Galaxy Formation in the early Universe was thought to be a chaotic series of collisions. Find out how a newly discovered disk galaxy calls that idea into question.
The Andromeda Galaxy is a fascinating object in our night sky. We can see it with the naked eye if we have good vision, and we can get to a place with no light pollution.
I have it down to an art in the backyard of the cottage in August. It’s right over a particular clump of trees. Once I’ve spotted it, I can quickly flip my binoculars into place and see its nebulous disk.
Andromeda is the nearest spiral galaxy to earth and the only one we can see without a telescope. It’s roughly 2.5 million light-years away and about 200,000 light-years across. It holds about a trillion stars.
Realized There Were Other Galaxies in the Last Century
We’ve only realized that there are other galaxies in the last century or so. It was a hotly debated topic back in the 1920s.
Before Edwin Hubble showed that Andromeda was too far away to be part of the Milky Way, people thought that our galaxy was the whole Universe. We now know that the Universe holds something like two trillion galaxies, each containing several hundred billion stars.
One of the most intriguing aspects of the Universe is galaxy formation. The Universe seems to have a mysterious self-organizing property. Something leads to the shape of the beautifully structured galaxies we observe, as well as the birth of individual stars from their molecular clouds.
When We Look Out Into Space, We Look Back Into Time
When we look out into space, we look back into time. Because of that, with powerful modern telescopes, astronomers have been able to study what galaxies were like shortly after the Big Bang.
Most of the ancient galaxies that they have found aren’t as picturesque as galaxies formed recently. They’re misshapen and lumpy. That led scientists to believe that early galaxy formation was the result of random collisions between smaller star clusters.
Astronomers don’t usually see symmetrical, organized galaxies like Andromeda or the Milky Way until about 6 billion years after the Big Bang. Most of astronomy’s current galaxy formation models are consistent with this idea, based on the assumption that early galaxies didn’t spin as contemporary ones do.
“Galaxies in the Early Universe Look Like Train Wrecks”
Marcel Neeleman of the Max Planck Institute for Astronomy explains it like this. “Most galaxies that we find early in the universe look like train wrecks because they underwent consistent and often ‘violent’ merging.”
The journal Nature published a research paper this week that challenges those galaxy formation models. The US National Radio Astronomy Observatory announced the discovery of a massive disk-shaped galaxy that existed just 1.5 billion years after the Big Bang.
It’s called the Wolfe Disk Galaxy in honour of astronomer Arthur M. Wolfe. Officially, its designation is Galaxy DLA0817g, and it’s the most distant, and therefore the oldest, disk galaxy ever discovered.
Most Distant and Oldest Disk Galaxy Ever Discovered
The Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescope made the discovery possible. Built-in 2003, it’s an array of 66 radio telescopes in the Chilean desert that together form an enormous astronomical interferometer.
Joe Pesce is the Astronomy Program Director at the National Science Foundation. He explained, “This observation epitomizes how our understanding of the universe is enhanced with the advanced sensitivity that ALMA brings to radio astronomy.” He went on to say, “ALMA allows us to make new, unexpected findings with almost every observation.”
The researchers came across the Wolfe Disk Galaxy indirectly. Professor Neeleman’s team was observing a quasar. They could see that a massive cloud of hydrogen gas was absorbing the quasar’s light.
Hydrogen Cloud Was the Telltale Sign of a Galaxy
The hydrogen cloud was the telltale sign of a galaxy. Astronomers call this approach the absorption method, and it allows them to identify fainter, and more regularly shaped galaxies.
According to Professor Neeleman, “The fact that we found the Wolfe Disk using this method, tells us that it belongs to the normal population of galaxies present at early times.” Galaxy formation seems to be a much more sophisticated process than a cosmic demolition derby.
J. Xavier Prochaska, of the University of California, Santa Cruz, is a co-author of the paper. He explained the galaxy formation process for the Wolfe Disk this way.
“Grown Primarily Through the Accretion of Cold Gas”
“We think the Wolfe Disk has grown primarily through the steady accretion of cold gas. Still, one of the questions that remains is how to assemble such a large gas mass while maintaining a relatively stable, rotating disk.”
The researchers went on to look at the formation of stars within the Wolfe Disk. For this, they used two other telescopes systems. The Karl G. Jansen Very Large Array (VLA) looked for molecular gas. At the same time, the Hubble Telescope observed massive stars in UV light.
Dr. Prochaska described their findings. “The star formation rate in the Wolfe Disk is at least ten times higher than in our own galaxy. It must be one of the most productive disk galaxies in the early Universe.”
“Most Productive Disk Galaxies in the Early Universe”
The team discovered another fascinating thing about the early galaxy. It was rotating, which contradicts the conventional wisdom about galaxies in the early Universe.
As Professor Neeleman explains, “When our newest observations with ALMA surprisingly showed that it is rotating, we realized that early rotating disk galaxies are not as rare as we thought and that there should be a lot more of them out there.”
Back in the 1920s, scientists inadvertently robbed humanity of our creation story. It’s mind-blowing to know that there are two trillion other galaxies out there.
Mind-Blowing to Know That There are Two Trillion Galaxies
Unfortunately, it also makes it harder to understand our place in the vastness of the cosmos. The next step for the researchers is to look for other examples of disk galaxy formation in the early Universe to determine just how common it was.
We always have more to learn if we dare to know.
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