Molecular Clouds, Larson’s Law And The Mechanics Of Star Formation

Brett Smith for – Your Universe Online

The molecular clouds that float about the universe hold the ingredients for star formation, and a new study from researchers at University of California, San Diego has confirmed the mechanics behind three observed relationships describing the internal forces acting within these clouds, called Larson’s Laws.

First postulated in 1981 by Richard Larson, a professor of astronomy at Yale, Larson’s Laws detail the observation-based relationships of the structure and supersonic internal movements of molecular clouds. The new study is based on recent observational data and the results of six computer simulations of the interstellar medium, including impacts of self-gravity, turbulence and magnetic fields. The researchers said their simulations support a turbulent interpretation of Larson’s relationships.

According to their report in the journal Monthly Notices of the Royal Astronomical Society, the UC San Diego researchers found that all three correlations are due to the same underlying physics: the properties of supersonic turbulence.

“After decades of inconclusive debate about the interpretation of the correlations among molecular cloud properties that I published in 1981, it’s gratifying to see that my original idea that they reflect a hierarchy of supersonic turbulent motions is well supported by these detailed new simulations showing that the debated complicating effects of gravity, magnetic fields, and multiphase structure do not fundamentally alter the basic picture of a turbulent cascade,” said Larson about the new study’s findings.

“This paper is essentially the culmination of seven years of research, aided by the use of large-scale supercomputer simulations conducted at SDSC and elsewhere,” said study author Alexei Kritsuk, a research physicist at UC San Diego. “Molecular clouds are the birth sites for stars, so this paper relates also to the theory of star formation.”

“None of these new findings and insights would have been possible without the tremendous advances in supercomputer simulations that allow not only cosmologists but scientists in countless other domains an unprecedented level of resolution and data-processing speed to further their research,” said study author Michael Norman, who has pioneered the use of advanced computational methods to explore the universe and its beginnings. “We believe that this paper paints the complete picture, drawing from earlier published works of ours as well as presenting new simulations that have not been published before.”

Earlier this month the Hubble Space Telescope discovered another so-called stellar nursery packed with molecular clouds. The discovery was particularly notable because it showed an effect called gravitational lensing.

First predicted by Albert Einstein, a gravitational lens occurs when light from one galaxy is bent, or distorted, by gravity. In the case of the new discovery, the light from the young “starburst dwarf” galaxy is being bent as it passes a nearer galaxy. The first observation of this effect was in 1979, a confirmation of Einstein’s earlier theory. The effect also gives researchers another tool to observe galaxies, the effect of gravity and dark matter.

The image captured by Hubble also showed an “Einstein Ring,” described as a “a perfect circle of light that is the projected and greatly magnified image of the distant light source.”

In the image, the closer galaxy is in the center while the projected light forms a ring around it, an extremely rare phenomenon according to Hubble researchers.

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