Capturing the Origin of Young Stars

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Have you ever looked at the dark night sky and been fascinated by the twinkling stars? Or have you ever been taken aback by the fact that you could see light traveling across time and space? Throughout history, stars and the sky have long served as sources of inspiration for imagination and inquiry.  

Sarah Betti, a Ph.D. candidate in Astronomy at UMass Amherst, is one of the scientists whose ambitions include unraveling the mysteries of the universe, particularly the formation of young stars.  

Her academic journey to Astronomy began in high school when she took an Astronomy class. Using telescopes at local astronomy clubs, Betti observed stars and planets in our solar system, including Mars and Saturn. Her first encounter with deep space inspired her to pursue graduate studies in astronomy.  

In doing so, the Five College Astronomy Consortium, which is a collaborative program of the Astronomy Departments of Amherst College, Hampshire College, Mount Holyoke College, Smith College, and the University of Massachusetts Amherst, provided Betti with diverse opportunities to work with the research community beyond the boundaries of UMass.  

Due to the collaborative program, Betti was able to study and research with Professor Kate Follette of Amherst College, who specializes in the techniques Betti desired to learn, such as observing and visualizing the surroundings of young stars using large ground-based telescopes. 

Betti developed her interest in stars and planet formation while assisting with observation runs with Professor Follette on the Gemini Planet Imager Exoplanet Survey (GPI) project, which produced images of exoplanets orbiting stars using the Gemini South Telescope in Chile. She also worked as a teaching assistant for the AST 337 and 341 observational astronomy courses, where she helped students take and analyze data of young variable brown dwarfs on the Kitt Peak WIYN 0.9 m telescope in Arizona. 

The research experience helped hone her ability to study an early stage of the formation and evolution of stars and planets—known as accretion. A solar system begins to form when a molecular cloud of gas and dust collapses, making a star surrounded by a disk. The newly-formed stars grow by gradually accumulating materials from the surrounding disk.  

Betti has worked on unraveling the mysteries of how environments surrounding stars and planets, particularly the location of icy dust grains in the circumstellar disks, affect the accretion process, and eventually formed stars.  

The set of images above is a snapshot of her efforts to depict the early stages of accretion, displaying icy dust grains in the circumstellar disk around the newborn star, AB Aurigae. The major component in determining what materials are within the circumstellar disk is to detect water ice (H20) in the disk.  

Contrary to popular belief, you cannot observe the materials by simply looking through a telescope lens. Instead, the visualization process requires several steps of scientific analysis: collecting raw data from telescopes and converting it into a final image.  

Because the star is so bright and large, the raw images taken from ground-based telescopes show only white little dots of stars. The disk appears too faint to be seen around the bright star. Therefore, Betti removes the starlight from the image, which is noise for the final product. This process is called data reduction.  

Then, she combines hundreds of similar images to increase the near-infrared signal and decrease the noise in the final image. This process is called the process of stacking.  

Finally, to extract and produce a final image of the actual disk as above, she takes another image of a star that does not have a disk and 'subtracts’ it from the stacked image (an image of a star with a disk minus an image of a star without a disk equals only a disk!!). This is a technique called reference differential imaging.  

There can be several dozen different images, as shown by the ten images above, because she can change parameters depending on the algorithms used. When a good algorithm is used, she can finally obtain the best image, such as the central one shown above, which vividly displays the bright disk.  

The process of producing an image is never simple and often takes several weeks to months, necessitating a broad range of scientific knowledge in astronomy, astrophysics, and computer science. However, Betti never finds it to be at all daunting. Rather, she enjoys the weeks-long journey where she can immerse herself in research into how planets form and grow, as well as what they are made of.   

“Astronomy is a way for people to wonder and marvel at something beyond our comprehension. It is fascinating that, with these beautiful images from a distance, we can probe a fundamental question about our existence, like where we came from. " 

During the pandemic, significant delays in collecting data and installing new instruments were quite common because most trips to observatories were halted, and there were frequently no operators to turn telescopes on and get them working. The unexpected emergency, however, could not deter her. Rather, she focused on continuing her research using the data she had gathered previously.  

This year, Betti won the NASA FINESST (Future Investigator in NASA Earth and Space Science and Technology) grant, which will fund her last year of graduate school. With the substantial grant, her passion and efforts to unravel the accretion onto young low-mass stars, brown dwarfs, and planets are expected to flourish as she nears the end of her Ph.D. program. 

Written by Jaeye Baek, PhD student in Political Science, as part of the Graduate School's Public Writing Fellows Program.