Science2014-06-10 6:00 PM

研究提示更准确的恒星形成速率 Unfolding the Laws of Star Formation: The Density Distribution of Molecular Clouds

论文摘要

由Jouni Kainulainen及其同事所进行的一项新的研究可帮助解释宇宙中最根本性的过程之一:恒星的形成。这一天体过程主要受到了在个体分子云内密度分布的控制,新的恒星就是从这些分子云中诞生的。但是在没有足够的有关这些分子云数据的情况下,天文学家在估计其密度分布时一直局限于理论模型。如今,Kainulainen及他的团队介绍用星尘消光图来确定在这些形成恒星的整个分子云中的密度是如何分布的一种方法;星尘消光图是对电磁辐射是如何被星尘及气体分散的观察。在将他们计算的密度分布插入至某经典的体积密度(ƥ-PDF)的概率密度函数后,研究人员能够为基于经验数据的恒星形成确定密度分布阈值;经典的体积密度(ƥ-PDF)概率密度函数在传统上提供了由分析模型预测的恒星形成速度。这转而能让他们对密度分布高于该阈值的分子云中的恒星形成效率进行衡量。研究人员用ƥ-PDF来探测16个附近分子云的密度结构及恒星形成活动;这些分子云中的每一个都位于地球的260个秒差距之内。有趣的是,他们确定的这些恒星形成的阈值比那些理论预测的阈值显著要低。据研究人员披露,这一新的方法可能最终会带来对像银河系这样的整个星系的恒星形成速度有更好的理解。

Abstract 

The formation of stars shapes the structure and evolution of entire galaxies. The rate and efficiency of this process are affected substantially by the density structure of the individual molecular clouds in which stars form. The most fundamental measure of this structure is the probability density function of volume densities (ρ-PDF), which determines the star formation rates predicted with analytical models. This function has remained unconstrained by observations. We have developed an approach to quantify ρ-PDFs and establish their relation to star formation. The ρ-PDFs instigate a density threshold of star formation and allow us to quantify the star formation efficiency above it. The ρ-PDFs provide new constraints for star formation theories and correctly predict several key properties of the star-forming interstellar medium.

Editor's Summary

Mapping Stardust

A galaxy's structure throughout time depends largely on its ability to convert the raw material of molecular clouds into stars. One of the most influential properties in determining star formation rates is the distribution of densities among individual molecular clouds, which can be described by a probability density function of volume densities. Kainulainen et al. (p. 183) devised a method to quantify these distributions from empirical dust extinction maps of nearby clouds. The threshold for star formation in these observationally based calculations was significantly lower than theoretical predictions.

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