doi.org/10.3847/2041-8213/ae1608
Credibility: 989
#galaxy
The Universe has been constantly evolving for billions of years. Thanks to the expansion of space, we can look back in time and observe almost from its beginning how everything happened.
Occasionally, however, something appears that doesn’t fit the theories we already have.
That’s exactly what happened with a galaxy discovered by a team led by doctoral student Sijia Cai from Tsinghua University in China.
They found a galaxy that formed about 11 billion years ago and appears to be completely “metal-free.” This means it may harbor the first generation of stars that existed in the Universe, the so-called Population III stars.
What are Population III stars?
Population III stars are considered the first stars that emerged shortly after the Big Bang.
They were made almost exclusively of hydrogen and helium – the lightest elements created at the very beginning of the Universe.
All the heavier elements (which astronomers call “metals,” such as oxygen, carbon, and iron) are only produced inside stars or in supernova explosions.
Therefore, the first stars couldn’t have contained any metals.
Scientists have been searching for these stars for decades, but had never found any with certainty.
The most obvious place to look would be during the Epoch of Reionization, a period that occurred up to 1 billion years after the Big Bang, when the Universe was still very young and the first stars were beginning to form.
A surprise 2 billion years later
What left researchers speechless was that this galaxy appeared well after that time – about 2 billion years later.
By then, many stars had already been born, lived, and died, scattering metals throughout the surrounding space.
Any cloud of gas that would form new stars should already be “contaminated” by these metals.
At least that’s what the theory predicted.
But, using data from the James Webb Space Telescope (James Webb), the Very Large Telescope (VLT), and the Subaru Telescope, the team identified a galaxy named MPG-CR3 (or simply CR3).
The spectrum of this galaxy is unique: very clean lines of hydrogen and helium and almost no presence of heavier elements, such as oxygen.
The maximum amount of metals in the stars of this galaxy is only 0.7% of the amount we have in the Sun.
Furthermore, the galaxy appears to be only 2 million years old – it’s a baby in cosmic terms! We can see it so young because the light that reaches us left it 11 billion years ago; the expansion of space causes us to look into the distant past.
CR3 also has little dust and relatively small stars, something rare for the time in which it existed, known as “Cosmic Noon,” when most galaxies contained gigantic stars.
One detail that’s still missing
To confirm that we are indeed seeing Population III stars, scientists would like to detect a specific line in the spectrum: the emission line of ionized helium (He II).
It usually appears when these primitive stars are shining brightly.
Unfortunately, this line was not seen in the VLT data.
The authors explain that there may be two reasons: either another strong line (of OH molecules) is masking the signal, or the brightness of He II has already decreased, as it weakens rapidly a few million years after the birth of the stars.
How did this galaxy escape “contamination”?
The most likely explanation is isolation.
CR3 is in a nearly empty region of space, called the “underdensified region.” When the gas cloud that gave rise to this galaxy finally collapsed and began to form stars, the metals produced by neighboring stars had not yet reached it.
It was alone, far from everything, and managed to create its own first generation of stars billions of years later than we expected.
Why is this so important?
If it is confirmed that CR3 actually contains Population III stars, it will be the first time we have found such a galaxy.
And the best part: it is much “closer” (in terms of cosmic time) than we imagined.
This would make these mysterious stars much easier to study with current telescopes.
More data still needs to be collected, especially to definitively confirm or explain the absence of the He II line.
But, if everything is confirmed, astronomers will spend a lot of time looking at this galaxy that is, at the same time, incredibly young and incredibly old – a true hidden treasure of the early Universe.
Published in 11/21/2025 12h38
Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.
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