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Puzzle of how spiral galaxies get their arms comes into focus

Puzzle of how spiral galaxies set their arms comes into focus

As the shapes of galaxies go, the spiral disk — with its characteristic pinwheel profile — is by far the most pedestrian.

Our own Milky Way, astronomers believe, is a spiral. Our solar system and Earth reside somewhere near one of its filamentous, swept-back arms. And nearly 70 percent of the galaxies closest to the Milky Way are spirals, suggesting they have taken the most ordinary of galactic forms in a universe with billions of galaxies.

But despite their common morphology, how galaxies like ours get and maintain their characteristic arms has proved to be an enduring puzzle in astrophysics. How do the arms of spiral galaxies arise? Do they change or come and go over time?

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. Writing April 1 in the Astrophysical Journal, a team of researchers from the University of Wisconsin-Madison and Harvard-Smithsonian Center for Astrophysics report simulations that seem to resolve longstanding questions about the origin and life history of spiral arms in disk galaxies.

“We show for the first time that stellar spiral arms are not transient features, as claimed for several decades,” says UW-Madison astrophysicist Elena D’Onghia, who led the new research along with Harvard-Smithsonian Center for Astrophysics colleagues Mark Vogelsberger and Lars Hernquist. “They are self-perpetuating, persistent and surprisingly long lived.”

The origin and fate of the emblematic spiral arms in disk galaxies have been debated by astrophysicists for decades, with two theories predominating: One holds that the arms come and go over time. 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.

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. Introduced into the simulation, the clouds, says D’Onghia, a UW-Madison professor of astronomy, act as “perturbers” and are enough to not only initiate the formation of spiral arms but to sustain them indefinitely.

“We find they are forming spiral arms,” explains D’Onghia. “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. It proves that once the arms are generated through these clouds, they can exist on their own through (the influence of) gravity, even in the extreme when the perturbations are no longer there.” …

via EurekaAlert

Using 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, researchers reveal new insights on how spiral galaxies get their arms.

Cambridge, Massachusetts – Spiral galaxies are some of the most beautiful and photogenic residents of the universe. Our own Milky Way is a spiral. Our solar system and Earth reside somewhere near one of its filamentous arms. And nearly 70 percent of the galaxies closest to the Milky Way are spirals.

But despite their common shape, how galaxies like ours get and maintain their characteristic arms has proved to be an enduring puzzle in astrophysics. How do the arms of spiral galaxies arise? Do they change or come and go over time?

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. 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.

“We show for the first time that stellar spiral arms are not transient features, as claimed for several decades,” says UW-Madison astrophysicist Elena D’Onghia, who led the new research along with Harvard colleagues Mark Vogelsberger and Lars Hernquist.

“The spiral arms are self-perpetuating, persistent, and surprisingly long lived,” adds Vogelsberger.

via SciDaily

The majority of galaxies aren’t spiral shaped. Most of the non-spiral ones are comprised of stars, planets, gas, and other cosmic dust clustered together, like a boring bowl of trail mix with all the M&Ms picked out. That stasis is partly why astrophysicists have long been enamored by the perplexing beauty of spiral galaxies, such as our own Milky Way. Spiral galaxies are a clear minority in the universe (just 15 percent of all galaxies spin), and they tend to raise more questions than they answer.

For instance, are a galaxy’s arms transient, merely a phase in its ongoing evolution? Or is the swirling, mesmerizing spin-cycle reflective of something stable, and quite possibly self-sustaining?

The answer, according to new research, may be the latter. Researchers from the University of Wisconsin and the Harvard-Smithsonian for Astrophysics have built an advanced new breed of simulation software to model just how disk galaxies form in the first place.

via TheWeek

In case you ever wondered.

 

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Fred Killer
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Fred Killer

If you start with a static gas cloud that gradually collapses under gravity, (Hydrogen being the basic building block of all matter, I would postulate), the center of gravity will become more dense and as it does it will have an asymmetrical gravitational effect on the surrounding particles. This asymmetry or imbalance will cause a galactically unique, directional turning moment or spin to occur at ever greater speed as more matter adds to it, so the initial creation of the arms is a result of the influence of the rotating center on the outer regions of the relatively static gas… Read more »

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