Zolotukhin, Ivan Yu.Ivan Yu.ZolotukhinBACHETTI, MatteoMatteoBACHETTISartore, NicolaNicolaSartoreChilingarian, Igor V.Igor V.ChilingarianWebb, Natalie A.Natalie A.Webb2020-07-272020-07-2720170004-637Xhttp://hdl.handle.net/20.500.12386/26640Neutron stars are thought to be born rapidly rotating and then exhibit a phase of rotation-powered pulsations as they slow down to 1-10 s periods. The significant population of millisecond pulsars observed in our Galaxy is explained by the recycling concept: during an epoch of accretion from a donor star in a binary system, the neutron star is spun up to millisecond periods. However, only a few pulsars are observed during this recycling process, with relatively high rotational frequencies. Here we report the detection of an X-ray pulsar with {P}<SUB>{spin</SUB>}=1.20 {{s}} in the globular cluster B091D in the Andromeda galaxy, the slowest pulsar ever found in a globular cluster. This bright (up to 30% of the Eddington luminosity) spinning-up pulsar, persistent over the 12 years of observations, must have started accreting less than 1 Myr ago and has not yet had time to accelerate to hundreds of Hertz. The neutron star in this unique wide binary with an orbital period {P}<SUB>{orb</SUB>}=30.5 {hr} in a 12 Gyr old, metal-rich star cluster accretes from a low-mass, slightly evolved post-main-sequence companion. We argue that we are witnessing a binary formed at a relatively recent epoch by getting a ∼0.8 {M}<SUB>☉ </SUB> star in a dynamical interaction—a viable scenario in a massive, dense globular cluster like B091D with high global and specific stellar encounter rates. This intensively accreting non-recycled X-ray pulsar therefore provides a long-sought missing piece in the standard pulsar recycling picture.STAMPAenArticle10.3847/1538-4357/aa689d2-s2.0-85018941274000403467800001https://iopscience.iop.org/article/10.3847/1538-4357/aa689d2017ApJ...839..125ZFIS/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::PE9_10 High energy and particle astronomy – X-rays, cosmic rays, gamma rays, neutrinos