January 16, 2023 - Podcast

Episode 337 — Understanding the stars and the Big Bang

New research by Indiana University astronomer Constantine Deliyannis provides new insights into the composition of the most common stars in the universe and may offer clues as to how the Big Bang occurred.  

Deliyannis' research looks at stellar interiors and stellar evolution. He observes stars' surface abundances of lithium, beryllium, and boron, which is crucial to our understanding the relative importance of a variety of physical processes that could be occurring inside stars. These fragile elements survive only in the outermost layers of stars, and so their surface abundances trace interior processes that connect to the surface. 

The abundances of these elements also have implications for other areas of astronomy, such as galactic chemical evolution and cosmology. According to Deliyannis, a fraction of the lithium in the universe today was made during the first several minutes of the Big Bang and was subsequently incorporated into the first generations of stars. So, to learn how much lithium was made during the Big Bang and thus test the Big Bang theory, scientists need to account for what has happened to the surface lithium of the oldest stars since they formed.  

The sun, Deliyannis says, has 0.7 percent of the lithium that it formed with. Nearby sun-like stars, which comprise approximately 90 percent of the stars in the universe, also contain amounts of lithium well below astronomers' standard predictions. These otherwise well-behaved stars have lost much more lithium than standard theory predicts.  

In his research Deliyannis uses the abundances of lithium, beryllium, and boron to test the various mechanisms mentioned above, using both stars in the field and stars belonging to star clusters. Star clusters are especially useful because their ages are known, and stars within a given cluster formed together so they all have the same age. Observations of lithium in many stars in a single cluster provide information about how the lithium abundance depends on stellar mass and studying clusters of different ages and compositions informs Deliyannis about how the lithium abundances changes and how the changes depend on composition. 

Deliyannis' research requires observations of at least dozens of stars in each cluster. He utilizes a high performing telescope, such as the WIYN telescope of which IU owns a fraction, to record the spectrum of each individual star. His analysis of the spectra then provides insight into the lithium abundance as well as other information about the stars.  

This research tells us that the loss of lithium is mostly due to the way stars gradually spin down, rotating more and more slowly as they age, and the specific ways in which this process causes mixing in the stellar interior and destruction of lithium. Knowing just how fast the lithium disappears helps astronomers understand how the related instabilities that instability affects the stars’ interiors.