This indicates the lunar crust is being pulled apart at these locations. These linear valleys, known as graben, form when the moon’s crust stretches, breaks and drops down along two bounding faults. A handful of these graben systems have been found across the lunar surface.

“We think the moon is in a general state of global contraction because of cooling of a still hot interior,” said Thomas Watters of the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington, and lead author of a paper on this research appearing in the March issue of the journal Nature Geoscience. “The graben tell us forces acting to shrink the moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the moon cannot be large, or the small graben might never form.”

The weak contraction suggests that the moon, unlike the terrestrial planets, did not completely melt in the very early stages of its evolution. Rather, observations support an alternative view that only the moon’s exterior initially melted forming an ocean of molten rock.

In August 2010, the team used LROC images to identify physical signs of contraction on the lunar surface, in the form of lobe-shaped cliffs known as lobate scarps. The scarps are evidence the moon shrank globally in the geologically recent past and might still be shrinking today. The team saw these scarps widely distributed across the moon and concluded it was shrinking as the interior slowly cooled.

Based on the size of the scarps, it is estimated that the distance between the moon’s center and its surface shank by approximately 300 feet. The graben were an unexpected discovery and the images provide contradictory evidence that the regions of the lunar crust are also being pulled apart.

“This pulling apart tells us the moon is still active,” said Richard Vondrak, LRO Project Scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “LRO gives us a detailed look at that process.”

As the LRO mission progresses and coverage increases, scientists will have a better picture of how common these young graben are and what other types of tectonic features are nearby. The graben systems the team finds may help scientists refine the state of stress in the lunar crust.

“It was a big surprise when I spotted graben in the far side highlands,” said co-author Mark Robinson of the School of Earth and Space Exploration at Arizona State University, principal investigator of LROC. “I immediately targeted the area for high-resolution stereo images so we could create a three-dimensional view of the graben. It’s exciting when you discover something totally unexpected and only about half the lunar surface has been imaged in high resolution. There is much more of the moon to be explored.”

The research was funded by the LRO mission, currently under NASA’s Science Mission Directorate at NASA Headquarters in Washington. LRO is managed by NASA’s Goddard Space Flight Center in Greenbelt, Md.
Source: NASA

The Chandra data reveal the huge spiral structure in the hot gas around the outside of the image. Zooming in on the cluster reveals “cavities” or “bubbles” surrounding the central giant elliptical galaxy. The spiral began when a small cluster of galaxies collided off-center with a larger one positioned around that central galaxy.

The gravitational attraction of the smaller cluster drew the hot gas out of the central cluster toward the smaller cluster. Once the smaller cluster passed by the central cluster core, the gas movement reversed and it was pulled back toward the center of the main cluster. The hot cluster gas overshot the cluster center, creating the “sloshing” effect that is like the sloshing that occurs when a glass holding a liquid is quickly jerked sideways. In the cluster, gravity pulls back on the gas cloud, creating the spiral pattern.

For scientists, the observation of the “sloshing” motion in Abell 2052 is important for two reasons. First, the “sloshing” helps to move some of the cooler, dense gas in the center of the core farther away from the core. This cooler gas is only about 10 million degrees, as compared to the average temperature of 30 million degrees. This movement reduces the amount of cooling in the cluster core and could limit the amount of new stars being formed in the central galaxy. The “sloshing” movement in Abell 2052 also helps redistribute heavy elements like iron and oxygen, which are created out of supernova explosions. These heavy elements are an important part of the make-up of future stars and planets. The fact that Chandra’s observation of Abell 2052 lasted more than a week was critical in providing scientists with the details detected in this image.

Besides the large-scale spiral feature, the Chandra observations also allowed scientists to see details in the center of the cluster related to outbursts from the supermassive black hole. The data reveal bubbles resulting from material blasted away from the black hole which are surrounded by dense, bright, cool rims. In the same way that the “sloshing” helps to reduce the cooling of the gas at the core of the cluster, the bubble activity has the same effect, limiting the growth of the galaxy and its supermassive black hole.

This research was published in the August 20, 2011 issue of The Astrophysical Journal. The authors were Elizabeth Blanton of Boston University, Boston, MA; Scott Randall of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA; Tracy Clarke of the Naval Research Laboratory, Remote Sensing Division, in Washington DC; Craig Sarazin of the University of Virginia in Charlottesville, VA; Brian McNamara of the University of Waterloo in Waterloo, Canada; Edmund Douglass of Boston University and Michael McDonald of the University of Maryland, College Park, MD.

Source: Naval Research Laboratory

It was the culmination of work started in 2003. Heeding lessons learned from the Hubble Space Telescope, the program adopted the strategy of tackling the most difficult technical challenges first. That decision proved to be the right one. In June, all 18 flight primary mirror segments, plus the secondary, tertiary and fine steering mirrors, were polished and coated yielding exquisite surfaces that will enable Webb to image the most distant galaxies.

Two of Webb’s supporting and pathfinder structures were also completed. To assemble the flight telescope on the ground, a 139,000 pound structure will install the flight mirrors using an overhead track system supporting a robotic arm. The huge platform has been completed and assembled in the ultra-clean room used for telescope assembly at Goddard.

Also finished was the pathfinder backplane, a full-scale engineering model of the center section of the flight backplane. The backplane holds the mirror segments in place to form a single primary mirror. The full pathfinder element will consist of 12 of the 18 hexagonal cells (the center section of the primary mirror) of the telescope and contain a subset of two primary mirror segment assemblies, the secondary mirror, and the subsystem containing the tertiary and fine steering mirrors. It will demonstrate integration and test procedures that will be used on the flight telescope.

Webb’s giant sunshield moved forward into a new testing phase last year, the final step before fabrication of the flight sunshield. Sunshield layer three became the first of five full-size flight-like layers stretched out in a fully simulated flight configuration. This enables engineers to make 3-D shape measurements that will tell them how the full-size sunshield layers will behave in space. Completing this test is a critical step in the sunshield’s development and gives the engineers confidence and experience needed to manufacture the five flight layers.

An important sunshield deployment flight structure also completed fabrication in 2011. The space-qualified graphite composite tubes that will enable the sunshield to deploy in space have finished fabrication. The telescoping tube system was designed at Astro Aerospace, a business unit of Northrop Grumman.

Capping the year’s achievements, Webb’s spacecraft also moved forward. The propulsion system’s 16 monopropellant rocket engine thrusters, which control momentum and station-keeping on orbit, were upgraded to accept higher heat loading from the sunshield. Propulsion engineers also completed building four flight secondary combustion augmented thrusters which maintain orbit after the launch vehicle finishes its burns. Engineers also verified the flight software responsible for ground commands and science data delivery.

Successor to the Hubble Space Telescope, the James Webb Space Telescope is the world’s next-generation space observatory. It is the most powerful space telescope ever built. Webb will observe the most distant objects in the universe, provide images of the very first galaxies ever formed and study planets around distant stars. The Webb Telescope is a joint project of NASA, the European Space Agency and the Canadian Space Agency.

For more information about the James Webb Space Telescope, visit: www.jwst.nasa.gov
Source: NASA

• Portable refractor telescope for aspiring astronomers
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Great areas for the lunar eclipse can be found in Alaska, Hawaii, northwestern Canada, Australia, New Zealand, and central and eastern Asia. Over the contiguous United States and Canada, the eastern zones will see either only the initial penumbral stages before moonset, or nothing at all.

The Large Magellanic Cloud (LMC) is a popular galaxy among astronomers both for its nearness to our Milky Way and for the spectacular view it provides, a big-picture vista impossible to capture of our own galaxy.

“If you imagine a galaxy being a disc, the LMC is tilted almost face-on so we can look down on it, which gives us a very clear view of what’s going on inside,” Wong said.

Although astronomers have a working theory of how individual stars form, they know very little about what triggers the process or the environmental conditions that are optimal for star birth. Wong’s team focused on areas called molecular clouds, which are dense patches of gas — primarily molecular hydrogen — where stars are born. By studying these molecular clouds and their relationship to new stars in the galaxy, the team hopes to learn more about the metamorphosis of gas clouds into stars.

“When we study star formation, an important question is, what is the environment doing? How does the location of star formation reflect the conditions of that environment? There’s no better place to study the wider environment than the LMC.”

Using a 22-meter-diameter radio telescope in Australia, the astronomers mapped more than 100 molecular clouds in the LMC and estimated their sizes and masses, identifying regions with ample material for making stars. This seemingly simple task engendered a surprising find.

Conventional wisdom states that most of the molecular gas mass in a galaxy is apportioned to a few large clouds. However, Wong’s team found many more low-mass clouds than they expected — so many, in fact, that a majority of the dense gas may be sprinkled across the galaxy in these small molecular clouds, rather than clumped together in a few large blobs.

“We thought that the big clouds hog most of the mass,” Wong said, “but we found that in this galaxy, it appears that the playing field is more level. The low-mass clouds are quite numerous and they actually contribute a significant amount of the mass. This provides the first evidence that the common wisdom about molecular clouds may not apply here.”

The large numbers of these relatively low-mass clouds means that star-forming conditions in the LMC may be relatively widespread and easy to achieve. The findings raise some interesting questions about why some galaxies stopped their star formation while others have continued it.

To better understand the connection between molecular clouds and star formation, the team compared their molecular cloud maps to maps of infrared radiation, which reveal where young stars are heating cosmic dust.

For the comparison, they exploited a carefully selected sample of newborn heavy stars compiled by U. of I. astronomy professor You-Hua Chu and resident scientist Robert Gruendl, who also were co-authors of the paper. These stars are so young that they are still deeply embedded in cocoons of gas and dust.

“It turns out that there’s actually very nice correspondence between these young massive stars and molecular clouds,” Wong said. “That’s not entirely surprising, but it’s reassuring. We assume that these stars have to form in molecular clouds, and it tells us that the molecular clouds do hang around long enough for us to see them associated with these massive young stars.”

Wong hopes to continue to study the relationship between molecular clouds and star formation in greater detail. If researchers can determine the relative ages of young stars, they can correlate these against molecular clouds to figure out which clouds have star formation, how long the clouds live and what eventually leads to their destruction. They also plan to use a newly constructed array of telescopes in Chile to see the cloud environment in higher resolution, pinpointing exactly where inside the molecular cloud star formation will occur.

“This study provides us with our most detailed view of an entire population of clouds in another galaxy,” Wong said. “We can say with great confidence that these clouds are where the stars form, but we are still trying to figure out why they have the properties they do.”

The National Science Foundation and NASA supported this work.

Source: University of Illinois at Urbana-Champaign

To better understand the complex conditions driving this type of supernova, the researchers performed new 3-D calculations of the turbulence that is thought to push a slow-burning flame past its limits, causing a rapid detonation — the so-called deflagration-to-detonation transition (DDT). How this transition might occur is hotly debated, and these calculations provide insights into what is happening at the moment when the white dwarf star makes this spectacular transition to supernova. “Turbulence properties inferred from these simulations provides insight into the DDT process, if it occurs,” said Aaron Jackson, currently an NRC Research Associate working in the Laboratory for Computational Physics and Fluid Dynamics at the Naval Research Laboratory in Washington, D.C. At the time of this research, Jackson was a graduate student at Stony Brook University on Long Island, New York.

Jackson and his colleagues Dean Townsley from the University of Alabama at Tuscaloosa, and Alan Calder also of Stony Brook, presented their data at the American Physical Society’s (APS) Division of Fluid Dynamics (DFD) meeting in Baltimore, Nov. 20-22, 2011.

While the deflagration-detonation transition mechanism is still not well understood, a prevailing hypothesis in the astrophysics community is that if turbulence is intense enough, DDT will occur. Extreme turbulent intensities inferred in the white dwarf from the researchers’ simulations suggest DDT is likely, but the lack of knowledge about the process allows a large range of

outcomes from the explosion. Matching simulations to observed supernovae can identify likely conditions for DDT.

“There are a few options for how to simulate how they [supernovae] might work, each of which has different advantages and disadvantages,” said Townsley. “Our goal is to provide a more realistic simulation of how a given supernova scenario will perform, but that is a long-term goal and involves many different improvements that are still in progress.”

The researchers speculate that this better understanding of the physical underpinnings of the explosion mechanism will give us more confidence in using Type Ia supernovae as standard candles, and may yield more precise distance estimates.

Source: American Physical Society

Temperatures and pressures in the cosmic plasma

The solar wind consists of charged particles and is permeated by a magnetic field. In the analysis of this plasma, researchers investigate two types of pressure: the magnetic pressure describes the tendency of the magnetic field lines to repel each other, the kinetic pressure results from the momentum of the particles. The ratio of kinetic to magnetic pressure is called plasma beta and is a measure of whether more energy per volume is stored in magnetic fields or in particle motion. In many cosmic sources, the plasma beta is around the value one, which is the same as energy equipartition. Moreover, in cosmic plasmas near temperature isotropy prevails, i.e. the temperature parallel and perpendicular to the magnetic field lines of the plasma is the same.

Explaining satellite data

For over a decade, the instruments of the near-earth WIND satellite have gathered various solar wind data. When the plasma beta measured is plotted against the temperature anisotropy (the ratio of the perpendicular to the parallel temperature), the data points form a rhombic area around the value one. “If the values move out of the rhombic configuration, the plasma is unstable and the temperature anisotropy and the plasma beta quickly return to the stable region within the rhombus” says Prof. Schlickeiser. However, a specific, detailed explanation of this rhombic shape has, until now, been lacking, especially for low plasma beta.

Collisions in the solar wind

In previous models it was assumed that, due to the low density, the solar wind particles do not directly collide, but only interact via electromagnetic fields. “Such assumptions are, however, no longer justified for small plasma beta, since the damping due to particle collisions needs to be taken into account” explains Dipl.-Phys. Michal Michno. Prof. Schlickeiser’s group included this additional damping in their model, which led to new rhombic thresholds i.e. new stability conditions. The Bochum model explains the solar wind data measured significantly better than previous theories.

Universally valid solution

The new model can be applied to other dilute cosmic plasmas which have densities, temperatures and magnetic field strengths similar to the solar wind. Even if the diagram of temperature anisotropy and plasma beta does not have exactly the rhombic shape that the researchers found for the solar wind, the newly discovered mechanism predicts that the values are always close to one. In this way, the theory also makes an important contribution to the explanation of the energy equipartition in cosmic plasmas outside of our solar system.

Source: Ruhr-Universitaet-Bochum

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