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Astronomers report the discovery of a rare nova super-remnant surrounding the recurrent nova LMCN 1971-08a in the Large Magellanic Cloud (LMC). This is the first nova super-remnant identified in the LMC. The findings are detailed in a paper September 17 on the arXiv preprint server.

Nova super-remnants (NSRs) are greatly extended shell-like structures significantly larger than singular eruption nova shells. They grow by repeated nova eruptions sweeping the surrounding material away from a nova into a dense outer shell. However, although NSRs are predicted to form around all novae, to date only four such structures have been identified, and three of them in our galaxy.

Now, a team of astronomers led by Michael W. Healy-Kalesh, of the Friedrich-Alexander University of Erlangen-Nuremberg in Germany, reports the detection of the fifth nova super-remnant. By analyzing the data from various astronomical surveys and from the MeerKAT radio telescope, they identified the first such structure in the LMC.

"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 researchers write.

LMCN 1971-08a is one of the four known recurrent novae in the LMC. It has a recurrence period of about 38 years and its last eruption was observed in 2009. Previous observations have found that LMCN 1971-08a is a very fast-declining nova comprising a white dwarf with a mass of 1.1-1.3 solar masses, accreting material from a sub-giant companion. The probable orbital period of the system was estimated to be 1.2 days.

Healy-Kalesh's team found a coherent, shell-like structure spatially coincident with LMCN 1971-08a. Exhibiting a circular morphology, the structure appears to be brighter to the northeast and southwest, with a fainter boundary connecting the two components to the northwest, defining the outer shell edge.

According to the study, the collected data indicate that the newfound structure is an NSR with a diameter of about 650 light years. The inner and outer boundaries of the NSR shell were measured to be 284 and 329 light years from the nova LMCN 1971-08a, respectively. The dimensions of this NSR make it the largest nova super-remnant found to date.

The observations also found that the outer shell of the NSR around LMCN 1971-08a should have a mass at a level of 4,130 solar masses and an expansion velocity of approximately 20 km/s. The age of the NSR was estimated to be some 2.4 million years.

In concluding remarks, the authors of the paper noted that the presence of a nova super-remnant in LMCN 1971-08a suggests that the nova may have a much shorter recurrence period than previously thought.

"Owing to the existence of such a 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 scientists conclude.