The «song» of interstellar cloud Musca reveals Star Formation Mysteries to European Astrophysicists
An important leap in our understanding of the star formation process was achieved by scientists at the University of Crete and the Institute of Electronic Structure and Laser at the Foundation for Research and Technology – Hellas. Using archival data from ESA’s Herschel mission, Aris Tritsis and Kostas Tassis have discovered, for the first time, an interstellar cloud – a nursery of stars – the magnetic field of which vibrates! Decrypting the «song» in this vibration, they managed to reveal the true 3D structure of the cloud, paving the way to solving one of the biggest mysteries in Astrophysics: what determines the number and kind of stars and planets that are formed in our Galaxy?
The discovery, which is published in Science, was part of Dr. Tritsis’s doctoral thesis, which he completed at the Physics Department of the University of Crete, under Prof. Tassis’s guidance.
«Star formation remains one of the biggest unsolved problems in Astrophysics», Prof. Tassis commented, and added: «We know that stars are born in interstellar gas clouds of “astronomical” dimensions, but exactly what happens when going from clouds to stars like our Sun, and to planets, is still a mystery. What determines whether a cloud will make many small stars, or a few large ones? What fraction of the cloud will turn into stars, and what fraction will be recycled? »
The physical processes governing star formation leave their imprint in the 3D shape of clouds. These are the clues that scientists would love to follow in order to decode the physical processes hiding behind star formation. But, until now, this was not possible: even the most advanced telescopes can only map the 2D projection of clouds on the sky, not their 3D structure.
«And here enters Musca, an isolated cloud in the southern sky which, in its 2D projection appears like a filament, like a needle» said Dr. Tritsis, who completed his studies in Crete in 2017 and is now a postdoctoral fellow at the Australian National University in Canberra. «We discovered that the magnetic field of Musca vibrates as a whole, it “sings”. The frequencies of this “song” encode the true 3D shape of the cloud, much like the frequencies of a musical instrument: a trumpet produces a sound much different than a tuba. A violin sounds distinctly different than a cello. So is the case with Musca: using the song that was imprinted in filamentary structures that thread the cloud, we calculated that its depth – the dimension that we cannot see in the direction along the line of sight – is not small at all. In fact, it is comparable to the size of the cloud as we see it on the sky. Musca is the largest object in the Galaxy that is vibrating as a whole».
«It was a big surprise », Prof. Tassis added. «Up to now, Musca was considered by all Astrophysicists, to be the poster-child of a filamentary cloud. However, its “song” proved that in fact it has the shape of a pancake, we just happen to see it edge-on. This shape is a strong indication that the magnetic field of the Galaxy plays an important role in the formation and structure of interstellar clouds. It has allowed us to simulate Musca’s structure in great detail, paving the way for scientists to use it as a prototype “laboratory” within which we can study the star formation process in greater detail than ever before».
The study was funded by the EU (FP7 actions Marie Curie, ERC-CoG, and REGPOT) and made use of the Metropolis HPC facility at the Center of Quantum Complexity and Nanotechnology of the University of Crete. It is published in Science, issue of 11 May 2018.
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