论文标题
黑寡妇的演化：磁制动的磁制动
Black widow evolution: magnetic braking by an ablated wind
论文作者
论文摘要
黑寡妇是紧密的二进制系统，其中一个毫秒的脉冲星是由同伴绕太阳的巨人绕的。有人提出，Pulsar的旋转动力$γ$ ray的光度逐渐蒸发了同伴，最终留下了一个孤立的毫秒脉冲星。蒸发效率取决于温度$ t _ {\ rm ch} \ propto f^{2/3} $，在动态时间尺度上流出了流出$ f $。对于填充Roche Lobes的同伴来说，蒸发是最有效的。在这种情况下，流出以L1点的盖子为主导，角度为$θ_g\ sim（t _ {\ rm ch}/t_g）^{1/2} $，蒸发时间为$ t _ {\ rm evap} = 0.46 = 0.46（ gyr} $，其中$ t_g> t _ {\ rm ch} $是伴侣的病毒温度。我们将模型应用于观察到的黑寡妇种群，考虑到每个系统的轨道时期，伴随质量和Pulsar旋转功率，该模型在过去十年中大大增加了。虽然原始的（Fruchter等人，1988年）黑寡妇在几个回旋时尺度上蒸发了其同伴，但直接蒸发本身太弱了，无法解释整体人群。相反，我们建议将蒸发风夫妇伴侣到同伴的磁场上，从二进制中去除角动量，并保持稳定的Roche-Lobe溢出。虽然强烈的风能更大，但它也降低了Alfvén半径，使这种间接的磁制动机制降低了限制助理$ t _ {\ rm mag} \ propto t _ {\ rm evap}^{1/3} $。这减少了观察到的系统的进化时间的散射，从而更好地解释了黑色寡妇和孤立的毫秒脉冲星人群。
Black widows are close binary systems in which a millisecond pulsar is orbited by a companion a few per cent the mass of the sun. It has been suggested that the pulsar's rotationally powered $γ$-ray luminosity gradually evaporates the companion, eventually leaving behind an isolated millisecond pulsar. The evaporation efficiency is determined by the temperature $T_{\rm ch}\propto F^{2/3}$ to which the outflow is heated by the flux $F$ on a dynamical time-scale. Evaporation is most efficient for companions that fill their Roche lobes. In this case, the outflow is dominated by a cap around the L1 point with an angle $θ_g\sim (T_{\rm ch}/T_g)^{1/2}$, and the evaporation time is $t_{\rm evap}=0.46(T_{\rm ch}/T_g)^{-2}\textrm{ Gyr}$, where $T_g>T_{\rm ch}$ is the companion's virial temperature. We apply our model to the observed black widow population, which has increased substantially over the last decade, considering each system's orbital period, companion mass, and pulsar spin-down power. While the original (Fruchter et al. 1988) black widow evaporates its companion on a few Gyr time-scale, direct evaporation on its own is too weak to explain the overall population. We propose instead that the evaporative wind couples to the companion's magnetic field, removes angular momentum from the binary, and maintains stable Roche-lobe overflow. While a stronger wind carries more mass, it also reduces the Alfvén radius, making this indirect magnetic braking mechanism less dependent on the flux $t_{\rm mag}\propto t_{\rm evap}^{1/3}$. This reduces the scatter in evolution times of observed systems, thus better explaining the combined black widow and isolated millisecond pulsar populations.
