An IU professor provides insight into the evolution of stars

As scientists’ understanding of the origins of the universe expands, IU Associate Professor Constantine Dilianis is working to explain inconsistencies with current models of star evolution in new research.

Most astronomers today say that our universe emerged in a violent explosion known as the Big Bang, about 13.8 billion years ago. The whole universe was once crammed into a very small region, Dilianis said, and then it suddenly expanded to the size of a galaxy in a split second.

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As the universe continued to expand and cool, protons and neutrons began to coalesce into nuclei, which formed the first atoms of hydrogen, helium, and trace amounts of lithium. As the universe expanded further, gravity pulled these elements closer to the first stars, and eventually galaxies.

“Gravity is what makes things pull together,” said Mike Berger, a professor of physics at the University of Iyo. “In the beginning of the universe, all things had about the same density, but as the universe grew, places with higher densities attracted more matter until larger structures formed.”

Professor Deliyaannis’ research mainly focuses on lithium levels in the upper atmosphere of stars. Throughout his career, he found that there were significant discrepancies between lithium levels expected to be present in stars from the Big Bang, and what was actually observed in them.

Delianis said that by using heliographs, the study of sound waves produced by the sun, astronomers have found that standard solar models have described the sun’s internal structures with great accuracy. However, lithium levels are off.

“This standard model of solar evolution predicts that the Sun’s current lithium abundance should be about one-third of what it started with,” Delianis said. “However, this is actually about 0.7%, which is a huge discrepancy, even in astronomy.”

The rotation of the stars must also be taken into account, Dilianis said. As stars age, they rotate, but they do not rotate uniformly. Because of angular momentum, the outer layers of stars tend to decelerate faster than the inner layers. This difference in rotation between the layers of the star creates shear, which eventually causes mixing between the layers, which explains the lithium paradox.

Once astronomers understand and accurately model these discrepancies, Delianis said, they will be able to carry their knowledge down to the first generation of stars, and they will be able to determine how much lithium was formed in the Big Bang.

“If we can work out how much lithium those stars formed with, that really provides a good test of the big bang theory,” Dilianis said.

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Deliyannis uses multiple telescopes to conduct his research, including the WIYN 3.5-meter telescope at Kitt Peak in Arizona. Using spectroscopy, which involves sending light from a star’s atmosphere through prisms to detect traces of the elements, Deliyannis can find precise measurements of lithium in stars.

When light is sent through the prisms, the elements reveal themselves as dark spots in the rainbow spectrum of visible light. By measuring these dark spots, astronomers can determine the amounts of certain elements in a sample of light, said Vinicius Plaku, an associate astronomer at the National Optical and Infrared Astronomy Research Laboratory.

“You’ll see colors go from violet to blue, then to red, and infrared,” Blackow said. “All these discontinuities, those are the imprints of chemical elements in the stars’ atmospheres.”

Through this method, astronomers like Deliyanis can explain inconsistencies in current theories about how the universe came to be the way it does, leading to confirmation of existing theories or perhaps inviting further investigation.

“What we’re trying to do is explain how the universe evolved chemically,” Blackow said. “I think it’s important in the sense that you can discover where we come from.”

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