Using tens of thousands of stars observed by the Gaia space telescope
, astronomers from Max Planck Institute of Astronomy and Chalmers University of Technology 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 – streaks of denser 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 (MPIA) 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 the article, Sara Rezaei Khoshbakht and co-author Jouni Kainulainen of Chalmers have applied a method which allows them to reconstruct 3D morphologies of molecular clouds to two giant star-forming clouds – 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, 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 completely different shapes. It is a almost like they are a pencil and a pancake, seen from the side in our viewpoint in space. 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.
Image 1: This image from the VISTA infrared survey telescope at ESO’s Paranal Observatory in northern Chile covers the Orion A molecular cloud, the nearest known massive star factory. Lying about 1350 light-years from Earth, it reveals many young stars and other objects normally buried deep inside the dusty clouds.. ESO/VISION survey. Full scale photo with more information is available at the ESO website.
The other image details the shapes of the California and Orion A Clouds from two different perspectives. The colours indicate density, with red colours representing higher values. The images are based on the 3D reconstruction by Sara Rezaei Khoshbakht and Jouni Kainulainen.