If you’ve ever been to a place with minimal light pollution and looked skywards at nighttime, you’ve probably seen our Milky Way galaxy. It manifests as a thick, hazy band of stars streaking across the sky.
“I like to think of the countless generations of our ancestors that looked up at the night sky and probably wondered, ‘Where did it come from? How old is it? Did it always look like this or did it look different in the past?’” said , a professor in the Department of Physics and Astronomy at the College of Letters and Science at 51ԹϺ Davis.
Our ancestors across the globe had many names for the Milky Way. Winter Street, Silver River, Spirit Road, to name just a few. The Romans called it Via Lactea and said it was formed when Hercules was flung from the breast of his mother Hera, resulting in spilled milk.
Wetzel, who was presenting to a packed room at the Feb. 20 event at , said that while our ancestors’ mythologies aren’t physically correct, the idea behind their stories is. Namely, the idea that out of chaos comes order.
How scientists study galaxy formation
Wetzel is a theoretical astrophysicist who ponders and models galaxy formation. Unlike the academics of yesteryear, the work isn’t all equations written in chalk on a blackboard. These days, it’s highly computational.
He translates the laws of physics into computer algorithms. He then uploads those algorithms to the world’s most powerful supercomputers, like the at NASA’s , and generates computer simulations that model galaxy formation.
The theoretical research circumvents an observational problem. Specifically, our limited view of the universe.
“We have images, snapshots and times of these individual galaxies, but it’s not enough to understand how they evolve,” Wetzel said.
“Galaxies form and evolve across the full 13.8 billion years of history of the universe,” he added. “It can take a galaxy a billion years to change appreciably.”
And that’s where Wetzel’s theoretical work comes into play. His advanced supercomputer simulations, which can take on the order of a few million to 100 million CPU hours to run, are revealing the lifecycle of galaxies like our Milky Way.
How scientists study galaxy formation
Wetzel is a theoretical astrophysicist who ponders and models galaxy formation. Unlike the academics of yesteryear, the work isn’t all equations written in chalk on a blackboard. These days, it’s highly computational.
He translates the laws of physics into computer algorithms. He then uploads those algorithms to the world’s most powerful supercomputers, like the at NASA’s , and generates computer simulations that model galaxy formation.
The theoretical research circumvents an observational problem. Specifically, our limited view of the universe.
“We have images, snapshots and times of these individual galaxies, but it’s not enough to understand how they evolve,” Wetzel said.
“Galaxies form and evolve across the full 13.8 billion years of history of the universe,” he added. “It can take a galaxy a billion years to change appreciably.”
And that’s where Wetzel’s theoretical work comes into play. His advanced supercomputer simulations, which can take on the order of a few million to 100 million CPU hours to run, are revealing the lifecycle of galaxies such as the Milky Way simulations.
At first, the simulation shows tendrils of hydrogen gas coalescing in a gravitational dance. “We sometimes say that galaxies form hierarchically. First little bits form and then gravity pulls them together to get bigger and bigger over time, but it’s quite chaotic,” Wetzel said. “Think about a bunch of cars entering an intersection from random directions all at the same time.”
Eventually, the hydrogen gas collapses and forms stars, which live out their lives and end in brilliant supernovae that push the hydrogen gas back out, becoming fodder for young stars. The process is a feedback loop.
“The early history of our Milky Way is marked by a lot of chaos,” Wetzel said. “However, as many billions of years go on, something remarkable happens. The Milky Way transitions from being chaotic to being ordered.”
This “order” is characterized by increasing inactivity, with the rate of star formation, supernovae and hydrogen gas feeding those processes all falling.
“This allowed the Milky Way to settle into a nice, stable, long-lived disk that we see today,” Wetzel said. “Out of chaos comes order.”
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Greg Watry, College of Letters and Science, gdwatry@ucdavis.edu