Using the James Webb Space Telescope to study supernovae as a source of heavy elements in the Universe

In the popular 1980 book “Cosmos,” Carl Sagan wrote of what makes us: “All the elements of the earth except hydrogen and some helium were cooked into stars by some sort of stellar alchemy billions of years ago, some of which are now nondescript whites.” Dwarfs on the other side of the Milky Way. The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made inside collapsing stars. We are made of “star stuff; star stuff; star stuff.'”

Chris Ashall, assistant professor of astrophysics in the physics department at Virginia Tech College of Science, wants to learn more about where and how this “star stuff” is made.

This week, Ashall began using NASA’s James Webb Space Telescope to collect data on the presence of heavy elements in exploding dying stars, or supernovae. While James Webb’s Baltimore-based Mission Operations Center relays commands to the distant telescope to collect observations of supernovae targeted by Ashall, his team at Virginia Tech, along with more than 30 other scientists from around the world, will use the collected data around the world as part of the Mid-Infrared Supernova Collaboration that Ashall leads.

Ashall is one of the few scientists selected to use the telescope for two projects during the mission’s first cycle. The projects will study two types of supernovae: Type Ia supernovae, which describe exploding carbon-oxygen white dwarf stars, and core-collapse supernovae.

“Pretty much everything around us comes from dying stars,” Ashall said. “We are made of stardust. Studying in detail this fact – what we are made of – and understanding where the elements around us come from is truly amazing.”

Stars produce heavy elements through the process of stellar nucleosynthesis. When stars burn, die, and explode, thermonuclear reactions take place within them.

Supernovae are one of the hottest and most dense places in the universe, Ashall said. The material in stars burns and burns to form heavier and heavier elements, from hydrogen to helium, helium to carbon, carbon to oxygen, and so on, all the way through the periodic table to iron.

When the stars eventually explode, they fling all that material back out into the universe at speeds up to 30 percent the speed of light to create the next generation of stars and planets. “So the planet and everything around us can have all these heavy elements,” Ashall said. “They were made in dying stars.”

It’s widely accepted that most of the heavy elements in the Universe are made by stellar nucleosynthesis, but Ashall wants to know more — to trace specific elements back to the different types of supernovae out there, and to measure at what levels those elements are made by stellar nucleosynthesis become stars.

In his first project, Ashall will search for elements commonly found on Earth, such as manganese, chromium, cobalt and nickel, by focusing the James Webb telescope specifically on an Ia supernova: a third-generation white dwarf with the Named SN2021aefx, it exploded a year ago in spiral galaxy NGC1566, also known as the Spanish Dancer.

“A year after it exploded, you can see right down to the center of the supernova,” Ashall said. “That’s where all this high-density burning happens. Nucleosynthesis takes place in just a few seconds, but we see the high-density central region a year after the explosion.”

Ashall will use the telescope to collect imaging and spectroscopy data of elements within SN2021aefx. Spectroscopy involves looking at spectra produced by material when it interacts with or emits light by breaking the light down into its component colors, according to NASA. “The spectroscopy tells us something about different elemental lines,” Ashall said. “If there is a line, we know the element is there.”

NASA’s new telescope is the first capable of collecting the kind of data Ashall needs. James Webb can observe wavelength regimes that Hubble simply couldn’t, Ashall said.

“Hubble could observe mostly in the ultraviolet, optical and a little bit in the near-infrared, but James Webb was tricked into observing in the near-infrared and mid-infrared,” he said. “It opens a whole new wavelength window for astrophysics.”

Ashall’s second project focuses on detecting carbon monoxide and silicon monoxide, also building blocks for life in the Universe, in core-collapse supernovae. Core-collapse supernovae are massive dying stars more than eight times the mass of our Sun. The supernova’s name comes from the type of explosion that occurs, Ashall said: When the massive star dies, it collapses in on itself, triggering an explosion more than 100 billion times brighter than the Sun.

Using observations from the James Webb Space Telescope, Ashall will work to not only find heavy elements, but also to study when they were ejected from the exploding supernova. His team will study how supernovae explode by coupling the data with computer simulations of explosions.

“By measuring these lines, we can determine the velocities of the explosion,” Ashall said. “So then we understand how fast these elements are being thrown out into the universe.”

Starting with the single Type Ia supernova, Ashall hopes to sample different types of supernovae to produce meaningful statistics about their role as element producers. He’s open to whatever they find.

“If we don’t find these elements that come from supernovae, we will have to reassess our knowledge of how stars die and how these elements are released into the universe,” Ashall said. “It’s interesting either way.”