What are the oldest stars in the universe?
Astronomers until now have only been able to theorize about what they believe is a distinctive category of stars that formed in the aftermath of the Big Bang.
Dr. Eli Visbal, an associate professor of astronomy, is a theorist who specializes in mathematical models of the early universe.
These Population III stars would be low in heavy elements that astronomers call metals, reflecting the unique hydrogen-and-helium environment in which they formed. And they’d be massive as a consequence of this distinctive chemistry.
The University of Toledo’s Dr. Eli Visbal believes he’s identified a cluster that fits these criteria and more using the James Webb Space Telescope. He and his collaborators recently published their findings, which break ground in suggesting the first direct detection of Population III stars, in the Astrophysical Journal Letters.
“It’s exciting,” said Visbal, an associate professor of astronomy. “We’ve been working on theoretical models of these stars for a long time, so to now be on the precipice of perhaps direct detections is very exciting.”
Visbal works out of UToledo’s Ritter Astrophysical Research Center, where faculty and student researchers routinely engage with some of the most advanced terrestrial observatories and space-based telescopes in the world. Visbal himself is a theorist who specializes in mathematical models of the early universe, including the Population III stars that are of interest to astronomers for several reasons beyond novelty.
“When we study Population III stars, we learn about the building blocks of our modern-day galaxies,” he said. “They can tell us about how the universe evolved.”
They can also offer key insights into the physical nature of dark matter, he added.
Population III stars are rare, however, and Visbal explained that the proverbial stars had to align in order for astronomers to see them in the galaxy they identify as LAP1-B.
One factor is the advanced capabilities of the James Webb Space Telescope, which launched as the latest and greatest in infrared astronomy in late 2021. The other is a phenomenon known as gravitational lensing.
“Where it happens to be situated, the light gets bent by gravity in such a way that it magnifies it like 100 times,” Visbal said. “LAP1-B would have ordinarily been impossible to see, even with the best telescopes, but we can see it because of this effect.”
Visbal and his colleagues — Ryan Hazlett, a doctoral student at UToledo, and Dr. Greg Bryan, an astronomy professor at Columbia University — weren’t looking for Population III stars when they came across LAP1-B, which at that point had already been observed by Webb. When they saw that a star cluster within the galaxy seemed to meet the criteria of Population III, they began to run simulations that predicted a Population III star cluster exactly where they found it.
Visbal is interested in building on this research to explore the transition between Population III and Population II stars, which formed later and contain more metals. Both are distinct from Population I stars like our sun.
He also anticipates more in-depth observations to follow on LAP1-B.
“Even in a case that this turns out to be some metal-enriched stars that aren’t Population III but are appearing similar, our calculations show that we should be able to detect some using Webb,” he said.
