3D Picture of an Interstellar Cloud: At Long Last, a Clue to Star Formation

A duo of astronomers has accomplished a difficult feat: determining the 3-D structure of an interstellar cloud, the birth site of stars. The advance not only reveals the true structure of the molecular cloud Musca, which differs from previous assumptions in looking more like a pancake than a needle, but it could also lead to a better understanding of the evolution of interstellar clouds in general, which will help astronomers answer the longstanding question: What determines the number and kind of stars formed in our Galaxy?

Visual representation of normal-mode analysis of striations in Musca: The first part of the movie gives an overview of the problem of viewing star-forming clouds in 2D projection. The second part of the video shows the striations in Musca, and the process through which the normal mode spatial frequencies are recovered. The third part of the movie demonstrates how the apparently complex profiles of the intensity cuts through striations are reproduced by progressively summing the theoretically predicted normal modes. At this part of the video (1:30-1:52) the spatial frequencies are scaled to the frequency range of human hearing and are represented by the musical crescendo. Finally, the results of a 3D MHD simulation of a cloud with dimensions comparable to those obtained for Musca through normal-mode analysis are presented. This material relates to a paper that appeared in the May 11, 2018, issue of Science, published by AAAS. The paper, by A. Tritsis at University of Crete in Crete, Greece, and colleagues was titled, “Magnetic seismology of interstellar gas clouds: Unveiling a hidden dimension.” Credit: Aris Tritsis, Nick Gikopoulos, Valerio Calisse, Kostas Tassis

Reconstructing the 3-D structure of interstellar clouds has been a major challenge, because astronomical objects can only be observed as 2-D projections on the sky. Determining the 3-D nature of the clouds is critical for a better understanding of the processes occurring within them. Here, Aris Tritsis and Konstantinos Tassis managed to reconstruct the full 3-D structure of Musca thanks to its striations (wispy stripe-like patterns). They show that these striations form by the excitation of fast magnetosonic waves (longitudinal magnetic pressure waves) – the cloud is vibrating, like a bell ringing after it has been struck. By analyzing the frequencies of these waves the authors produce a model of the cloud, showing that Musca is not a long, thin filament as once thought, but rather a vast sheet-like structure. From the 3-D reconstruction, the authors were able to determine the cloud’s density. Tritsis and Tassis note that, with its geometry now determined, Musca can be used to test theoretical models of interstellar clouds.

Reference: “Magnetic seismology of interstellar gas clouds: Unveiling a hidden dimension” by Aris Tritsis and Konstantinos Tassis, 11 May 2018, Science.
DOI: 10.1126/science.aao1185

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