Strong neutrino cooling by cycles of electron capture and β− decay in neutron star crusts
Strong neutrino cooling by cycles of electron capture and β− decay in neutron star crusts
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DOI：
10.1038/nature12757
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发表时间：
2013-12
期刊：
影响因子：
64.8
通讯作者：
H. Schatz;Sanjib S. Gupta;P. Moller;M. Beard;E. Brown;Alex Deibel;L. Gasques;W. Hix;L. Keek;R. Lau;A. Steiner;M. Wiescher
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作者：
H. Schatz;Sanjib S. Gupta;P. Moller;M. Beard;E. Brown;Alex Deibel;L. Gasques;W. Hix;L. Keek;R. Lau;A. Steiner;M. Wiescher
在一个吸积中子星星的外壳中，包括它的最外层公里，温度是由大密度核反应加热、中微子冷却和来自内部的热传输确定的。被加热的地壳被认为会影响较浅深度的可观测现象，例如吸积包层中的热核爆发。在这里，我们报告说，电子捕获和它的逆β-衰变的循环，涉及在典型深度约150米的富中子核，通过发射中微子冷却外部中子星星地壳，同时也使表面层与更深的地壳热解耦。这种“厄卡”机制已经在白色矮星和Ia型超新星的背景下进行了研究，但迄今为止还没有考虑中子星，因为以前的模型使用零温度近似计算地壳反应，并假设在任何给定的深度只有一个单一的核物种。热退耦意味着X射线爆发和其他地表现象在很大程度上与地壳深部加热的强度无关。因此，观测到的高能热核超级爆发的重现时间出乎意料地短，大约为几年，并不是热地壳的指示，而是可能指向中子星星表面附近未知的局部加热机制。
The temperature in the crust of an accreting neutron star, which comprises its outermost kilometre, is set by heating from nuclear reactions at large densities,,,, neutrino cooling,and heat transport from the interior,,,,. The heated crust has been thought to affect observable phenomena at shallower depths, such as thermonuclear bursts in the accreted envelope,. Here we report that cycles of electron capture and its inverse,β−decay, involving neutron-rich nuclei at a typical depth of about 150 metres, cool the outer neutron star crust by emitting neutrinos while also thermally decoupling the surface layers from the deeper crust. This ‘Urca’ mechanism has been studied in the context of white dwarfs and type Ia supernovae,, but hitherto was not considered in neutron stars, because previous models,computed the crust reactions using a zero-temperature approximation and assumed that only a single nuclear species was present at any given depth. The thermal decoupling means that X-ray bursts and other surface phenomena are largely independent of the strength of deep crustal heating. The unexpectedly short recurrence times, of the order of years, observed for very energetic thermonuclear superbursts are therefore not an indicator of a hot crust, but may point instead to an unknown local heating mechanism near the neutron star surface.