论文标题
电离前线的结构和不稳定在移动黑洞周围
Structure and Instability of the Ionization Fronts around Moving Black Holes
论文作者
论文摘要
在本文中，我们专注于理解在移动黑洞（BHS）模拟中观察到的稳定或不稳定电离方面（I-Fronts）的物理过程。前不稳定性可能会触发气体积聚，使BH比稳态更加发光。我们执行了一系列理想化的三维辐射流体动力学模拟，从质量$ $ m_ \ mathrm {bh} $和速度$ v_ \ infty $中的质量$ n_ \ n_ \ mathrm {h h} $中添加$ v_ \ infty $。 i-front，带有半径$ r_ \ mathrm {i} $的i-front从d型到r型，因为bh速度变得大于临界值$ v_ \ mathrm {r} \ sim 40 \，\ sim 40 \，\ mathrm {km/s} $。 D型前沿之前是厚度$ΔR_\ MATHRM {i} $的弓形，该$ v_ \ infty $接近$ v_ \ mathrm {r} $。我们发现，在以下两个条件下，D型和R型方面都可以不稳定：i）对于d型的前面，壳的厚度必须为$Δr_\ mathrm {i}/r_ \ mathrm {i} R型前沿也有类似的限制； ii）跨I前的温度跳跃必须为$ t_ \ mathrm {ii}/t_ \ mathrm {i}> 3 $。如果$ t_ \ mathrm {i} <5000 \，\ mathrm {k} $或$ n_ \ mathrm {h} \，m_ \ mathrm {bH} \ gtrsim 10^6 \，m_ \ odot \，\ odot \，\ m m马理，如果$ t_ \ mathrm {i} <5000 \，\ mathrm {k} $，则满足第二个条件。由于X射线预热，通常$ t_ \ mathrm {i} \ sim 10^4 \，\ mathrm {k} $，除非D-Type shell在光学上厚至X射线，X射线也会发生$ N_ \ MATHRM {h} {H} \，M_ \ Mathrm {bh bh bh bh a n offiention crigation。因此，我们得出的结论是，仅对于相对较大的BHS移动的小槽非常密集的分子云而言，i-front在BHS周围是不稳定的。我们简要讨论可能与这种不稳定有关的X射线光度爆发的观察结果。
In this paper we focus on understanding the physical processes that lead to stable or unstable ionization fronts (I-fronts) observed in simulations of moving black holes (BHs). The front instability may trigger bursts of gas accretion, rendering the BH significantly more luminous than at steady-state. We perform a series of idealized three dimensional radiation hydrodynamics simulations resolving the I-fronts around BHs of mass $M_\mathrm{BH}$ and velocity $v_\infty$ accreting from a medium of density $n_\mathrm{H}$. The I-front, with radius $R_\mathrm{I}$, transitions from D-type to R-type as the BH velocity becomes larger than a critical value $v_\mathrm{R}\sim 40\,\mathrm{km/s}$. The D-type front is preceded by a bow-shock of thickness $ΔR_\mathrm{I}$ that decreases as $v_\infty$ approaches $v_\mathrm{R}$. We find that both D-type and R-type fronts can be unstable given the following two conditions: i) for D-type fronts the shell thickness must be $ΔR_\mathrm{I}/R_\mathrm{I}<0.05$ (i.e., $v_\infty \gtrsim 20\,\mathrm{km/s}$.), while no similar restriction holds for R-type fronts; ii) the temperature jump across the I-front must be $T_\mathrm{II}/T_\mathrm{I}>3$. This second condition is satisfied if $T_\mathrm{I}<5000\,\mathrm{K}$ or if $n_\mathrm{H}\,M_\mathrm{BH} \gtrsim 10^6\,M_\odot\,\mathrm{cm^{-3}}$. Due to X-ray pre-heating typically $T_\mathrm{I} \sim 10^4\,\mathrm{K}$, unless the D-type shell is optically thick to X-rays, which also happens when $n_\mathrm{H}\,M_\mathrm{BH}$ is greater than a metallicity-dependent critical value. We thus conclude that I-fronts around BHs are unstable only for relatively massive BHs moving trough very dense molecular clouds. We briefly discuss the observational consequences of the X-ray luminosity bursts likely associated with this instability.
