Formation of Gravitationally Bound Primordial Gas Clouds
Formation of Gravitationally Bound Primordial Gas Clouds
复制标题
引力束缚的原始气体云的形成
DOI：
10.1143/ptp.42.9
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发表时间：
1969
影响因子：
--
通讯作者：
K. Tomita
中科院分区：
文献类型：
--
作者：
K. Tomita
研究了由原始气体形成的引力束缚系统。托尔曼解决类尘埃物质的方法。导出了密度对比度的临界值及其在初始时期的增长速率，这是在最古老的恒星出现之前，不均匀凝聚成束缚系统所必需的。物质分布在一个。对孤立的不均匀和包含在较大的不均匀中的不均匀(将是一团气体云团)，随着时间的推移，假定了简单的非均匀模型，并显示了边界区域是如何向外扩展的。此外，还研究了气云可以分解成的碎片的最小质量。目前分散在宇宙中各处的星系的形成已被许多学者研究过。他们中的一些人认为，宇宙演化早期的小密度波动是由于引力不稳定而增长的，直到它们凝聚成原星系。然而，基于Lifshitz的假设！)早期非常安静，波动是统计的，引力不稳定是不起作用的。这是因为与星系相对应的统计涨落的密度对比太小(r-J10-34)，在宇宙年龄内不能增长到引力约束的系统。线性化的理论足以描述如此微小的波动。在Lifshitz之后，人们相继在线性近似下研究了涨落的行为。2)虽然Lifshitz的假设并不总是被使用。另一方面，人们一直认为宇宙的早期阶段是非常动荡的，密度波动也不小。S)在辐射密度大于物质密度，物质被完全电离的阶段，物质受到光子粒子的强烈踢打，阻碍了凝聚。但是，一旦物质被中和，密度涨落就会迅速凝聚成束缚系统。然而，我们目前不知道早期阶段的平静或动荡程度。因此，我们仍然可以假设存在不同幅度的波动。在凝聚过程中，引力起了主要作用，随着密度差的增大，密度差增加到0 GB量级
The formation of gravitationally bound systems from primordial gas is studied by . means of Tolman's solution for dust-like matter. The critical values of density contrast and its growth rate at an initial epoch are derived, which are necessary for an inhomogeneity to condense into a bound system before the appearance of the oldest stars. The matter distributions in an . isolated inhomogeneity and an inhomogeneity included in a larger one (which will be a cluster of gas clouds) are followed with time by assuming simple models for inhomogeneities, and it is shown how the bound region spreads outwards. Moreover, the minimum mass of fragments into which the gas clouds may break up is examined. The formation of galaxies which are dispersed everywhere at present in the universe has been studied by many authors. Some of them have assumed that small density fluctuations in an early stage of cosmic evolution grow owing to gravitational instability, until they condense into protogalaxies. However, on Lifshitz's assumption!) that the early stage was very quiet and the fluctua tions were statistical, gravitational instability was not effective. This is because the density contrasts of the statistical fluctuations corresponding to galaxies are too small (r-J 10- 34 ) to grow to gravitationally bound systems within the cosmic age. The linearized theories were sufficient for the description of such small fluctuations. After Lifshitz, the behavior of the fluctuations has been studied successively in the linear approximation,2) while Lifshitz's assumption was not always used. On the other hand, it has been assumed that an early stage of the UnIverse was very turbulent and density fluctuations were not small. S ) At the stage when radiation density was larger than matter density and matter was wholly ionized, matter was strongly kicked by photon particles and hindered from condensing. But, once matter was neutrarized, density fluctuations condensed promptly into bound systems. However, we do not know at present how quiet or turbulent the early stages were. Accordingly, still we could assume the existence of fluctuations with vari ous amplitudes. In the process of their condensation, gravitation would have played the main role, and, as the density contrasts increased to the order o£