Study Reveals Water on Earth is Older Than Our Sun

An illustration of water in our Solar System through time from before the Sun’s birth through the creation of the planets. The image is credited to Bill Saxton, NSF/AUI/NRAO.

A newly published study from the Carnegie Institution for Science reveals that a significant fraction of our Solar System’s water is older than the Sun and that it most likely originated from ices that formed in interstellar space.

Washington, D.C. — Water was crucial to the rise of life on Earth and is also important to evaluating the possibility of life on other planets. Identifying the original source of Earth’s water is key to understanding how life-fostering environments come into being and how likely they are to be found elsewhere. New work from a team including Carnegie’s Conel Alexander found that much of our Solar System’s water likely originated as ices that formed in interstellar space. Their work is published in Science.

Water is found throughout our Solar System. Not just on Earth, but on icy comets and moons, and in the shadowed basins of Mercury. Water has been found included in mineral samples from meteorites, the Moon, and Mars.

Comets and asteroids in particular, being primitive objects, provide a natural “time capsule” of the conditions during the early days of our Solar System. Their ices can tell scientists about the ice that encircled the Sun after its birth, the origin of which was an unanswered question until now.

In its youth, the Sun was surrounded by a protoplanetary disk, the so-called solar nebula, from which the planets were born. But it was unclear to researchers whether the ice in this disk originated from the Sun’s own parental interstellar molecular cloud, from which it was created, or whether this interstellar water had been destroyed and was re-formed by the chemical reactions taking place in the solar nebula.

“Why this is important? If water in the early Solar System was primarily inherited as ice from interstellar space, then it is likely that similar ices, along with the prebiotic organic matter that they contain, are abundant in most or all protoplanetary disks around forming stars,” Alexander explained. “But if the early Solar System’s water was largely the result of local chemical processing during the Sun’s birth, then it is possible that the abundance of water varies considerably in forming planetary systems, which would obviously have implications for the potential for the emergence of life elsewhere.”

In studying the history of our Solar System’s ices, the team—led by L. Ilsedore Cleeves from the University of Michigan—focused on hydrogen and its heavier isotope deuterium. Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. The difference in masses between isotopes results in subtle differences in their behavior during chemical reactions. As a result, the ratio of hydrogen to deuterium in water molecules can tell scientists about the conditions under which the molecules formed.

For example, interstellar water-ice has a high ratio of deuterium to hydrogen because of the very low temperatures at which it forms. Until now, it was unknown how much of this deuterium enrichment was removed by chemical processing during the Sun’s birth, or how much deuterium-rich water-ice the newborn Solar System was capable of producing on its own.

So the team created models that simulated a protoplanetary disk in which all the deuterium from space ice has already been eliminated by chemical processing, and the system has to start over “from scratch” at producing ice with deuterium in it during a million-year period. They did this in order to see if the system can reach the ratios of deuterium to hydrogen that are found in meteorite samples, Earth’s ocean water, and “time capsule” comets. They found that it could not do so, which told them that at least some of the water in our own Solar System has an origin in interstellar space and pre-dates the birth of the Sun.

“Our findings show that a significant fraction of our Solar System’s water, the most-fundamental ingredient to fostering life, is older than the Sun, which indicates that abundant, organic-rich interstellar ices should probably be found in all young planetary systems,” Alexander said.

Publication: L. Ilsedore Cleeves, et al., “The ancient heritage of water ice in the solar system,” Science 26 September 2014: Vol. 345 no. 6204 pp. 1590-1593; DOI: 10.1126/science.1258055

Astronomers Detect Iso-Propyl Cyanide Close to the Galactic Center

In the center of the Milky Way: the background image shows the dust emission in a combination of data obtained with the APEX telescope and the Planck space observatory at a wavelength around 860 micrometers. The organic molecule iso-propyl cyanide with a branched carbon backbone (i-C3H7CN, left) as well as its straight-chain isomer normal-propyl cyanide (n-C3H7CN, right) were both detected with the Atacama Large Millimeter/submillimeter Array in the star-forming region Sgr B2, about 300 light years away from the Galactic center Sgr A*.

A team of astronomers has detected the presence of iso-propyl cyanide in interstellar space, opening a new frontier in the chemistry of star formation.

There is large number of organic molecules in space. One of which, iso-propyl cyanide (i-C3H7CN), was now discovered by scientists in a giant gas cloud called Sagittarius B2, a region of intensive star formation close to the center of our Milky Way. The branched structure of the carbon atoms within the iso-propyl cyanide molecule is unlike any other molecules that have been detected so far in interstellar space. This discovery opens a new frontier in the chemistry of regions of star formation, and indicates the presence of amino acids, for which this branched structure is a key characteristic.

While various types of molecules have been detected in space, the kind of hydrogen-rich, carbon-bearing (organic) molecules that are most closely related to the ones necessary for life on Earth appear to be most plentiful in the gas clouds from which new stars are being formed. “Understanding the production of organic material at the early stages of star formation is critical to piecing together the gradual progression from simple molecules to potentially life-bearing chemistry,” says Arnaud Belloche from the Max Planck Institute for Radio Astronomy, the lead author of the paper.

The search for molecules in interstellar space began in the 1960’s, and around 180 different molecular species have been discovered so far. Each type of molecule emits light at particular wavelengths, in its own characteristic pattern, or spectrum, acting like a fingerprint that allows it to be detected in space using radio telescopes.

Until now, the organic molecules discovered in star-forming regions have shared one major structural characteristic: they each consist of a “backbone” of carbon atoms that are arranged in a single and more or less straight chain. The new molecule discovered by the team, iso-propyl cyanide, is unique in that its underlying carbon structure branches off in a separate strand. “This is the first ever interstellar detection of a molecule with a branched carbon backbone,” says Holger Müller, a spectroscopist at the University of Cologne and co-author on the paper, who measured the spectral fingerprint of the molecule in the laboratory, allowing it to be detected in space.

But it is not just the structure of the molecule that surprised the team – it is also plentiful, at almost half the abundance of its straight-chain sister molecule, normal-propyl cyanide (n-C3H7CN), which the team had already detected using the single-dish radio telescope of the Institut de Radioastronomie Millimétrique (IRAM) a few years ago. “The enormous abundance of iso-propyl cyanide suggests that branched molecules may in fact be the rule, rather than the exception, in the interstellar medium,” says Robin Garrod, an astrochemist at Cornell University and a co-author of the paper.

The team used the Atacama Large Millimeter/submillimeter Array (ALMA), in Chile, to probe the molecular content of the star-forming region Sagittarius B2 (Sgr B2). This region is located close to the Galactic Center, at a distance of about 27,000 light years from the Sun, and is uniquely rich in emission from complex interstellar organic molecules. “Thanks to the new capabilities offered by ALMA, we were able to perform a full spectral survey toward Sgr B2 at wavelengths between 2.7 and 3.6 mm, with sensitivity and spatial resolution ten times greater than our previous survey,” explains Belloche. “But this took only a tenth of the time.” The team used this spectral survey to search systematically for the fingerprints of new interstellar molecules. “By employing predictions from the Cologne Database for Molecular Spectroscopy, we could identify emission features from both varieties of propyl cyanide,” says Müller. As many as 50 individual features for i-propyl cyanide and even 120 for n-propyl cyanide were unambiguously identified in the ALMA spectrum of Sgr B2. The two molecules, each consisting of 12 atoms, are also the joint-largest molecules yet detected in any star-forming region.

The team constructed computational models that simulate the chemistry of formation of the molecules detected in Sgr B2. In common with many other complex organics, both forms of propyl cyanide were found to be efficiently formed on the surfaces of interstellar dust grains. “But,” says Garrod, “the models indicate that for molecules large enough to produce branched side-chain structure, these may be the prevalent forms. The detection of the next member of the alkyl cyanide series, n-butyl cyanide (n-C4H9CN), and its three branched isomers would allow us to test this idea”.

“Amino acids identified in meteorites have a composition that suggests they originate in the interstellar medium,” adds Belloche. “Although no interstellar amino acids have yet been found, interstellar chemistry may be responsible for the production of a wide range of important complex molecules that eventually find their way to planetary surfaces.”

“The detection of iso-propyl cyanide tells us that amino acids could indeed be present in the interstellar medium because the side-chain structure is a key characteristic of these molecules”, says Karl Menten, director at MPIfR and head of its Millimeter and Submillimeter Astronomy research department. “Amino acids have already been identified in meteorites and we hope to detect them in the interstellar medium in the future”, he concludes.

Publication: Arnaud Belloche, et al., “Detection of a branched alkyl molecule in the interstellar medium: iso-propyl cyanide,” Science 26 September 2014: Vol. 345 no. 6204 pp. 1584-1587; DOI: 10.1126/science.1256678

Newly Released Hubble Image of AG Carinae

This newly released Hubble image shows AG Carinae – a luminous star classified as a Luminous Blue Variable.

In this new Hubble image, the strikingly luminous star AG Carinae — otherwise known as HD 94910 — takes center stage. Found within the constellation of Carina in the southern sky, AG Carinae lies 20,000 light-years away, nestled in the Milky Way.

AG Carinae is classified as a Luminous Blue Variable. These rare objects are massive evolved stars that will one day become Wolf-Rayet Stars — a class of stars that are tens of thousands to several million times as luminous as the Sun. They have evolved from main sequence stars that were twenty times the mass of the Sun.

Stars like AG Carinae lose their mass at a phenomenal rate. This loss of mass is due to powerful stellar winds with speeds of up to 7 million km/hour. These powerful winds are also responsible for the shroud of material visible in this image. The winds exert enormous pressure on the clouds of interstellar material expelled by the star and force them into this shape.

Despite HD 94910’s intense luminosity, it is not visible with the naked eye as much of its output is in the ultraviolet.

This image was taken with the Wide Field and Planetary Camera 2 (WFPC2), that was installed on Hubble during the Shuttle mission STS-61 and was Hubble’s workhorse for many years. It is worth noting that the bright glare at the center of the image is not the star itself. The star is tiny at this scale and hidden within the saturated region. The white cross is also not an astronomical phenomenon but rather an effect of the telescope.

NASA’s Cold Atom Laboratory to Study Ultra-Cold Quantum Gases

Artist’s concept of an atom chip for use by NASA’s Cold Atom Laboratory (CAL) aboard the International Space Station. CAL will use lasers to cool atoms to ultracold temperatures. Image Credit: NASA

Researchers will use NASA’s Cold Atom Laboratory to study ultra-cold quantum gases, exploring how atoms interact in microgravity when they have almost no motion due to such cold temperatures.

Like dancers in a chorus line, atoms’ movements become synchronized when lowered to extremely cold temperatures. To study this bizarre phenomenon, called a Bose-Einstein condensate, researchers need to cool atoms to a temperature just above absolute zero – the point at which atoms have the least energy and are close to motionless.

The goal of NASA’s Cold Atom Laboratory (CAL) is to study ultra-cold quantum gases in a facility instrument developed for use on the International Space Station. Scientists will use the facility to explore how differently atoms interact in microgravity when they have almost no motion due to such cold temperatures. With less pull toward the ground from Earth, matter can stay in the form of a Bose Einstein condensate longer, giving researchers the opportunity to observe it better.

The CAL team announced this week that it has succeeded in producing a Bose-Einstein condensate at NASA’s Jet Propulsion Laboratory, a key breakthrough for the instrument leading up to its debut on the space station in late 2016.

A Bose-Einstein condensate is a collection of atoms in a dilute gas that have been lowered to extremely cold temperatures and all occupy the same quantum state, in which all of the atoms have the same energy levels. At a critical temperature, atoms begin to coalesce, overlap and move in synch. The resulting condensate is a new state of matter that behaves like a giant – by atomic standards – wave.

“It’s official. CAL’s ground testbed is the coolest spot at NASA’s Jet Propulsion Laboratory at 200 nano-Kelvin [200 billionths of 1 Kelvin],” said CAL Project Scientist Rob Thompson at JPL in Pasadena, California. “Achieving Bose-Einstein condensation in our prototype hardware is a crucial step for the mission.”

Although these quantum gases had been created before elsewhere on Earth, CAL will explore the condensates in an entirely new regime: the microgravity environment of the space station. It will enable unprecedented research in temperatures colder than any found on Earth.

This sequence of false-color images shows the formation of a Bose-Einstein condensate in the Cold Atom Laboratory prototype at NASA’s Jet Propulsion Laboratory as the temperature gets progressively closer to absolute zero. Red in each figure indicates higher density. Image Credit: NASA/JPL-Caltech

In the station’s microgravity environment, long interaction times and temperatures as low as one picokelvin (one trillionth of one Kelvin, or 293 trillion times less than room temperature) should be achievable. That’s colder than anything known in nature, and the experiments with CAL could potentially create the coldest matter ever observed in the universe. These breakthrough temperatures unlock the potential to observe new quantum phenomena and test some of the most fundamental laws of physics. The CAL investigation could advance our knowledge in the development of exquisitely sensitive quantum detectors, which could be used for monitoring the gravity of the Earth and other planetary bodies, or for building advanced navigation devices.

“Ultra-cold atoms will also be useful for space-based optical clocks that will be future time standards,” Thompson said.

First observed in 1995, Bose-Einstein condensation has been one of the “hottest” topics in physics ever since. The condensates are different from normal gases; they represent a distinct state of matter that starts to form typically below a millionth of a degree above absolute zero. Familiar concepts of “solid,” “liquid,” and “gas” no longer apply at such cold temperatures; instead, atoms do bizarre things governed by quantum mechanics, such as behaving as waves and particles at the same time.

CAL researchers used lasers to optically cool atoms of the chemical element rubidium to temperatures almost a million times colder than that of the depths of space. The atoms were then magnetically trapped, and radio waves were used to cool the atoms 100 times lower. The radiofrequency radiation acts like a knife, slicing away the hottest atoms from the trap so that only the coldest remain.

The research is at the point where this process can reliably create a Bose-Einstein condensate in just seconds.

“This was a tremendous accomplishment for the CAL team. It confirms the fidelity of the instrument system design and provides us a facility to perform science and hardware verifications before we get to the space station,” said CAL project manager Anita Sengupta of JPL.

JPL is developing the Cold Atom Laboratory sponsored by the International Space Station Program at NASA’s Johnson Space Center in Houston. The Space Life and Physical Sciences Division of NASA’s Human Exploration and Operations Mission Directorate at NASA Headquarters in Washington manages the Fundamental Physics Program.

While so far CAL researchers have created Bose-Einstein condensates with rubidium atoms, eventually they also will add in potassium.

“The behavior of two condensates mixing together will be fascinating for physicists to observe, especially in space,” Sengupta said.

Besides merely creating Bose-Einstein condensates, CAL provides a suite of tools to manipulate and probe these quantum gases in a variety of ways. CAL has a unique role as a facility for the atomic, molecular and optical physics community to study cold atomic physics in microgravity, said David Aveline of JPL, CAL ground testbed lead.

“Instead of a state-of-the-art telescope looking outward into the cosmos, CAL will look inward, exploring physics at the atomic scale,” Aveline said.

You may have thought that the coldest place in the universe might be a vast tract of space between distant stars. But in a couple of years, the coldest place we know of will be orbiting our own planet, creating atomic dances to dazzle the scientific imagination.

Source: Elizabeth Landau, Jet Propulsion Laboratory

Cassini Spacecraft Views “Painted” Saturn

Using a spectral filter, this wide-angle camera view of Saturn was taken on April 2, 2014 by the Cassini spacecraft.

Saturn’s many cloud patterns, swept along by high-speed winds, look as if they were painted on by some eager alien artist.

With no real surface features to slow them down, wind speeds on Saturn can top 1,100 mph (1,800 kph), more than four times the top speeds on Earth.

This view looks toward the sunlit side of the rings from about 29 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on April 4, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 1.1 million miles (1.8 million kilometers) from Saturn. Image scale is 68 miles (109 kilometers) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

Biologist Reveal Boost in Certain Amino Acids is an Early Sign of Cancer

Based on an analysis of blood samples from 1,500 people participating in long-term health studies, biologists found that people with a surge in amino acids known as branched chain amino acids were far more likely to be diagnosed with pancreatic cancer within one to 10 years.

Years before they show any other signs of disease, pancreatic cancer patients have very high levels of certain amino acids in their bloodstream, according to a new study from MIT, Dana-Farber Cancer Institute, and the Broad Institute.

This finding, which suggests that muscle tissue is broken down in the disease’s earliest stages, could offer new insights into developing early diagnostics for pancreatic cancer, which kills about 40,000 Americans every year and is usually not caught until it is too late to treat.

The study, which appears today in the journal Nature Medicine, is based on an analysis of blood samples from 1,500 people participating in long-term health studies. The researchers compared samples from people who were eventually diagnosed with pancreatic cancer and samples from those who were not. The findings were dramatic: People with a surge in amino acids known as branched chain amino acids were far more likely to be diagnosed with pancreatic cancer within one to 10 years.

“Pancreatic cancer, even at its very earliest stages, causes breakdown of body protein and deregulated metabolism. What that means for the tumor, and what that means for the health of the patient — those are long-term questions still to be answered,” says Matthew Vander Heiden, an associate professor of biology, a member of MIT’s Koch Institute for Integrative Cancer Research, and one of the paper’s senior authors.

The paper’s other senior author is Brian Wolpin, an assistant professor of medical oncology at Dana-Farber. Wolpin, a clinical epidemiologist, assembled the patient sample from several large public-health studies. All patients had their blood drawn when they began participating in the studies and subsequently filled out annual health questionnaires.

Working with researchers at the Broad Institute, the team analyzed blood samples for more than 100 different metabolites — molecules, such as proteins and sugars, produced as the byproducts of metabolic processes.

“What we found was that this really interesting signature fell out as predicting pancreatic cancer diagnosis, which was elevation in these three branched chain amino acids: leucine, isoleucine, and valine,” Vander Heiden says. These are among the 20 amino acids — the building blocks for proteins — normally found in the human body.

Some of the patients in the study were diagnosed with pancreatic cancer just one year after their blood samples were taken, while others were diagnosed two, five, or even 10 years later.

“We found that higher levels of branched chain amino acids were present in people who went on to develop pancreatic cancer compared to those who did not develop the disease,” Wolpin says. “These findings led us to hypothesize that the increase in branched chain amino acids is due to the presence of an early pancreatic tumor.”

Early protein breakdown

Vander Heiden’s lab tested this hypothesis by studying mice that are genetically programmed to develop pancreatic cancer. “Using those mouse models, we found that we could perfectly recapitulate these exact metabolic changes during the earliest stages of cancer,” Vander Heiden says. “What happens is, as people or mice develop pancreatic cancer, at the very earliest stages, it causes the body to enter this altered metabolic state where it starts breaking down protein in distant tissues.”

“This is a finding of fundamental importance in the biology of pancreatic cancer,” says David Tuveson, a professor at the Cancer Center at Cold Spring Harbor Laboratory who was not involved in the work. “It really opens a window of possibility for labs to try to determine the mechanism of this metabolic breakdown.”

The researchers are now investigating why this protein breakdown, which has not been seen in other types of cancer, occurs in the early stages of pancreatic cancer. They suspect that pancreatic tumors may be trying to feed their own appetite for amino acids that they need to build cancerous cells. The researchers are also exploring possible links between this early protein breakdown and the wasting disease known as cachexia, which often occurs in the late stages of pancreatic cancer.

Also to be answered is the question of whether this signature could be used for early detection. The findings need to be validated with more data, and it may be difficult to develop a reliable diagnostic based on this signature alone, Vander Heiden says. However, he believes that studying this metabolic dysfunction further may reveal additional markers, such as misregulated hormones, that could be combined to generate a more accurate test.

The findings may also allow scientists to pursue new treatments that would work by targeting tumor metabolism and cutting off a tumor’s nutrient supply, Vander Heiden says.

MIT’s contribution to this research was funded by the Lustgarten Foundation, the National Institutes of Health, the Burroughs Wellcome Fund, and the Damon Runyon Cancer Research Foundation.

Publication: Jared R Mayers, et al., “Elevation of circulating branched-chain amino acids is an early event in human pancreatic adenocarcinoma development,” Nature Medicine, 2014; doi:10.1038/nm.3686

Engineers Develop New System to Harness the Full Spectrum of Available Solar Radiation

This rendering shows the metallic dielectric photonic crystal that stores solar energy as heat. Credit: Jeffrey Chou

Engineers at MIT have developed a two-dimensional metallic dielectric photonic crystal that has the ability to absorb sunlight from a wide range of angles while withstanding extremely high temperatures.

The key to creating a material that would be ideal for converting solar energy to heat is tuning the material’s spectrum of absorption just right: It should absorb virtually all wavelengths of light that reach Earth’s surface from the sun — but not much of the rest of the spectrum, since that would increase the energy that is reradiated by the material, and thus lost to the conversion process.

Now researchers at MIT say they have accomplished the development of a material that comes very close to the “ideal” for solar absorption. The material is a two-dimensional metallic dielectric photonic crystal, and has the additional benefits of absorbing sunlight from a wide range of angles and withstanding extremely high temperatures. Perhaps most importantly, the material can also be made cheaply at large scales.

The creation of this material is described in a paper published in the journal Advanced Materials, co-authored by MIT postdoc Jeffrey Chou, professors Marin Soljacic, Nicholas Fang, Evelyn Wang, and Sang-Gook Kim, and five others.

The material works as part of a solar-thermophotovoltaic (STPV) device: The sunlight’s energy is first converted to heat, which then causes the material to glow, emitting light that can, in turn, be converted to an electric current.

Some members of the team worked on an earlier STPV device that took the form of hollow cavities, explains Chou, of MIT’s Department of Mechanical Engineering, who is the paper’s lead author. “They were empty, there was air inside,” he says. “No one had tried putting a dielectric material inside, so we tried that and saw some interesting properties.”

When harnessing solar energy, “you want to trap it and keep it there,” Chou says; getting just the right spectrum of both absorption and emission is essential to efficient STPV performance.

Most of the sun’s energy reaches us within a specific band of wavelengths, Chou explains, ranging from the ultraviolet through visible light and into the near-infrared. “It’s a very specific window that you want to absorb in,” he says. “We built this structure, and found that it had a very good absorption spectrum, just what we wanted.”

In addition, the absorption characteristics can be controlled with great precision: The material is made from a collection of nanocavities, and “you can tune the absorption just by changing the size of the nanocavities,” Chou says.

Another key characteristic of the new material, Chou says, is that it is well matched to existing manufacturing technology. “This is the first-ever device of this kind that can be fabricated with a method based on current … techniques, which means it’s able to be manufactured on silicon wafer scales,” Chou says — up to 12 inches on a side. Earlier lab demonstrations of similar systems could only produce devices a few centimeters on a side with expensive metal substrates, so were not suitable for scaling up to commercial production, he says.

In order to take maximum advantage of systems that concentrate sunlight using mirrors, the material must be capable of surviving unscathed under very high temperatures, Chou says. The new material has already demonstrated that it can endure a temperature of 1,000 degrees Celsius (1,832 degrees Fahrenheit) for a period of 24 hours without severe degradation.

And since the new material can absorb sunlight efficiently from a wide range of angles, Chou says, “we don’t really need solar trackers” — which would add greatly to the complexity and expense of a solar power system.

“This is the first device that is able to do all these things at the same time,” Chou says. “It has all these ideal properties.”

While the team has demonstrated working devices using a formulation that includes a relatively expensive metal, ruthenium, “we’re very flexible about materials,” Chou says. “In theory, you could use any metal that can survive these high temperatures.”

“This work shows the potential of both photonic engineering and materials science to advance solar energy harvesting,” says Paul Braun, a professor of materials science and engineering at the University of Illinois at Urbana-Champaign, who was not involved in this research. “In this paper, the authors demonstrated, in a system designed to withstand high temperatures, the engineering of the optical properties of a potential solar thermophotovoltaic absorber to match the sun’s spectrum. Of course much work remains to realize a practical solar cell, however, the work here is one of the most important steps in that process.”

The group is now working to optimize the system with alternative metals. Chou expects the system could be developed into a commercially viable product within five years. He is working with Kim on applications from this project.

The team also included MIT research scientist Ivan Celanovic and former graduate students Yi Yeng, Yoonkyung Lee, Andrej Lenert, and Veronika Rinnerbauer. The work was supported by the Solid-State Solar Thermal Energy Conversion Center and the U.S. Department of Energy.

Publication: Jeffrey B. Chou, et al., “Enabling Ideal Selective Solar Absorption with 2D Metallic Dielectric Photonic Crystals,” Advanced Materials, 2014; DOI: 10.1002/adma.201403302

New ‘Cloaking’ Device Uses Ordinary Lenses to Hide Objects

A multidirectional `perfect paraxial’ cloak using four lenses. From a continuous range of viewing angles, the hand remains cloaked, and the grids seen through the device match the background on the wall (about 2 m away), in color, spacing, shifts, and magnification. // photo by J. Adam Fenster / University of Rochester

Using a combination of four standard lenses, researchers at the University of Rochester have developed a “cloaking” device that hides objects when you look at them straight on.

Inspired perhaps by Harry Potter’s invisibility cloak, scientists have recently developed several ways—some simple and some involving new technologies—to hide objects from view. The latest effort, developed at the University of Rochester, not only overcomes some of the limitations of previous devices, but it uses inexpensive, readily available materials in a novel configuration.

“There have been many high tech approaches to cloaking and the basic idea behind these is to take light and have it pass around something as if it isn’t there, often using high-tech or exotic materials,” said John Howell, a professor of physics at the University of Rochester. Forgoing the specialized components, Howell and graduate student Joseph Choi developed a combination of four standard lenses that keeps the object hidden as the viewer moves up to several degrees away from the optimal viewing position.

“This is the first device that we know of that can do three-dimensional, continuously multidirectional cloaking, which works for transmitting rays in the visible spectrum,” said Choi, a PhD student at Rochester’s Institute of Optics.

Many cloaking designs work fine when you look at an object straight on, but if you move your viewpoint even a little, the object becomes visible, explains Howell. Choi added that previous cloaking devices can also cause the background to shift drastically, making it obvious that the cloaking device is present.

In order to both cloak an object and leave the background undisturbed, the researchers determined the lens type and power needed, as well as the precise distance to separate the four lenses. To test their device, they placed the cloaked object in front of a grid background. As they looked through the lenses and changed their viewing angle by moving from side to side, the grid shifted accordingly as if the cloaking device was not there. There was no discontinuity in the grid lines behind the cloaked object, compared to the background, and the grid sizes (magnification) matched.

The Rochester Cloak can be scaled up as large as the size of the lenses, allowing fairly large objects to be cloaked. And, unlike some other devices, it’s broadband so it works for the whole visible spectrum of light, rather than only for specific frequencies.

Their simple configuration improves on other cloaking devices, but it’s not perfect. “This cloak bends light and sends it through the center of the device, so the on-axis region cannot be blocked or cloaked,” said Choi. This means that the cloaked region is shaped like a doughnut. He added that they have slightly more complicated designs that solve the problem. Also, the cloak has edge effects, but these can be reduced when sufficiently large lenses are used.

In a new paper submitted to the journal Optics Express, Howell and Choi provide a mathematical formalism for this type of cloaking that can work for angles up to 15 degrees, or more. They use a technique called ABCD matrices that describes how light bends when going through lenses, mirrors, or other optical elements.

While their device is not quite like Harry Potter’s invisibility cloak, Howell had some thoughts about potential applications, including using cloaking to effectively let a surgeon “look through his hands to what he is actually operating on,” he said. The same principles could be applied to a truck to allow drivers to see through blind spots on their vehicles.

Howell became interested in creating simple cloaking devices with off-the-shelf materials while working on a holiday project with his children. Together with his 14 year-old son and Choi, he recently published a paper about some of the possibilities, and also demonstrated simple cloaking with mirrors, like magicians would use, in a brief video (below).

For their demonstration cloak, the researchers used 50mm achromatic doublets with focal lengths f1 = 200mm and f2 = 75mm

To build your own Rochester Cloak, follow these simple steps:

• Purchase 2 sets of 2 lenses with different focal lengths f1 and f2 (4 lenses total, 2 with f1 focal length, and 2 with f2 focal length)
• Separate the first 2 lenses by the sum of their focal lengths (So f1 lens is the first lens, f2 is the 2nd lens, and they are separated by t1= f1+ f2).
• Do the same in Step 2 for the other two lenses.
• Separate the two sets by t2=2 f2 (f1+ f2) / (f1— f2) apart, so that the two f2 lenses are t2 apart.

NOTES:

• Achromatic lenses provide best image quality.
• Fresnel lenses can be used to reduce the total length (2t1+t2)
• Smaller total length should reduce edge effects and increase the range of angles.
• For an easier, but less ideal, cloak, you can try the 3 lens cloak in the paper.

Supercomputer Simulations Reveal an Unusual Death for Ancient Supermassive Stars

This image is a slice through the interior of a supermassive star of 55,500 solar masses along the axis of symmetry. It shows the inner helium core in which nuclear burning is converting helium to oxygen, powering various fluid instabilities (swirling lines). This “snapshot” from a CASTRO simulation shows one moment a day after the onset of the explosion, when the radius of the outer circle would be slightly larger than that of the orbit of the Earth around the sun. Visualizations were done in VisIT. Image Credit: Ken Chen, UCSC

New supercomputer simulations show that non-rotating supermassive primordial stars can die as highly energetic thermonuclear supernovae powered by explosive helium burning, releasing about 10,000 times the energy of a Type Ia supernova and leaving no compact remnant.

Certain primordial stars—those between 55,000 and 56,000 times the mass of our Sun, or solar masses—may have died unusually. In death, these objects—among the Universe’s first-generation of stars—would have exploded as supernovae and burned completely, leaving no remnant black hole behind.

Astrophysicists at the University of California, Santa Cruz (UCSC) and the University of Minnesota came to this conclusion after running a number of supercomputer simulations at the Department of Energy’s (DOE’s) National Energy Research Scientific Computing Center (NERSC) and Minnesota Supercomputing Institute at the University of Minnesota. They relied extensively on CASTRO, a compressible astrophysics code developed at DOE’s Lawrence Berkeley National Laboratory’s (Berkeley Lab’s) Computational Research Division (CRD). Their findings were recently published in Astrophysical Journal (ApJ).

First-generation stars are especially interesting because they produced the first heavy elements, or chemical elements other than hydrogen and helium. In death, they sent their chemical creations into outer space, paving the way for subsequent generations of stars, solar systems and galaxies. With a greater understanding of how these first stars died, scientists hope to glean some insights about how the Universe, as we know it today, came to be.

“We found that there is a narrow window where supermassive stars could explode completely instead of becoming a supermassive black hole—no one has ever found this mechanism before,” says Ke-Jung Chen, a postdoctoral researcher at UCSC and lead author of the ApJ paper. “Without NERSC resources, it would have taken us a lot longer to reach this result. From a user perspective, the facility is run very efficiently and it is an extremely convenient place to do science.”

The Simulations: What’s Going On?

To model the life of a primordial supermassive star, Chen and his colleagues used a one-dimensional stellar evolution code called KEPLER. This code takes into account key processes like nuclear burning and stellar convection. And relevant for massive stars, photo-disintegration of elements, electron-positron pair production and special relativistic effects. The team also included general relativistic effects, which are important for stars above 1,000 solar masses.

They found that primordial stars between 55,000 to 56,000 solar masses live about 1.69 million years before becoming unstable due to general relativistic effects and then start to collapse. As the star collapses, it begins to rapidly synthesize heavy elements like oxygen, neon, magnesium and silicon starting with helium in its core. This process releases more energy than the binding energy of the star, halting the collapse and causing a massive explosion: a supernova.

To model the death mechanisms of these stars, Chen and his colleagues used CASTRO—a multidimensional compressible astrophysics code developed at Berkeley Lab by scientists Ann Almgren and John Bell. These simulations show that once collapse is reversed, Rayleigh-Taylor instabilities mix heavy elements produced in the star’s final moments throughout the star itself. The researchers say that this mixing should create a distinct observational signature that could be detected by upcoming near-infrared experiments such as the European Space Agency’s Euclid and NASA’s Wide-Field Infrared Survey Telescope.

Depending on the intensity of the supernovae, some supermassive stars could, when they explode, enrich their entire host galaxy and even some nearby galaxies with elements ranging from carbon to silicon. In some cases, supernova may even trigger a burst of star formation in its host galaxy, which would make it visually distinct from other young galaxies.

“My work involves studying the supernovae of very massive stars with new physical processes beyond hydrodynamics, so I’ve collaborated with Ann Almgren to adapt CASTRO for many different projects over the years,” says Chen. “Before I run my simulations, I typically think about the physics I need to solve a particular problem. I then work with Ann to develop some code and incorporate it into CASTRO. It is a very efficient system.”

To visualize his data, Chen used an open source tool called VisIt, which was architected by Hank Childs, formerly a staff scientist at Berkeley Lab. “Most of the time I did my own visualizations, but when there were things that I needed to modify or customize I would shoot Hank an email and that was very helpful.”

Chen completed much of this work while he was a graduate student at the University of Minnesota. He completed his Ph.D. in physics in 2013.

Publication: Ke-Jung Chen, et al., “General Relativistic Instability Supernova of a Supermassive Population III Star,” 2014, ApJ, 790, 162; doi:10.1088/0004-637X/790/2/162