(Press-News.org) MADISON — 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."
The new study modeled stand-alone disk galaxies, those not influenced by another nearby galaxy or object. Some recent studies have explored the likelihood that spiral galaxies with a close neighbor — a nearby dwarf galaxy, for example — get their arms as gravity from the satellite galaxy pulls on the disk of its neighbor.
According to Vogelsberger and Hernquist, the new simulations can be used to reinterpret observational data, looking at both the high-density molecular clouds as well as gravitationally induced holes in space as the mechanisms that drive the formation of the characteristic arms of spiral galaxies.
###
Terry Devitt
608-262-8282
trdevitt@wisc.edu
EDITORS: Images are available to accompany this story: High-resolution still image at http://www.news.wisc.edu/newsphotos/galaxies13.html; video at https://www.youtube.com/watch?v=-ii0nksV2lY.
Puzzle of how spiral galaxies set their arms comes into focus.
Puzzle of how spiral galaxies set their arms comes into focus
2013-04-03
ELSE PRESS RELEASES FROM THIS DATE:
Epileptic seizures can propagate using functional brain networks
2013-04-03
New Rochelle, NY, April 2, 2013—The seizures that affect people with temporal-lobe epilepsy usually start in a region of the brain called the hippocampus. But they are often able to involve other areas outside the temporal lobe, propagating via anatomically and functionally connected networks in the brain. New research findings that link decreased brain cell concentration to altered functional connectivity in temporal-lobe epilepsy are reported in an article in Brain Connectivity, a bimonthly peer-reviewed publication from Mary Ann Liebert, Inc., publishers. The article ...
Negative emotions in response to daily stress take a toll on long-term mental health
2013-04-03
Our emotional responses to the stresses of daily life may predict our long-term mental health, according to a new study published in Psychological Science, a journal of the Association for Psychological Science.
Psychological scientist Susan Charles of the University of California, Irvine and colleagues conducted the study in order to answer a long-standing question: Do daily emotional experiences add up to make the straw that breaks the camel's back, or do these experiences make us stronger and provide an inoculation against later distress?
Using data from two national ...
Access to mental health care lacking for children, teens across the US
2013-04-03
ANN ARBOR, Mich. – Everyday, news reports detail the impact of the deficiencies in the nation's mental health care services. Even more startling, a survey from the University of Michigan reveals that many adults across the U.S. believe children and teens have extremely limited or no access to appropriate mental health care services.
The W.K. Kellogg Foundation commissioned the National Voices Project to facilitate a five year study to gauge opportunities available for children and teens at the local level in communities across the U.S. Officials at the National Voices ...
Total buzz kill: Metals in flowers may play role in bumblebee decline
2013-04-03
PITTSBURGH—Beekeepers and researchers nationally are reporting growing evidence that a powerful new class of pesticides may be killing off bumblebees. Now, research at the University of Pittsburgh points toward another potential cause: metal pollution from aluminum and nickel.
Published in the journal Environmental Pollution, the Pitt study finds that bumblebees are at risk of ingesting toxic amounts of metals like aluminum and nickel found in flowers growing in soil that has been contaminated by exhaust from vehicles, industrial machinery, and farming equipment. The ...
UC research examines ancient Puebloans and the myth of maize
2013-04-03
Research from the University of Cincinnati shows that perhaps the ancient Puebloans weren't as into the maize craze as once thought.
Nikki Berkebile, a graduate student in anthropology in UC's McMicken College of Arts & Sciences, has been studying the subsistence habits of Puebloans, or Anasazi, who lived on the southern rim of the Grand Canyon in the late 11th century. Traditional ethnographic literature indicates these ancient American Indians were heavily dependent on maize as a food source, but Berkebile isn't so sure about that.
"I'm trying to assess sustainable ...
Heart failure doesn't discriminate
2013-04-03
CHICAGO --- Lifetime risk for heart failure is similar for blacks and whites and higher than expected for both groups -- ranging from 20 to 45 percent -- according to a new Northwestern Medicine® study.
"This is a bad news scenario for both race groups," said Northwestern Medicine researcher Mark Huffman, M.D., the first author of the study. "With lifetime risks this high, heart failure prevention is paramount for all Americans."
Huffman is an assistant professor in preventive medicine and medicine-cardiology at Northwestern University Feinberg School of Medicine and ...
UC research on Maya village uncovers 'invisible' crops, unexpected agriculture
2013-04-03
The University of Cincinnati's mastery of ancient Maya mysteries continues with new research from professor of biological sciences David Lentz.
UC faculty have been involved in multiple research projects concerning ancient Maya culture for more than a decade. This latest Maya study from Lentz focuses on Cerén, a farming village that was smothered under several meters of volcanic ash in the late sixth century.
Lentz will present his research, "The Lost World of the Zapotitan Valley: Cerén and its Paleoecological Context," at the 78th annual meeting of the Society for ...
White blood cell enzyme contributes to inflammation and obesity
2013-04-03
ORLANDO, Fla., April 2, 2013 – Many recent studies have suggested that obesity is associated with chronic inflammation in fat tissues. Researchers at Sanford-Burnham Medical Research Institute (Sanford-Burnham) have discovered that an imbalance between an enzyme called neutrophil elastase and its inhibitor causes inflammation, obesity, insulin resistance, and fatty liver disease. This enzyme is produced by white blood cells called neutrophils, which play an important role in the body's immune defense against bacteria. The researchers found that obese humans and mice have ...
Fatty acid metabolite shows promise against cancer in mice
2013-04-03
(SACRAMENTO, Calif.) — A team of UC Davis scientists has found that a product resulting from a metabolized omega-3 fatty acid helps combat cancer by cutting off the supply of oxygen and nutrients that fuel tumor growth and spread of the disease.
The scientists report their discovery in the Proceedings of the National Academy of Sciences (PNAS). The groundbreaking study was a collaboration among multiple UC Davis laboratories and Harvard University.
The metabolite is epoxy docosapentaenoic acid (EDP), an endogenous compound produced by the human body from the omega-3 ...
An inside look at carnivorous plants
2013-04-03
When we imagine drama playing out between predators and prey, most of us picture stealthy lions and restless gazelle, or a sharp-taloned hawk latched on to an unlucky squirrel. But Ben Baiser, a post-doctoral fellow at the Harvard Forest and lead author of a new study in Oikos, thinks on a more local scale. His inter-species drama plays out in the humble bogs and fens of eastern North America, home to the carnivorous pitcher plant, Sarracenia purpurea. "It's shocking, the complex world you can find inside one little pitcher plant," says Baiser.
A pitcher plant's work ...