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arXiv 1808.01007gr-qc
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广义相对论中自引力费米子的量热曲线

Caloric curves of self-gravitating fermions in general relativity

Giuseppe Alberti, Pierre-Henri Chavanis

摘要:

在广义相对论中,研究了非零温度下自引力费米气体从气态到凝聚态的相变性质。凝聚态可以代表紧凑的物体,如白矮星,中子星或暗物质费米子球。热量曲线取决于两个参数:系统大小$R$和粒子数$N$。当$N<N_{\rm OV}$,其中$N_{\rm OV}$是奥本海默-柯伊伯极限时,对于任何温度$T$和能量$E$值,都存在一个平衡态,就像在非相对论情况下一样[P.H. Chavanis,Int.J.Mod.Phys.B20,3113(2006)]。引力坍缩被量子力学(泡利不相容原理)阻止。当$N>N_{\rm OV}$时,在临界能量以下和临界温度以下没有平衡态。在这种情况下,系统预计会向黑洞坍缩。我们绘制了广义相对论费米气体的热量曲线,研究了系统中发生的不同类型的相变,并确定了$(R,N)$平面上的相图。恢复了$N\ll N_{\rm OV}$和$NR^3$固定的$R\gg R_{\rm OV}$的非相对论性结果。对于$N\gg N_{\rm OV}$和$R\gg R_{\rm OV}$,在$N/R$固定的情况下,恢复了经典结果。我们强调了一种物理感兴趣的情况下,气态费米气体,通过冷却,首先经历了一个相变到一个紧凑的对象(白矮星,中子星,暗物质费米子球),然后崩溃成一个黑洞。这种情况发生在微正则系综时,$N_{\rm OV}<N<3.73\, N_{\rm OV}$。我们还涉及到从气态到核心晕状态的微正则系综的红巨星结构的发病和超新星现象的相变。

英文摘要:

We study the nature of phase transitions between gaseous and condensed states in the self-gravitating Fermi gas at nonzero temperature in general relativity. The condensed states can represent compact objects such as white dwarfs, neutron stars, or dark matter fermion balls. The caloric curves depend on two parameters: the system size $R$ and the particle number $N$. When $N<N_{\rm OV}$, where $N_{\rm OV}$ is the Oppenheimer-Volkoff limit, there exists an equilibrium state for any value of the temperature $T$ and of the energy $E$ as in the nonrelativistic case [P.H. Chavanis, Int. J. Mod. Phys. B 20, 3113 (2006)]. Gravitational collapse is prevented by quantum mechanics (Pauli's exclusion principle). When $N>N_{\rm OV}$, there is no equilibrium state below a critical energy and below a critical temperature. In that case, the system is expected to collapse towards a black hole. We plot the caloric curves of the general relativistic Fermi gas, study the different types of phase transitions that occur in the system, and determine the phase diagram in the $(R,N)$ plane. The nonrelativistic results are recovered for $N\ll N_{\rm OV}$ and $R\gg R_{\rm OV}$ with $NR^3$ fixed. The classical results are recovered for $N\gg N_{\rm OV}$ and $R\gg R_{\rm OV}$ with $N/R$ fixed. We highlight a situation of physical interest where a gaseous Fermi gas, by cooling, first undergoes a phase transition towards a compact object (white dwarf, neutron star, dark matter fermion ball), then collapses into a black hole. This situation occurs in the microcanonical ensemble when $N_{\rm OV}<N<3.73\, N_{\rm OV}$. We also relate the phase transitions from a gaseous state to a core-halo state in the microcanonical ensemble to the onset of red-giant structure and to the supernova phenomenon.

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