Sigma Xi lecturer sheds light on planetary nebulae research

Karen Kwitter, a professor of astronomy at the College, gave the College’s annual Sigma Xi lecture last Thursday about her research in planetary nebulae. Fellow math and science professors were in attendance, and many students were present as well. Kwitter described her lecture as focused on the research “that I’ve spent my life doing.” She then added, “I hope at the end of the hour you’ll agree that it was worthwhile.”
Kwitter began by explaining the inner workings of stars and the process of nuclear fusion through which stars such as our own sun consume hydrogen at a core temperature of 15 million degrees Fahrenheit. This remarkable feat produces helium nuclei at a rate of approximately 1038 times per second. When all of the hydrogen at the core of the star has been consumed, the reactions stop and the star’s core will grow into a red giant. To put this into perspective, Kwitter noted that a red giant placed at the center of the sun would reach all the way into Earth’s orbit.
Kwitter mentioned that when discussing astronomy or even geology, it is important to remember that “a million years ain’t nothing.” All of the processes she explained take place over gross amounts of time.
Continuing with the life cycle, Kwitter explained that planetary nebulae are the most common pre-death stages of stars. Planetary nebulae are misnamed, as they have nothing to do with planets but can appear similar to very large planets through small telescopes. These objects are formed by the expanding glowing shell of ionized gases ejected by many stars in the late stages of their lives. They are a relatively short-lived phenomenon, lasting only a few tens of thousands of years. They can be studied through the use of spectroscopy, the spreading of light into its various colors, because planetary nebulae only emit light at specific characteristic wavelengths. This allows for the identification of the elements they contain. Analysis of the relative strengths of the emission lines can reveal the gas temperature and density as well as the composition.
Kwitter went on to describe her collaborative research in the field, which pertains to using planetary nebulae to study galactic chemical evolution. She uses radial abundance gradients within various galaxies to predict the amount of more highly enriched elements as you move closer to the center of the galaxy.
Kwitter also mentioned that several student researchers have been invaluable to her studies, including Emma Lehman ’10. Lehman traveled to the Gemini North Observatory last year and also attended the American Astronomical Society meeting in Seattle, where participants measured and discussed the oxygen gradient. A few years ago a team of students from the College and other peer institutions also developed computer software to analyze planetary nebulae data, and that software is now used across the country.
Future research in the field will work to improve the accuracy of the abundance gradients while finding out why sulfur is the only known element to behave differently than all others in this regard.
Kwitter ended the lecture inviting attendees to follow her research, adding jokingly that for those looking at planetary nebulae, “While you’re observing them, they’re observing you.”

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