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Wrapping Around The Mystery Of Spiral Galaxy Arms

Credit: Thiago Ize & Chris Johnson (Scientific Computing and Imaging Institute)

Credit: Thiago Ize & Chris Johnson (Scientific Computing and Imaging Institute)

How disk galaxies form their spiral arms have been puzzling astrophysicists for almost as long as they have been observing them. With time, they have come to two conclusions… either this structure is caused by differences in gravity sculpting the gas, dust and stars into this familiar shape, or its just a random occurrence which comes and goes with time.

Now researchers are beginning to wrap their conclusions around findings based on new supercomputer simulations – simulations which involve the motion of up to 100 million “stellar particles” that mimic gravitational and astrophysical forces which shape them into natural spiral structure. The research team from the University of Wisconsin-Madison and the Harvard-Smithsonian Center for Astrophysics are excited about these conclusions and report the simulations may hold the essential clues of how spiral arms are formed.

“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.

When it comes to spiral structure, it’s probably the most widely occurring of universal shapes. Our own Milky Way galaxy is considered to be a spiral galaxy and around 70% of the galaxies near to us are also spiral structured. When we think in a broader sense, just how many things take on this common formation? Whisking up dust with a broom causes particles to swirl into a spiral shape… draining water invokes a swirling pattern… weather formations go spiral. It’s a universal happening and it happens for a reason. Apparently that reason is gravity and something to perturb it. In the case of a galaxy, it’s a giant molecular cloud – the star-forming regions. 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.”

So, what of companion galaxies? Can spiral structure be caused by proximity? The new research also takes that into account and models for “stand alone” galaxies as well. However, that’s not all the study included. According to Vogelsberger and Hernquist, the new computer-generated simulations are focusing on clarifying observational data. They are taking a closer look at the high-density molecular clouds and the “gravitationally induced holes in space” which act as ” the mechanisms that drive the formation of the characteristic arms of spiral galaxies.”

Until then, we know spiral structure isn’t just a chance happening and – to wrap things up – it’s probably the most common form of galaxy in our Universe.

Original Story Source: Harvard-Smithsonian Center for Astrophysics.

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

Comments on this entry are closed.

  • Torbjörn Larsson April 3, 2013, 7:47 PM

    Cool. So unless it is an elliptical or irregular, it has to be a spiral. I assume that is pretty much what we see?

  • Aqua4U April 3, 2013, 8:02 PM

    Now that’s a ‘trippy’ video! This is an animation of the actual computational results – right? My sound card and bass speakers were vibrating BIG TIME! Those long, low ‘lunar notes’ DO have a tendency to inspire awe – church organ like. Worked for me anyway!

    oTay then… Big bang primordial dust clouds being gravitationally induced to ‘spin up’ do make sense as per the computationally induced parameters. My question is, how much of this is a result of a ‘confirmation bias’? Or in other words, working within the given standard model the numbers and data can be coerced to conform to the desired results.

    Another possibility (?) is that we live in a multiverse where the confluence of accumulative multidimensional vertices rotate when slowed below the speed of light and release copious amounts of energy upon entering the 4 dimensional restrictions of our space time? Now, if only I had a quantum computer to show that, I think I’d use Vivaldi for the background music!

    • Me April 3, 2013, 9:52 PM

      I must aquire a solid sound system for my ‘puter. Looks like I am missing out Aqua. I got a great sound system for Led Zeppelin, Rare Earth & etc, but not for my ‘puter. Thanks for reminding me Aqua ;-).

      • Aqua4U April 3, 2013, 11:26 PM

        Yeah.. I like to listen to Astronomy.fm or other web radio stations while cruising science sites, answering emails, working on my aqua farm layouts or checking out the cool YouTube videos UT posts!

  • Erin Fritz April 5, 2013, 6:36 AM

    Am I missing something? It appears in the simulation that the stars are all moving with the arms. That is the intuitive understanding of a spiral galaxy (similar to water spiraling in to a drain). But aren’t the arms formed by gravity waves that pass through regions of space creating stars but moving on. I always imagined this as an invisible wave moving faster than the stars and moving through them. The stars are still orbiting the galactic center, but I pictured this orbit as separate from the gravity waves.

    See also:

    http://www.universetoday.com/30217/spiral-galaxy/

  • Prism2Spectrum April 12, 2013, 3:01 PM

    The top-view simulation, in 2nd half of video, is especially dramatic.

    From alternate worldview, no surprise that the elegant design and artful beauty of the spiral structure in Space, appears not of “random occurrence which comes and goes with time.” But rather, emerges “self-perpetuating, persistent, and surprisingly long lived,…” One could say, purposeful – through fashioning laws of physics in space, and shaping forces of time.

    Elegant form and artful beauty, not of chance arise.

    “When it comes to spiral structure, it’s probably the most widely occurring of universal shapes.”

    From Nautilus Shell of inner space, to pine cone of highland place; from sea whirlpools of brief turn, to field Sunflowers of unfolded growth, that geometry pattern is everywhere evident:

    “The spiral has universal appeal and has a mysterious resonance with the human spirit, it is complex yet simple, intriguing and beautiful. The spiral pattern is found extensively in nature – encoded into plants, animals, humans, the earth and galaxies around us. Mathematics can explain the complex algorithms, sequences and equations that make up a spiral pattern, but it can’t explain the lure and fascination of the spiral to the human heart.” – Original Beauty

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