Unveiling the nature of ultra-long period transients

01/02/2026 to 31/01/2029

International radio surveys have been steadily revealing a new population of astrophysical objects referred to as `long-period transients' or ‘ultra-long period objects’ (ULPs). While these sources pulse coherently in a manner that is reminiscent of neutron stars, it is difficult to reconcile their observed properties with conventional evolutionary tracks. For example, as the name suggests, a typical pulse period for a ULP is ~several hours. This suggests that strong magnetic fields are necessary to slow the object down and yet they were invisible in followup X-ray surveys indicating a lack of magnetic activity. These and other seemingly-contradictory facts have prompted alternative interpretations, notably involving white dwarfs in binaries. Since the first discovery of a ULP in 2022, a handful of sources have indeed been confirmed as binaries with white-dwarf primaries via optical and other data. On the other hand, optical, ultraviolet, and near-infrared limits are especially tight for other sources which makes it very difficult to imagine a tight binary system. It is clear in any case that neither interpretation has been scoped out thoroughly on a theoretical level and many issues remain to be understood.

The purpose of this proposal is to revisit conventional wisdom using state-of-the-art magnetic-evolution codes that I have become an active developer of in recent years, incorporating new ingredients tailored to ULPs. By performing a suite of simulations with varying microphysical, initial, and boundary data, this proposal promises to unveil the nature of these mysterious objects. For neutron stars we can try and understand how to maintain a strong field and yet be cold, while for dwarfs we can study the field geometry in the exterior and how this may be conducive to radio pulsing when interacting with a companion.

Regardless of the outcome with respect to progenitors, the fact that ULPs reside within hitherto unexplored parameter spaces implies that difficult-to-access areas of fundamental physics can be studied by comparing their behaviour to theoretical models. This theoretical project thereby gives promise to explore new areas of physics by comparing cutting-edge data to outputs from world-class evolution codes.