An international team of astronomers has uncovered remarkable details about SN 2024acyl. This Type Ibn supernova was an astonishing 398 million light years away from Earth. On December 1, 2024, the Asteroid Terrestrial-Impact Last Alert System (ATLAS) recorded this extraordinary astronomical feat. It’s been making waves for a slightly different reason, as it’s predicted to be at least 114,000 light years from its host galaxy. In their new paper, researchers take a deep look at the properties and possible origins of SN 2024acyl. They posted the results to their arXiv preprint server on November 6.
On February 22, 2025, all day the astronomers were using the Gemini-North Observatory for high-detail photometric and spectroscopic follow-up observations of SN 2024acyl. The underluminous supernova is indeed classified as a normal Type Ibn. Farther afield, its unique spectra reveal low-velocity helium emission lines that really set J2157 apart. These features emphasize the defining characteristics of Type Ibn supernovae. They are famous for their quick development and short time to maximum brightness, which can happen in less than 2 weeks.
After its maximum brightness, SN 2024acyl showed a rapid decline, a pattern seen in other rapidly-evolving Type Ibn supernovae. The observational campaign that followed was all about trying to reveal what this supernova looked like. It sought to explore possible links to its natal environment. Most notably, astronomers discovered seven extended sources around SN 2024acyl, with one candidate possibly indicating the point of its origin.
SN 2024acyl is particularly interesting because it is a Type Ibn supernova. Added to its mystery, though, is its odd distance from its host galaxy. This unusual offset is interesting because it invites queries about what mechanisms might have led to the production and detonation of such an interesting offset. This research has deep implications for our understanding of stellar evolution. It also illuminates the life cycles of gargantuan stars.