Astronomers have discovered a galaxy so large and so old that it should not exist, at least based on our current understanding of how the first galaxies formed.
The galaxy, named ZF-UDS-7329, contains more stars than the Milky Way and appears to have formed about 13 billion years ago.
It was detected with NASA’s James Webb Space Telescope (JWST), a tool built to observe these types of ancient galaxies and go back to the early ages of the universe.
What is notable about this is that a galaxy this large should not have been able to form so early in the universe because dark matter did not yet exist, meaning that a galaxy this size should not have been supported 800 million years after the Big Bang. .
Astronomers could not clearly see the galaxy ZF-UDS-7329 before the launch of the James Webb Space Telescope. Now you can see that it was formed about 13 billion years ago.
Dr Themiya Nanayakkara, who led the spectral analysis of the JWST data, said: “We are now going beyond what is possible to confirm the oldest massive dormant monsters that exist deep in the universe.
‘This pushes the limits of our current understanding of how galaxies form and evolve.
“The key question now is how they form so quickly and at such an early stage in the universe, and what mysterious mechanisms lead to preventing stars from forming abruptly when the rest of the universe does.”
Our universe is about 13.8 billion years old, which means that ZF-UDS-7329 formed when the universe was in its infancy, about 800 million years ago.
Astronomers have long thought that dark matter is essential for a galaxy to grow.
The halos of this mysterious substance, they say, formed the seed that supports the center of a galaxy and allows it to accumulate stars.
There’s only one problem with ZF-UDS-7329: according to today’s astronomers, dark matter didn’t exist then, at least not in sufficient quantities to support such a massive galaxy.
However, this galaxy exists.
This points to “significant gaps in our understanding” of how the first stars and galaxies formed, the scientists behind the discovery wrote.
The article describing the galaxy was published in the magazine Nature.
Due to the time it takes for light to travel through the vastness of space, when they reach Earth, they are displaced.
Astronomers have developed techniques to detect how big this change is, allowing them to determine that the image captured by JWST is probably about 11.5 billion years old.
Its stars probably formed about 1.5 billion years earlier, the researchers wrote, meaning the galaxy is about 13 billion years old.
Scientists had been trying to get a clear image of this galaxy for seven years, but it was so distant and so faint that even the largest telescopes on Earth couldn’t get a clear enough image to measure its age.
With the JWST, they were finally able to do it.
A close-up image of ZF-UDS-7329 shows its enormous size. The scale bar indicates 2 kiloparsecs, or 6,530 light years.
“Galaxy formation depends largely on how dark matter is concentrated,” study co-author Claudia Lagos, an associate professor of astronomy at the University of Western Australia, said in a paper. statement.
The way galaxies form is a fundamental area of study in astronomy.
And while it’s difficult to say with absolute certainty what the early universe was like, modern astrophysicists have built numerous models that use current data to make predictions about it.
One of these predictions, which astronomers tend to agree on, is that there were fewer and fewer supermassive galaxies the farther back you go in time.
These new observations of ZF-UDS-7329, if accurate, call these models into question.
“Having these extremely massive galaxies at such an early stage in the Universe poses significant challenges to our standard model of cosmology,” Lagos said. «This is because we do not believe that dark matter structures as massive as those that host these massive galaxies have not yet had time to form.
“More observations are needed to understand how common these galaxies may be and help us understand how massive they really are.”
The team’s next steps will be to find more galaxies like this one, confirm the finding and find answers about how it could have happened.