In a surprising discovery, astronomers have found an enormous, shell-like structure called a nova super-remnant (NSR) in the Large Magellanic Cloud (LMC), a galaxy located approximately 160,000 light-years from Earth.
An NSR is simply the leftover shells of gas and dust that get swept up and pushed outward when a star repeatedly erupts (recurrent nova). The newfound structure spans approximately 650 light-years across, making it the largest NSR ever detected.
“Here we present the discovery of the first NSR in the Large Magellanic Cloud and only the second extragalactic nova shell to be identified, hosted by the recurrent nova LMCN 1971-08a,” the study authors note.
This finding offers new insights into the life cycles of stars and the science of stellar explosions, challenging previous assumptions about nova recurrence rates and shell formation.
Finding the cosmic wonder
The research team utilized data from various astronomical surveys and the MeerKAT radio telescope to investigate the region around LMCN 1971-08a. This recurrent nova, known for its rapid eruptions approximately every 38 years, was last observed in 2009.
By studying the region with narrowband filters sensitive to hydrogen (H-alpha) and sulfur (S II) emissions, the team detected a coherent, circular shell structure centered on the nova. The shell appeared brighter in the northeast and southwest, with a fainter arc connecting the two regions to the northwest, outlining the outer edge.
Additional hydrogen gas (HI) data revealed a matching structure, confirming that it was indeed a large shell. Measurements showed that the inner and outer boundaries of the nova super-remnant lie about 284 and 329 light-years from the nova, respectively.
Computer modeling indicated that the shell contains roughly 4,130 times the mass of the Sun, is expanding at a speed of about 20 kilometers per second, and is around 2.4 million years old. These results suggest the remnant was built up by repeated nova eruptions, which gradually swept surrounding material outward into a dense outer shell.
The researchers further add that “owing to the existence of such an NSR, LMCN 1971-08a may have a much shorter recurrence period than the 38 years currently presumed and may therefore be observed in eruption much sooner than 2047,” the researchers said.
There might be larger NSRs
These findings challenge existing models of nova recurrence and shell formation, indicating that nova systems may evolve more rapidly than previously thought.
Beyond refining nova recurrence models, this NSR also provides a rare opportunity to study the life cycles of stars and the dynamics of galactic material over millions of years.
The team notes that while this is the largest NSR observed, more such remnants likely exist but have been overlooked due to their faint and diffuse nature. Future work will involve deeper surveys of the LMC and other galaxies to uncover such NSRs.
The study is published in arXiv.