosmic Dawn.

Our universe is transparent, with dazzling stars and galaxies shining against a pristine, pitch-black background. This, however, wasn't always the case because the universe's early history was veiled by a cloud of hydrogen atoms that blocked the light from the first stars and galaxies.

It is believed that the hydrogen fog was burned away by the powerful ultraviolet radiation from the earliest generations of stars and galaxies, converting the cosmos into what it is today. Astronomers are now employing the James Webb Space Telescope's cutting-edge equipment to examine the stars and galaxies that originated right after the Big Bang, whereas earlier generations of telescopes were unable to investigate those early cosmic objects.

I am an astronomer who uses the most advanced ground- and space-based observatories to study the furthest galaxies in the universe. My team has verified the presence of the weakest galaxy known to exist in the early universe using fresh Webb telescope observations and a gravitational lensing event. The galaxy, known as JD1, is shown as it was 480 million years ago, or 4% of the universe's current age.

An overview of the early universe's history

The universe's first billion years were a critical stage in its development. As soon as the Big Bang occurred, matter and light were entangled in a hot, dense "soup" of elementary particles.

However, the cosmos began to expand extraordinarily quickly a nanosecond after the Big Bang. As a result of this expansion, the cosmos finally became cool enough for light and matter to separate from their "soup" and, some 380,000 years later, to produce hydrogen atoms. The cosmos was black since there was no light from stars and galaxies, and the hydrogen atoms appeared as an intergalactic fog. The cosmic dark ages cover this time frame.

A few hundred million years after the Big Bang, the first generations of stars and galaxies emerged, bathing the universe in incredibly hot UV light that burnt or ionized the hydrogen fog. The translucent, intricate, and exquisite universe we see today is the result of this process.

The first billion years of the universe, when this hydrogen fog was dissipating, are referred to as the epoch of reionization by astronomers like me. We investigate when the earliest stars and galaxies formed, what their primary characteristics were, and whether they were able to generate enough UV radiation to burn through all the hydrogen in order to properly comprehend this time period.

The quest for early universe dim galaxies

Discovering and validating the distances to galaxies that astronomers believe may be responsible for this process may help us comprehend the epoch of reionization. Due to the limited speed at which light can travel, it takes time for light to reach our telescopes, allowing astronomers to observe objects as they were in the past.

For instance, it takes light from the Milky Way, the galactic center of our galaxy, around 27,000 years to reach us on Earth, thus we perceive that light as existing 27,000 years ago. The universe is 13.8 billion years old, thus if we wish to view back to the initial moments after the Big Bang, we must search for particles at Extremely long lengths.

Because they are so far away, galaxies in this time period look very faint and minuscule to our telescopes and produce the majority of their light in the infrared. Therefore, to discover them, astronomers require large infrared telescopes like the Webb. Due to the fact that our telescopes were not sensitive enough to see the fainter, smaller galaxies, almost all of the distant galaxies discovered by astronomers prior to the Webb Space Telescope were unusually bright and enormous.

The latter demographic, not the intelligent ones, is much larger, more representative, and most likely to be the primary force behind the reionization process. Astronomers must therefore focus their attention on these dim galaxies. It's comparable to trying to comprehend human evolution by looking at entire populations rather than a small number of exceptionally tall individuals. Webb is providing up a new window into understanding the early universe by enabling us to observe dim galaxies.

standard early galaxy

One such "typical" dim galaxy is JD1. It was identified in 2014 as a possible far-off galaxy by the Hubble Space Telescope. Hubble could only make an informed assessment because it lacked the capacity and sensitivity to validate the object's distance.

Before making any assertions about the characteristics of small, faint, local galaxies, astronomers must be certain of their distances because they can occasionally be confused for more distant galaxies. Therefore, until they are verified, distant galaxies are still considered "candidates". These may now be verified thanks to the Webb telescope, and JD1 was one of its first significant confirmations of a candidate for an exceptionally far-off galaxy discovered by Hubble. This affirmation places it among the faintest galaxies currently observed in the early universe.

I obtained infrared spectra of the galaxy with Webb's near-infrared spectrograph, NIRSpec, and a global team of researchers to confirm JD1. The spectrum let us determine the star's age, how many young stars it had spawned, how much dust and heavy elements it had produced, and how far it was from Earth.

The magnifying glass of nature is gravitational lensing.

JD1 would be difficult to view without assistance from nature, not even for Webb. The light from JD1 is bent and amplified by the Abell 2744 galaxy cluster, a massive group of close-by galaxies that is situated behind JD1. The gravitational lensing effect makes JD1 appear 13 times brighter and larger than it actually is.

Even with Webb, gravitational lensing allowed astronomers to glimpse JD1. Our team was able to investigate the galaxy's structure in unprecedented detail and resolution thanks to the gravitational magnification of JD1 and fresh data from NIRCam, one more of Webb's near-infrared detectors.

This not only allows us to investigate the interiors of these early galaxies, but it also allows us to begin figuring out whether or not these galaxies were small, compact, and isolated sources, or whether they were merging and interacting with other neighboring galaxies. We can trace back to the fundamental elements that formed the cosmos and gave origin to our cosmic home by studying these galaxies.