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arXiv 2008.10683gr-qc
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关于“超大质量”中子星的形成和向自发标量化的动力学跃迁

On the formation of "supermassive" neutron stars and dynamical transition to spontaneous scalarization

Juan Carlos Degollado, Marcelo Salgado, Miguel Alcubierre

摘要:

众所周知,中子星在一定的标量引力张量理论下会发生相变,此时恒星内部会出现一个新的序参量{ \it标量电荷}。这是Damour和Esposito-Farèse在1993年发现的著名的自发标量化现象。在这样的机制下,中子星原则上可以提供比广义相对论(GR)更大的最大质量,对于给定的状态方程,而不考虑额外的观测约束(例如双星系统)。这就开启了一种可能性,即中子星可能形成质量与$\sim 2 M_\odot$一样大的中子星,而不需要严格的或更奇特的核物质的状态方程。因此,STT到SC可以解释最近在天空中观察到的具有大质量的紧凑物体,其形式为双星(2013年观察到的PSR J 0348 +0432与$M= 2.01 M_\pm 0.04\odot$,2010年观察到的PSR J1614-2230与$M= 1.97\pm 0.04 M_\odot$或2019年观察到的J 0740 +6620 $M= 2.14^{+0.10}_{-0.09} M_\odot$)。然而,我们认为,即使这是可能的,这样的最大质量模型在STT不能形成完全从初始的动态过渡的“孤立的”非标度化的中子星的质量不能超过最大质量的GR。这是因为SC,是一个积极的首选配置,产生一个最终的静态星的质量低于初始的一个固定的重子质量。初始和最终构型之间的质量差以标量场的形式辐射出去。因此,标量化中子星的最大质量模型,如果在自然界中存在的话,一定是通过不同的过程形成的,也许是宇宙学的起源,或者是通过随后附加的标量电荷和质量的吸积。

英文摘要:

It is well known that neutron stars can undergo a phase transition under a certain class of Scalar Tensor Theories of gravity (STT's) where a new order parameter, the {\it scalar charge}, appears within the star. This is the well known phenomenon of spontaneous scalarization (SC) discovered by Damour and Esposito-Farèse in 1993. Under such mechanism neutron stars can afford in principle a maximum mass larger than in general relativity (GR) for a given equation of state without taking into account additional observational constraints (e.g. binary systems). This opens the possibility that neutron stars might be formed with masses as large as $\sim 2 M_\odot$ without the need of stiff, or more exotic, equations of state for the nuclear matter. Thus, STT's through SC may account for compact objects with large masses observed recently in the sky in the form of pulsars (PSR J0348+0432 with $M= 2.01 M_\pm 0.04\odot$ observed in 2013, PSR J1614-2230 with $M= 1.97\pm 0.04 M_\odot$ observed in 2010 or J0740+6620 $M= 2.14^{+0.10}_{-0.09} M_\odot$ observed in 2019). However, we argue that even if that was possible such maximum mass models within STT cannot be formed solely from the dynamic transition of an initial "isolated" unscalarized neutron star whose mass cannot exceed the maximum mass in GR. This is because SC, being an energetic-preferred configuration, produces a final static star with a mass lower that the initial one with a fixed baryon mass. The mass difference between the initial and final configurations is radiated away in the form of a scalar-field. Thus, maximum mass models of scalarized neutron stars, if present in nature, must have formed by a different process, perhaps of cosmological origin or by the subsequent accretion of additional scalar charge and mass.

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