Formation of bulge on far side of moon explained

A bulge of elevated topography on the far side of the moon -- known as the lunar far side highlands -- has defied explanation for decades. But a new study led by researchers at the University of California, Santa Cruz, shows that the highlands may be the result of tidal forces acting early in the moon's history when its solid outer crust floated on an ocean of liquid rock.

Ian Garrick-Bethell, an assistant professor of Earth and planetary sciences at UC Santa Cruz, found that the shape of the moon's bulge can be described by a surprisingly simple mathematical function. "What's interesting is that the form of the mathematical function implies that tides had something to do with the formation of that terrain," said Garrick-Bethell, who is the first author of a paper on the new findings published in the November 11 issue of Science.

The paper describes a process for formation of the lunar highlands that involves tidal heating of the moon's crust about 4.4 billion years ago. At that time, not long after the moon's formation, the crust was decoupled from the mantle below it by an intervening ocean of magma. As a result, the gravitational pull of the Earth caused tidal flexing and heating of the crust. At the polar regions, where the flexing and heating was greatest, the crust became thinner, while the thickest crust would have formed in the regions in line with the Earth.

This process still does not explain why the bulge is now found only on the far side of the moon. "You would expect to see a bulge on both sides, because tides have a symmetrical effect," Garrick-Bethell said. "It may be that volcanic activity or other geological processes over the past 4.4 billion years have changed the expression of the bulge on the nearside."

The paper's coauthors include Francis Nimmo, associate professor of Earth and planetary sciences at UCSC, and Mark Wieczorek, a planetary geophysicist at the Institut de Physique du Globe in Paris. The researchers analyzed topographical data from NASA's Lunar Reconnaissance Orbiter and gravitational data from Japan's Kaguya orbiter.

A map of crustal thickness based on the gravity data showed that an especially thick region of the moon's crust underlies the lunar far side highlands. The variations in crustal thickness on the moon are similar to effects seen on Jupiter's moon Europa, which has a shell of ice over an ocean of liquid water. Nimmo has studied the effects of tidal heating on the structure of Europa, and the researchers applied the same analytical approach to the moon.

"Europa is a completely different satellite from our moon, but it gave us the idea to look at the process of tidal flexing of the crust over a liquid ocean," Garrick-Bethell said.

The mathematical function that describes the shape of the moon's bulge can account for about one-fourth of the moon's shape, he said. Although mysteries still remain, such as what made the nearside so different, the new study provides a mathematical framework for further investigations into the shape of the moon.

"It's still not completely clear yet, but we're starting to chip away at the problem," Garrick-Bethell said.

Simulating black hole radiation with lasers: Lasers produce the first Hawking radiation ever detected

A team of Italian scientists has fired a laser beam into a hunk of glass to create what they believe is an optical analogue of the Hawking radiation that many physicists expect is emitted by black holes.

Although the laser experiment superficially bears little resemblance to ultra-dense black holes, the mathematical theories used to describe both are similar enough that confirmation of laser-induced Hawking radiation would bolster confidence that black holes also emit Hawking radiation.

When Stephen Hawking first predicted the radiation bearing his name in 1974, he hypothesized that photons could be spontaneously generated from the vacuum at the edge of a black hole. However, Hawking radiation emitted from a black hole would be so weak that many scientists believe it to be nearly impossible to detect.

Scientists have turned to lasers before in attempts to create Hawking radiation, but have had difficulty isolating Hawking radiation from other forms of light emitted during experiments. Franco Belgiorno et al. combined a tunable laser beam with a bulk glass target, which allowed them to limit the Hawking radiation to certain wavelengths of infrared light and to capture the apparent Hawking radiation with an infrared sensitive digital camera.

A paper describing the possible production of a laser induced analogue of Hawking radiation appears in the current issue of Physical Review Letters, and is the subject of a Viewpoint article by John Dudley (CNRS, France) and Dmitry Skryabin (University of Bath, UK) in this week's edition of Physics.

WISE image reveals strange specimen in starry sea: Dying star surrounded by fluorescing gas, unusual rings

A new image from NASA's Wide-field Infrared Survey Explorer shows what looks like a glowing jellyfish floating at the bottom of a dark, speckled sea. In reality, this critter belongs to the cosmos -- it's a dying star surrounded by fluorescing gas and two very unusual rings.

"I am reminded of the jellyfish exhibition at the Monterey Bay Aquarium -- beautiful things floating in water, except this one is in space," said Edward (Ned) Wright, the principal investigator of the WISE mission at UCLA, and a co-author of a paper on the findings, reported in The Astronomical Journal.

The object, known as NGC 1514 and sometimes the "Crystal Ball" nebula, belongs to a class of objects called planetary nebulae, which form when dying stars toss off their outer layers of material. Ultraviolet light from a central star, or in this case a pair of stars, causes the gas to fluoresce with colorful light. The result is often beautiful -- these objects have been referred to as the butterflies of space.

NGC 1514 was discovered in 1790 by Sir William Herschel, who noted that its "shining fluid" meant that it could not be a faint cluster of stars, as originally suspected. Herschel had previously coined the term planetary nebulae to describe similar objects with circular, planet-like shapes.

Planetary nebulae with asymmetrical wings of nebulosity are common. But nothing like the newfound rings around NGC 1514 had been seen before. Astronomers say the rings are made of dust ejected by the dying pair of stars at the center of NGC 1514. This burst of dust collided with the walls of a cavity that was already cleared out by stellar winds, forming the rings.

"I just happened to look up one of my favorite objects in our WISE catalogue and was shocked to see these odd rings," said Michael Ressler, a member of the WISE science team at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and lead author of the Astronomical Journal paper. Ressler first became acquainted with the object years ago while playing around with his amateur telescope on a desert camping trip. "It's funny how things come around full circle like this."

WISE was able to spot the rings for the first time because their dust is being heated and glows with the infrared light that WISE can detect. In visible-light images, the rings are hidden from view, overwhelmed by the brightly fluorescing clouds of gas.

"This object has been studied for more than 200 years, but WISE shows us it still has surprises," said Ressler.

Infrared light has been color-coded in the new WISE picture, such that blue represents light with a wavelength of 3.4 microns; turquoise is 4.6-micron light; green is 12-micron light; and red is 22-micron light. The dust rings stand out in orange. The greenish glow at the center is an inner shell of material, blown out more recently than an outer shell that is too faint to be seen in WISE's infrared view. The white dot in the middle is the central pair of stars, which are too close together for WISE to see separately.

Ressler says NGC 1514's structure, though it looks unique, is probably similar in overall geometry to other hour-glass nebulae, such as the Engraved Hourglass Nebula (http://hubblesite.org/newscenter/archive/releases/1996/07). The structure looks different in WISE's view because the rings are detectable only by their heat; they do not fluoresce at visible wavelengths, as do the rings in the other objects.

Serendipitous findings like this one are common in survey missions like WISE, which comb through the whole sky. WISE has been surveying the sky in infrared light since January 2010, cataloguing hundreds of millions of asteroids, stars and galaxies. In late September, after covering the sky about one-and-a-half times, it ran out of the frozen coolant needed to chill its longest-wavelength detectors. The mission, now called NEOWISE, is still scanning the skies with two of its infrared detectors, focusing primarily on comets and asteroids, including near-Earth objects, which are bodies whose orbits pass relatively close to Earth's orbit around the sun.

The WISE science team says that more oddballs like NGC 1514 are sure to turn up in the plethora of WISE data -- the first batch of which will be released to the astronomical community in spring 2011.

Other study authors are Martin Cohen of the Monterey Institute for Research in Astronomy, Marina, Calif.; Stefanie Wachter and Don Hoard of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena; and Amy Mainzer of JPL.

JPL manages and operates the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. More information is online at http://www.nasa.gov/wise , http://wise.astro.ucla.edu and http://www.jpl.nasa.gov/wise .

What will Webb see? Supercomputer models yield sneak previews

As scientists and engineers work to make NASA's James Webb Space Telescope a reality, they find themselves wondering what new sights the largest space-based observatory ever constructed will reveal. With Webb, astronomers aim to catch planets in the making and identify the universe's first stars and galaxies, yet these are things no telescope -- not even Hubble -- has ever shown them before.

"It's an interesting problem," said Jonathan Gardner, the project's deputy senior project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "How do we communicate the great scientific promise of the James Webb Space Telescope when we've never seen what it can show us?"

So the project turned to Donna Cox, who directs the Advanced Visualization Laboratory (AVL) at the National Center for Supercomputing Applications (NCSA). Located at the University of Illinois in Urbana-Champaign, NCSA provides enormous computing resources to researchers trying to simulate natural processes at the largest and smallest scales, from the evolution of the entire universe to the movement of protein molecules through cell walls.

Cox and her AVL team developed custom tools that can transform a model's vast collection of ones and zeroes into an incredible journey of exploration. "We take the actual data scientists have computed for their research and translate them into state-of-the-art cinematic experiences," she said.

Armed with an ultra-high-resolution 3D display and custom software, the AVL team choreographs complex real-time flights through hundreds of gigabytes of data. The results of this work have been featured in planetariums, IMAX theaters and TV documentaries. "Theorists are the only scientists who have ventured where Webb plans to go, and they did it through complex computer models that use the best understanding of the underlying physics we have today," Cox said. "Our challenge is to make these data visually understandable -- and reveal their inherent beauty."

The new visualizations reflect the broad science themes astronomers will address with Webb. Among them: How did the earliest galaxies interact and evolve to create the present-day universe? How do stars and planets form?

"When we look at the largest scales, we see galaxies packed into clusters and clusters of galaxies packed into superclusters, but we know the universe didn't start out this way," Gardner said. Studies of the cosmic microwave background -- the remnants of light emitted when the universe was just 380,000 years old -- show that the clumpy cosmic structure we see developed much later on. Yet the farthest galaxies studied are already more than 500 million years old.

"Webb will show us what happened in between," Gardner added.

Cox and her AVL team visualized this epoch of cosmic construction from a simulation developed by Renyue Cen and Jeremiah Ostriker at Princeton University in New Jersey. It opens when the universe was 20 million years old and continues to the present-day, when the universe is 13.7 billion years old.

AVL team members Robert Patterson, Stuart Levy, Matthew Hall, Alex Betts and A. J. Christensen visualized how stars, gas, dark matter and colliding galaxies created clusters and superclusters of galaxies. Driven by the gravitational effect of dark matter, these structures connect into enormous crisscrossing filaments that extend over vast distances, forming what astronomers call the "cosmic web."

"We worked with nine scientists at five universities to visualize terabytes of computed data in order to take the viewer on a visual tour from the cosmic web, to smaller scales of colliding galaxies, to deep inside a turbulent nebula where stars and disks form solar systems like our own," Cox said. "These visuals represent current theories that scientists will soon re-examine through the eyes of Webb."

Closer to home, Webb will peer more deeply than ever before into the dense, cold, dusty clouds where stars and planets are born. Using data from models created by Aaron Boley at the University of Florida in Gainesville and Alexei Kritsuk and Michael Norman at the University of California, San Diego, the AVL team visualized the evolution of protoplanetary disks over tens of thousands of years.

Dense clumps develop far out in a disk's fringes, and if these clumps survive they may become gas giant planets or substellar objects called brown dwarfs. The precise outcome depends on the detailed makeup of the disk. "Dr. Boley was interested in what happened in the disk and did not include the central star," Cox said, "so to produce a realistic view we worked with him to add a young star."

This is astrophysics with a pinch of Hollywood sensibility, work at the crossroads of science and art. "The theoretical digital studies that form the basis of our work are so advanced that cinematic visualization is the most effective way to share them with the public," Cox said. "It's the art of visualizing science."

"What AVL has done for the Webb project is truly amazing and inspiring," Gardner noted. "It really whets our appetites for the science we'll be doing when the telescope begins work a few years from now."

Pushing black-hole mergers to the extreme: Scientists achieve 100:1 mass ratio in simulation

Scientists have simulated, for the first time, the merger of two black holes of vastly different sizes, with one mass 100 times larger than the other. This extreme mass ratio of 100:1 breaks a barrier in the fields of numerical relativity and gravitational wave astronomy.

Until now, the problem of simulating the merger of binary black holes with extreme size differences had remained an unexplored region of black-hole physics.

"Nature doesn't collide black holes of equal masses," says Carlos Lousto, associate professor of mathematical sciences at Rochester Institute of Technology and a member of the Center for Computational Relativity and Gravitation. "They have mass ratios of 1:3, 1:10, 1:100 or even 1:1 million. This puts us in a better situation for simulating realistic astrophysical scenarios and for predicting what observers should see and for telling them what to look for.

"Leaders in the field believed solving the 100:1 mass ratio problem would take five to 10 more years and significant advances in computational power. It was thought to be technically impossible."

"These simulations were made possible by advances both in the scaling and performance of relativity computer codes on thousands of processors, and advances in our understanding of how gauge conditions can be modified to self-adapt to the vastly different scales in the problem," adds Yosef Zlochower, assistant professor of mathematical sciences and a member of the center.

A paper announcing Lousto and Zlochower's findings was submitted for publication in Physical Review Letters.

The only prior simulation describing an extreme merger of black holes focused on a scenario involving a 1:10 mass ratio. Those techniques could not be expanded to a bigger scale, Lousto explained. To handle the larger mass ratios, he and Zlochower developed numerical and analytical techniques based on the moving puncture approach -- a breakthrough, created with Manuela Campanelli, director of the Center for Computational Relativity and Gravitation, that led to one of the first simulations of black holes on supercomputers in 2005.

The flexible techniques Lousto and Zlochower advanced for this scenario also translate to spinning binary black holes and for cases involving smaller mass ratios. These methods give the scientists ways to explore mass ratio limits and for modeling observational effects.

Lousto and Zlochower used resources at the Texas Advanced Computer Center, home to the Ranger supercomputer, to process the massive computations. The computer, which has 70,000 processors, took nearly three months to complete the simulation describing the most extreme-mass-ratio merger of black holes to date.

"Their work is pushing the limit of what we can do today," Campanelli says. "Now we have the tools to deal with a new system."

Simulations like Lousto and Zlochower's will help observational astronomers detect mergers of black holes with large size differentials using the future Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) and the space probe LISA (Laser Interferometer Space Antenna). Simulations of black-hole mergers provide blueprints or templates for observational scientists attempting to discern signatures of massive collisions. Observing and measuring gravitational waves created when black holes coalesce could confirm a key prediction of Einstein's general theory of relativity.