The winds on these planets have been observed on their outer surfaces; but to get a grasp of their weather systems, we need to have an idea of what is going on underneath. For instance, do the atmospheric patterns arise from deep down in the planet, or are they confined to shallower processes nearer the surface?

New research at the Weizmann Institute of Science, the University of Arizona and Tel Aviv University, which was published online in Nature, shows that the wind patterns seen on the surface can extend only so far down on these two worlds.

Understanding the atmospheric circulation is not simple for a planet without a solid surface, where Earth-style boundaries between solid, liquid and gas layers do not exist. Since the discovery of these strong atmospheric winds in the 1980s by the Voyager II spacecraft, the vertical extent of these winds has been a major puzzle - one that influences our understanding of the physics governing the atmospheric dynamics and internal structure of these planets.

But a team led by Dr. Yohai Kaspi of the Weizmann Institute's Environmental Sciences and Energy Research Department realized they had a way, based on a novel method for analyzing the gravitational field of the planets, to determine an upper limit for the thickness of the atmospheric layer.

Deviations in the distribution of mass in planets cause measurable fluctuations in the gravitational field. On Earth, for example, an airplane flying near a large mountain feels the slight extra gravitational pull of that mountain.

Like Earth, the giant planets of the solar system are rapidly rotating bodies. In fact all of them rotate faster than Earth; the rotation periods of Uranus and Neptune are about 17 and 16 hours, respectively. Because of this rapid rotation, the winds swirl around regions of high and low pressure. (In a non-rotating body, flow would be from high to low pressure.)

This enables researchers to deduce the relations between the distribution of pressure and density, and the planets' wind field. These physical principles enabled Kaspi and his co-authors to calculate, for the first time, the gravity signature of the wind patterns and thus create a wind-induced gravity map of these planets.

By computing the gravitational fields of a large range of ideal planet models - ones with no wind, a task conducted by team member Dr. Ravit Helled of Tel Aviv University - and comparing them with the observed gravitational fields, upper limits to the meteorological contribution to the gravitational fields were obtained.

This enabled Kaspi's team, which included Profs. Adam Showman and Bill Hubbard of the University of Arizona, and Prof. Oded Aharonson of the Weizmann Institute, to show that the streams of gas observed in the atmosphere are limited to a "weather-layer" of no more than about 1000 km in depth, which makes up only a fraction of a percent of the mass of these planets.

Although no spacecraft missions to Uranus and Neptune are planned for the near future, Kaspi anticipates that the team's findings will be useful in the analysis of another set of atmospheric circulation patterns that will be closely observed soon: those of Jupiter. Kaspi, Helled and Hubbard are part of the science team of NASA's Juno spacecraft to Jupiter.

Juno was launched in 2011; upon reaching Jupiter in 2016 it will provide very accurate measurements of the gravity field of this giant gaseous planet. Using the same methods as the present study, Kaspi anticipates that they will be able to obtain the same type of information they acquired for Uranus and Neptune: namely, placing constraints on the depth of the atmospheric dynamics of this planet.

Uranus and Neptune are the farthest planets in the solar system, and there are still many open questions regarding their formation and composition. This study has implications for revealing the mysteries of their deep, dark interiors, and may even provide information about how these planets were formed.

Moreover, many of the extrasolar planets detected around other stars have been found to have similar masses to those of Uranus and Neptune, so this research will be important for understanding like-sized extrasolar planets, as well.

Published online in Nature.

]]> Mon, 20 MAY 2013 12:30:03 AEST Heidelberg, Germany (SPX) May 20, 2013 - This dramatic new image of cosmic clouds in the constellation of Orion reveals what seems to be a fiery ribbon in the sky. This orange glow represents faint light coming from grains of cold interstellar dust, at wavelengths too long for human eyes to see. It was observed by the ESO-operated Atacama Pathfinder Experiment (APEX) in Chile.

Clouds of gas and interstellar dust are the raw materials from which stars are made. But these tiny dust grains block our view of what lies within and behind the clouds - at least at visible wavelengths - making it difficult to observe the processes of star formation.

This is why astronomers need to use instruments that are able to see at other wavelengths of light. At submillimetre wavelengths, rather than blocking light, the dust grains shine due to their temperatures of a few tens of degrees above absolute zero [1]. The APEX telescope with its submillimetre-wavelength camera LABOCA, located at an altitude of 5000 metres above sea level on the Chajnantor Plateau in the Chilean Andes, is the ideal tool for this kind of observation.

This spectacular new picture shows just a part of a bigger complex called the Orion Molecular Cloud, in the constellation of Orion (The Hunter). A rich melting pot of bright nebulae, hot young stars and cold dust clouds, this region is hundreds of light-years across and located about 1350 light-years from us.

The submillimetre-wavelength glow arising from the cold dust clouds is seen in orange in this image and is overlaid on a view of the region taken in the more familiar visible light.

The large bright cloud in the upper right of the image is the well-known Orion Nebula, also called Messier 42. It is readily visible to the naked eye as the slightly fuzzy middle "star" in the sword of Orion. The Orion Nebula is the brightest part of a huge stellar nursery where new stars are being born, and is the closest site of massive star formation to Earth.

The dust clouds form beautiful filaments, sheets, and bubbles as a result of processes including gravitational collapse and the effects of stellar winds. These winds are streams of gas ejected from the atmospheres of stars, which are powerful enough to shape the surrounding clouds into the convoluted forms seen here.

Astronomers have used these and other data from APEX along with images from ESA's Herschel Space Observatory, to search the region of Orion for protostars - an early stage of star formation. They have so far been able to identify 15 objects that appeared much brighter at longer wavelengths than at shorter wavelengths. These newly discovered rare objects are probably among the youngest protostars ever found, bringing astronomers closer to witnessing the moment when a star begins to form.

[1] Hotter objects give off most of their radiation at shorter wavelengths and cooler ones at longer wavelengths. As an example very hot stars (surface temperatures around 20 000 degrees Kelvin) look blue and cooler ones (surface temperatures of around 3000 degrees Kelvin) look red. And a cloud of dust with a temperature of only ten degrees Kelvin has its peak of emission at a much longer wavelength - around 0.3 millimetres - in the part of the spectrum where APEX is very sensitive.

The research on protostars in this region is described in the paper "A Herschel and APEX Census of the Reddest Sources in Orion: Searching for the Youngest Protostars" by A. Stutz et al., in the Astrophysical Journal. The APEX observations used in this image were led by Thomas Stanke (ESO), Tom Megeath (University of Toledo, USA), and Amelia Stutz (Max Planck Institute for Astronomy, Heidelberg, Germany). APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. Operation of APEX at Chajnantor is entrusted to ESO.

]]> Mon, 20 MAY 2013 12:30:03 AEST Moffett Field CA (SPX) May 16, 2013 - Scientists at NASA's Ames Research Center now have the capability to systematically investigate the molecular evolution of cosmic carbon. For the first time, these scientists are able to automatically interpret previously unknown infrared emissions from space that come from surprisingly complex organic molecules, called polycyclic aromatic hydrocarbons (PAHs), which are abundant and important across the universe.

Between 2003 and 2005, thanks to its unprecedented sensitivity, NASA's Spitzer Space Telescope, managed and operated by NASA's Jet Propulsion Laboratory, Pasadena, Calif., created maps of the tell-tale PAH signature across large regions of space, from hot regions of harsh ultraviolet (UV) radiation close to stars, to cold, dark clouds where stars and planets form.

By exclusively using their unique collection of authentic PAH spectra, coupled with algorithm-driven, blind-computational analyses, scientists at Ames were able to interpret the cosmic infrared maps with complex organic molecules.

They found that PAHs changed significantly in size, electrical charge and structure, to adjust to the different environment at each spot in the map. Carbon is one of the most abundant atoms in space and scientists believe that the spectral changes across these maps trace the molecular evolution of carbon across the universe.

"At the time of our discovery, the 'signature,' or identifying spectrum, of this unexpected, but common infrared (IR) radiation from space hinted that PAHs might be responsible, but we were limited to a handful of small PAHs and very few were available to study," said Louis Allamandola, an astrophysics researcher at Ames.

"To test the idea that PAHs were responsible, we measured and computed PAH spectra under astronomical conditions, creating the world's largest collection of PAH spectra. Today, our collection contains more than 700 PAH spectra.

To determine the spectral changes across these maps, these astrophysicists used the PAH spectra collected in the PAH IR Spectroscopic Database (http://www.astrochem.org/pahdb/) at Ames. They analyzed the Spitzer infrared map of the Iris Nebula (NGC 7023) that hosts both the extreme environment of a region close to a star, as well as the more shielded, benign environment of a cold molecular cloud.

The new maps showed that small, electrically neutral, irregularly shaped PAHs are most common near the cold molecular cloud that is far from the star that excites PAH emission. However, when PAHs move closer to the exciting star and away from the cold cloud, they become large, symmetric and are electrically charged.

"The large PAHs take over because they are more robust than the smaller, irregularly-shaped PAHs, which are destroyed by the unshielded star light," said Christiaan Boersma, an astrophysicist at Ames.

Finally, these large PAHs are themselves broken down, as they are stripped of hydrogen and become small fragments. At this point, the emission from the dehydrogenated PAHs takes over in the observed region.

There were two findings that are especially important: the first is that positively-charged, nitrogen-containing PAHs are needed to complete the match between the correct spectral signature and the observed emission, and the second is that dehydrogenation and fragmentation occur close to the exciting star.

"The indication of nitrogen-containing PAHs (PANHs) is significant, as these have not been seriously considered previously. They represent an important class of prebiotic molecules, which are precursors to life," said Jesse Bregman, also an astrophysicist at Ames. "If borne out, this indicates complex, nitrogen-containing, aromatic molecules are present across the universe."

This approach of analyzing the aromatic infrared bands using the spectra of individual PAHs provides new, fundamental information about the UV-driven, spatial evolution of PAH subpopulations. It also ties these variations to changes in local conditions, such as those due to the physical shape and history of the region, radiation field, etc.

"Spitzer detected the PAH signature across the universe and showed PAHs were already forming only a couple of billion years after the Big Bang. Since PAHs are so sensitive to local conditions, analyzing the PAH bands, as we did here, represents a powerful new astronomical tool to trace the evolution of cosmic carbon and, at the same time, probe conditions across the universe," concluded Allamandola.

This work was supported by NASA's Carbon in the Galaxy Consortium under the auspices of the Astrophysics Research and Analysis Program (APRA).

Results will be published May 14 in "Properties of PAHs in the Northwest PDR of NGC 7023 1: PAH size, charge, composition and structure distribution," Astrophysical Journal, vol. 769 (2) article 117, 2013.

]]> Mon, 20 MAY 2013 12:30:03 AEST Washington DC (SPX) May 14, 2013 - Scientific studies done with the "PAPER" array, one of the world-class scientific instruments in South Africa's Karoo Radio Astronomy Reserve, are producing ground-breaking science and spectacular cosmic images, resulting in several important articles in top astronomy journals.

The primary goal of PAPER (Precision Array to Probe the Epoch of Reionization) is to detect emission from the neutral gas that pervaded the universe before the first galaxies and black holes were formed. This 'epoch of reionization', as it is called, is the last frontier in observational cosmology.

Recent observations with PAPER were used to set the first physically interesting limits on emission from the neutral hydrogen during this key epoch in cosmic structure formation. Besides providing important constraints on the very early evolution of the universe, the PAPER observations are helping to define the techniques and instrumentation that will translate into the design of a next generation 'Hydrogen Epoch of Reionization Array' (HERA), and eventually, the low-frequency SKA.

Beyond the cosmological studies, PAPER has produced unprecedented images of the southern radio sky at low frequency. PAPER comprises a unique combination of very wide field ('full-sky imaging'), reasonable spatial resolution, and wide frequency range.

Spectacular images of the closest powerful radio galaxy, Centaurus A, have been made with PAPER, revealing very large structure in this giant radio galaxy, some 200 kpc in extent. This is 10 times the size of the entire Milky Way.

The PAPER data provide interesting insight into the interaction between these giant radio 'jets' emanating from the massive black hole at the center of the Centaurus A galaxy, with the large scale intergalactic medium surrounding the galaxy.

(kpc = kiloparsec, a unit that astronomers use to measure distances between parts of a galaxy, or within groups of galaxies; 1 kpc ~ 3,000 light-years)

PAPER involves a close collaboration with South African astronomers and engineers on all aspects of the project, from design and construction, to scientific discovery.

PAPER team member and chief scientist at the US National Radio Astronomy Observatory (NRAO) Chris Carilli emphasized: "The help of the SKA project office, and the intern-student support for work in the Karoo, have been fundamental to the success of PAPER, as well as an important educational resource for South Africa. The Karoo has now been established as a world-leading site for studies of the radio cosmos. We look forward to the coming years, as the collaboration matures with next generation instruments in the Karoo, leading to profound insights into the nature of the universe."

"The PAPER instrument, in concert with site infrastructure and support, showed remarkable stability with not a single interruption during our recent six-month observation window," says William Walbrugh, PAPER project manager at SKA SA.

"Hosting PAPER successfully confirms the integrity of the South Africa SKA site, and the technical expertise of the South African team," Prof. Justin Jonas, associate director for science and engineering at SKA South Africa adds.

PAPER has been operating on the Karoo site in South Africa for over two years. The Karoo provides a unique environment on planet Earth, with remarkably low interference from man-made radio transmissions, thereby enabling sensitive observations at low radio frequencies.

PAPER currently consists of 64 dipole antennas arranged in a grid formation over a 300 m clearing. Plans are under way to double the number of antennas at the Karoo site to 128 by September 2013.

The correlator, a custom built array of supercomputers responsible for processing data received from the antennas, will also double in size. This will be amongst the world's largest and most powerful correlators used for radio astronomy. The effective doubling in collecting area will dramatically increase the combined sensitivity of the instrument and thereby improve the probability of making a detection of the faint Epoch of Reionization emissions -- this would be a major scientific breakthrough.

PAPER operates two arrays, the primary science instrument in the Karoo and a secondary, smaller, sister array in Green Bank, West Virginia, in the USA. Together, these two arrays provide full sky coverage of both the northern and southern hemispheres.

Scientists from the SKA Project office working on PAPER collaborate with partners at American research institutions, such as the National Radio Astronomy Observatory, the University of California, Berkeley, and the University of Pennsylvania.

]]> Mon, 20 MAY 2013 12:30:03 AEST Charlottesville VA (SPX) May 10, 2013 - In a dark, starless patch of intergalactic space, astronomers have discovered a never-before-seen cluster of hydrogen clouds strewn between two nearby galaxies, Andromeda (M31) and Triangulum (M33). The researchers speculate that these rarefied blobs of gas - each about as massive as a dwarf galaxy - condensed out of a vast and as-yet undetected reservoir of hot, ionized gas, which could have accompanied an otherwise invisible band of dark matter.

The astronomers detected these objects using the National Science Foundation's Green Bank Telescope (GBT) at the National Radio Astronomy Observatory (NRAO) in Green Bank, W.Va. The results were published in the journal Nature.

"We have known for some time that many seemingly empty stretches of the Universe contain vast but diffuse patches of hot, ionized hydrogen," said Spencer Wolfe of West Virginia University in Morgantown.

"Earlier observations of the area between M31 and M33 suggested the presence of colder, neutral hydrogen, but we couldn't see any details to determine if it had a definitive structure or represented a new type of cosmic feature. Now, with high-resolution images from the GBT, we were able to detect discrete concentrations of neutral hydrogen emerging out of what was thought to be a mainly featureless field of gas."

Astronomers are able to observe neutral atomic hydrogen, which is referred to as HI (H and the Roman numeral one), because of the characteristic signal it emits at radio wavelengths, which can be detected by radio telescopes on Earth. Though this material is abundant throughout the cosmos, in the space between galaxies it can be very tenuous and the faint signal it emits can be extremely difficult to detect.

A little more than a decade ago, astronomers had the first speculative hints that a previously unrecognized reservoir of hydrogen lay between M31 and M33. The signal from this gas, however, was too faint to draw any firm conclusions about its nature, origin, or even certain existence. Last year, preliminary data taken with the GBT confirmed that there was indeed hydrogen gas, and a lot of it, smeared out between the galaxies.

These preliminary observations, however, lacked the necessary sensitivity to see any fine-grain structure in the gas or deduce whence it came and what it signified.

The most likely explanation at the time was that a few billion years earlier, these two galaxies had a close encounter and the resulting gravitational perturbations pulled off some wispy puffs of gas, leaving a tenuous bridge between the two.

New and more thorough studies of this region with the GBT, however, revealed that the hydrogen gas was not simply in the form of wispy streamers, as would be expected by the interactions of two galaxies in a gravitational ballet.

Instead, a full 50 percent of the gas was conspicuously clumped together into very discrete and very massive blobs that - apart for their lack of stars - would be dead ringers for dwarf galaxies. Dwarf galaxies, as their name implies, are relatively small collections of stars bound together by gravity. They can contain anywhere from a few thousand to a few million stars.

The GBT was also able to track the motion of these newly discovered clouds, showing that they were traveling through space at velocities similar to M31 and M33. "These observations suggest that they are independent entities and not the far-flung suburbs of either galaxy," said Felix J. Lockman, an astronomer at the NRAO in Green Bank.

"Their clustered orientation is equally compelling and may be the result of a filament of dark matter. The speculation is that a dark-matter filament, if it exists, could provide the gravitational scaffolding upon which clouds could condense from a surrounding field of hot gas."

The researchers also speculate that these clouds may represent a new and previously unrecognized source of neutral hydrogen gas that could eventually fall into M31 and M33, fueling future generations of star formation.

The GBT, because of its enormous size, unique design, and location in the National Radio Quiet Zone of West Virginia, was able to detect this signal, which was simply too faint for other radio telescopes to detect with precision. "The GBT is unique in this regard," said Lockman.

Astronomers are also interested in these cold, dark regions between galaxies because there is a great deal of unaccounted-for normal matter in the cosmos, and a significant fraction may be contained in intergalactic clouds like the ones observed by the GBT.

Further studies in this region and around other galaxies in our Local Group (the galaxies found relatively close to the Milky Way) may yield additional clues as to the amount of hydrogen yet to be accounted for in the Universe.

"The region we have studied is only a fraction of the area around M31 reported to have diffuse hydrogen gas," said D.J. Pisano of West Virginia University. "The clouds observed here may be just the tip of a larger population out there waiting to be discovered."

]]> Mon, 20 MAY 2013 12:30:03 AEST Munich, Germany (SPX) May 10, 2013 - In fossil remnants of iron-loving bacteria, researchers of the Cluster of Excellence Origin and Structure of the Universe at the Technische Universitaet Muenchen (TUM), found a radioactive iron isotope that they trace back to a supernova in our cosmic neighborhood. This is the first proven biological signature of a starburst on our earth.

The age determination of the deep-drill core from the Pacific Ocean showed that the supernova must have occurred about 2.2 million years ago, roughly around the time when the modern human developed.

Most of the chemical elements have their origin in core collapse supernovae. When a star ends its life in a gigantic starburst, it throws most of its mass into space.

The radioactive iron isotope Fe-60 is produced almost exclusively in such supernovae. Because its half-life of 2.62 million years is short compared to the age of our solar system, no supernova iron should be present on Earth. Therefore, any discovery of Fe-60 on Earth would indicate a supernova in our cosmic neighborhood.

In the year 2004 scientists at TU Muenchen discovered Fe-60 on Earth for the first time in a ferromanganese crust obtained from the floor of the equatorial Pacific Ocean. Its geological dating puts the event around 2.2 million years ago.

So-called magnetotactic bacteria live within the sediments of the Earth's oceans, close to the water-sediment interface. They make within their cells hundreds of tiny crystals of magnetite (Fe3O4), each approximately 80 nanometers in diameter. The magnetotactic bacteria obtain the iron from atmospheric dust that enters the ocean.

Nuclear astrophysicist Shawn Bishop from the Technische Universitaet Muenchen conjectured, therefore, that Fe-60 should also reside within those magnetite crystals produced by magnetotactic bacteria extant at the time of the supernova interaction with our planet. These bacterially produced crystals, when found in sediments long after their host bacteria have died, are called "magnetofossils."

Shawn Bishop and his colleagues analyzed parts of a Pacific Ocean sediment core obtained from the Ocean Drilling Program, dating between about 1.7 million and 3.3 million years ago.

They took sediment samples corresponding to intervals of about 100,000 years and treated them chemically to selectively dissolve the magnetofossils - thereby extracting any Fe-60 they might contain.

Finally, using the ultra sensitive accelerator mass spectrometry system at the Maier Leibnitz Laboratory in Garching, Munich, they found a tantalizing hint of Iron-60 atoms occurring around 2.2 million years ago, which matches the expected time from the ferromanganese study.

"It seems reasonable to suppose that the apparent signal of Fe-60 could be remains of magnetite chains formed by bacteria on the sea floor as a starburst showered on them from the atmosphere", Shawn Bishop says.

He and his team are now preparing to analyze a second sediment drill core, containing upwards of 10 times the amount of material as the first drill core, to see if it also holds the Fe-60 signal and, if it does, to map out the shape of the signal as a function of time.

Publication: APS April Meeting 2013, Volume 58, Number 4; Nature News, 15. April 2013, DOI: 10.1038/nature.2013.12797.

]]> Mon, 20 MAY 2013 12:30:03 AEST Greenbelt MD (SPX) May 08, 2013 - A record-setting blast of gamma rays from a dying star in a distant galaxy has wowed astronomers around the world. The eruption, which is classified as a gamma-ray burst, or GRB, and designated GRB 130427A, produced the highest-energy light ever detected from such an event.

"We have waited a long time for a gamma-ray burst this shockingly, eye-wateringly bright," said Julie McEnery, project scientist for the Fermi Gamma-ray Space Telescope at NASA's Goddard Space Flight Center in Greenbelt, Md.

"The GRB lasted so long that a record number of telescopes on the ground were able to catch it while space-based observations were still ongoing."

Just after 3:47 a.m. EDT on Saturday, April 27, Fermi's Gamma-ray Burst Monitor (GBM) triggered on an eruption of high-energy light in the constellation Leo. The burst occurred as NASA's Swift satellite was slewing between targets, which delayed its Burst Alert Telescope's detection by less than a minute.

Fermi's Large Area Telescope (LAT) recorded one gamma ray with an energy of at least 94 billion electron volts (GeV), or some 35 billion times the energy of visible light, and about three times greater than the LAT's previous record. The GeV emission from the burst lasted for hours, and it remained detectable by the LAT for the better part of a day, setting a new record for the longest gamma-ray emission from a GRB.

The burst subsequently was detected in optical, infrared and radio wavelengths by ground-based observatories, based on the rapid accurate position from Swift. Astronomers quickly learned that the GRB was located about 3.6 billion light-years away, which for these events is relatively close.

Gamma-ray bursts are the universe's most luminous explosions. Astronomers think most occur when massive stars run out of nuclear fuel and collapse under their own weight. As the core collapses into a black hole, jets of material shoot outward at nearly the speed of light.

The jets bore all the way through the collapsing star and continue into space, where they interact with gas previously shed by the star and generate bright afterglows that fade with time.

If the GRB is near enough, astronomers usually discover a supernova at the site a week or so after the outburst.

"This GRB is in the closest 5 percent of bursts, so the big push now is to find an emerging supernova, which accompanies nearly all long GRBs at this distance," said Goddard's Neil Gehrels, principal investigator for Swift.

Ground-based observatories are monitoring the location of GRB 130427A and expect to find an underlying supernova by midmonth.

]]> Mon, 20 MAY 2013 12:30:03 AEST Evanston IL (SPX) May 07, 2013 - Northwestern University physicist Eric Dahl is part of a group of physicists that has just launched an unusual new experiment in an attempt to be the first to directly confirm the existence of dark matter.

Scientists this week heard their first pops in an experiment that searches for signs of dark matter in the form of tiny bubbles. The experiment's one-of-a-kind detector is located in a laboratory a mile and a half underground in Sudbury, Ontario.

The physicists will need to analyze the data to discern whether dark matter caused any of the COUPP-60 experiment's first bubbles. COUPP stands for the Chicagoland Observatory for Underground Particle Physics.

The experiment, which includes 23 physicists, is being led by the University of Chicago, Northwestern and the U.S. Department of Energy's Fermi National Accelerator Laboratory. Fermilab managed the assembly and installation of the dark-matter detector.

"For every gram of light matter, or atoms, in the universe, there are 5.5 grams of dark matter," said Dahl, an assistant professor of physics and astronomy in the Weinberg College of Arts and Sciences. "It is still unknown what this dark matter is actually made of, but whatever it is, it's something new. Physicists already have ruled out every known particle.

"If we do find dark matter, not only will we answer one of the biggest mysteries in cosmology and astrophysics, we'll be seeing into a new world of particle physics as well," he said. "The potential payoff is huge."

Gravitational evidence for the existence of dark matter abounds. As early as 1933 astrophysicists found that the observed motions of galaxies require much more gravitational matter than can be accounted for by the matter we can see (in the form of stars and gas).

Since then, a series of astrophysical and cosmological measurements, from observations of light bending around distant galaxy clusters to studies of the microwave background radiation left over from the big bang, all confirm that most of the matter in the universe is dark.

Fortunately there is lots of dark matter on hand to study, Dahl said. In a volume the size of your fist there is on average one dark matter particle, typical flying by at a few hundred kilometers-per-second.

Most of these particles do absolutely nothing, but many dark matter theories predict that, very rarely, these particles will collide with the nucleus of an atom. Just like two balls on a pool table, that nucleus will carry away some kinetic energy - in this case an energy equivalent to a single X-ray photon.

Picking out this weakly recoiling nucleus is the task of Dahl and the other members of COUPP. The COUPP collaborators build bubble chambers - large volumes of liquid heated to temperatures slightly above their boiling point.

Like a mug of water heated in a microwave, however, the super-heated liquid will not boil without a nucleation site. In this case, that nucleation site is created by the dark-matter interaction. One dark-matter particle hitting one nucleus creates a single bubble in the chamber.

To date, no experiment has actually seen a dark-matter interaction, but that could change with the latest COUPP chamber.

Containing a dark-matter target of 30-liters (60 kg) of superheated trifluoroiodomethane (CF3I), the COUPP-60 experiment was turned on May 1 in a laboratory 6,800 feet underground at SNOLAB in Sudbury, Ontario.

The underground location is necessary to eliminate particle backgrounds from cosmic rays that might create bubbles in the chamber. Acoustic sensors sensitive to the ultrasonic "plink" from a forming bubble also let the COUPP scientists distinguish between dark-matter events and less interesting particle backgrounds.

While waiting for the rare bubble from a dark-matter interaction, Dahl and the rest of COUPP are already at work building their next bubble chamber, which will weigh half a ton and also be located at SNOLAB.

The COUPP collaborators are not alone in their quest - there is plenty of competition from a variety of scientists and technologies to be the first to observe a dark-matter particle. In fact, COUPP is a relative newcomer to the field, but the low cost and fast deployment of the COUPP technology has quickly made it a front-runner in the hunt for dark matter.

]]> Mon, 20 MAY 2013 12:30:03 AEST Munich, Germany (SPX) May 06, 2013 - The Danish 1.54-metre telescope located at ESO's La Silla Observatory in Chile has captured a striking image of NGC 6559, an object that showcases the anarchy that reigns when stars form inside an interstellar cloud.

NGC 6559 is a cloud of gas and dust located at a distance of about 5000 light-years from Earth, in the constellation of Sagittarius (The Archer).

The glowing region is a relatively small object, just a few light-years across, in contrast to the one hundred light-years and more spanned by its famous neighbour, the Lagoon Nebula (Messier 8, eso0936). Although it is usually overlooked in favour of its distinguished companion, NGC 6559 has the leading role in this new picture.

The gas in the clouds of NGC 6559, mainly hydrogen, is the raw material for star formation. When a region inside this nebula gathers enough matter, it starts to collapse under its own gravity. The centre of the cloud grows ever denser and hotter, until thermonuclear fusion begins and a star is born. The hydrogen atoms combine to form helium atoms, releasing energy that makes the star shine.

These brilliant hot young stars born out of the cloud energise the hydrogen gas still present around them in the nebula [1]. The gas then re-emits this energy, producing the glowing threadlike red cloud seen near the centre of the image. This object is known as an emission nebula.

But NGC 6559 is not just made out of hydrogen gas. It also contains solid particles of dust, made of heavier elements, such as carbon, iron or silicon. The bluish patch next to the red emission nebula shows the light from the recently formed stars being scattered - reflected in many different directions - by the microscopic particles in the nebula.

Known to astronomers as a reflection nebula, this type of object usually appears blue because the scattering is more efficient for these shorter wavelengths of light.

In regions where it is very dense, the dust completely blocks the light behind it, as is the case for the dark isolated patches and sinuous lanes to the bottom left-hand side and right-hand side of the image. To look through the clouds at what lies behind, astronomers would need to observe the nebula using longer wavelengths that would not be absorbed.

The Milky Way fills the background of the image with countless yellowish older stars. Some of them appear fainter and redder because of the dust in NGC 6559.

This eye-catching image of star formation was captured by the Danish Faint Object Spectrograph and Camera (DFOSC) on the 1.54-metre Danish Telescope at La Silla in Chile. This national telescope has been in use at La Silla since 1979 and was recently refurbished to turn it into a remote-controlled state-of-the-art telescope.

[1] These young stars are usually of spectral type O and B, with temperatures between 10 000 and 60 000 K, which radiate huge amounts of high energy ultraviolet light that ionises the hydrogen atoms.

]]> Mon, 20 MAY 2013 12:30:03 AEST Tucson AZ (SPX) May 06, 2013 - Astronomers at the Southern Observatory for Astrophysical Research (SOAR) and the Cerro Tololo Inter-American Observatory (CTIO) have demonstrated the significant difference that sharp stellar images can make in our understanding of the properties of stars. They have observed the globular cluster NGC 6496 using a new instrument dubbed SAM, for SOAR Adaptive Module, which creates an artificial laser guide star. SAM, built by CTIO/NOAO-S, is mounted on the SOAR 4.1-meter telescope.

From the surface of the Earth, stars twinkle as their image wobbles around due to the effects of the Earth's atmosphere, rather like observing a penny on the bottom of a swimming pool. By removing this wobble, using an adaptive optics system that utilizes a laser guide star, the stellar images are sharpened, and fainter stars appear.

The accompanying figure shows this globular cluster and the difference between the image of NGC 6496 with the artificial laser-produced guide star turned on and off. Turning on the artificial guide star allows the effect of the atmosphere to be determined so that the adaptive optical system can sharpen the image.

The resulting stellar images allow astronomers to make more precise measures of the colors of the stars, and for a globular cluster, this translates into a better measurement of distance, age, and what astronomers call metallicity: how much the stars are enriched with elements that are heavier than hydrogen and helium. This, in turn, allows for better understanding of the stellar evolution of the stars in these dense clusters.

There are only about 150 known globular clusters in Milky Way, important because they represent some of the oldest objects in the galaxy. Because NGC 6496 is on the other side of the galactic center, it is seen through a thick layer of dust. The position of this globular cluster has made it difficult to determine its basic properties. For example, previous measurements of its distance do not agree well with each other.

Luciano Fraga, Andrea Kunder, and Andrei Tokovinin (in a paper accepted for publication by the Astronomical Journal [preprint: http://arxiv.org/abs/1304.4880]) used the capabilities of SAM to sharpen star images to peer deep into this crowded cluster, obtaining more accurate results than done previously from the ground.

The authors find a distance of 32,600 light-years, an age of 10.5 billion years, and a value for metallicity that is much higher than in most globular clusters. To do this, they measured over 7,000 stars in the cluster.

Then they plotted the color and brightness of each star, resulting in a diagram referred to as a color-magnitude diagram. This diagram immediately tells astronomers a great deal about the evolutionary phase of the stars in the cluster.

SAM works in the visible spectral region and can cover a field of 3 arc minutes, about one tenth the diameter of the full Moon. It compensates for the lower atmospheric turbulence by using an artificial guide star created by a powerful ultraviolet laser. While this technique, called adaptive optics, has been used on other telescopes before, SAM covers a wider field of view and shorter wavelengths.

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