Astrophysicists to wield James Webb Space Telescope in three new supernova studies
Nearby explosions of dying stars present now-or-never opportunities for observations by physics’ Chris Ashall and his lab.
Assistant Professor Chris Ashall of the Virginia Tech Department of Physics. Photo by Hunter Gresham for Virginia Tech.
In May, a newly visible supernova dotted one of the spiral arms of Messier 101, also known as the Pinwheel Galaxy.
Dubbed SN 2023ixf by NASA, it’s the closest supernova spotted in five years. An explosion of a dying star, the supernova was visible through amateur telescopes and had both hobbyist astronomers and experts abuzz over catching a glimpse, sharing tips for getting it in sight, and taking long-exposure photographs.
This kind of dying star — a massive, hydrogen-rich, core-collapse supernova — goes off in Messier 101 once in 100 to 200 years, said Chris Ashall, assistant professor of astrophysics in the Department of Physics, part of the Virginia Tech College of Science. For his research group, the chance to study such a rare, nearby, and young supernova over the course of the James Webb Space Telescope’s lifespan, recently projected to last up to 20 years, was irresistible.
“If we don’t observe this now, we may not have the ability within our lifetime to understand how supernovae produce dust unless they build a James Webb 2.0,” Ashall said. “Humankind would have to wait a long time for another chance.”
Ashall submitted a proposal for off-cycle use of the telescope to NASA, known as director’s discretionary time, to begin collecting spectroscopic data on heavy elements inside the supernova. It’s one of three new projects focused on tracing heavy elements — the material produced by exploding dying stars and the building blocks for all life in our universe — back to supernovae. These breadcrumbs left behind by dying stars may hold answers to life’s origins.
The team also had two other projects recently selected by NASA for the James Webb Space Telescope’s second cycle of observations. For those, Ashall’s team will point the telescope at the explosion of a uniquely massive, young star called a stripped-envelope supernova as well as that of a white dwarf star the team began observing during the telescope's first cycle.
These projects will collect data throughout the telescope’s second and third cycles, guaranteeing Ashall’s team time with the James Webb Space Telescope for the next two years. It’s rare for a single team to have this much time with the telescope, he said. In the second cycle alone, NASA received more than 1,600 submissions from scientists in 52 countries. About one in seven submissions were accepted to grab a slice of the telescope’s observation hours.
Spectroscopy
Ashall’s team specializes in mid-infrared study of supernovae. Inside the hot, high-density setting of these dying stars, nuclear fusion takes place. The material in stars burns to form heavier and heavier elements, going from hydrogen to helium and on to heavier elements in the Periodic Table such as iron. As dying stars explode, they eject these elements into the universe.
Ashall’s team will look into the stars for spectral lines given off by heavy elements. Spectroscopy involves studying spectra — bands of color produced by material as it interacts with or emits light — by breaking the light into its component colors, per NASA. These fixed spectral lines confirm the element’s presence, like imprints. Some of the most interesting elements are detectable in the mid-infrared light wavelength, Ashall said, which only the James Webb Space Telescope is set up to capture.
Ashall’s team is already getting data back from the telescope’s observations of SN 2023ixf in the Messier 101 galaxy. Its members will use this data as baseline measurements. “We needed to look at the supernova right away to see if it already had any molecules or dust nearby,” Ashall said. “Based on the data we’ve received, there’s no dust, no molecules yet. When we collect data from the star at the end of the year, if we see molecules, we’ll know the supernova made them.”
Along with the study of SN 2023ixf, team members will collect data on another massive supernova nearby: a stripped-envelope supernova. Stripped stars have burned off their hydrogen and helium, and they tend to be much greater in mass than a star like our sun, which still holds those elements. They’re on the young side as well, which means they were around at the beginning of the universe, Ashall said.
“One of the things we’re trying to understand is how dust, molecules, and complex organisms were made at the beginning of the universe,” Ashall said. “Studying the explosion of the most massive and youngest stars we can is going to tell us more about that. Because these stars have more carbon and oxygen, they can make more dust, molecules, and the complex organisms needed for life.”
Artist’s illustration of the James Webb Space Telescope. NASA Godard Space Flight Center / Conceptual Image Laboratory. Image by Adriana Manrique Gutierre/NASA.
Dwarf star
Ashall’s team also is building on the work it did in the first cycle of the James Webb Space Telescope’s observations. One of its two projects in that cycle involved studying a dying white dwarf star, a type 1a supernova, which explodes after stealing matter from a companion star, per NASA. James DerKacy, a postdoctoral researcher in Ashall’s group, will lead a project to extend observation of the type 1a supernova from 400 days post-explosion to 1,000 days.
Venturing into these later phases of the explosion will allow the researchers to see farther into the “heart” of the supernova, Ashall said, revealing more heavy elements in new areas of the explosion.
“This data is groundbreaking,” said James DerKacy, a postdoctoral researcher in Ashall’s lab. “Astronomers haven’t looked this deep into a type 1a supernova before. The elements we’ll detect directly correlate with the properties of the white dwarf when it exploded, which is a major unanswered question for astronomers.”
On these projects, Ashall’s team is working closely with collaborators from Florida State University, the Planetary Science Institute, and the Space Telescope Institute, which houses both the James Webb Space Telescope (JWST) and the Hubble Telescope. These researchers work with Ashall’s team as part of the Mid-Infrared Supernova Collaboration.
“We have a close-knit group that goes all the way from exploding a star on a computer to people who really use the telescope,” Ashall said. “In my opinion, our edge is that we add more physical insight to the data than other groups. Over the coming years, we are excited to help push Virginia Tech to the forefront of space-based astrophysics and JWST research.”
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