原初黑洞团簇能在星系中幸存吗？碰撞破坏及微引力透镜效应的影响
Do Primordial Black Hole Clusters Survive the Galaxy? Collisional Disruption and Microlensing Implications
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中文总结 AI 辅助
研究银河系晕中原初黑洞团簇的碰撞破坏，结合多种模拟方法，得出不同质量团簇的碰撞率及幸存质量分数，发现团簇 - 团簇破坏显著，微引力透镜调查需考虑径向变化的平滑分数。
中文摘要 AI 辅助
我们研究了银河系晕中原初黑洞（PBH）团簇的碰撞破坏。团簇间的碰撞会将PBH剥离成一个弥散成分，沿视线方向该平滑成分中PBH质量的占比决定了微引力透镜约束在孤立致密天体和扩展团簇透镜之间的分配方式。我们结合了基于解析NFW的碰撞率模型、72次直接N体二元碰撞模拟（校准逃逸质量分数作为相对速度和碰撞参数的通用函数$\tilde f(\tilde v,\tilde b)$，以团簇速度尺度和半质量半径为单位）以及类银河系晕（$M_{200}\simeq 8\times10^{11}\,M_\odot$，$c_{200}\simeq 11$）的宇宙学N体模拟（记录从$z = 9$到$z = 0$每个团簇的碰撞历史）。对于$10^6$和$10^7\,M_\odot$的团簇（涵盖Carr等人形成情景中的最大质量范围），太阳圆处的局部碰撞率分别为$2.9\times10^{-3}$和$1.2\times10^{-2}\,\rm Myr^{-1}$，与模拟结果在约40%的范围内一致。由于Carr半径团簇的峰值破坏速度（12 - 20 km/s）远低于典型晕碰撞速度，破坏通过许多弱碰撞累积，在晕组装的早期冷阶段最为有效：总质量损失的一半发生在$z\approx2$之前，这是$z = 0$解析估计完全忽略的一个渠道。太阳圆处的幸存质量分数为$S\simeq0.50$（$10^6\,M_\odot$）和$0.04$（$10^7\,M_\odot$），朝向大麦哲伦星系和小麦哲伦星系的暗物质质量加权平滑分数分别为0.49和0.92。因此，在星系的生命周期中团簇 - 团簇破坏相当显著，对微引力透镜调查的重新分析必须考虑这里推导的径向变化的平滑分数$f_{\rm sm}(r)$。
英文摘要
We study the collisional disruption of primordial black hole (PBH) clusters in the Milky Way halo. Encounters between clusters strip PBHs into a diffuse component, and the fraction of PBH mass in this smooth component along a sightline determines how microlensing constraints divide between isolated compact objects and extended cluster lenses. We combine an analytic NFW-based collision-rate model, $72$ direct N-body binary collision simulations that calibrate the escaped-mass fraction as a universal function $\tilde f(\tilde v,\tilde b)$ of the relative velocity and impact parameter in units of the cluster velocity scale and half-mass radius, and cosmological N-body simulations of a Milky Way-like halo ($M_{200}\simeq 8\times10^{11}\,M_\odot$, $c_{200}\simeq 11$) that record the encounter history of every cluster from $z=9$ to $z=0$. For $10^6$ and $10^7\,M_\odot$ clusters -- bracketing the maximum mass in the Carr et al.\ formation scenario -- the local encounter rate at the Solar circle is $2.9\times10^{-3}$ and $1.2\times10^{-2}\,\rm Myr^{-1}$, consistent with the simulations to within ${\sim}40\%$. Because the peak-disruption velocity of Carr-radius clusters ($12$--$20\,\rm km\,s^{-1}$) lies far below typical halo encounter velocities, disruption accumulates through many weak encounters, most effectively during the early, cold phases of halo assembly: half of the total mass loss is inflicted before $z\approx2$, a channel that $z=0$ analytic estimates miss entirely. The surviving mass fraction at the Solar circle is $S\simeq0.50$ ($10^6\,M_\odot$) and $0.04$ ($10^7\,M_\odot$), and the DM-mass-weighted smooth fraction toward the LMC and SMC is $0.49$ and $0.92$, respectively. Cluster-cluster disruption is thus substantial over the Galaxy's lifetime, and reanalyses of microlensing surveys must account for the radially varying smooth fraction $f_{\rm sm}(r)$ derived here.
