Ng, C.C.NgKruckow, M. U.M. U.KruckowTauris, T. M.T. M.TaurisLyne, A. G.A. G.LyneFreire, P. C. C.P. C. C.FreireRIDOLFI, ALESSANDROALESSANDRORIDOLFICaiazzo, I.I.CaiazzoHeyl, J.J.HeylKramer, M.M.KramerCameron, A. D.A. D.CameronChampion, D. J.D. J.ChampionStappers, B.B.Stappers2022-06-212022-06-2120180035-8711http://hdl.handle.net/20.500.12386/32441Radio pulsars found in binary systems with short orbital periods are usually fast spinning as a consequence of recycling via mass transfer from their companion stars; this process is also thought to decrease the magnetic field of the neutron star being recycled. Here, we report on timing observations of the recently discovered binary PSR J1755-2550 and find that this pulsar is an exception: with a characteristic age of 2.1 Myr, it is relatively young; furthermore, with a spin period of 315 ms and a surface magnetic field strength at its poles of 0.88 × 10<SUP>12</SUP> G, the pulsar shows no sign of having been recycled. Based on its timing and orbital characteristics, the pulsar either has a massive white dwarf (WD) or a neutron star (NS) companion. To distinguish between these two cases, we searched radio observations for a potential recycled pulsar companion and analysed archival optical data for a potential WD companion. Neither work returned conclusive detections. We apply population synthesis modelling and find that both solutions are roughly equally probable. Our population synthesis also predicts a minimum mass of 0.90 M<SUB>☉</SUB> for the companion star to PSR J1755-2550 and we simulate the systemic runaway velocities for the resulting WDNS systems which may merge and possibly produce Ca-rich supernovae. Whether PSR J1755-2550 hosts a WD or a NS companion star, it is certainly a member of a rare subpopulation of binary radio pulsars.STAMPAenArticle10.1093/mnras/sty482https://academic.oup.com/mnras/article/476/4/4315/49041352018MNRAS.476.4315NFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation