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Scientists Shed Light on How Spiral Galaxies are Formed

Apr 02, 2013 01:57 PM EDT
The Whirlpool Galaxy, a classic spiral galaxy, is pictured in this NASA handout photo. At only 30 million light years distant and fully 60 thousand light years across, M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies on the sky. This image is a digital combination of a ground-based image from the 0.9-meter telescope at Kitt Peak National Observatory and a space-based image from the Hubble Space Telescope highlighting sharp features normally too red to be seen.

Despite the fact that nearly 70 percent of the galaxies closest to the Milky Way - not to mention the Milky Way itself - is a spiral galaxy, exactly how they came to be shaped the way they are has long eluded scientists.

Previous debates in science have pitted two theories against one another, one stating that the spirals come and go over time and the other that the debris comprising them are caught in a massive, galactic traffic jam due to differences in gravity.

Using powerful new computer simulations, however, scientists from the University of Wisconsin-Madison and the Harvard-Smithsonian Center for Astrophysics believe they have solved the puzzle and that the answer lies somewhere in the middle of these two.

Simulating the motion of as many as 100 million "stellar particles," the team ascribes the formation of spirals to mass concentrations similar to giant molecular clouds that act as "perturbers" capable of generating spirals and sustaining them indefinitely through a process called "swing amplification."

"We show for the first time that stellar spiral arms are not transient features, as claimed for several decades," UW-Madison astrophysicist and study leader Elena D'Onghia said, according to Space Ref.

The reason for this, explained fellow researcher and Harvard scientist Mark Vogelsberger, is that the arms are in fact self-perpetuating, and thus "surprisingly long lived."

This notion, the idea that the spirals will continue even if these neublae are removed, is a radical realization for many scientists who for years thought that as soon as the "perturbers" disappeared, so would the spirals.

The reason they do, said D'Onghia, is the sustaining influence of their own gravity.

The study was published in the March 20th issue of The Astrophysical Journal and also included help from Vogelsberger's Harvard colleague Lars Hernquist.



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