亚毫秒脉冲星：缺失还是不可能存在？
Sub-Millisecond Pulsars: Missing or Impossible?
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中文总结 AI 辅助
本文探讨亚毫秒脉冲星缺失的原因，指出其罕见性源于吸积低效等因素，恒星质量黑洞可达到亚毫秒视界自旋周期。
中文摘要 AI 辅助
自1982年发现首颗毫秒脉冲星以来，中子星所能达到的最小自转周期一直存在争议。自转快于1毫秒的中子星会对致密物态方程、引力波辐射以及吸积与自旋加速物理产生深远影响。尽管已发现700多颗自转周期在1.4至10毫秒之间的毫秒脉冲星，但尚未识别出任何亚毫秒脉冲星。本文综述了制约超快中子星形成、存活及可探测性的物理与观测约束，讨论了中子星物态方程施加的物理约束及其对可达到的最小自转周期的影响，总结了吸积型和旋转动力型毫秒脉冲星的引力波辐射。我们认为，亚毫秒自转并非主要受平衡自旋极限、磁层物理或选择效应排除，而是由吸积效率低下、最有利双星系统中质量转移寿命短暂以及除非磁场极弱否则形成后快速自旋下降等因素共同导致，这些效应使亚毫秒脉冲星本质上极为罕见。若它们确实存在，最可能在吸积过程中被短暂探测到，而非作为长寿命射电脉冲星。最后，我们表明恒星质量黑洞可达到亚毫秒视界自旋周期，反映出根本不同的自旋约束。
英文摘要
The minimum spin period attainable by a neutron star has been debated since the discovery of the first millisecond pulsar in 1982. A neutron star rotating faster than 1 ms would have far-reaching implications for the dense-matter equation of state, gravitational-wave emission, and the physics of accretion and spin-up. Yet despite the discovery of over 700 millisecond pulsars with spin periods between 1.4 and 10 ms, no sub-millisecond pulsar has been identified. Here we review the physical and observational constraints governing the formation, survival, and detectability of ultra-fast neutron stars. We discuss physical constraints imposed by the neutron star equation of state and their implications for the minimum attainable spin period, and we summarise gravitational-wave emission from both accreting and rotation-powered millisecond pulsars. We argue that sub-millisecond spins are not primarily excluded by equilibrium spin limits, magnetospheric physics, or selection effects, but instead by a combination of inefficient recycling, short mass-transfer lifetimes in the most favourable binaries, and rapid post-formation spin-down unless magnetic fields are exceptionally weak. Together, these effects make sub-millisecond pulsars intrinsically rare. If they exist at all, they are most likely to be detected transiently during accretion, rather than as long-lived radio pulsars. Finally, we show that stellar-mass black holes can attain sub-millisecond horizon spin periods, reflecting fundamentally different spin constraints.
