To uncover how massive stars form, recent University of Arizona graduate Jenny Calahan, spent the majority of her undergraduate weekends looking through the 12-meter radio telescope on Kitt Peak, 50 miles southwest of Tucson.
After three years of data collection and analysis, Calahan’s work was published in Astrophysical Journal in July.
Stars at least eight times more massive than the sun “are still kind of a mystery,” Calahan said. “There are a lot of open questions about the way those stars can form. We know it probably happens really fast compared to normal star formation, so it’s really hard to catch.”
Calahan started this research her sophomore year when she was looking for an interesting endeavour to pursue . By chance, her academic adviser, Yancy Shirley, associate professor in the UA’s astronomy department, was looking for a student to work on his star formation project.
Brian Svoboda, who was a graduate student under Shirley at the time of the project and has since graduated, helped Calahan with the research, along with students from the UA’s astronomy club.
Their research explored one of two current theories about how massive stars form: That many small star cores form in huge gas clouds, pulling in more material and forcing the gas to collapse inward until they form a massive star.
Not much work has been done on this topic, so the goal was to find gas clouds that showed signs of collapsing gas, known as inflow. Out of 100 clouds of gas and dust the project examined, only six showed signs of collapse.
“It seems like it can’t be common on the very large scale of the clumps, because we only saw it on six out of 100,” Svoboda said.
The way Calahan did the research, via a random selection of gas clouds, sets her research apart from other studies on the subject.
“A blind survey allows us to have a large data set of random candidates, so our result we can then extrapolate to the wider galaxy itself,” Calahan said. “We can then say that only around 6 percent of all clumps like this in our galaxy are undergoing star formation or look like they’re undergoing star formation.”
The impact of this research is far-reaching. Calahan called star formation the most important process in all of astronomy.
“Star formation affects what types of stars are born, and the exoplanets, and protostellar disks, and astrochemistry, and even reaches to galactic scales,” Calahan said. “We classify galaxies based on how many stars they’re forming. They’re either dead or really young and active, all because of star formation.”
Calahan spent most of a year making observations. It took about one semester each to analyze the data, come up with conclusions and write the paper, she says. But the analysis felt like it took longer.
“I was young, I was into astronomy, I was like ‘yeah, let’s go to the telescope every weekend, I’m into it.’ It was amazing, but I feel like every scientist gets bogged down with the data analysis afterward,” Calahan said.
Svoboda provided background data and helped fit models to the information.
Calahan has been accepted to the University of Michigan’s astronomy doctoral program and will focus on a later stage of star formation. She said her research experience at the UA gave her a leg up in the field.
“Now that I’ve met people that are my age with similar goals who go to different institutions around America and around the world, the UA really has super unique opportunities, and I super appreciate that,” Calahan said. “I want students to take advantage of them, because they’re world-class.”
