“Past theory held the arms would go away with the perturbations removed, but we see that (once formed) the arms self-perpetuate, even when the perturbations are removed. ![]() “We find they are forming spiral arms,” said D’Onghia. Credit: Thiago Ize & Chris Johnson (Scientific Computing and Imaging Institute) These simulations suggest that the arms arise as a result of the influence of giant molecular clouds – star forming regions or nurseries common in galaxies. Powerful new computer simulations are allowing astronomers to understand how spiral arms in galaxies form and survive. Introduced into the simulation, the clouds act as “perturbers” and are enough to not only initiate the formation of spiral arms but to sustain them indefinitely. The new results fall somewhere in between the two theories and suggest that the arms arise in the first place as a result of the influence of giant molecular clouds-star forming regions or nurseries common in galaxies. A second and widely held theory is that the material that makes up the arms – stars, gas and dust – is affected by differences in gravity and jams up, like cars at rush hour, sustaining the arms for long periods. One holds that the arms come and go over time. The origin and fate of the emblematic spiral arms in disk galaxies have been debated by astrophysicists for decades, with two theories predominating. “The spiral arms are self-perpetuating, persistent, and surprisingly long lived,” said Vogelsberger. New research finds that spiral arms are self-perpetuating, persistent, and surprisingly long lived. Nearly 70 percent of the galaxies closest to the Milky Way are spirals. This Hubble Space Telescope photo of Messier 74 reminds us that spiral galaxies are some of the most beautiful and photogenic residents of the universe. “We show for the first time that stellar spiral arms are not transient features, as claimed for several decades,” said UW-Madison astrophysicist Elena D’Onghia, who led the new research along with Harvard colleagues Mark Vogelsberger and Lars Hernquist. A team of researchers from the University of Wisconsin-Madison and the Harvard-Smithsonian Center for Astrophysics reports simulations that seem to resolve long-standing questions about the origin and life history of spiral arms in disk galaxies. The answers to these and other questions are now coming into focus as researchers capitalize on powerful new computer simulations to follow the motions of as many as 100 million “stellar particles” as gravity and other astrophysical forces sculpt them into familiar galactic shapes. ![]() How do the arms of spiral galaxies arise? Do they change or come and go over time? And nearly 70 percent of the galaxies closest to the Milky Way are spirals.īut despite their common shape, how galaxies like ours get and maintain their characteristic arms has proved to be an enduring puzzle in astrophysics. Our solar system and Earth reside somewhere near one of its filamentous arms. Spiral galaxies are some of the most beautiful and photogenic residents of the universe.
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