[论文解读] Do micro brown dwarf detections explain the galactic dark matter?

Theo M. Nieuwenhuizen, Rudolph E. Schild+1 more|arXiv (Cornell University)|Nov 10, 2010

Galaxies: Formation, Evolution, Phenomena参考文献 72被引用 4

一句话总结

该论文提出，银河系暗物质由数万亿个地球质量的微型棕矮星（μBDs）组成，这些μBDs通过Jeans团块中的引力流体动力学形成，其集体动力学与热力学特性可解释微引力透镜效应、射电爆发、冷尘埃卷云以及莱曼-α森林吸收现象。该重子模型无需引入新粒子即可解释缺失质量，且在射电事件速率和角结构方面与观测结果定量吻合。

ABSTRACT

Context: The baryonic dark matter dominating the structures of galaxies is widely considered as mysterious, but hints for it have been in fact detected in several astronomical observations at optical, infrared, and radio wavelengths. We call attention to the nature of galaxy merging, the observed rapid microlensing of a quasar, the detection of "cometary knots" in planetary nebulae, and the Lyman-alpha clouds as optical phenomena revealing the compact objects. Radio observations of "extreme scattering events" and "parabolic arcs" and microwave observations of "cold dust cirrus" clouds are observed at 15 - 20 K temperatures are till now not considered in a unifying picture. Aims: The theory of gravitational hydrodynamics predicts galactic dark matter arises from Jeans clusters that are made up of almost a trillion micro brown dwarfs (mBDs) of earth weight. It is intended to explain the aforementioned anomalous observations and to make predictions within this framework. Methods: We employ analytical isothermal modeling to estimate various effects. Results: Estimates of their total number show that they comprise enough mass to constitute the missing baryonic matter. Mysterious radio events are explained by mBD pair merging in the Galaxy. The "dust" temperature of cold galaxy halos arises from a thermostat setting due to a slow release of latent heat at the 14 K gas to solid transition at the mBD surface. The proportionality of the central black hole mass of a galaxy and its number of globular clusters is explained. The visibility of an early galaxy at redshift 8.6 is obvious with most hydrogen locked up in mBDs. Conclusions: Numerical simulations of various steps would further test the approach. It looks promising to redo MACHO searches against the Magellanic clouds.

研究动机与目标

• 解释星系中重子暗物质的本质为通过引力流体动力学形成的数万亿个地球质量的微型棕矮星（μBDs）。
• 在单一μBD基础框架下统一解释微引力透镜效应、射电事件、冷尘埃卷云及莱曼-α森林等不同天文观测现象。
• 检验假设：Jeans团块（JCs）中的μBDs可解释缺失的重子质量，并解释平坦旋转曲线以及Tully-Fisher/Faber-Jackson关系。
• 为观测到的极端散射事件与抛物线弧的速率提供定量解释，基于银晕中μBD对的并合过程。
• 解释冷尘埃卷云14–20 K的温度为μBD表面在气态向固态转变过程中释放潜热所导致的恒温机制。

提出的方法

• 采用Jeans团块（JCs）的解析等温建模，估算μBD数密度、质量分布及角尺度。
• 应用Jeans不稳定性判据，预测每个JC可形成约2×10¹¹个μBD，源自z ≈ 5100时的6×10⁵ M☉团块碎片化。
• 通过有效半径R_bd = v_bd × t_ev及JC体积内的单元统计计数，估算μBD对并合产生的射电事件速率。
• 建模合并μBD的微波与射电辐射，假设能量释放约10⁵ J/kg，持续1天，频率为10 GHz，产生1 Jy信号。
• 通过角直径距离与JC尺寸估算沿类星体视线方向的μBD数量，计算莱曼-α森林吸收。
• 通过θ = 2R_jc / d₂与dJ/dΩ ≈ J / Ω推导JC的角直径与表面亮度，与观测到的2 MJy/sr强度一致。

实验结果

研究问题

• RQ1 类星体的微引力透镜效应是否可由Jeans团块中数万亿个地球质量的微型棕矮星的引力透镜效应解释？
• RQ2 射电观测中极端散射事件与抛物线弧的速率与特征是否源于银晕中μBD对的并合？
• RQ3 冷尘埃卷云14–20 K的温度是否可由μBD表面在气态向固态转变过程中释放潜热所形成的恒温机制解释？
• RQ4 观测到的扩展射电结构的数密度与角分布是否与Jeans团块中μBD发射的射电辐射一致？
• RQ5 莱曼-α森林吸收线是否可通过对类星体视线方向Jeans团块中μBD的累积吸收进行定量解释？

主要发现

• 银河系中μBD的总数估计为每Jeans团块约2×10¹¹个，足以解释缺失的重子质量，总质量与约4.5%临界密度匹配。
• 观测到的射电事件速率约1000 deg⁻² yr⁻¹，与μBD并合速率估算值约7400 deg⁻² yr⁻¹定量一致，Hubble时空中约发生6×10¹⁷次并合。
• 典型JC的角直径约为0.57°，与银河系平面中大尺度射电结构的观测尺度一致。
• JC的表面亮度可达约11.7 MJy/sr，与DIRBE巡天观测到的2 MJy/sr峰值强度一致。
• 在15°×12°区域内可观测的JC结构数量估计为~67 v₂₀₀² / v₃₀²，与射电图中观测到的团块数量一致。
• 每个JC沿类星体视线的莱曼-α森林吸收量估计为约890个μBD，与因团块状重子物质导致的观测窄吸收线一致。