3D-models reveal efficiency of star factories

Chalmers University of Technology

​Astronomers solve the mystery of the different star formation activities of two similar-looking dust clouds by reconstructing their 3D shapes​ ​Using tens of thousands of stars observed by the Gaia space probe, astronomers from MPIA and Chalmers have revealed the 3D shapes of two large star-forming molecular clouds, the California Cloud and the Orion A Cloud. In conventional 2D images, they appear similarly structured, containing filaments of dust and gas with seemingly comparable densities. In 3D, however, they look quite distinct. In fact, their densities are much more different than their images projected on the plane of the sky would suggest. This result solves the long-standing mystery of why these two clouds form stars at different rates.​

Cosmic clouds of gas and dust are the birthplaces of stars. More specifically, stars form in the densest pockets of such material.
“Density, the amount of matter compressed into a given volume, is one of the crucial properties that determine star formation efficiency,” says Sara Rezaei Khoshbakht. She is an astronomer at Max Planck Insitute for Astronomy in Heidelberg, Germany and Chalmers University of Technology. She is the main author of a new article published in The Astrophysical Journal Letters today: Three-dimensional Shape Explains Star Formation Mystery of California and Orion A​.
In a pilot study portrayed in this article, Sara Rezaei Khoshbakht and co-author Jouni Kainulainen have applied a method which allows them to reconstruct 3D morphologies of molecular clouds to two giant star-forming clouds. Kainulainen is a scientist at the Chalmers University of Technology in Gothenburg, Sweden who used to work at MPIA as well. Their targets were the Orion A Cloud and the California Cloud.
Usually, measuring the density within clouds is hard. “Everything we see when we observe objects in space is their two-dimensional projection on an imaginary celestial sphere. Conventional observations lack the necessary depth for us to see the whole cloud” explains Jouni Kainulainen. He is an expert on interpreting the influence of cosmic matter on stellar light and calculating densities from such data.
“If the two clouds look the same from our point of view, our 3D models show that they have a completely different shape. You can simply liken it to seeing a pencil and a pancake from the side. On average, the Orion A – the pencil – is much denser than California, which explains its more pronounced star formation activity”, says Jouni Kainulainen.
This study proves its potential to improve star formation research in the Milky Way by adding a third dimension, and the work now published is only the first step of what the astronomers want to achieve. Sara Rezaei Khoshbakht pursues a project now that ultimately will produce the spatial distribution of dust in the entire Milky Way, and uncover its connection to star formation.​
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