Ghostly Gamma-Ray Beams Blast from Milky Way's Center


Milky Way galaxy. This artist's conception shows an edge-on view of the Milky Way galaxy. Newly discovered gamma-ray jets (pink) extend for 27,000 light-years above and below the galactic plane, and are tilted at an angle of 15 degrees. Previously known gamma-ray bubbles are shown in purple. The bubbles and jets suggest that our galactic center was much more active in the past than it is today. (Credit: David A. Aguilar (CfA))

ScienceDaily (May 29, 2012) — As galaxies go, our Milky Way is pretty quiet. Active galaxies have cores that glow brightly, powered by supermassive black holes swallowing material, and often spit twin jets in opposite directions. In contrast, the Milky Way's center shows little activity. But it wasn't always so peaceful. New evidence of ghostly gamma-ray beams suggests that the Milky Way's central black hole was much more active in the past.

"These faint jets are a ghost or after-image of what existed a million years ago," said Meng Su, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and lead author of a new paper in theAstrophysical Journal.

"They strengthen the case for an active galactic nucleus in the Milky Way's relatively recent past," he added.

The two beams, or jets, were revealed by NASA's Fermi space telescope. They extend from the galactic center to a distance of 27,000 light-years above and below the galactic plane. They are the first such gamma-ray jets ever found, and the only ones close enough to resolve with Fermi.

The newfound jets may be related to mysterious gamma-ray bubbles that Fermi detected in 2010. Those bubbles also stretch 27,000 light-years from the center of the Milky Way. However, where the bubbles are perpendicular to the galactic plane, the gamma-ray jets are tilted at an angle of 15 degrees. This may reflect a tilt of the accretion disk surrounding the supermassive black hole.

"The central accretion disk can warp as it spirals in toward the black hole, under the influence of the black hole's spin," explained co-author Douglas Finkbeiner of the CfA. "The magnetic field embedded in the disk therefore accelerates the jet material along the spin axis of the black hole, which may not be aligned with the Milky Way."

The two structures also formed differently. The jets were produced when plasma squirted out from the galactic center, following a corkscrew-like magnetic field that kept it tightly focused. The gamma-ray bubbles likely were created by a "wind" of hot matter blowing outward from the black hole's accretion disk. As a result, they are much broader than the narrow jets.

Both the jets and bubbles are powered by inverse Compton scattering. In that process, electrons moving near the speed of light collide with low-energy light, such as radio or infrared photons. The collision increases the energy of the photons into the gamma-ray part of the electromagnetic spectrum.

The discovery leaves open the question of when the Milky Way was last active. A minimum age can be calculated by dividing the jet's 27,000-light-year length by its approximate speed. However, it may have persisted for much longer.

"These jets probably flickered on and off as the supermassive black hole alternately gulped and sipped material," said Finkbeiner.

It would take a tremendous influx of matter for the galactic core to fire up again. Finkbeiner estimates that a molecular cloud weighing about 10,000 times as much as the Sun would be required.

"Shoving 10,000 suns into the black hole at once would do the trick. Black holes are messy eaters, so some of that material would spew out and power the jets," he said.

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Reproduction is very costly, and if you don't use it, you can live much longer-Monarch Butterfly-

Mystery of Monarch Butterfly Migration Takes New Turn

ScienceDaily (May 31, 2012) — During the fall, hundreds of millions of monarch butterflies living in eastern North America fly up to 1,500 miles to the volcanic forests of Mexico to spend the winter, while monarchs west of the Rocky Mountains fly to the California coast. The phenomenon is both spectacular and mysterious: How do the insects learn these particular routes and why do they stick to them?

A prevailing theory contends that eastern and western monarchs are genetically distinct, and that genetic mechanisms trigger their divergent migratory paths.

An analysis led by Emory University biologists, however, finds that the two groups of monarchs are genetically mixed. Their research, published in the journal Molecular Ecology, suggests that environmental factors may be the key to the butterflies' choice of winter homes, and to where they wind up in the spring.

"Our data gives the strongest signal yet that the eastern and western monarchs belong to a single genetic population," says Emory biologist Jaap de Roode, who led the research. "This distinction is important to help us better understand the behavior of the organism, and to conserve the monarch flyways."

In addition to researchers in the de Roode lab, the study involved a scientist from the Institute of Integrative Biology in Zurich, Switzerland.

Biologists have long been fascinated by the innate and learned behaviors underlying animal migrations. When monarchs are breeding, for instance, they can live up to four weeks, but when they are migrating, they can live as long as six months.

"As the day length gets shorter, their sexual organs do not fully mature and they don't put energy into reproduction. That enables them to fly long distances to warmer zones, and survive the winter," de Roode says. "It's one of the basic lessons in biology: Reproduction is very costly, and if you don't use it, you can live much longer."

Mass movements of animals have huge ecological impacts. They are also visually arresting, from the spectacle of giant herds of wildebeest trekking across the Serengeti to hundreds of thousands of sandhill cranes flocking along the banks of Nebraska's Platte River.

In the case of long-lived mammals and birds, the younger animals may learn some of the behaviors associated with migration. That's not the case with the monarchs, notes Amanda Pierce, a graduate student in Emory's Population Biology, Ecology and Evolution program, and a co-author of the study.

"We know there is no learning component for the butterflies, because each migration is separated by two to three generations," Pierce says. "To me, that makes the problem even more interesting. How can these small, delicate animals travel thousands of kilometers and arrive at the same destination as their great-great grandparents?"

The question of whether eastern and western monarchs are genetically the same has been hotly debated, and may be an essential piece to the puzzle of their divergent migration patterns.

The researchers used 11 genetic markers to compare the genetic structures of eastern and western monarchs, as well as non-migratory monarch populations in Hawaii and New Zealand. The results showed extensive gene flow between the eastern and western monarchs, and a genetic divergence between these North American butterflies and those from Hawaii and New Zealand.

"In a sense, the genetic markers provide a DNA 'fingerprint' for the butterflies," de Roode says. "Just by looking at this fingerprint, you can easily separate the butterflies of North America from those in Hawaii and New Zealand, but you can't tell the difference between the eastern and western monarchs."

The Emory researchers have now joined a project headed by Harvard, which also involves the University of Georgia and the University of Massachusetts, to sequence the full genomes of monarch butterflies from places around the world. That data should rule out genetic differences between the eastern and western monarchs, or reveal whether any smaller genetic differences, beyond the 11 markers used in the study, may be at play between the two groups.

The idea that eastern and western monarchs are distinct populations has been bolstered by tagging-and-tracking efforts based in the United States. That data, gathered through citizen science, indicates that the butterflies stay on separate sides of the Rocky Mountains -- a formidable high-altitude barrier.

De Roode, however, theorizes that when spring signals the eastern monarchs to leave the overwintering grounds in Mexico, they may simply keep radiating out, reproducing and expanding as long as they find milkweed plants, the food for their caterpillars.

"Few people have tagged the monarchs within Mexico to see where they go," he says, "because Mexico doesn't have as much citizen science as the U.S."

If the theory is correct, some of the monarchs leaving Mexico each spring may wind up in western North America, while others may filter into the eastern United States. This influx to the western U.S. could be crucial to survival of monarchs on that side of the continental divide.

"There are far fewer monarchs west of the Rockies," de Roode says. He notes that all of the overwintering monarchs on a typical overwintering site along the California coast consist of about the same number clustered onto a single big tree in Mexico's Monarch Butterfly Biosphere Reserve, where hundreds of millions of monarchs blanket the landscape in the winter.

The monarch butterfly migration has been called an endangered phenomenon, due to the loss of habitat along the routes. The Mexican overwintering sites, located in the Trans-Mexican Volcanic Belt region northwest of Mexico City, particularly suffer from deforestation. Drug trafficking in the region has decimated eco-tourism and hampered efforts to protect the trees.

"We hope our research can aid in the conservation of the monarch flyways," de Roode says.

Raising monarchs for release at weddings, memorials and other events is a growing industry, but U.S. Department of Agriculture regulations restrict shipping the butterflies across state lines.

De Roode stresses that this regulation should remain in force, even if further research confirms that eastern and western monarchs are genetically identical, because parasites that the butterflies carry can differ by region. "It's not a good idea to be shipping parasites around," he says.

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Fishy secrets could reverse spinal injury



The science behind the zebra fish’s ability to repair its spinal cord after an injury has been unlocked, the same technique could soon be used to heal human spines

Mirror Bureau

Posted On Thursday, May 31, 2012 at 08:05:27 AM


Scientists have unlocked the secrets of the zebra fish’s ability to heal its spinal cord after injury, in research that could deliver therapy for paraplegics and quadriplegics in the future.

A team from Monash University, led by Yona Goldshmit and Peter Currie, discovered the role of a protein in the remarkable self-healing ability of the fish.

The findings, detailed in The Journal of Neuroscience, could eventually lead to ways to stimulate spinal cord regeneration in humans.

When the spinal cord is severed in humans and other mammals, the immune system kicks in, activating specialised cells called glia to prevent bleeding into it, Currie said.

“Glia are the workmen of nervous system. The glia proliferate, forming bigger cells that span the wound site in order to prevent bleeding into it. They come in and try to sort out problems. A glial scar forms,” Currie said.

However, the scar prevents axons, threadlike structures of nerve cells that carry impulses to the brain, of neighbouring nerve cells from penetrating the wound. The result is paralysis.

“The axons upstream and downstream of the lesion sites are never able to penetrate the glial scar to reform. This is a major barrier in spinal cord regeneration,” Currie said.

In contrast, the zebra fish glia form a bridge that spans the injury site but allow the penetration of axons into it. The fish can fully regenerate its spine within two months of injury.

“You can’t tell there’s been any wound at all,” Currie said.

Scientists discovered the protein, called fibroblast growth factor (fgf), controlled the shape of the glia, and accounted for the difference in the response to spinal cord injury between humans and zebra fish. They showed the protein could be manipulated in the zebra fish to speed up tissue repair even more.

“The hope is that fgf could eventually be used to promote better results in spinal cord repair in people,” Currie said.



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