Ancient Nova Shells of RX Pup Indicate Evolution of Mass Transfer Rate

RX Pup is a symbiotic binary that experienced a nova outburst in the 1970s. Here we report a discovery of a ∼1300 yr old nova shell around the system and a possible detection of a ∼7000 yr old nova shell. Together with the nova shell ejected in the 1970s, this makes RX Pup the first system with three nova shells observed. This triad of eruptions suggests a change in the nova recurrence time. The most likely explanation is an alteration in the mass transfer rate attributed to evolutionary changes of the mass donor in the system. Notably, comparative analyses with theoretical models indicate an increase in the average mass transfer rate by a factor of 3 over the past 10,000 yr. This makes RX Pup a unique system, which allows us to probe millennium-scale evolution of mass transfer rates in binary systems.