Novel supernova observations grant astronomers a peek into the cosmic past

This rare supernova, called 2023ufx, originated from the core collapse of a red supergiant star, exploded on the outskirts of a nearby dwarf galaxy. Results of the study showed that observations of both this supernova and the galaxy it was discovered in are of low metallicity, meaning they lack an abundance of elements heavier than hydrogen or helium.

Since the metals produced within supernovae inform their properties, including how stars evolve and die, learning more about their formation can tell astronomers much about the state of the universe when it began, especially since there were essentially no metals around during the time of its birth, said Michael Tucker, lead author of the study and a fellow at the Center for Cosmology and AstroParticle Physics at The Ohio State University.

"If you're someone who wants to predict how the Milky Way came to be, you want to have a good idea of how the first exploding stars seeded the next generation," said Tucker. "Understanding that gives scientists a great example of how those first objects affected their surroundings."

Dwarf galaxies in particular are useful local analogs to conditions scientists might expect to see in the early universe. Because of them, astronomers know that while the first galaxies were metal-poor, all the big, bright galaxies near the Milky Way had plenty of time for stars to explode and increase the amount of metal content, said Tucker.

The amount of metals a supernova has also influences aspects like the number of nuclear reactions it may have or how long its explosion remains bright. It's also one of the reasons that many low-mass stars also occasionally run the risk of collapsing into black holes.

The study was published recently in The Astrophysical Journal.

While the event observed by Tucker's team is only the second supernova to be found with low metallicity, what's most unusual about it is its location relative to the Milky Way, said Tucker.

Typically, any metal-poor supernova that astronomers would expect to find would likely be too faint to see from our galaxy because of how far away they are. Now, due to the advent of more powerful instruments like NASA's James Webb Space Telescope, detecting distant metal-poor galaxies has been made exponentially easier.

"There are not that many metal-poor locations in the nearby universe and before JWST, it was difficult to find them," said Tucker.

But the sighting of 2023ufx turned out to be a happy accident for researchers. New-found observations of this particular supernova revealed that many of its properties and behaviors are distinctly different from other supernovae in nearby galaxies.

For example, this supernova had a period of brightness that stayed steady for about 20 days before declining, whereas the brightness of its metal-rich counterparts usually lasted for about 100 days. The study also showed that a large amount of fast-moving material was ejected during the explosion, suggesting that it must have been spinning very quickly when it exploded.

This result implies that rapidly spinning metal-poor stars must have been relatively common during the early days of the universe, said Tucker. His team's theory is that the supernova likely had weak stellar winds -- streams of particles emitted from the atmosphere of the star -- which led it to cultivate and release so much energy.

Overall, their observations lay the groundwork for astronomers to better investigate how metal-poor stars survive in different cosmic environments, and may even help some theorists more accurately model how supernovae behaved in the early universe.

"If you're someone who wants to predict how galaxies form and evolve, the first thing you want is a good idea of how the first exploding stars influenced their local area," said Tucker.

Future research may aim to determine if the supernova was larger at one point, whether just by being a super-massive star or if its materials were stripped away by a still undiscovered binary companion.

Until then, researchers will have to wait for more data to become available.

"We're so early in the JWST era that we're still finding so many things we don't understand about galaxies," said Tucker. "The long-term hope is that this study acts as a benchmark for similar discoveries."

This work was supported by the National Science Foundation, the European Research Council (ERC), the Australian Research Council Discovery Early Career Researcher Award (DECRA), and NASA. Christopher S. Kochanek from Ohio State was also a co-author.