Astronomers discover oldest disk galaxy ever hiding deep in the cosmos

Wolf slice

The Wolfe Disk is a massive rotating disk from the earliest days of the universe.

NRAO / AUI / NSF / S. Dagnello

How do you build a galaxy? This is a question that astronomers continue to ask themselves when formulating theories about how these gigantic systems full of dust, gas and stars come together. In search of answers, they turn their telescopes to the sky and look for distant galaxies that could help solve the puzzle.

In a new study published in the journal Nature on WednesdayAn international team of astronomers spotted light from an ancient, giant galactic disk lurking in a distant corner of the universe. It took about 12.5 billion years for the light to reach us on Earth, which means that the disk was formed about 1.5 billion years after the Big Bang – in the earliest days of the universe.

Using one of the most powerful telescopes in the world, the Atacama Large Millimeter / Submillimeter Array, the team found the galaxy when it examined bright light from a distant, huge black hole called a quasar. Part of the light was absorbed by the galaxy on its way to Earth, revealing that it was hiding in the darkness of space. By examining the galaxy with ALMA and using Hubble data, the team was able to more clearly resolve some of its features.

“Previous studies indicated the existence of these early rotating, gas-rich disk galaxies,” said Marcel Neeleman, astronomer at the Max Planck Institute for Astronomy and lead author of the study. “Thanks to ALMA, we now have clear evidence that they occur 1.5 billion years after the Big Bang.”

Officially, they named the galaxy DLA0817g, but they nicknamed them “Wolfe Disk” in honor of the astronomer Arthur M. Wolfe.

The team compared their observations to analytical models and put together a case for what happened in the galaxy. They found their models most precisely aligned with a galaxy made of a dusty, gaseous disk that rotates at a speed of approximately 272 kilometers per second, with an estimated mass that is about 50 to 100 times higher than that of the sun. It also appears to form stars exceptionally quickly.

“It must be one of the most productive disk galaxies in the early universe,” said Xavier Prochaska, an astronomer at the University of California at Santa Cruz and co-author of the study.


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The discovery provides some clues as to how galaxies are constructed and why we so often see structures that resemble giant disks while others don’t.

“If we find out when slices appear in the comic story within the galaxy population, we can report on the mechanisms by which galaxies grew and formed in the early universe,” said Alfred Tiley, astrophysicist at the University of Western Australia and Author of a companion article about discovery in nature Wednesday.

The current understanding of galaxy formation suggests that giant invisible spheres of dark matter in the cosmos are a kind of skeleton, into which gas and dust can fall and eventually form stars and entire galaxies. Across eons, the incoming hot gas and dust create huge disks that we see in galaxies scattered throughout the cosmos. Other galaxies collide, a common phenomenon in the early universe where all gases, dust, stars and galaxies are somewhat closer together.

But these models suggest that you wouldn’t see galactic disks at such an early stage after the Big Bang. The team suggests that the immense Wolfe Disk was discovered from such an early date because it was built in a different way – by cold gas.

Earlier theories assumed that these types of cold gas disks should only appear around 3 billion years after the Big Bang. The new analysis shifts this time frame by another 1.5 billion years.

However, Tiley notes that there are other possible explanations for creating the hard drive. To prove this, however, further observations of DLA0817g are required.

“One possible explanation is that the gas disk observed is the result of a merging event between one or more galaxies that could have directed cold gas into the center of the resulting halo,” he says. “But the authors argue that the cold accretion scenario is more likely.”

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