Monday, December 7, 2009

A GALACTIC FOSSIL IN THE CORE OF THE MILKY WAY

0 comentarios

Astronomers using the W. M. Keck Observatory and the European Southern Observatory’s Very Large Telescope have identified two distinct groups of stars within the Milky Way Galaxy’s globular cluster Terzan 5. The two stellar populations have different ages and iron abundances, which are rare features among globular clusters, suggesting that Terzan 5 could be a surviving remnant of pre-existing galaxy.

Orbiting the Milky Way’s Galactic Center, Terzan 5 is among the brightest star clusters and would easily be seen through binoculars were it not for the veil of dust between the Earth and this cluster. It was thought to be a “common” globular cluster, a compact population of stars bound by gravity with the same age and chemical composition. The new observations of this cluster, published in the Nov. 26 issue of Nature, demonstrate that Terzan 5 is not a genuine globular cluster but is the remnant of a proto-galaxy that merged with similar systems to form the Galactic bulge.

This discovery opens a new window on the formation mechanisms of galaxies and could be the first observational evidence to confirm that the bulge of a galaxy originates from the merging of pre-formed, internally evolved systems of stars, said the study’s lead author, Francesco Ferraro of the University of Bologna in Italy.

Ferraro and his colleagues studied Terzan 5, which is located in the central bulge of the Galaxy—a region that has been hard to study because of its high concentration of interstellar dust. Yet, the astronomers were able to identify two, distinct stellar populations—a bright one whose stars are centrally concentrated and a second one, whose stars are fainter—within Terzan 5.

Spectral data taken with the Keck II telescope and its NIRSPEC instrument also demonstrated that the brighter branch is roughly three times richer in metals, specifically, iron, which is formed in supernovae, said team member R. Michael Rich, of the University of California at Los Angeles.

“This new population is in fact among the most metal rich stars that we know of; it’s kind of like finding a buried treasure in this unusual star cluster,” said Dr. Livia Origlia of the Bologna Observatory, who discovered the iron-rich stars.

Astronomers have not previously observed such an anomaly in a Galactic Globular Cluster. The Milky Way has roughly 150 globular clusters, and, until now, omega Centauri was the only stellar system where distinct stellar populations with different iron content and age have been detected. This suggests it is the remnant of a disrupted dwarf galaxy that merged with the Milky Way late during its evolution. The striking peculiarity of Terzan 5 is that its oldest population has the same metal content as the most metal rich bulge stars. This strongly suggests that it is the relic of a building block of the Bulge: similar stellar systems would have merged together to finally form the Bulge during the early epoch of galaxy assembly.

Modeling the differing ages and abundances of metals among the star population in the Terzan 5 cluster suggests the entire cluster experienced a second burst of star formation six billion years after the initial burst, Ferraro said.

The models also suggest that ejecta of supernova explosions are the likely source of the heavier elements within the metal rich, bright star population of Terzan 5. Supernova ejecta, however, can only remain in systems much more massive than the current globular clusters. Therefore, we surmise that Terzan 5 is very likely to be yet another tattered relic of a pre-existing galaxy that was shredded and engulfed by the Milky Way, and the dust-obscured central region of the Galaxy may harbor many more similar objects, Ferraro added.

(Photo: R. Ferraro (University of Bologna))

Keck Observatory

WHEN CAMOUFLAGE IS A PLANT'S BEST PROTECTION

0 comentarios

It is well known that some animal species use camouflage to hide from predators. Individuals that are able to blend in to their surroundings and avoid being eaten are able to survive longer, reproduce, and thus increase their fitness (pass along their genes to the next generation) compared to those who stand out more. This may seem like a good strategy, and fairly common in the animal kingdom, but who ever heard of a plant doing the same thing?

In plants, the use of coloration or pigmentation as a vital component of acquiring food (e.g., photosynthesis) or as a means of attracting pollinators (e.g., flowers) has been well studied. However, variation in pigmentation as a means of escaping predation has received little attention. In the December issue of the American Journal of Botany, Matthew Klooster from Harvard University and colleagues empirically investigated whether the dried bracts on a rare woodland plant, Monotropsis odorata, might serve a similar purpose as the stripes on a tiger or the grey coloration of the wings of the peppered moth, namely to hide.

"Monotropsis odorata is a fascinating plant species, as it relies exclusively upon mycorrhizal fungus, that associates with its roots, for all of the resources it needs to live," notes Klooster. "Because this plant no longer requires photosynthetic pigmentation (i.e., green coloration) to produce its own energy, it is free to adopt a broader range of possibilities in coloration, much like fungi or animals."

Using a large population of Monotropsis odorata, Klooster and colleagues experimentally removed the dried bracts that cover the 3- to 5-cm tall stems and flower buds of these woodland plants. The bracts are a brown color that resembles the leaf litter from which the reproductive stems emerge and cover the pinkish-purple colored buds and deep purple stems. When Klooster and colleagues measured the reflectance pattern of the different plant parts, they indeed found that the bracts functioned as camouflage, making the plant blend in with its surroundings; the bract reflectance pattern closely resembled that of the leaf litter, and both differed from that of the reproductive stem and flowers hidden underneath the bracts. Furthermore, they experimentally demonstrated that this camouflage actually worked to hide the plant from its predators and increased its fitness. Individuals with intact bracts suffered only a quarter of the herbivore damage and produced a higher percentage of mature fruits compared to those whose bracts were removed.

"It has long been shown that animals use cryptic coloration (camouflage) as a defense mechanism to visually match a component of their natural environment, which facilitates predator avoidance," Klooster said. "We have now experimentally demonstrated that plants have evolved a similar strategy to avoid their herbivores."

Drying its bracts early to hide its reproductive parts is a good strategy when the stems are exposed to predators for long periods of time: all the other species in the subfamily Monotropoideae have colorful fleshy bracts and are reproductively active for only a quarter of the length of time. Somewhat paradoxically however Monotropsis odorata actually relies on animals for pollination and seed dispersal. How does it accomplish this when it is disguised as dead leaf material and is able to hide so well? The authors hypothesize that the flowers emit highly fragrant odors that serve to attract pollinators and seed dispersal agents; indeed they observed bumble bees finding and pollinating many reproductive stems that were entirely hidden by the leaf litter itself.

(Photo: Matthew R. Klooste)

American Journal of Botany

'SAFETY VALVE' PROTECTS PHOTOSYNTHESIS FROM TOO MUCH LIGHT

0 comentarios
Photosynthetic organisms need to cope with a wide range of light intensities, which can change over timescales of seconds to minutes. Too much light can damage the photosynthetic machinery and cause cell death. Scientists at the Carnegie Institution were part of a team that found that specific proteins in algae can act as a safety valve to dissipate excess absorbed light energy before it can wreak havoc in cells.

The research, performed mostly by Graham Peers in the laboratory of Krishna Niyogi from the University of California, Berkeley, included researchers at the University of Münster, Germany, and used a mutant strain of the single-celled green alga Chlamydomonas reinhardtii, originally isolated at the Carnegie Institution, to show that a specific protein of the light harvesting family of proteins plays a critical role in eliminating excess absorbed light energy. A mutant lacking this protein, designated LHCSR, suffered severely when exposed to fluctuating light conditions. "Photosynthetic organisms must be able to manage absorbed light energy," says study co-author Arthur Grossman of Carnegie's Department of Plant Biology, "and the LHCSR proteins appear to be critical for algae to eliminate absorbed light energy as heat as light levels in the environment fluctuate, becoming potentially toxic."

Grossman points out that photosynthetic organisms have developed a number of different mechanisms for managing the absorption of light energy and that these different mechanisms may be tailored to the diversity of environments in which organisms have evolved. Some have evolved in deserts where both light levels and temperatures can be very high while others have evolved in alpine environments where the light levels can be very high and temperatures very low.

"As we understand more about the ways in which the environment impacts the evolution of the photosynthetic machinery, we may be able to introduce specific mechanisms into plants that allow them to better manage absorbed light energy, which in turn would let them survive harsher environmental conditions" Grossman says, "which would have obvious benefits for agriculture."

He also notes the current interest in using algae to generate biofuels, and the possibility of cultivating algae in deserts, where solar input can be extremely high. As he states, "If we are going to attempt this we have to make sure that we use the right algae that can thrive and produce oils at high levels under harsh environmental conditions. It's possible that we can also tailor various features of the photosynthetic machinery to let algae use light energy more efficiently and suffer less damage under extremely high light and temperature conditions, but I would emphasize that there are many extreme challenges associated with the creation of such robust, commercially viable strains."

Carnegie Institution of Washington

OCEANIC CRUST FORMATION IS DYNAMIC AFTER ALL

0 comentarios

Imagine the Earth’s crust as the planet’s skin: Some areas are old and wrinkled while others have a fresher, more youthful sheen, as if they had been regularly lathered with lotion.

Carry the metaphor a little further and a good picture emerges of the geological processes leading to the creation of the planet’s crust. On land, continental crust, once created, can remain more or less unaltered for billions of years. But the oldest oceanic crust is only about 200 million years old, as new crust is continually forming at midocean ridge spreading centers.

While geologists have known that oceanic crust continually replenishes itself, they have been unsure what occurs below the surface that leads to the resurfacing. What geodynamics are occurring in the mantle that eventually produces new crust, that new layer of skin on the ocean’s bottom?

The answer has been elusive in part because oceanic crust is difficult to reach and instruments that can measure seismic activity have not fully covered the terrain to obtain an accurate picture of forces below the surface. Now earth scientists led by Brown University have observed — in detail and at unprecedented depths — a geological phenomenon known as dynamic upwelling in the underlying mantle beneath a spreading center. Their findings, reported in this week’s Nature, may resolve a longstanding debate regarding the relative importance of passive and dynamic upwelling in the shallow mantle beneath spreading centers on the seafloor.

“We know the crust of the ocean is produced by upwelling beneath separating plates,” said Don Forsyth, professor of geological sciences at Brown. “We just didn’t know the upwelling pattern that took place, that there are concentrated upwelling centers rather than uniform upwelling.”

Mantle upwelling and melting beneath spreading centers has been thought to be mostly a passive response to the separating oceanic plates above. The new finding shows there appears to be a dynamic component as well, driven by the buoyancy of melt retained in the rock or by the lighter chemical composition of rock from which melt has been removed.

The scientists from Brown and the University of Rhode Island based their findings on a high-resolution seismic study in the Gulf of California. In that region, there are 25 seismometers spaced along the western coast of Mexico and the Baja California peninsula, which lie on either side of the Gulf of California. Yun Wang, a Brown graduate student and the paper’s lead author, tracked the velocity of seismic waves that traveled from one station to another. She noticed a pattern: The seismic waves in three localized centers, spaced about 250 kilometers (155 miles) apart, traveled more slowly than waves in the surrounding mantle, implying the presence of more melt in the localized centers and thus a more vigorous upwelling. From that, the geologists determined the centers, located 40-90 kilometers (25 to 56 miles) below the surface, showed evidence of dynamic upwelling in the mantle.

“We found a pattern that was predicted by some of the theoretical models of upwelling in midoceanic ridges,” Forsyth said.

While other studies have been done of mantle geodynamics, most notably an experiment on the East Pacific Rise, the Brown-URI study imaged seismic activity, or the shear velocity of the seismic waves, some 200 kilometers (124 miles) below the surface — a far deeper seismic penetration into the mantle than previous experiments.

Brian Savage, assistant professor of geophysics at the University of Rhode Island and a contributing author on the paper, said the finding is important, because it helps to provide “a basic understanding of how a majority of the earth’s crust is formed, how it emerges from the mantle below to create the oceanic crust. It's a basic science question that helps understand how crust is created.”

(Photo: Yun Wang/Brown University)

Brown University

CUTTING GREENHOUSE POLLUTANTS COULD DIRECTLY SAVE MILLIONS OF LIVES WORLDWIDE

0 comentarios

Tackling climate change by reducing carbon dioxide and other greenhouse emissions will have major direct health benefits in addition to reducing the risk of climate change, especially in low-income countries, according to a series of six papers appearing in the British journal The Lancet.

Two University of California, Berkeley, authors of the papers - Kirk R. Smith, professor of global environmental health, and Michael Jerrett, associate professor of environmental health sciences - discussed the results at a press conference in Washington, D.C.

The studies, three of them coauthored by Smith and one coauthored by Jerrett, use case studies to demonstrate the co-benefits of tackling climate change in four sectors: electricity generation, household energy use, transportation, and food and agriculture.

"Policymakers need to know that if they exert their efforts in certain directions, they can obtain important public health benefits as well as climate benefits," said Smith, who was the principal investigator in the United States for the overall research effort. "Climate change threatens us all, but its impact will likely be greatest on the poorest communities in every country. Thus, it has been called the most regressive tax in human history. Carefully choosing how we reduce greenhouse gas emissions will have the added benefit of reducing global health inequities."

Each study in the series examines the health implications in both high- and low-income countries of actions designed to reduce the release of carbon dioxide (CO2) and other greenhouse gases. Climate change due to emission of greenhouse gases from fossil fuel energy sources causes air pollution by increasing ground-level ozone and concentrations of fine particulate matter.

The studies were commissioned by the NIEHS, part of the National Institutes of Health (NIH), in part to help inform discussions next month at the U.N. Framework Convention on Climate Change in Copenhagen. The NIEHS is one of the key sponsors of the international event.

"These papers demonstrate there are clear and substantive improvements for health if we choose the right mitigation strategies for reducing greenhouse gas emissions," said Birnbaum. "We now have real life examples of how we can save the environment, reduce air pollution and decrease related health effects; it's really a win-win situation for everyone."

A case study led by Smith on the health and climate benefits from a potential 150-million-stove program in India from 2010-2020 gives the largest co-benefit of any examined in the six papers. Smith has shown that providing low-emission stove technologies in poor countries that currently rely on solid fuel household stoves to cook and heat their homes is a very cost-effective climate change linkage. The 10-year program could prevent 2 million premature deaths in India, he said, in addition to reducing greenhouse pollution by hundreds of millions of tons.

The paper coauthored by Jerrett contains analysis of 18 years of data on the long-term health effects of black carbon - the first study of its kind ever conducted. The study followed 352,000 people in 66 U.S. cities and was conducted by a team of U.S. and Canadian researchers led by Jerrett and Smith. Black carbon is a short-lived greenhouse pollutant which, along with ozone, is responsible for a significant proportion of global warming. Unlike CO2, these short-lived greenhouse pollutants exert significant direct impacts on health. Also, because they are short-lived, emission controls are almost immediately reflected in changes in warming.

"Combustion-related air pollution is estimated to be responsible for nearly 2.5 million premature deaths annually around the world and also for a significant portion of greenhouse warming," said Smith. "These studies provide the kind of concrete information needed to choose actions that efficiently reduce this health burden as well as reduce the threat of climate change"

In a statement issued today to the media, Secretary of the U.S. Department of Health and Human Services Kathleen Sebelius thanked the international research team for bringing the world's attention to the co-benefits of tackling climate change.

"Although much of the climate change discussion to date has focused on the environmental impacts, we are learning more about how climate change is likely going to affect the health of millions of people," she said. "Climate change is not a problem that one country or one organization can solve on its own. It's a problem that affects us all."

(Photo: Matt Evans)

University of California, Berkeley

STUDY SHEDS LIGHT ON BRAIN'S FEAR PROCESSING CENTER

0 comentarios
Breathing carbon dioxide can trigger panic attacks, but the biological reason for this effect has not been understood. A new study by University of Iowa researchers shows that carbon dioxide increases brain acidity, which in turn activates a brain protein that plays an important role in fear and anxiety behavior.

The study, published in the Nov. 25 issue of the journal Cell, offers new possibilities for understanding the biological basis of panic and anxiety disorders in general and may suggest new approaches for treating these conditions.

The researchers focused on a brain protein known as acid-sensing ion channel 1a (ASIC1a). This protein is abundant in the amygdala -- the region deep in the brain that processes fear signals and directs fear behavior. The UI team previously found that blocking or removing ASIC1a reduces innate fear and alters fear memory in mice.

"As long ago as 1918, scientists learned that carbon dioxide triggers abnormal responses in patients with anxiety disorders, but our study provides the first molecular evidence for a mechanism that explains how carbon dioxide can trigger fear and anxiety," said John Wemmie, M.D., Ph.D., associate professor of psychiatry and neurosurgery at the UI Carver College of Medicine and a staff physician and researcher at the Iowa City Veterans Affairs Medical Center. "The findings are a foundation for saying that ASIC proteins in the amygdala might play a key role in sensitivity to carbon dioxide."

In addition to helping explain why breathing carbon dioxide can trigger panic attacks, the study also suggests a new role for the amygdala as a sensor that can detect certain fear signals for itself.

"This is a new finding that the amygdala, which is considered the brain's computer processor for fear, can also function as a sensor for detecting chemical signals -- carbon dioxide and acidity (low pH) -- that are known to trigger panic attacks in susceptible individuals," Wemmie said.

Carbon dioxide inhalation can be deadly at high doses. The study suggests that evolution may have provided humans with a vital ability to detect and respond rapidly to carbon dioxide by placing within the same brain region the ability to detect the threat posed by carbon dioxide and the ability to initiate a "fight or flight" response.

The new study shows that inhaled carbon dioxide increases brain acidity and evokes fear behavior in mice by activating ASIC1a in the amygdala. Fear memory is also enhanced when carbon dioxide activates the protein.

Conversely, the study team, including first author Adam Ziemann, M.D., Ph.D., found that making brain tissue less acidic (raising brain pH) blunted fear behavior produced by carbon dioxide and reduced learned fear.

"It's been suggested that controlling breathing with breath exercises could have anti-anxiety effects," Wemmie said. "Our results make me wonder if some of those breath exercises to control fear and anxiety might be acting by inhibiting the ASIC channels in the amygdala by raising the pH."

Wemmie and his colleagues are now investigating whether ASIC1a abnormalities contribute to panic and anxiety disorder in people or to carbon dioxide sensitivity in patients with panic disorder.

If ASIC1a plays the same role in people as the studies suggest it does in mice, then drugs that target ASIC channels or strategies that alter brain acidity could hold promise for treating a wide range of panic and anxiety disorders.

University of Iowa

Followers

Archive

 

Selected Science News. Copyright 2008 All Rights Reserved Revolution Two Church theme by Brian Gardner Converted into Blogger Template by Bloganol dot com