Astrophysicists have just discovered a new heating source in cosmological structure formation. Until now, astrophysicists thought that super-massive black holes could only influence their immediate surroundings. A collaboration of scientists at the Heidelberg Institute for Theoretical Studies (HITS) and in Canada and the US have now discovered that diffuse gas in the universe can absorb luminous gamma-ray emission from black holes, heating it up strongly. This surprising result has important implications for the formation of structures in the universe. Every galaxy hosts a supermassive black hole at its center. Such black holes can emit high-energy gamma rays and are then called blazars. Whereas other radiation such as visible light and radio waves traverses the universe without problems, this is not the case for high-energy gamma rays. This particular radiation interacts with the optical light that is emitted by galaxies, transforming it into the elementary particles electrons and positrons. Initially, these elementary particles move almost at the speed of light. But as they are slowed down by the ambient diffuse gas, their energy is converted into heat, just like in other braking processes. As a result, the surrounding gas is heated efficiently. In fact, the temperature of the gas at mean density becomes ten times higher, and in "under-dense" regions more than one hundred times higher than previously thought. "Blazars rewrite the thermal history of the universe," emphasizes Dr. Christoph Pfrommer (HITS), one of the authors. But how can this idea be tested? In the optical spectra of quasars there is a plethora of lines, called the "line forest." The forest originates from the absorption of ultra-violet light by neutral hydrogen in the young Universe. If the gas becomes hotter, weak lines in the forest are broadened. This effect represents an excellent opportunity to measure temperatures in the early Universe, while it was still growing up. The astrophysicists at HITS checked this newly postulated heating process for the first time with detailed supercomputer simulations of the cosmological growth of structures. Surprisingly, the lines were broadened just enough so that their properties perfectly matched those of the observed lines. "This allows us to elegantly solve a long-standing problem with the quasar data," says Dr. Ewald Puchwein, who conducted the large simulations on the supercomputer at HITS. What are the further consequences of this new heating process? The forest of lines in the quasar spectra originates from density fluctuations in the Universe. In the course of cosmic evolution, the densest fluctuations collapse to form galaxies and galaxy clusters, as observed in the local Universe. Diffuse gas that is too hot cannot collapse. Hence, the formation of dwarf galaxies is slowed or even entirely suppressed. This could be the key to the solution of another long-standing problem in the theory of galaxy formation: why do we observe fewer dwarf galaxies in the vicinity of the Milky Way and in the underdense regions than predicted by cosmological simulations? Prof. Volker Springel, scientific group leader at HITS, explains: "The process of blazar heating is especially exciting since this single effect is able to simultaneously solve several different puzzles in cosmological structure formation." The group plans to further improve their simulation models for a still deeper understanding of the nature of blazar heating and its implications for today's Universe. »

 strong laser beam can remove an electron from an atom -- a process which takes place almost instantly. At the Vienna University of Technology, this phenomenon could now be studied with a time resolution of less than ten attoseconds (ten billionths of a billionth of a second). Scientists succeeded in watching an atom being ionized and a free electron being "born." These measurements yield valuable information about the electrons in the atom, which up until now hasn't been experimentally accessible, such as the time evolution of the electron's quantum phase -- the beat to which the quantum waves oscillate. In the experiment, short laser pulses are fired at atoms. Each laser pulse can be described as a light wave -- the wave sweeps over the atom, and therefore, the electric field around the atom changes. The electric field rips an electron away from the atom -- but the precise moment at which this happens cannot be defined. "The electron is not removed from the atom at one point in time during the interaction with the laser pulse. There is a superposition of several processes, as it is often the case in quantum mechanics," says Markus Kitzler from the Photonics Institute at TU Vienna. One single electron leaves the atom at different points in time, and these processes combine, much like waves on a water surface, combining to a complex wave pattern. "These quantum mechanical wave-interferences give us information about the initial quantum state of the electron during the ionization process," says Professor Joachim Burgdörfer (Institute for Theoretical Physics, TU Vienna), whose research team closely collaborated with the experimentalists at the Photonics Institute. Like waves, quantum particles in this experiment can interfere constructively or destructively. The wave cycle of the electrons is extremely short, the quantum phase changes rapidly. "Usually, this quantum phase can hardly be measured," says Markus Kitzler. Combining high precision measurements and elaborate theoretical calculations, information about the electron's quantum phase can now be obtained. An important tool for these measurements was a very special laser beam, containing two different wavelengths. The laser pulse interacting with the atom could be tailored very precisely. Using these pulses, the scientists could measure the quantum phase which the electron had inside the atom (with respect to the beat defined by the laser light) before it was removed by the laser. "This quantum phase that we can measure now, also tells us about the electron's energy states inside the atom, and about the precise position at which the ionization took place," says Markus Kitzler. To do that, the scientists had to measure the quantum phase with an incredible precision of less than ten attoseconds. The time span of ten attoseconds (10*10^(-18) seconds) is so short that any comparison to everyday timescales fails. The ratio of ten years to a second is 300 million to one. Dividing a second by the same factor takes us to the incredibly short time scale of three nanoseconds -- in this period, light travels one meter. This is the time scale of microelectronics. Again dividing this tiny period of time by a factor of 300 million, we arrive at about ten attoseconds. This, is the timescale of atomic processes. It is the order of magnitude of an electron's period orbiting the nucleus. In order to measure or to influence these processes, scientists have been striving to access these timescales for years. »

 Drawing on powerful computational tools and a state-of-the-art scanning transmission electron microscope, a team of University of Wisconsin-Madison and Iowa State University materials science and engineering researchers has discovered a new nanometer-scale atomic structure in solid metallic materials known as metallic glasses. Published May 11 in the journal Physical Review Letters, the findings fill a gap in researchers' understanding of this atomic structure. This understanding ultimately could help manufacturers fine-tune such properties of metallic glasses as ductility, the ability to change shape under force without breaking, and formability, the ability to form a glass without crystalizing. Glasses include all solid materials that have a non-crystalline atomic structure: They lack a regular geometric arrangement of atoms over long distances. "The fundamental nature of a glass structure is that the organization of the atoms is disordered-jumbled up like differently sized marbles in a jar, rather than eggs in an egg carton," says Paul Voyles, a UW-Madison associate professor of materials science and engineering and principal investigator on the research. Researchers widely believe that atoms in metallic glasses are arranged only as pentagons in an order known as five-fold rotational symmetry. However, in studies of a zirconium-copper-aluminum metallic glass, Voyles' team found there are clusters of squares and hexagons-in addition to clusters of pentagons, some of which form chains-all located within the space of just a few nanometers. "One or two nanometers is a group of about 50 atoms-and it's how those 50 atoms are arranged with respect to one another that's the new and interesting part," he says. Measuring the atomic structure of glass at this scale has been extremely difficult. Researchers know that, at a few tenths of a nanometer, atoms in metallic glasses have the same distances between them as they do in crystals. They also know that at long distances-hundreds of nanometers-there's no order left. "But what happens in between, at this 'magic' length of one to three nanometers, is very hard to measure experimentally and is essentially unexplored in experiments and simulations," says Voyles. An expert in electron microscopy, Voyles used a powerful, state-of-the-art scanning transmission electron microscope at UW-Madison as his window into this nanometer-scale atomic structure. The microscope can generate an electron probe beam two nanometers in diameter-the ideal size for examining atoms on a length scale of one to three nanometers. "And that, fundamentally, is what makes the experiments work and gives us access to this information that's otherwise very difficult to obtain," he says. "We can match our experimental probe in size right to the size of what we want to measure." Voyles and his team coupled the experimental data from the microscope with state-of-the-art computational methods to conduct simulations that accurately reflect the experiments. "It's the combination of those two things that gives us this new insight," he says. "We can look at the results and abstract general principles about rotational symmetry and nanoscale clustering." There were several clues in the properties of some metallic glasses that these competing geometric structures might exist. Those arise from the interrelationships of structure, processing and properties, says Voyles. "If we understand how the structure controls, for example, glass-forming ability or the ability to change shape on bending or pulling, and we understand how different elements participate in these different kinds of structures, that gives us a handle on controlling properties by adjusting the composition or adjusting the rate at which the material was cooled or heated to change the structure in some useful way," he says. »

Evidence for a forgotten ancient language which dates back more than 2,500 years, to the time of the Assyrian Empire, has been found by archaeologists working in Turkey.Researchers working at Ziyaret Tepe, the probable site of the ancient Assyrian city of Tušhan, believe that the language may have been spoken by deportees originally from the Zagros Mountains, on the border of modern-day Iran and Iraq. In keeping with a policy widely practised across the Assyrian Empire, these people may have been forcibly moved from their homeland and resettled in what is now south-east Turkey, where they would have been set to work building the new frontier city and farming its hinterland. The evidence for the language they spoke comes from a single clay tablet, which was preserved after it was baked in a fire that destroyed the palace in Tušhan at some point around the end of the 8th century BCE. Inscribed with cuneiform characters, the tablet is essentially a list of the names of women who were attached to the palace and the local Assyrian administration. Writing in the new issue of the Journal of Near Eastern Studies, Dr John MacGinnis, from the McDonald Institute for Archaeological Research, University of Cambridge, explains how the nature of these names has piqued the interest of researchers. "Altogether around 60 names are preserved," MacGinnis said. "One or two are actually Assyrian and a few more may belong to other known languages of the period, such as Luwian or Hurrian, but the great majority belong to a previously unidentified language." "If the theory that the speakers of this language came from western Iran is correct, then there is the potential here to complete the picture of the world's first multi-ethnic empire. We know from existing texts that the Assyrians did conquer people from that region. Now we know that there is another language, perhaps from the same area, and maybe more evidence of its existence waiting to be discovered." Ziyaret Tepe is on the River Tigris in south east Turkey, and has been the subject of extensive archaeological excavations since 1997. Recent work has revealed evidence that it was probably once the site of the Assyrian frontier city of Tušhan. In particular, it is thought that the remains of a monumental building excavated on the site are those of the governor's palace, built by the Assyrian King Ashurnasirpal II (883 -- 859 BCE). »

The idea of discovering a new form of life has not only excited astronomers and astrobiologists for decades, but also the wider public. The notion that we are the only example of a successful life form in the galaxy has, for many, seemed like an unlikely statistic, as we discover more and more habitable planetary bodies and hear yet more evidence of life's ability to survive in extreme conditions. A new essay, published May 8 in the online, open-access journal PLoS Biology, examines what really constitutes 'life' and the probability of discovering new life forms. Professor Gerald Joyce, from The Scripps Research Institute in La Jolla, California, discusses in the essay the basic requirements for a life form to exist. He says, "Life self-reproduces, transmits heritable information to its progeny, and undergoes Darwinian evolution based on natural existing biology. For the former, a life form would self-organize "into a bit-generating system." It's thought that this is how life originated on Earth; from a primordial soup of chemicals in an aqueous environment that generated self-replicating molecules, which then mutated and evolved. Joyce argues, "A life form that arises directly from bit-free chemistry would be considered 'new' from the outset, while one that derives from a biological cell would have a long way to go before reaching the threshold." It is in these differences between chemical or biological initiation -- that is to say, whether the life form has developed from an existing life or seemingly independently -- that confusion and misinformation occurs surrounding the probability of a new life being discovered or created. Given that we only know of one life form -- our own -- we can't meaningfully estimate the probability of new life arising, either on Earth or elsewhere. "I think humans are lonely and long for another form of life in the universe," says Joyce, "preferably one that is intelligent and benevolent. But wishing upon a star does not make it so. We must either discover alternative life or construct it in the laboratory. Someday it may be discovered by a Columbus who travels to a distant world or, more likely in my opinion, invented by a Geppetto who toils at the workbench." »

An optical switch developed at the Joint Quantum Institute (JQI) spurs the prospective integration of photonics and electronics. What, isn’t electronics good enough? Well, nothing travels faster than light, and in the effort to speed up the processing and transmission of information, the combined use of light parcels (photons) along with electricity parcels (electrons) is desirable for developing a workable opto-electronic protocol. The JQI switch can steer a beam of light from one direction to another in only 120 picoseconds (120 trillionths of a second), requiring very little power, only about 90 attojoules (90 x 10-18 joules). At the wavelength used, in the near infrared (921 nm), this amounts to about 140 photons.  The centerpiece of most electronic gear is the transistor, a solid-state component in which a gate signal is applied to a nearby tiny conducting pathway, thus switching on and off the passage of an information signal. The analogous process in photonics would be a solid-state component which acts as a gate, enabling or disabling the passage of light through a nearby waveguide, or as a router, for switching beams in different directions. In the JQI experiment, prepared and conducted at the University of Maryland and at the National Institute for Standards and Technology (NIST) by Edo Waks and his colleagues, an all-optical switch has been created using a quantum dot (the equivalent of a gate) placed inside a resonant cavity. The dot, consisting of a nm-sized sandwich of the elements indium and arsenic, is so tiny that electrons moving inside can emit light at only discrete wavelengths, as if the dot were an atom. The quantum dot sits inside a photonic crystal, a material that has been bored with many tiny holes. The holes preclude the passage of light through the crystal except for a narrow wavelength range. Actually, the dot sits inside a small hole-free arcade which acts like a resonant cavity. When light travels down the nearby waveguide some of it makes its way into the cavity, where it interacts with the quantum dot. And it is this interaction which can transform the waveguide’s transmission properties. Although 140 photons are needed in the waveguide to produce switching action, only about 6 photons actually are needed to bring about modulation of the QD, thus throwing the switch. Previous optical switches have been able to work only by using bulky nonlinear-crystals and high input power. The JQI switch, by contrast, achieves high-nonlinear interactions using a single quantum dot and very low power input. Switching required only 90 aJ of power, some five times less than the best previous reported device made at labs in Japan (***), which itself used 100 times less power than other all-optical switches. The Japanese switch, however, has the advantage of operating at room temperature, while the JQI switch requires a temperature of around 40 K. Continuing our analogy with electronics: light traveling down the waveguide (the equivalent of the conducting pathway in a transistor) in the form of an information-carrying (probe) beam can be switched from one direction to another using the presence of a second pulse, a control (pump) beam. To steer the probe beam out the side of the device, the slightly detuned pump beam needs to arrive simultaneously with the probe beam, which is on resonance with the dot. The dot lies just off the center track of the waveguide, inside the cavity. The temperature of the quantum dot is tuned to be resonant with the cavity, resulting in strong coupling. If the pump beam does not arrive at the same time as the probe, the probe beam will exit in another direction. So, is this quantum-dot switch an “optical transistor”? Not quite, says JQI scientist Ranojoy Bose. “Our waveguide-dot setup can’t yet be used to modulate a beam of light using only a weak control pulse of light---what we would call a low-photon-number pulse. But Bose says he expects an improvement (reduction) in the number of photons needed to switch the resonant cavity on and off. In the meantime, the JQI switch represents a great start toward creating a usable ultrafast, low-energy on-chip signal router. “Our paper shows that switching can be achieved physically by using only 6 photons of energy, which is completely unprecedented. This is the achievement of fundamental physical milestones—sub-100-aJ switching and switching near the single photon level,” Bose says. »

Astronomers have gathered the most direct evidence yet of a supermassive black hole shredding a star that wandered too close. NASA's Galaxy Evolution Explorer, a space-based observatory, and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were among the first to help identify the stellar remains. Supermassive black holes, weighing millions to billions times more than the Sun, lurk in the centers of most galaxies. These hefty monsters lay quietly until an unsuspecting victim, such as a star, wanders close enough to get ripped apart by their powerful gravitational clutches. Astronomers have spotted these stellar homicides before, but this is the first time they can identify the victim. Using a slew of ground- and space-based telescopes, a team of astronomers led by Suvi Gezari of The Johns Hopkins University in Baltimore, Md., has identified the victim as a star rich in helium gas. The star resides in a galaxy 2.7 billion light-years away. "When the star is ripped apart by the gravitational forces of the black hole, some part of the star's remains falls into the black hole, while the rest is ejected at high speeds. We are seeing the glow from the stellar gas falling into the black hole over time. We're also witnessing the spectral signature of the ejected gas, which we find to be mostly helium. It is like we are gathering evidence from a crime scene. Because there is very little hydrogen and mostly helium in the gas we detect, we know from the carnage that the slaughtered star had to have been the helium-rich core of a stripped star," Gezari explained. This observation yields insights about the harsh environment around black holes and the types of stars swirling around them. This is not the first time the unlucky star had a brush with the behemoth black hole. Gezari and her team think the star's hydrogen-filled envelope surrounding its core was lifted off a long time ago by the same black hole. In their scenario, the star may have been near the end of its life. After consuming most of its hydrogen fuel, it had probably ballooned in size, becoming a red giant. The astronomers think the bloated star was looping around the black hole in a highly elliptical orbit, similar to a comet's elongated orbit around the Sun. On one of its close approaches, the star was stripped of its puffed-up atmosphere by the black hole's powerful gravity. Only its core remained intact. The stellar remnant continued its journey around the black hole, until it ventured even closer to the behemoth monster and faced its ultimate demise. Astronomers have predicted that stripped stars circle the central black hole of our Milky Way galaxy, Gezari pointed out. These close encounters, however, are rare, occurring roughly every 100,000 years. To find this one event, Gezari's team monitored hundreds of thousands of galaxies in ultraviolet light with NASA's Galaxy Evolution Explorer (GALEX), a space-based observatory, and in visible light with the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii. Pan-STARRS, short for Panoramic Survey Telescope and Rapid Response System, scans the entire night sky for all kinds of transient phenomena, including supernovae. The team was looking for a bright flare in ultraviolet light from the nucleus of a galaxy with a previously dormant black hole. They found one in June 2010, which was spotted with both telescopes. Both telescopes continued to monitor the flare as it reached peak brightness a month later and then slowly began to fade over the next 12 months. The brightening event was similar to that of a supernova, but the rise to the peak was much slower, taking nearly one and a half months. »

 It takes a gutsy insect to sneak up on a huge dinosaur while it sleeps, crawl onto its soft underbelly and give it a bite that might have felt like a needle going in -- but giant "flea-like" animals, possibly the oldest of their type ever discovered, probably did just that. And a few actually lived through the experience, based on the discovery by Chinese scientists of remarkable fossils of these creatures, just announced in Current Biology, a professional journal. These flea-like animals, similar but not identical to modern fleas, were probably 10 times the size of a flea you might find crawling on the family dog -- with an extra-painful bite to match. "These were insects much larger than modern fleas and from the size of their proboscis we can tell they would have been mean," said George Poinar, Jr., a professor emeritus of zoology at Oregon State University, who wrote a commentary on this find in the same journal. "You wouldn't talk much about the good old days if you got bit by this insect," Poinar said. "It would have felt about like a hypodermic needle going in -- a flea shot, if not a flu shot. We can be thankful our modern fleas are not nearly this big." Poinar, who is an international expert in ancient and extinct insect life forms, said it's possible that the soft-bodied, flea-like insects found in these fossils from Inner Mongolia are the evolutionary ancestors of modern fleas, but most likely they belong to a separate and now extinct lineage. Called Pseudopulex jurassicus and Pseudopulex magnus, they had bodies that were more flat, like a bedbug or tick, and long claws that could reach over scales on the skin of dinosaurs so they could hold onto them tightly while sucking blood. Modern fleas are more laterally compressed and have shorter antennae, and are able to move quickly through the fur or feathers of their victims. "These are really well-preserved fossils that give us another glimpse of life into the really distant past, the Cretaceous and Jurassic," said Poinar, who has also studied "younger" fleas from 40-50 million years ago preserved in amber. All true fleas are adapted to feeding on warm-blooded vertebrates, Poinar said, and today 94 percent of the 2,300 known species attack mammals, while the remainder feed on birds. But the unusual characteristics and abilities of the flea-like animals found in these fossils lead scientists to believe their prey were some of the biggest kids on the block -- dinosaurs in which they could have fed on the softer skin between scales. Modern fleas, the report noted, have done plenty of damage. Hardly a dog or cat alive has escaped their attack, and they brought humankind such diseases as bubonic plague, which has killed 75 million people. But their bite itself, at least, didn't feel like a needle going in, by an insect that wasn't even afraid of a dinosaur. »

Research by a Danish physicist suggests that the explosion of massive stars -- supernovae -- near the Solar System has strongly influenced the development of life. Prof. Henrik Svensmark of the Technical University of Denmark (DTU) sets out his novel work in a paper in the journal Monthly Notices of the Royal Astronomical Society. When the most massive stars exhaust their available fuel and reach the end of their lives, they explode as supernovae, tremendously powerful explosions that are briefly brighter than an entire galaxy of normal stars. The remnants of these dramatic events also release vast numbers of high-energy charged particles known as galactic cosmic rays (GCR). If a supernova is close enough to the Solar System, the enhanced GCR levels can have a direct impact on the atmosphere of Earth. Prof. Svensmark looked back through 500 million years of geological and astronomical data and considered the proximity of the Sun to supernovae as it moves around our Galaxy, the Milky Way. In particular, when the Sun is passing through the spiral arms of the Milky Way, it encounters newly forming clusters of stars. These so-called open clusters, which disperse over time, have a range of ages and sizes and will have started with a small proportion of stars massive enough to explode as supernovae. From the data on open clusters, Prof. Svensmark was able to deduce how the rate at which supernovae exploded near the Solar System varied over time. Comparing this with the geological record, he found that the changing frequency of nearby supernovae seems to have strongly shaped the conditions for life on Earth. Whenever the Sun and its planets have visited regions of enhanced star formation in the Milky Way Galaxy, where exploding stars are most common, life has prospered. Prof. Svensmark remarks in the paper, "The biosphere seems to contain a reflection of the sky, in that the evolution of life mirrors the evolution of the Galaxy." In the new work, the diversity of life over the last 500 million years seems remarkably well explained by tectonics affecting the sea-level together with variations in the supernova rate, and virtually nothing else. To obtain this result on the variety of life, or biodiversity, he followed the changing fortunes of the best-recorded fossils. These are from invertebrate animals in the sea, such as shrimps and octopuses, or the extinct trilobites and ammonites. They tended to be richest in their variety when continents were drifting apart and sea levels were high and less varied when the land masses gathered 250 million years ago into the supercontinent called Pangaea and the sea-level was lower. But this geophysical effect was not the whole story. When it is removed from the record of biodiversity, what remains corresponds closely to the changing rate of nearby stellar explosions, with the variety of life being greatest when supernovae are plentiful. A likely reason, according to Prof. Svensmark, is that the cold climate associated with high supernova rates brings a greater variety of habitats between polar and equatorial regions, while the associated stresses of life prevent the ecosystems becoming too set in their ways. He also notices that most geological periods seem to begin and end with either an upturn or a downturn in the supernova rate. The changes in typical species that define a period, in the transition from one to the next, could then be the result of a major change in the astrophysical environment. Life's prosperity, or global bioproductivity, can be tracked by the amount of carbon dioxide in the air at various times in the past as set out in the geological record. When supernova rates were high, carbon dioxide was scarce, suggesting that flourishing microbial and plant life in the oceans consumed it greedily to grow. Support for this idea comes from the fact that microbes and plants dislike carbon dioxide molecules that contain a heavy form of carbon atom, carbon-13. As a result, the ocean water is left enriched by carbon-13. The geological evidence shows high carbon-13 when supernovae were commonest -- again pointing to high productivity. As to why this should be, Prof. Svensmark notes that growth is limited by available nutrients, especially phosphorus and nitrogen, and that cold conditions favour the recycling of the nutrients by vigorously mixing the oceans. Although the new analysis suggests, perhaps surprisingly, that supernovae are on the whole good for life, high supernova rates can bring the cold and changeable climate of prolonged glacial episodes. And they can have nasty shocks in store. Geoscientists have long been puzzled by many relatively brief falls in sea-level by 25 metres or more that show up in seismic soundings as eroded beaches. Prof. Svensmark finds that they are what can be expected when chilling due to very close supernovae causes short-lived glacial episodes. With frozen water temporarily bottled up on land, the sea-level drops. The data also support the idea of a long-term link between cosmic rays and climate, with these climatic changes underlying the biological effects. And compared with the temperature variations seen on short timescales as a consequence of the Sun's influence on the influx of cosmic rays, the heating and cooling of Earth due to cosmic rays varying with the prevailing supernova rate have been far larger. »

Although cosmic rays were discovered 100 years ago, their origin remains one of the most enduring mysteries in physics. Now, the IceCube Neutrino Observatory, a massive detector in Antarctica, is homing in on how the highest energy cosmic rays are produced. "Although we have not discovered where cosmic rays come from, we have taken a major step towards ruling out one of the leading predictions," said IceCube principal investigator and University of Wisconsin-Madison physics professor Francis Halzen. Cosmic rays are electrically charged particles, such as protons, that strike Earth from all directions, with energies up to one hundred million times higher than those created in human-made accelerators. The intense conditions needed to generate such energetic particles have focused physicists' interest on two potential sources: the massive black holes at the centers of active galaxies, and the exploding fireballs observed by astronomers as gamma ray bursts (GRBs). IceCube is using neutrinos, which are believed to accompany cosmic ray production, to explore these theories. In a paper published in the April 19 issue of the journal Nature, the IceCube collaboration describes a search for neutrinos emitted from 300 gamma ray bursts observed, most recently in coincidence with the SWIFT and Fermi satellites, between May 2008 and April 2010. Surprisingly, they found none -- a result that contradicts 15 years of predictions and challenges one of the two leading theories for the origin of the highest energy cosmic rays. "The result of this neutrino search is significant because for the first time we have an instrument with sufficient sensitivity to open a new window on cosmic ray production and the interior processes of GRBs," said IceCube spokesperson and University of Maryland physics professor Greg Sullivan. "The unexpected absence of neutrinos from GRBs has forced a re-evaluation of the theory for production of cosmic rays and neutrinos in a GRB fireball and possibly the theory that high energy cosmic rays are generated in fireballs." IceCube is a high energy neutrino telescope at the geographical South Pole in Antarctica, operated by a collaboration of 250 physicists and engineers from the USA, Germany, Sweden, Belgium, Switzerland, Japan, Canada, New Zealand, Australia and Barbados. IceCube observes neutrinos by detecting the faint blue light produced in neutrino interactions in ice. Neutrinos are of a ghostly nature; they can easily travel through people, walls, or the planet Earth. To compensate for the antisocial nature of neutrinos and detect their rare interactions, IceCube is built on an enormous scale. One cubic kilometer of glacial ice, enough to fit the great pyramid of Giza 400 times, is instrumented with 5,160 optical sensors embedded up to 2.5 kilometers deep in the ice. GRBs, the universe's most powerful explosions, are usually first observed by satellites using X-rays and/or gamma rays. GRBs are seen about once per day, and are so bright that they can be seen from half way across the visible Universe. The explosions usually last only a few seconds, and during this brief time they can outshine everything else in the universe. Improved theoretical understanding and more data from the compete IceCube detector will help scientists better understand the mystery of cosmic ray production. IceCube is currently collecting more data with the finalized, better calibrated, and better understood detector. »