Researchers have assisted in peering inside a nova (a type of astronomical nuclear explosion) without leaving Earth. These star events contribute to the formation of the universe’s chemical elements, and astronomers have investigated their nature using an intense isotope beam and a specialized experimental instrument with unprecedented sensitivity.
Michigan State University researchers have assisted in peering inside a nova (a sort of astronomical nuclear explosion) without leaving Earth. These stellar events help construct the universe’s chemical elements, and Spartans helped probe their nature at the National Superconducting Cyclotron Laboratory, or NSCL, with a powerful isotope beam and a specialized experimental apparatus with record-breaking sensitivity. The team’s findings were published in the journal Physical Review Letters.
“We’ve been working on this project for almost five years, so it’s incredibly wonderful to see this publication come out,” said Christopher Wrede, a physics professor at MSU’s Department of Physics and Astronomy and the Facility for Rare Isotope Beams. The multinational research initiative was led by Wrede, an MSU/FRIB faculty member.
For decades, NSCL was a National Science Foundation site that served the scientific community. FRIB, a user facility of the US Department of Energy Office of Science, became live on May 2. Now, FRIB will usher in a new era of experimentation that will allow scientists like Wrede to better test and validate their theories about the universe.
This agreement helps solidify theories underlying the nuclear physics of novae, which is saying something. Our understanding of novae has come a long way since people first observed them hundreds of years ago — a fact exemplified by the name nova itself, which means “new.”
“A long time ago, if something in the sky popped out of nowhere, you can imagine people thinking ‘Wait a minute. What the heck is that?'” Wrede said. “‘It must be a star that wasn’t there before.'”
We’ve been working on this project for almost five years, so it’s incredibly wonderful to see this publication come out. Our understanding of novae has come a long way since people first observed them hundreds of years ago — a fact exemplified by the name nova itself, which means “new.”
Christopher Wrede
Novae are not new stars, but rather distant extant stars that become visible on Earth when they explode or induce explosions. A supernova, which occurs when an entire star explodes, is perhaps the most well-known example of a “new star.” This occurs just about once every hundred years or so in our galaxy, the Milky Way.
The nuclear reactions studied by Wrede and his colleagues, on the other hand, are found in what are known as classical novae, which are more abundant in our cosmic vicinity. In a typical year, scientists observe about a dozen, frequently with the assistance of amateur astronomers. Because a classical nova does not totally erupt, the same star can appear more than once.
A classical nova is formed when two stars orbit each other so closely that one star can steal nuclear fuel from the other. When the siphoning star borrows enough fuel, it can set off a flurry of nuclear explosions.
Understanding the nuclear processes of all stars helps researchers understand where elements in the universe come from, and those involving two stars are especially essential in the Milky Way, according to Wrede.
“About half of the stars we see in the sky are actually two-star systems, or binary star systems,” he said. “If we really want to understand how our galaxy is working to produce chemical elements, there’s no way we can ignore them.”
Wrede has been researching a specific nuclear process within novae that occurs in nature and involves phosphorus isotopes. Phosphorus inside a nova can consume an additional proton to produce sulfur isotopes, but scientists have yet to replicate this process at star conditions on Earth. So Wrede and his colleagues did the next best thing. Instead, they began with chlorine isotopes, which decay into sulfur isotopes. They then watched as those sulfur isotopes emitted protons, converting to phosphorus. It’s the opposite reaction of interest that allows the researchers to create an instant replay of the action that they can rewind to better comprehend nature’s playbook.
But there was one more complication. The team needed to collect record-breaking measurements of the lowest-energy protons that came out of the sulfur to achieve its goal. To accomplish this, the researchers created the Gaseous Detector with Germanium Tagging, or GADGET.
“These protons have very little energy, and with traditional approaches, the signal would be overwhelmed by background,” Wrede explained. To reach the sensitivity required to view the protons, GADGET employed an unorthodox technique, employing a gaseous detector component rather than solid silicon.
“In terms of sensitivity, it’s a world record,” Wrede said.
Of course, tools and procedures are only a portion of the puzzle. The team also need talent to develop the equipment, execute the experiments, and evaluate the data. Wrede, in particular, praised Spartan graduate student researcher Tamas Budner, the paper’s first author who was involved in every stage of the project.
Budner will receive his doctorate in nuclear physics this summer from MSU’s top-ranked graduate program, thanks in large part to this study, which he describes as “fortuitous.” He had no idea which lab he’d work in or which project he’d take on when he started his graduate program in 2016.
“When I first arrived at MSU, I had no idea what I wanted to do. But it appeared to be an interesting setting where individuals were working on a variety of projects using cutting-edge technology “Budner stated.
“I wrote Chris about this idea, and it ticked all of my criteria. I’d get to watch every step of the process, from developing a new detector to conducting a new experiment and analyzing the results “He stated. “It had everything I wanted to try.”
Researchers from all over the world collaborated with the Spartans on this initiative. Team members came from France, Spain, China, Israel, Canada, and South Korea. There was also a domestic cohort of collaborators from Indiana’s University of Notre Dame and Tennessee’s Oak Ridge National Laboratory.
MSU, on the other hand, was the focus of the tests due to its proximity to NSCL, which produced the required high-intensity beam of chlorine isotopes. FRIB will now carry on the heritage of NSCL by attracting outstanding researchers from around the world to tackle some of science’s most pressing issues through experiments that aren’t possible anyplace else.
