Scientists pin down the origins of the moon's tenuous atmosphere

While the moon lacks any breathable air, it does host a barely-there atmosphere. Since the 1980s, astronomers have observed a very thin layer of atoms bouncing over the moon's surface. This delicate atmosphere -- technically known as an "exosphere" -- is likely a product of some kind of space weathering. But exactly what those processes might be has been difficult to pin down with any certainty.

Now, scientists at MIT and the University of Chicago say they have identified the main process that formed the moon's atmosphere and continues to sustain it today. In a study appearing in Science Advances, the team reports that the lunar atmosphere is primarily a product of "impact vaporization."

In their study, the researchers analyzed samples of lunar soil collected by astronauts during NASA's Apollo missions. Their analysis suggests that over the moon's 4.5-billion-year history its surface has been continuously bombarded, first by massive meteorites, then more recently, by smaller, dust-sized "micrometeoroids." These constant impacts have kicked up the lunar soil, vaporizing certain atoms on contact and lofting the particles into the air. Some atoms are ejected into space, while others remain suspended over the moon, forming a tenuous atmosphere that is constantly replenished as meteorites continue to pelt the surface.

The researchers found that impact vaporization is the main process by which the moon has generated and sustained its extremely thin atmosphere over billions of years.

"We give a definitive answer that meteorite impact vaporization is the dominant process that creates the lunar atmosphere," says the study's lead author, Nicole Nie, an assistant professor in MIT's Department of Earth, Atmospheric, and Planetary Sciences. "The moon is close to 4.5 billion years old, and through that time the surface has been continuously bombarded by meteorites. We show that eventually, a thin atmosphere reaches a steady state because it's being continuously replenished by small impacts all over the moon."

Nie's co-authors are Nicolas Dauphas, Zhe Zhang, and Timo Hopp at the University of Chicago, and Menelaos Sarantos at NASA Goddard Space Flight Center.

Weathering's roles

In 2013, NASA sent an orbiter around the moon to do some detailed atmospheric reconnaissance. The Lunar Atmosphere and Dust Environment Explorer (LADEE, pronounced "laddie") was tasked with remotely gathering information about the moon's thin atmosphere, surface conditions, and any environmental influences on the lunar dust.

LADEE's mission was designed to determine the origins of the moon's atmosphere. Scientists hoped that the probe's remote measurements of soil and atmospheric composition might correlate with certain space weathering processes that could then explain how the moon's atmosphere came to be.

Researchers suspect that two space weathering processes play a role in shaping the lunar atmosphere: impact vaporization and "ion sputtering" -- a phenomenon involving solar wind, which carries energetic charged particles from the sun through space. When these particles hit the moon's surface, they can transfer their energy to the atoms in the soil and send those atoms sputtering and flying into the air.

"Based on LADEE's data, it seemed both processes are playing a role," Nie says. "For instance, it showed that during meteorite showers, you see more atoms in the atmosphere, meaning impacts have an effect. But it also showed that when the moon is shielded from the sun, such as during an eclipse, there are also changes in the atmosphere's atoms, meaning the sun also has an impact. So, the results were not clear or quantitative."

Answers in the soil

To more precisely pin down the lunar atmosphere's origins, Nie looked to samples of lunar soil collected by astronauts throughout NASA's Apollo missions. She and her colleagues at the University of Chicago acquired 10 samples of lunar soil, each measuring about 100 milligrams -- a tiny amount that she estimates would fit into a single raindrop.

Nie sought to first isolate two elements from each sample: potassium and rubidium. Both elements are "volatile," meaning that they are easily vaporized by impacts and ion sputtering. Each element exists in the form of several isotopes. An isotope is a variation of the same element, that consists of the same number of protons but a slightly different number of neutrons. For instance, potassium can exist as one of three isotopes, each one having one more neutron, and there being slightly heavier than the last. Similarly, there are two isotopes of rubidium.

The team reasoned that if the moon's atmosphere consists of atoms that have been vaporized and suspended in the air, lighter isotopes of those atoms should be more easily lofted, while heavier isotopes would be more likely to settle back in the soil. Furthermore, scientists predict that impact vaporization, and ion sputtering, should result in very different isotopic proportions in the soil. The specific ratio of light to heavy isotopes that remain in the soil, for both potassium and rubidium, should then reveal the main process contributing to the lunar atmosphere's origins.

With all that in mind, Nie analyzed the Apollo samples by first crushing the soils into a fine powder, then dissolving the powders in acids to purify and isolate solutions containing potassium and rubidium. She then passed these solutions through a mass spectrometer to measure the various isotopes of both potassium and rubidium in each sample.

In the end, the team found that the soils contained mostly heavy isotopes of both potassium and rubidium. The researchers were able to quantify the ratio of heavy to light isotopes of both potassium and rubidium, and by comparing both elements, they found that impact vaporization was most likely the dominant process by which atoms are vaporized and lofted to form the moon's atmosphere.

"With impact vaporization, most of the atoms would stay in the lunar atmosphere, whereas with ion sputtering, a lot of atoms would be ejected into space," Nie says. "From our study, we now can quantify the role of both processes, to say that the relative contribution of impact vaporization versus ion sputtering is about 70:30 or larger." In other words, 70 percent or more of the moon's atmosphere is a product of meteorite impacts, whereas the remaining 30 percent is a consequence of the solar wind.

"The discovery of such a subtle effect is remarkable, thanks to the innovative idea of combining potassium and rubidium isotope measurements along with careful, quantitative modeling," says Justin Hu, a postdoc who studies lunar soils at Cambridge University, who was not involved in the study. "This discovery goes beyond understanding the moon's history, as such processes could occur and might be more significant on other moons and asteroids, which are the focus of many planned return missions."

"Without these Apollo samples, we would not be able to get precise data and measure quantitatively to understand things in more detail," Nie says. "It's important for us to bring samples back from the moon and other planetary bodies, so we can draw clearer pictures of the solar system's formation and evolution."

Read more at Science Daily

Exploding stars

When massive stars or other stellar objects explode in the Earth's cosmic neighborhood, ejected debris can also reach our solar system. Traces of such events are found on Earth or the Moon and can be detected using accelerator mass spectrometry, or AMS for short. An overview of this exciting research is provided in the scientific journal Annual Review of Nuclear and Particle Science (DOI: 10.1146/annurev-nucl-011823-045541) by Prof. Anton Wallner of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), who soon plans to decisively advance this promising branch of research with the new, ultrasensitive AMS facility "HAMSTER."

In their paper, HZDR physicist Anton Wallner and colleague Prof. Brian D. Fields from the University of Illinois in Urbana, USA, provide an overview of near-Earth cosmic explosions with a particular focus on events that occurred three and, respectively, seven million years ago.

"Fortunately, these events were still far enough away, so they probably did not significantly impact the Earth's climate or have major effects on the biosphere. However, things get really uncomfortable when cosmic explosions occur at a distance of 30 light-years or less," Wallner explains. Converted into the astrophysical unit parsec, this corresponds to less than eight to ten parsecs.

Once massive stars have burned up all their fuel, their cores collapse into an ultra-dense neutron star or a black hole, while at the same time, hot gas is ejected outward at a high velocity. A large part of the gas and dust finely dispersed between the stars is carried away by an expanding shock wave. Like a giant balloon with bumps and dents, this envelope also sweeps up any material already present in space. After many thousands of years, the remnants of a supernova have expanded to a diameter of several 10 parsecs, spreading out ever more slowly until the motion finally ceases.

A nearby explosion has the potential to severely disrupt the Earth's biosphere and cause a mass extinction similar to the asteroid impact 66 million years ago. The dinosaurs and many other animal species fell victim to that event. "If we consider the time period since the solar system's formation, which spans billions of years, very close cosmic explosions cannot be ruled out," Wallner emphasizes.

Nevertheless, supernovae only occur in very heavy stars with more than eight to ten times the mass of our sun. Such stars are rare. One of the closest candidates of this size is the red supergiant Betelgeuse in the constellation of Orion, located at a safe distance of about 150 parsecs from our solar system.

Production of interstellar isotopes

Many new atoms are generated during cosmic explosions or shortly before and during the supernova -- among them also a number of radioactive atoms. Wallner is particularly interested in the radioactive iron isotope with the atomic mass of 60. About half of these isotopes, called iron-60 for short, have turned into a stable nickel isotope after 2.6 million years. Therefore, all iron-60 that was present at the Earth's formation some 4,500 million years ago has long since disappeared.

"Iron-60 is extremely rare on Earth because, by natural means, it is not produced in any significant amount. However, it is produced in large quantities just before a supernova takes place. If this isotope now turns up in sediments from the ocean floor or in material from the surface of the moon, it probably came from a supernova or another similar process in space that has taken place near Earth only a few million years ago," Wallner summarizes.

The same applies to the plutonium isotope with the atomic mass of 244. However, this plutonium-244 is more likely generated by the collision of neutron stars than by supernovae. Thus, it is an indicator of the nucleosynthesis of heavy elements. After a period of 80 million years, about half of the plutonium-244 isotope has turned into other elements. Therefore, the slowly decaying plutonium-244 is, in addition to iron-60, another indicator of galactic events and the production of new elements in the last millions of years.

"Exactly how often, where, and under what conditions these heavy elements are produced is currently the subject of intense scientific debate. Plutonium-244 also requires explosive events and, according to theory, is produced similarly to the elements gold or platinum, which have always occurred naturally on Earth but consist of stable atoms today," Wallner explains.

Dust particles as cosmic cargo vessels

But how do these isotopes get to Earth in the first place? The iron-60 atoms ejected by the supernova like to congregate in dust particles. So do the plutonium-244 isotopes, which were possibly created in other events and swept up by the supernova's expanding envelope. After cosmic explosions at a distance of more than ten but less than 150 parsecs, according to theory, the solar wind and the magnetic field of the heliosphere prevent individual atoms from reaching the Earth. However, the iron-60 and plutonium-244 atoms trapped in dust particles continue to fly toward the Earth and the Moon, where they can eventually trickle down to the surface.

Even with a supernova occurring within the so-called "kill radius" of less than ten parsecs, not even a microgram of matter from the envelope will land on each square centimeter. In fact, only very few iron-60 atoms per square centimeter reach the Earth each year. This poses an enormous challenge to "investigators" like physicist Anton Wallner: Within a one-gram sediment sample, perhaps a few thousand iron-60 atoms are distributed like needles in a haystack among billions times billions of the ubiquitous and stable iron atoms with the atomic mass of 56. On top of that, even the most sensitive measurement method may only detect every five thousandth particle, i.e., a maximum of only a few iron-60 atoms in a typical measurement sample.

Such extremely low concentrations can only be determined with Accelerator Mass Spectrometry, short AMS. One of these facilities, the Dresden AMS (DREAMS), is located at the HZDR, soon to be joined by the Helmholtz Accelerator Mass Spectrometer Tracing Environmental Radionuclides (HAMSTER). Since AMS facilities around the globe are designed differently, the various facilities can complement each other in the search for rare isotopes from supernova explosions.

20 years for just one thousand iron-60 atoms

Isotopes of the same element but with a different mass, like the naturally occurring iron-56, are removed with mass filters. Atoms of other elements with the same mass as the target object iron-60, for example, the naturally occurring nickel-60, also interfere. Even after very complex chemical preparation of the samples, they are still billions of times more abundant than iron-60 and must be separated in a special accelerator facility using nuclear physics methods.

In the end, perhaps five individual iron-60 atoms are identified in a measuring process that lasts several hours. Pioneering work on iron-60 detection was conducted at TU Munich. Presently, however, Canberra at the Australian National University is the only existing facility worldwide that is sensitive enough to perform such measurements.

In total, only about one thousand iron-60 atoms have been measured in the past 20 years. For the interstellar plutonium-244, which occurs in concentrations more than 10,000 times lower, only data for individual atoms were available for a long time. Only recently has it been possible to determine about a hundred plutonium-244 atoms at a specialized infrastructure in Sydney -- similar to the HAMSTER facility currently under development at the HZDR.

However, only certain samples are suitable for investigation, which act as archives to preserve these atoms coming from space for millions of years. Samples from the Earth's surface, for example, are rapidly "diluted" by geological processes. Sediments and crusts from the deep sea, which slowly form undisturbed on the ocean floor, are ideal. Alternatively, samples from the lunar surface are suitable because disruptive processes are hardly a problem.

On a research trip until the beginning of November 2023, Wallner and his colleagues will hunt for further cosmic isotopes at particularly suitable AMS facilities in the Australian cities of Canberra (iron-60) and Sydney (plutonium-244). For this purpose, he has received a number of lunar samples from the U.S. space agency NASA.

Read more at Science Daily

Using supernovae to study neutrinos' strange properties

In a new study, researchers have taken an important step toward understanding how exploding stars can help reveal how neutrinos, mysterious subatomic particles, secretly interact with themselves.

One of the less well-understood elementary particles, neutrinos rarely interact with normal matter, and instead travel invisibly through it at almost the speed of light. These ghostly particles outnumber all the atoms in the universe and are always passing harmlessly through our bodies, but due to their low mass and lack of an electric charge they can be incredibly difficult to find and study.

But in a study published today in the journal Physical Review Letters, researchers at The Ohio State University have established a new framework detailing how supernovae -- massive explosions that herald the death of collapsing stars -- could be used as powerful tools to study how neutrino self-interactions can cause vast cosmological changes in the universe.

"Neutrinos only have very small rates of interaction with typical matter, so it's difficult to detect them and test any of their properties," said Po-Wen Chang, lead author of the study and a graduate student in physics at Ohio State. "That's why we have to use astrophysics and cosmology to discover interesting phenomena about them."

Thought to have been important to the formation of the early universe, neutrinos are still puzzling to scientists, despite having learned that they originate from a number of sources, such as in nuclear reactors or the insides of dying stars. But by calculating how self-interactions would affect the neutrino signal from Supernova 1987A, the nearest supernova observed in modern times, researchers found that when neutrinos do interact with themselves, they form a tightly coupled fluid that expands under relativistic hydrodynamics -- a branch of physics that deals with how flows impact solid objects in one of two different ways.

In the case of what's called a "burst outflow," the team theorizes that much like popping a highly pressurized balloon in the vacuum of space would push energy outward, a burst produces a neutrino fluid that moves in all directions. The second case, described as a "wind outflow," imagines a highly pressurized balloon with many nozzles, wherein neutrinos escape at a more constant flow rate, similar to a jet of steady wind.

While the wind-outflow theory is more likely to take place in nature, said Chang, if the burst case is realized, scientists could see new observable neutrino signatures emitted from supernovae, allowing unprecedented sensitivity to neutrino self-interactions.

One of the reasons it's so vital to understand these mechanisms is that if neutrinos are acting as a fluid, that means they are acting together, as a collective. And if the properties of neutrinos are different as a collective than individually, then the physics of supernovae could experience changes too. But whether these changes are due solely to the burst case or the outflow case remains to be seen.

"The dynamics of supernovae are complicated, but this result is promising because with relativistic hydrodynamics we know there's a fork in the road in understanding how they work now," said Chang.

Still, further research needs to be done before scientists can cross off the possibility of the burst case happening inside supernovae as well.

Despite these uncertainties, the study is a huge milestone in answering the decades-old astrophysical issue of how neutrinos actually scatter when ejected from supernovae, said John Beacom, co-author of the study and a professor of physics and astronomy at Ohio State. This study found that in the burst case, unprecedented sensitivity to neutrino self-interactions is possible even with sparse neutrino data from SN 1987A and conservative analysis assumptions.

"This problem has lain basically untouched for 35 years," said Beacom. "So even though we were not able to completely solve how neutrinos affect supernovae, what we're excited about is that we were able to make a substantial step forward."

Down the road, the team hopes their work will be used as a stepping stone to further investigate neutrino self-interactions. Yet because only about two or three supernovae happen per century in the Milky Way, it's likely researchers will have to wait decades more to collect enough new neutrino data to prove their ideas.

"We're always praying for another galactic supernova to happen somewhere and soon, but the best we can do is try to build on what we know as much as possible before it happens," said Chang.

Read more at Science Daily

First X-ray of a single atom

A team of scientists from Ohio University, Argonne National Laboratory, the University of Illinois-Chicago, and others, led by Ohio University Professor of Physics, and Argonne National Laboratory scientist, Saw Wai Hla, have taken the world's first X-ray SIGNAL (or SIGNATURE) of just one atom. This groundbreaking achievement was funded by the U.S. Department of Energy, Office of Basic Energy Sciences and could revolutionize the way scientists detect the materials.

Since its discovery by Roentgen in 1895, X-rays have been used everywhere, from medical examinations to security screenings in airports. Even Curiosity, NASA's Mars rover, is equipped with an X-ray device to examine the materials composition of the rocks in Mars. An important usage of X-rays in science is to identify the type of materials in a sample. Over the years, the quantity of materials in a sample required for X-ray detection has been greatly reduced thanks to the development of synchrotron X-rays sources and new instruments. To date, the smallest amount one can X-ray a sample is in attogram, that is about 10,000 atoms or more. This is due to the X-ray signal produced by an atom being extremely weak so that the conventional X-ray detectors cannot be used to detect it. According to Hla, it is a long-standing dream of scientists to X-ray just one atom, which is now being realized by the research team led by him.

"Atoms can be routinely imaged with scanning probe microscopes, but without X-rays one cannot tell what they are made of. We can now detect exactly the type of a particular atom, one atom-at-a-time, and can simultaneously measure its chemical state," explained Hla, who is also the director of the Nanoscale and Quantum Phenomena Institute at Ohio University. "Once we are able to do that, we can trace the materials down to ultimate limit of just one atom. This will have a great impact on environmental and medical sciences and maybe even find a cure that can have a huge impact for humankind. This discovery will transform the world."

Their paper, published in the scientific journal Nature on May 31, 2023, and gracing the cover of the print version of the scientific journal on June 1, 2023, details how Hla and several other physicists and chemists, including Ph.D. students at OHIO, used a purpose-built synchrotron X-ray instrument at the XTIP beamline of Advanced Photon Source and the Center for Nanoscale Materials at Argonne National Laboratory.

For demonstration, the team chose an iron atom and a terbium atom, both inserted in respective molecular hosts. To detect X-ray signal of one atom, the research team supplemented conventional detectors in X-rays with a specialized detector made of a sharp metal tip positioned at extreme proximity to the sample to collect X-ray excited electrons -- a technique known as synchrotron X-ray scanning tunneling microscopy or SX-STM. X-ray spectroscopy in SX-STM is triggered by photoabsorption of core level electrons, which constitutes elemental fingerprints and is effective in identifying the elemental type of the materials directly.

According to Hla, the spectrums are like fingerprints, each one being unique and able to detect exactly what it is.

"The technique used, and concept proven in this study, broke new ground in X-ray science and nanoscale studies," said Tolulope Michael Ajayi, who is the first author of the paper and doing this work as part of his Ph.D. thesis. "More so, using X-rays to detect and characterize individual atoms could revolutionize research and give birth to new technologies in areas such as quantum information and the detection of trace elements in environmental and medical research, to name a few. This achievement also opens the road for advanced materials science instrumentation."

For the last 12 years, Hla has been involved in the development of an SX-STM instrument and its measurement methods together with Volker Rose, a scientist at the Advanced Photon Source at Argonne National Laboratory.

"I have been able to successfully supervise four OHIO graduate students for their Ph.D. theses related to SX-STM method development over a 12-year period. We have come a long way to achieve the detection of a single atom X-ray signature," Hla said.

Hla's study is focused on nano and quantum sciences with a particular emphasis on understanding materials' chemical and physical properties at the fundamental level -- on an individual atom basis. In addition to achieving X-ray signature of one atom, the team's key goal was to use this technique to investigate the environmental effect on a single rare-earth atom.

"We have detected the chemical states of individual atoms as well," Hla explained. "By comparing the chemical states of an iron atom and a terbium atom inside respective molecular hosts, we find that the terbium atom, a rare-earth metal, is rather isolated and does not change its chemical state while the iron atom strongly interacts with its surrounding."

Many rare-earth materials are used in everyday devices, such as cell phones, computers and televisions, to name a few, and are extremely important in creating and advancing technology. Through this discovery, scientists can now identify not only the type of element but its chemical state as well, which will allow them to better manipulate the atoms inside different materials hosts to meet the ever-changing needs in various fields. Moreover, they have also developed a new method called "X-ray excited resonance tunneling or X-ERT" that allows them to detect how orbitals of a single molecule orient on a material surface using synchrotron X-rays.

"This achievement connects synchrotron X-rays with quantum tunneling process to detect X-ray signature of an individual atom and opens many exciting research directions including the research on quantum and spin (magnetic) properties of just one atom using synchrotron X-rays," Hla said.

Read more at Science Daily

Unusual atom helps in search for Universe's building blocks

An unusual form of caesium atom is helping a University of Queensland-led research team unmask unknown particles that make up the Universe.

Dr Jacinda Ginges, from UQ's School of Mathematics and Physics, said the unusual atom -- made up of an ordinary caesium atom and an elementary particle called a muon -- may prove essential in better understanding the Universe's fundamental building blocks.

"Our Universe is still such a mystery to us," Dr Ginges said.

"Astrophysical and cosmological observations have shown that the matter we know about -commonly referred to as 'Standard Model' particles in physics -- makes up only five percent of the matter and energy content of the Universe.

"Most matter is 'dark', and we currently know of no particle or interaction within the Standard Model that explains it.

"The search for dark matter particles lies at the forefront of particle physics research, and our work with caesium might prove essential in solving this mystery."

The work may also one day improve technology.

"Atomic physics plays a major role in technologies we use every day, such as navigation with the Global Positioning System (GPS), and atomic theory will continue to be important in the advancement of new quantum technologies based on atoms," Dr Ginges said.

Through theoretical research, Dr Ginges and her team have improved the understanding of the magnetic structure of caesium's nucleus, its effects in atomic caesium and the effects of the weird and wonderful muon.

"A muon is basically a heavy electron -- 200 times more massive -- and it orbits the nucleus 200 times closer than the electrons," Dr Ginges said.

"Because of this, it can pick up on details of the structure of the nucleus.

"It sounds complicated, but in a nutshell, this work will help to improve atomic theory calculations that are used in the search for new particles."

The researchers said the new approach can offer greater sensitivity and an alternative technique to finding new particles, through the use of precision atomic measurements.

"You may have heard of the Large Hadron Collider at CERN, the world's largest and most powerful particle accelerator, which smashes together subatomic matter at high energies to find previously unseen particles," Dr Ginges said.

"But our research can offer greater sensitivity, with an alternative technique to find new particles -- through precision atomic measurements.

"It doesn't need a giant collider, and instead uses precision instruments to look for atomic changes at low energy.

"Rather than explosive, high-energy collisions, it's the equivalent of creating an ultra-sensitive 'microscope' to witness the true nature of atoms.

"This can be a more sensitive technique, unveiling particles that particle colliders simply can't see."

Caesium is having a moment, after being featured in the news recently, as the element in the radioactive capsule that went missing, and was subsequently found, in Western Australia's outback.

Read more at Science Daily

Detecting new particles around black holes with gravitational waves

Clouds of ultralight particles can form around rotating black holes. A team of physicists from the University of Amsterdam and Harvard University now show that these clouds would leave a characteristic imprint on the gravitational waves emitted by binary black holes.

Black holes are generally thought to swallow all forms of matter and energy surrounding them. It has long been known, however, that they can also shed some of their mass through a process called superradiance. While this phenomenon is known to occur, it is only effective if new, so far unobserved particles with very low mass exist in nature, as predicted by several theories beyond the Standard Model of particle physics.

Ionizing gravitational atoms

When mass is extracted from a black hole via superradiance, it forms a large cloud around the black hole, creating a so-called gravitational atom. Despite the immensely larger size of a gravitational atom, the comparison with sub-microscopic atoms is accurate because of the similarity of the black hole plus its cloud with the familiar structure of ordinary atoms, where clouds of electrons surround a core of protons and neutrons.

In a publication that appeared in Physical Review Letters this week, a team consisting of UvA physicists Daniel Baumann, Gianfranco Bertone, and Giovanni Maria Tomaselli, and Harvard University physicist John Stout, suggest that the analogy between ordinary and gravitational atoms runs deeper than just the similarity in structure. They claim that the resemblance can in fact be exploited to discover new particles with upcoming gravitational wave interferometers.

In the new work, the researchers studied the gravitational equivalent of the so-called 'photoelectric effect'. In this well-known process, which for example is exploited in solar cells to produce an electric current, ordinary electrons absorb the energy of incident particles of light and are thereby ejected from a material -- the atoms 'ionize'. In the gravitational analogue, when the gravitational atom is part of a binary system of two heavy objects, it gets perturbed by the presence of the massive companion, which could be a second black hole or a neutron star. Just as the electrons in the photoelectric effect absorb the energy of the incident light, the cloud of ultralight particles can absorb the orbital energy of the companion, so that some of the cloud gets ejected from the gravitational atom.

Read more at Science Daily

Time crystals 'impossible' but obey quantum physics

Scientists have created the first "time-crystal" two-body system in an experiment that seems to bend the laws of physics.

It comes after the same team recently witnessed the first interaction of the new phase of matter.

Time crystals were long believed to be impossible because they are made from atoms in never-ending motion. The discovery, published in Nature Communications, shows that not only can time crystals be created, but they have potential to be turned into useful devices.

Time crystals are different from a standard crystal -- like metals or rocks -- which is composed of atoms arranged in a regularly repeating pattern in space.

First theorised in 2012 by Nobel Laureate Frank Wilczek and identified in 2016, time crystals exhibit the bizarre property of being in constant, repeating motion in time despite no external input. Their atoms are constantly oscillating, spinning, or moving first in one direction, and then the other.

EPSRC Fellow Dr Samuli Autti, lead author from Lancaster University's Department of Physics, explained: "Everybody knows that perpetual motion machines are impossible. However, in quantum physics perpetual motion is okay as long as we keep our eyes closed. By sneaking through this crack we can make time crystals."

"It turns out putting two of them together works beautifully, even if time crystals should not exist in the first place. And we already know they also exist at room temperature."

A "two-level system" is a basic building block of a quantum computer. Time crystals could be used to build quantum devices that work at room temperature.

An international team of researchers from Lancaster University, Royal Holloway London, Landau Institute, and Aalto University in Helsinki observed time crystals by using Helium-3 which is a rare isotope of helium with one missing neutron. The experiment was carried out in Aalto University.

Read more at Science Daily

196 lasers help scientists recreate the conditions inside gigantic galaxy clusters

Galaxies rarely live alone. Instead, dozens to thousands are drawn together by gravity, forming vast clusters that are the largest objects in the universe.

"Galaxy clusters are one of the most awe-inspiring things in the universe," said Prof. Emeritus Don Lamb, a University of Chicago astrophysicist and co-author on a new paper published March 9 -- one that may point the way towards solving a decades-long mystery.

Scientists have long known that the hydrogen gas in galaxy clusters is searingly hot -- about 10 million degrees Kelvin, or roughly the same temperature as the center of the sun -- which is so hot that hydrogen atoms cannot exist. Instead the gas is a plasma consisting of protons and electrons.

But a puzzle persists: There is no straightforward explanation for why or how the gas stays so hot. According to the normal rules of physics, it should have cooled within the age of the universe. But it hasn't.

The challenge for anyone trying to solve this puzzle is that you can't exactly create these kinds of powerfully hot and magnetic conditions in your backyard.

However, there is now one place on Earth where you can: the most energetic laser facility in the world. The National Ignition Facility at Lawrence Livermore National Laboratory is able to create such extreme conditions -- though only for a tiny fraction of a second in a volume the size of a dime.

Scientists from UChicago, the University of Oxford, and the University of Rochester worked together to use the National Ignition Facility -- located in Livermore, California -- to create conditions similar to the hot gas in gigantic galaxy clusters. "The experiments conducted at the NIF are literally out of this world," said Jena Meinecke, who was the first author on the paper.

The scientists focused 196 lasers onto a single tiny target, creating a white-hot plasma with intense magnetic fields that exists for a few billionths of a second.

This was long enough for them to determine that instead of a uniform temperature, there were hot and cold spots in the plasma.

This dovetails with one of the theories that has been proposed for how heat is trapped inside galaxy clusters. Normally, heat would be easily distributed as electrons collide with each other. But the tangled magnetic fields inside the plasma can affect these electrons, causing them to spiral along the direction of magnetic fields -- which can prevent them from evenly distributing and dispersing their energy.

In fact, in the experiment they saw that the conduction of energy was suppressed by more than a factor of 100.

"This is an incredibly exciting result because we've been able to show that what astrophysicists have proposed is on the right track," said Lamb, the Robert A. Millikan Distinguished Service Professor Emeritus in Astronomy and Astrophysics.

"This is indeed an astonishing result," added study co-author University of Rochester Prof. Petros Tzeferacos, who oversaw computer simulations of the complicated experiment. "The simulations were key to untangling the physics at play in the turbulent, magnetized plasma, but the level of thermal transport suppression was beyond what we expected."

The simulations were done with a computer code called the FLASH codes, which was developed at the University of Chicago and is now hosted at the University of Rochester's Flash Center for Computational Science, which is led by Tzeferacos. The code allows scientists to simulate their laser experiments in exquisite detail before they do them, so that they can achieve the results they seek.

This is critical because the scientists only get a precious few shots at the facility -- if something goes wrong, there's no redo. And because the experiment conditions only last nanoseconds, the scientists have to make sure they make the measurements they need at exactly the right time. This means everything has to be precisely plotted out far ahead of time.

"It's a challenge when you're at the very extremes of what can be done, but that's where the frontier is," said Lamb.

More questions remain about the physics of galaxy clusters, however. Though the hot and cold spots are solid evidence for the impact of magnetic fields on the cooling of the hot gas in galaxy clusters, further experiments are needed to understand exactly what is happening. The group is planning its next round of experiments at NIF later this year.

For the moment, though, they're happy to have shed light on why the gas in galaxy clusters is still hot even after billions of years.

Galaxies rarely live alone. Instead, dozens to thousands are drawn together by gravity, forming vast clusters that are the largest objects in the universe.

"Galaxy clusters are one of the most awe-inspiring things in the universe," said Prof. Emeritus Don Lamb, a University of Chicago astrophysicist and co-author on a new paper published March 9 -- one that may point the way towards solving a decades-long mystery.

Scientists have long known that the hydrogen gas in galaxy clusters is searingly hot -- about 10 million degrees Kelvin, or roughly the same temperature as the center of the sun -- which is so hot that hydrogen atoms cannot exist. Instead the gas is a plasma consisting of protons and electrons.

But a puzzle persists: There is no straightforward explanation for why or how the gas stays so hot. According to the normal rules of physics, it should have cooled within the age of the universe. But it hasn't.

The challenge for anyone trying to solve this puzzle is that you can't exactly create these kinds of powerfully hot and magnetic conditions in your backyard.

However, there is now one place on Earth where you can: the most energetic laser facility in the world. The National Ignition Facility at Lawrence Livermore National Laboratory is able to create such extreme conditions -- though only for a tiny fraction of a second in a volume the size of a dime.

Scientists from UChicago, the University of Oxford, and the University of Rochester worked together to use the National Ignition Facility -- located in Livermore, California -- to create conditions similar to the hot gas in gigantic galaxy clusters. "The experiments conducted at the NIF are literally out of this world," said Jena Meinecke, who was the first author on the paper.

The scientists focused 196 lasers onto a single tiny target, creating a white-hot plasma with intense magnetic fields that exists for a few billionths of a second.

This was long enough for them to determine that instead of a uniform temperature, there were hot and cold spots in the plasma.

This dovetails with one of the theories that has been proposed for how heat is trapped inside galaxy clusters. Normally, heat would be easily distributed as electrons collide with each other. But the tangled magnetic fields inside the plasma can affect these electrons, causing them to spiral along the direction of magnetic fields -- which can prevent them from evenly distributing and dispersing their energy.

In fact, in the experiment they saw that the conduction of energy was suppressed by more than a factor of 100.

"This is an incredibly exciting result because we've been able to show that what astrophysicists have proposed is on the right track," said Lamb, the Robert A. Millikan Distinguished Service Professor Emeritus in Astronomy and Astrophysics.

"This is indeed an astonishing result," added study co-author University of Rochester Prof. Petros Tzeferacos, who oversaw computer simulations of the complicated experiment. "The simulations were key to untangling the physics at play in the turbulent, magnetized plasma, but the level of thermal transport suppression was beyond what we expected."

The simulations were done with a computer code called the FLASH codes, which was developed at the University of Chicago and is now hosted at the University of Rochester's Flash Center for Computational Science, which is led by Tzeferacos. The code allows scientists to simulate their laser experiments in exquisite detail before they do them, so that they can achieve the results they seek.

This is critical because the scientists only get a precious few shots at the facility -- if something goes wrong, there's no redo. And because the experiment conditions only last nanoseconds, the scientists have to make sure they make the measurements they need at exactly the right time. This means everything has to be precisely plotted out far ahead of time.

"It's a challenge when you're at the very extremes of what can be done, but that's where the frontier is," said Lamb.

More questions remain about the physics of galaxy clusters, however. Though the hot and cold spots are solid evidence for the impact of magnetic fields on the cooling of the hot gas in galaxy clusters, further experiments are needed to understand exactly what is happening. The group is planning its next round of experiments at NIF later this year.

Read more at Science Daily

Time crystals leave the lab

We have all seen crystals, whether a simple grain of salt or sugar, or an elaborate and beautiful amethyst. These crystals are made of atoms or molecules repeating in a symmetrical three-dimensional pattern called a lattice, in which atoms occupy specific points in space. By forming a periodic lattice, carbon atoms in a diamond, for example, break the symmetry of the space they sit in. Physicists call this "breaking symmetry."

Scientists have recently discovered that a similar effect can be witnessed in time. Symmetry breaking, as the name suggests, can arise only where some sort of symmetry exists. In the time domain, a cyclically changing force or energy source naturally produces a temporal pattern.

Breaking of the symmetry occurs when a system driven by such a force faces a déjà vu moment, but not with the same period as that of the force. 'Time crystals' have in the past decade been pursued as a new phase of matter, and more recently observed under elaborate experimental conditions in isolated systems. These experiments require extremely low temperatures or other rigorous conditions to minimize undesired external influences, called noise.

In order for scientists to learn more about time crystals and employ their potential in technology, they need to find ways to produce time crystalline states and keep them stable outside the laboratory.

Cutting-edge research led by UC Riverside and published this week in Nature Communications has now observed time crystals in a system that is not isolated from its ambient environment. This major achievement brings scientists one step closer to developing time crystals for use in real-world applications.

"When your experimental system has energy exchange with its surroundings, dissipation and noise work hand-in-hand to destroy the temporal order," said lead author Hossein Taheri, an assistant research professor of electrical and computer engineering in UC Riverside's Marlan and Rosemary Bourns College of Engineering. "In our photonic platform, the system strikes a balance between gain and loss to create and preserve time crystals."

The all-optical time crystal is realized using a disk-shaped magnesium fluoride glass resonator one millimeter in diameter. When bombarded by two laser beams, the researchers observed subharmonic spikes, or frequency tones between the two laser beams, that indicated breaking of temporal symmetry and creation of time crystals.

The UCR-led team utilized a technique called self-injection locking of the two lasers to the resonator to achieve robustness against environmental effects. Signatures of the temporally repeating state of this system can readily be measured in the frequency domain. The proposed platform therefore simplifies the study of this new phase of matter.

Without the need for a low temperature, the system can be moved outside a complex lab for field applications. One such application could be highly accurate measurements of time. Because frequency and time are mathematical inverses of each other, accuracy in measuring frequency enables accurate time measurement.

"We hope that this photonic system can be utilized in compact and lightweight radiofrequency sources with superior stability as well as in precision timekeeping," said Taheri.

Read more at Science Daily

Less than a nanometer thick, stronger and more versatile than steel

 Scientists create stable nanosheets containing boron and hydrogen atoms with potential applications in nanoelectronics and quantum information technology.

What's thinner than thin? One answer is two-dimensional materials -- exotic materials of science with length and width but only one or two atoms in thickness. They offer the possibility of unprecedented boosts in device performance for electronic devices, solar cells, batteries and medical equipment.

In collaboration with Northwestern University and the University of Florida, scientists from the U.S. Department of Energy's (DOE) Argonne National Laboratory report in Science magazine a breakthrough involving a 2D material called borophane, a sheet of boron and hydrogen a mere two atoms in thickness.

One of the most exciting developments in materials science in recent decades has been a 2D sheet of carbon (graphene), which is one atom thick and 200 times stronger than steel. A similarly promising and newer material is an atom-thick sheet of boron, called borophene -- with an "e." A multi-institutional team, including researchers in Argonne's Center for Nanoscale Materials (a DOE Office of Science User Facility), first synthesized borophene in 2015.

While graphene is simply one atomic layer out of the many same layers in the common material graphite, borophene has no equivalent parent structure and is very difficult to prepare. What's more, the rapid reaction of borophene with air means it is very unstable and changes form readily.

"Borophene by itself has all kinds of problems," said Mark Hersam, Professor of Materials Science and Engineering at Northwestern University. "But when we mix borophene with hydrogen, the product suddenly becomes much more stable and attractive for use in the burgeoning fields of nanoelectronics and quantum information technology."

The research team grew borophene on a silver substrate then exposed it to hydrogen to form the borophane. They then unraveled the complex structure of borophane by combining a scanning tunneling microscope with a computer-vision based algorithm that compares theoretical simulations of structures with experimental measurements. Computer vision is a branch of artificial intelligence that trains high performance computers to interpret and understand the visual world.

Even though the borophane material is only two atoms thick, its structure is quite complex because of the many possible arrangements for the boron and hydrogen atoms. "We have tackled a significant challenge in determining the atomic structures from scanning tunneling microscopy images and computational modeling at the atomic scale with the help of computer vision," said Argonne's Maria Chan, nanoscientist at the Center for Nanoscale Materials. Given the success in unraveling this complex structure, the team's automated analytical technique should be applicable in identifying other complex nanostructures in the future.

"What is really encouraging from our results is that we found a borophane nanosheet on a silver substrate to be quite stable, unlike borophene," said Pierre Darancet, nanoscientist at Argonne's Center for Nanoscale Materials. "This means it should be easily integrated with other materials in the construction of new devices for optoelectronics, devices combining light with electronics." Such light-controlling and light-emitting devices could be incorporated into telecommunications, medical equipment and more.

Read more at Science Daily

Discoveries at the edge of the periodic table: First ever measurements of einsteinium

 Since element 99 -- einsteinium -- was discovered in 1952 at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) from the debris of the first hydrogen bomb, scientists have performed very few experiments with it because it is so hard to create and is exceptionally radioactive.A team of Berkeley Lab chemists has overcome these obstacles to report the first study characterizing some of its properties, opening the door to a better understanding of the remaining transuranic elements of the actinide series.

Published in the journal Nature, the study,"Structural and Spectroscopic Characterization of an Einsteinium Complex,"was co-led by Berkeley Lab scientist Rebecca Abergel and Los Alamos National Laboratory scientist Stosh Kozimor, and included scientists from the two laboratories, UC Berkeley, and Georgetown University, several of whom are graduate students and postdoctoral fellows. With less than 250 nanograms of the element, the team measured the first-ever einsteinium bond distance, a basic property of an element's interactions with other atoms and molecules.

"There's not much known about einsteinium," said Abergel,who leads Berkeley Lab'sHeavy Element Chemistry groupand is an assistant professor in UC Berkeley's Nuclear Engineering department. "It's a remarkable achievement that we were able to work with this small amount of material and do inorganic chemistry. It's significant because the more we understand about its chemical behavior, the more we can apply this understanding for the development of new materials or new technologies, not necessarily just with einsteinium, but with the rest of the actinides too. And we can establish trends in the periodic table."

Short-lived and hard to make

Abergel and her team used experimental facilities not available decades ago when einsteinium was first discovered -- theMolecular Foundryat Berkeley Lab and theStanford Synchrotron Radiation Lightsource (SSRL)at SLAC National Accelerator Laboratory, both DOE Office of Science user facilities -- to conduct luminescence spectroscopy and X-ray absorption spectroscopy experiments.

But first, getting the sample in a usable form was almost half the battle. "This whole paper is a long series of unfortunate events," she said wryly.

The material was made at Oak Ridge National Laboratory's High Flux Isotope Reactor, one of only a few places in the world that is capable of making einsteinium, which involves bombarding curium targets with neutrons to trigger a long chain of nuclear reactions. The first problem they encountered was that the sample was contaminated with a significant amount of californium, as making pure einsteinium in a usable quantity is extraordinarily challenging.

So they had to scrap their original plan to use X-ray crystallography -- which is considered the gold standard for obtaining structural information on highly radioactive molecules but requires a pure sample of metal -- and instead came up with a new way to make samples and leverage element-specific research techniques. Researchers at Los Alamos provided critical assistance in this step by designing a sample holder uniquely suited to the challenges intrinsic to einsteinium.

Then, contending with radioactive decay was another challenge. The Berkeley Lab team conducted their experiments with einsteinium-254, one of the more stable isotopes of the element. It has a half-life of 276 days, which is the time for half of the material to decay. Although the team was able to conduct many of the experiments before the coronavirus pandemic, they had plans for follow-up experiments that got interrupted thanks to pandemic-related shutdowns. By the time they were able to get back into their lab last summer, most of the sample was gone.

Bond distance and beyond

Still, the researchers were able to measure a bond distance with einsteinium and also discovered some physical chemistry behavior that was different from what would be expected from the actinide series, which are the elements on the bottom row of the periodic table.

"Determining the bond distance may not sound interesting, but it's the first thing you would want to know about how a metal binds to other molecules. What kind of chemical interaction is this element going to have with other atoms and molecules?" Abergel said.

Once scientists have this picture of the atomic arrangement of a molecule that incorporates einsteinium, they can try to find interesting chemical properties and improve understanding of periodic trends. "By getting this piece of data, we gain a better, broader understanding of how the whole actinide series behaves. And in that series, we have elements or isotopes that are useful for nuclear power production or radiopharmaceuticals," she said.

Tantalizingly, this research also offers the possibility of exploring what is beyond the edge of the periodic table, and possibly discovering a new element. "We're really starting to understand a little better what happens toward the end of the periodic table, and the next thing is, you could also envision an einsteinium target for discovering new elements," Abergel said. "Similar to the latest elements that were discovered in the past 10 years, like tennessine, which used a berkelium target, if you were to be able to isolate enough pure einsteinium to make a target, you could start looking for other elements and get closer to the (theorized)island of stability," where nuclear physicists have predicted isotopes may have half-lives of minutes or even days, instead of the microsecond or less half-lives that are common in the superheavy elements.

Read more at Science Daily

Targeting the shell of the Ebola virus

 As the world grapples with the coronavirus (COVID-19) pandemic, another virus has been raging again in the Democratic Republic of the Congo in recent months: Ebola. Since the first terrifying outbreak in 2013, the Ebola virus has periodically emerged in Africa, causing horrific bleeding in its victims and, in many cases, death.

How can we battle these infectious agents that reproduce by hijacking cells and reprogramming them into virus-replicating machines? Science at the molecular level is critical to gaining the upper hand -- research you'll find underway in the laboratory of Professor Juan Perilla at the University of Delaware.

Perilla and his team of graduate and undergraduate students in UD's Department of Chemistry and Biochemistry are using supercomputers to simulate the inner workings of Ebola, observing the way molecules move, atom by atom, to carry out their functions. In the team's latest work, they reveal structural features of the virus's coiled protein shell, or nucleocapsid, that may be promising therapeutic targets, more easily destabilized and knocked out by an antiviral treatment.

The research is highlighted in the Tuesday, Oct. 20 issue of the Journal of Chemical Physics, which is published by the American Institute of Physics, a federation of societies in the physical sciences representing more than 120,000 members.

"The Ebola nucleocapsid looks like a Slinky walking spring, whose neighboring rings are connected," Perilla said. "We tried to find what factors control the stability of this spring in our computer simulations."

The life cycle of Ebola is highly dependent on this coiled nucleocapsid, which surrounds the virus's genetic material consisting of a single strand of ribonucleic acid (ssRNA). Nucleoproteins protect this RNA from being recognized by cellular defense mechanisms. Through interactions with different viral proteins, such as VP24 and VP30, these nucleoproteins form a minimal functional unit -- a copy machine -- for viral transcription and replication.

While nucleoproteins are important to the nucleocapsid's stability, the team's most surprising finding, Perilla said, is that in the absence of single-stranded RNA, the nucleocapsid quickly becomes disordered. But RNA alone is not sufficient to stabilize it. The team also observed charged ions binding to the nucleocapsid, which may reveal where other important cellular factors bind and stabilize the structure during the virus's life cycle.

Perilla compared the team's work to a search for molecular "knobs" that control the nucleocapsid's stability like volume control knobs that can be turned up to hinder virus replication.

The UD team built two molecular dynamics systems of the Ebola nucleocapsid for their study. One included single-stranded RNA; the other contained only the nucleoprotein. The systems were then simulated using the Texas Advanced Computing Center's Frontera supercomputer -- the largest academic supercomputer in the world. The simulations took about two months to complete.

Graduate research assistant Chaoyi Xu ran the molecular simulations, while the entire team was involved in developing the analytical framework and conducting the analysis. Writing the manuscript was a learning experience for Xu and undergraduate research assistant Tanya Nesterova, who had not been directly involved in this work before. She also received training as a next-generation computational scientist with support from UD's Undergraduate Research Scholars program and NSF's XSEDE-EMPOWER program. The latter has allowed her to perform the highest-level research using the nation's top supercomputers. Postdoctoral researcher Nidhi Katyal's expertise also was essential to bringing the project to completion, Perilla said.

While a vaccine exists for Ebola, it must be kept extremely cold, which is difficult in remote African regions where outbreaks have occurred. Will the team's work help advance new treatments?

"As basic scientists we are excited to understand the fundamental principles of Ebola," Perilla said. "The nucleocapsid is the most abundant protein in the virus and it's highly immunogenic -- able to produce an immune response. Thus, our new findings may facilitate the development of new antiviral treatments."

Read more at Science Daily

Citizen science discovers a new form of the northern lights

Working together with space researchers, Finnish amateur photographers have discovered a new auroral form. Named 'dunes' by the hobbyists, the phenomenon is believed to be caused by waves of oxygen atoms glowing due to a stream of particles released from the Sun.

In the recently published study, the origins of the dunes were tracked to a wave guide formed within the mesosphere and its boundary, the mesopause. The study also posits that this new auroral form provides researchers with a novel way to investigate conditions in the upper atmosphere.

The study was published in the first issue of the journal AGU Advances.

An unknown fingerprint appears in the sky

Minna Palmroth, Professor of Computational Space Physics at the University of Helsinki, heads a research group developing the world's most accurate simulation of the near-Earth space and space weather that cause auroral emissions.

The sun releases a steady flow of charged particles, known as the solar wind. Reaching Earth's ionised upper atmosphere, the ionosphere, they create auroral emissions by exciting atmospheric oxygen and nitrogen atoms. The excitation state is released as auroral light.

In late 2018, Palmroth published a book entitled 'Revontulibongarin opas' ('A guide for aurora borealis watchers'). The book was born out of Palmroth's cooperation with Northern Lights enthusiasts and the answers she provided to questions about the physics of the phenomenon in the hobbyists' Facebook group.

Thousands of magnificent photographs of the Northern Lights taken by hobbyists were surveyed and categorised for the book. Each auroral form is like a fingerprint, typical only of a certain phenomenon in the auroral zone. During the classification, hobbyists pointed out that a certain auroral form did not fit into any of the pre-existing categories. Palmroth set aside these unusual forms for later consideration.

By an almost unbelievable coincidence, just days after the book was published, the hobbyists saw this unusual form again and immediately informed Palmroth. The form appeared as a green-tinged and even pattern of waves resembling a striped veil of clouds or dunes on a sandy beach.

"One of the most memorable moments of our research collaboration was when the phenomenon appeared at that specific time and we were able to examine it in real time," says Northern Lights and astronomy hobbyist Matti Helin.

Waves newly revealed by the aurora

Investigations into the phenomenon were launched, with hobbyist observations and scientific methods coming together to explain the waves.

"It was like piecing together a puzzle or conducting detective work," says Helin. "Every day we found new images and came up with new ideas. Eventually, we got to the bottom of it..."

The phenomenon was photographed at the same time in both Laitila and Ruovesi, southwest Finland, with the same detail observed in the auroral emission in both images. Maxime Grandin, a postdoctoral researcher in Palmroth's team, identified stars behind the emission and determined the azimuths and elevations of the stars with the help of the astronomy software program Stellarium. This made it possible to use the stars as points of reference when calculating the altitude and extent of the auroral phenomenon.

Grandin found that the auroral dunes occur at a relatively low altitude of 100 kilometres, in the upper parts of the mesosphere. The wavelength of the wave field was measured to be 45 kilometres.

A total of seven similar events -- where a camera had recorded the same even pattern of waves -- were further identified from the 'Taivaanvahti' ('Sky Watch') service maintained by the Finnish Amateur Astronomer Association, Ursa.

Unexplored region

The part of the auroral zone where Earth's electrically-neutral atmosphere meets the edge of space is an extremely challenging environment for satellites and other space-borne instruments. Palmroth says this is why it is one of the least studied places on our planet.

"Due to the difficulties in measuring the atmospheric phenomena occurring between 80 and 120 kilometres in altitude, we sometimes call this area 'the ignorosphere'," she says.

The dunes were observed precisely in that particular region of the auroral zone. The observed phenomenon guided the researchers towards a middle ground between atmospheric research and space research, as the usual methodology of space physics could not explain it alone.

"The differences in brightness within the dune waves could be due to either waves in the precipitating particles coming from space, or in the underlying atmospheric oxygen atoms," says Palmroth. "We ended up proposing that the dunes are a result of increased oxygen atom density."

Next, the team had to determine how the variability in the density of the oxygen atoms caused by gravity waves in the atmosphere results in such an even and widespread field of waves. Normally at the altitude of study there are many different kinds of gravity waves travelling in different directions at different wavelengths, which is why they do not easily form the even wavefields exhibited by the dunes.

The Northern Lights illuminate a tidal bore

The study suggests that the phenomenon in question is a mesospheric bore, a rare and little-studied phenomenon that takes place in the mesosphere. The tidal bore phenomenon is a wave common to many rivers, where the tide travels up the river channel.

Various types of gravity wave are born in the atmosphere and then rise. In very rare cases, gravity waves can get filtered as they rise between the mesopause and an inversion layer that is intermittently formed below the mesopause. The inversion layer makes the filtered waves bend and enables them to travel long distances through the channel without attenuation.

When the oxygen atoms in the bore collide with the electrons precipitating down upon the atmosphere, they become excited. When releasing this excitation, they create the auroral light. This is why mesospheric bores -- a phenomenon thus far considered a very challenging subject of research -- can occasionally be seen with the naked eye.

Space researchers focus on the atmosphere

Prior to this discovery, mesospheric bores were not observed in the auroral zone, nor have they been investigated via auroral emissions.

"The auroral zone as a whole is usually discounted in studies focused on the bore, as auroral emissions impair the technique used to identify mesospheric bores," says Palmroth.

Traditionally, researchers specialising in the atmosphere and space have largely investigated their topics of interest separate from each other. This is because there are only a handful of known mechanisms of interaction between the ionosphere bathing in the precipitating electrons, and the neutral atmosphere.

With the help of measuring devices operated by the Finnish Meteorological Institute, the dunes were found to occur simultaneously and in the same region where the electromagnetic energy originating in space is transferred to the ignorosphere.

Read more at Science Daily

Atomic 'Trojan horse' could inspire new generation of X-ray lasers and particle colliders

How do researchers explore nature on its most fundamental level? They build "supermicroscopes" that can resolve atomic and subatomic details. This won't work with visible light, but they can probe the tiniest dimensions of matter with beams of electrons, either by using them directly in particle colliders or by converting their energy into bright X-rays in X-ray lasers. At the heart of such scientific discovery machines are particle accelerators that first generate electrons at a source and then boost their energy in a series of accelerator cavities.

Now, an international team of researchers, including scientists from the Department of Energy's SLAC National Accelerator Laboratory, has demonstrated a potentially much brighter electron source based on plasma that could be used in more compact, more powerful particle accelerators.

The method, in which the electrons for the beam are released from neutral atoms inside the plasma, is referred to as the Trojan horse technique because it's reminiscent of the way the ancient Greeks are said to have invaded the city of Troy by hiding their forceful soldiers (electrons) inside a wooden horse (plasma), which was then pulled into the city (accelerator).

"Our experiment shows for the first time that the Trojan horse method actually works," says Bernhard Hidding from the University of Strathclyde in Glasgow, Scotland, the principal investigator of a study published today in Nature Physics. "It's one of the most promising methods for future electron sources and could push the boundaries of today's technology."

Replacing metal with plasma

In current state-of-the-art accelerators, electrons are generated by shining laser light onto a metallic photocathode, which kicks electrons out of the metal. These electrons are then accelerated inside metal cavities, where they draw more and more energy from a radiofrequency field, resulting in a high-energy electron beam. In X-ray lasers, such as SLAC's Linac Coherent Light Source (LCLS), the beam drives the production of extremely bright X-ray light.

But metal cavities can only support a limited energy gain over a given distance, or acceleration gradient, before breaking down, and therefore accelerators for high-energy beams become very large and expensive. In recent years, scientists at SLAC and elsewhere have looked into ways to make accelerators more compact. They demonstrated, for example, that they can replace metal cavities with plasma that allows much higher acceleration gradients, potentially shrinking the length of future accelerators 100 to 1,000 times.

The new paper expands the plasma concept to the electron source of an accelerator.

"We've previously shown that plasma acceleration can be extremely powerful and efficient, but we haven't been able yet to produce beams with high enough quality for future applications," says co-author Mark Hogan from SLAC. "Improving beam quality is a top priority for the next years, and developing new types of electron sources is an important part of that."

According to previous calculations by Hidding and colleagues, the Trojan horse technique could make electron beams 100 to 10,000 times brighter than today's most powerful beams. Brighter electron beams would also make future X-ray lasers brighter and further enhance their scientific capabilities.

"If we're able to marry the two major thrusts -- high acceleration gradients in plasma and beam creation in plasma -- we could be able to build X-ray lasers that unfold the same power over a distance of a few meters rather than kilometers," says co-author James Rosenzweig, the principal investigator for the Trojan horse project at the University of California, Los Angeles.

Producing superior electron beams

The researchers carried out their experiment at SLAC's Facility for Advanced Accelerator Experimental Tests (FACET). The facility, which is currently undergoing a major upgrade, generates pulses of highly energetic electrons for research on next-generation accelerator technologies, including plasma acceleration.

First, the team flashed laser light into a mixture of hydrogen and helium gas. The light had just enough energy to strip electrons off hydrogen, turning neutral hydrogen into plasma. It wasn't energetic enough to do the same with helium, though, whose electrons are more tightly bound than those for hydrogen, so it stayed neutral inside the plasma.

Then, the scientists sent one of FACET's electron bunches through the plasma, where it produced a plasma wake, much like a motorboat creates a wake when it glides through the water. Trailing electrons can "surf" the wake and gain tremendous amounts of energy.

In this study, the trailing electrons came from within the plasma (see animation above and movie below). Just when the electron bunch and its wake passed by, the researchers zapped the helium in the plasma with a second, tightly focused laser flash. This time the light pulse had enough energy to kick electrons out of the helium atoms, and the electrons were then accelerated in the wake.

The synchronization between the electron bunch, rushing through the plasma with nearly the speed of light, and the laser flash, lasting merely a few millionths of a billionth of a second, was particularly important and challenging, says UCLA's Aihua Deng, one of the study's lead authors: "If the flash comes too early, the electrons it produces will disturb the formation of the plasma wake. If it comes too late, the plasma wake has moved on and the electrons won't get accelerated."

The researchers estimate that the brightness of the electron beam obtained with the Trojan horse method can already compete with the brightness of existing state-of-the-art electron sources.

"What makes our technique transformative is the way the electrons are produced," says Oliver Karger, the other lead author, who was at the University of Hamburg, Germany, at the time of the study. When the electrons are stripped off the helium, they get rapidly accelerated in the forward direction, which keeps the beam narrowly bundled and is a prerequisite for brighter beams.

More R&D work ahead

But before applications like compact X-ray lasers could become a reality, much more research needs to be done.

Next, the researchers want to improve the quality and stability of their beam and work on better diagnostics that will allow them to measure the actual beam brightness, instead of estimating it.

Read more at Science Daily

New state of matter: Elements can be solid and liquid at same time

Potassium.

Scientists have discovered a new state of physical matter in which atoms can exist as both solid and liquid simultaneously.

Until now, the atoms in physical material were understood to exist typically in one of three states -- solid, liquid or gas. Researchers have found, however, that some elements can, when subjected to extreme conditions, take on the properties of both solid and liquid states.

Applying high pressures and temperatures to potassium -- a simple metal -- creates a state in which most of the element's atoms form a solid lattice structure, the findings show. However, the structure also contains a second set of potassium atoms that are in a fluid arrangement.

Under the right conditions, over half a dozen elements -- including sodium and bismuth -- are thought to be capable of existing in the newly discovered state, researchers say.

Until now, it was unclear if the unusual structures represented a distinct state of matter, or existed as transition stages between two distinct states.

A team led by scientists from the University of Edinburgh used powerful computer simulations to study the existence of the state -- known as the chain-melted state. Simulating how up to 20,000 potassium atoms behave under extreme conditions revealed that the structures formed represent the new, stable state of matter.

Applying pressure to the atoms leads to the formation of two interlinked solid lattice structures, the team says. Chemical interactions between atoms in one lattice are strong, meaning they stay in a solid form when the structure is heated, while the other atoms melt into a liquid state.

The study, published in the journal Proceedings of the National Academy of Sciences, was supported by the European Research Council and the Engineering and Physical Sciences Research Council. The work was carried out in collaboration with scientists from Xi'an Jiantong University in China.

Read more at Science Daily

The coolest experiment in the universe

The International Space Station, shown here in 2018, is home to many scientific experiments, including NASA's Cold Atom Laboratory.

What's the coldest place you can think of? Temperatures on a winter day in Antarctica dip as low as -120ºF (-85ºC). On the dark side of the Moon, they hit -280ºF (-173ºC). But inside NASA's Cold Atom Laboratory on the International Space Station, scientists are creating something even colder.

The Cold Atom Lab (CAL) is the first facility in orbit to produce clouds of "ultracold" atoms, which can reach a fraction of a degree above absolute zero: -459ºF (-273ºC), the absolute coldest temperature that matter can reach. Nothing in nature is known to hit the temperatures achieved in laboratories like CAL, which means the orbiting facility is regularly the coldest known spot in the universe.

NASA's Cold Atom Laboratory on the International Space Station is regularly the coldest known spot in the universe. But why are scientists producing clouds of atoms a fraction of a degree above absolute zero? And why do they need to do it in space? Quantum physics, of course.

Seven months after its May 21, 2018, launch to the space station from NASA's Wallops Flight Facility in Virginia, CAL is producing ultracold atoms daily. Five teams of scientists will carry out experiments on CAL during its first year, and three experiments are already underway.

Why cool atoms to such an extreme low? Room-temperature atoms typically zip around like hyperactive hummingbirds, but ultracold atoms move much slower than even a snail. Specifics vary, but ultracold atoms can be more than 200,000 times slower than room-temperature atoms. This opens up new ways to study atoms as well as new ways to use them for investigations of other physical phenomena. CAL's primary science objective is to conduct fundamental physics research -- to try to understand the workings of nature at the most fundamental levels.

"With CAL we're starting to get a really thorough understanding of how the atoms behave in microgravity, how to manipulate them, how the system is different than the ones we use on Earth," said Rob Thompson, a cold atom physicist at NASA's Jet Propulsion Laboratory in Pasadena, California, and the mission scientist for CAL. "This is all knowledge that is going to build a foundation for what I hope is a long future of cold atom science in space."

Laboratories on Earth can produce ultracold atoms, but on the ground, gravity pulls on the chilled atom clouds and they fall quickly, giving scientists only fractions of a second to observe them. Magnetic fields can be used to "trap" the atoms and hold them still, but that restricts their natural movement. In microgravity, the cold atom clouds float for much longer, giving scientists an extended view of their behavior.

The process to create the cold atom clouds starts with lasers that begin to lower the temperature by slowing the atoms down. Radio waves cut away the warmest members of the group, further lowering the average temperature. Finally, the atoms are released from a magnetic trap and allowed to expand. This causes a drop in pressure that, in turn, naturally causes another drop in the cloud's temperature (the same phenomenon that causes a can of compressed air to feel cold after use). In space, the cloud has longer to expand and thus reach even lower temperatures than what can be achieved on Earth -- down to about one ten billionth of a degree above absolute zero, perhaps even lower.

Ultracold atom facilities on Earth typically occupy an entire room, and in most, the hardware is left exposed so that scientists can adjust the apparatus if need be. Building a cold atom laboratory for space posed several design challenges, some of which change the fundamental nature of these facilities. First, there was the matter of size: CAL flew to the station in two pieces -- a metal box a little larger than a minifridge and a second one about the size of a carry-on suitcase. Second, CAL was designed to be operated remotely from Earth, so it was built as a fully enclosed facility.

CAL also features a number of technologies that have never been flown in space before, such as specialized vacuum cells that contain the atoms, which have to be sealed so tightly that almost no stray atoms can leak in. The lab needed to be able to withstand the shaking of launch and extreme forces experienced during the flight to the space station. It took the teams several years to develop unique hardware that could meet the precise needs for cooling atoms in space.

"Several parts of the system required redesigning, and some parts broke in ways we'd never seen before," said Robert Shotwell, chief engineer for JPL's Astronomy, Physics and Space Technology Directorate and CAL project manager. "The facility had to be completely torn apart and reassembled three times."

All the hard work and problem solving since the mission's inception in 2012 turned the CAL team's vision into reality this past May. CAL team members talked via live video with astronauts Ricky Arnold and Drew Feustel aboard the International Space Station for the installation of the Cold Atom Laboratory, the second ultracold atom facility ever operated in space, the first to reach Earth orbit and the first to remain in space for more than a few minutes. Along the way, CAL has also met the minimum requirements NASA set to deem the mission a success and is providing a unique tool for probing nature's mysteries.

Read more at Science Daily

Superradiance: Quantum effect detected in tiny diamonds

In the diamond lattice, there are special kinds of defects, consisting of a nitrogen atom (white) and a missing carbon atom.

The effect has been predicted theoretically decades ago -- but it is very hard to provide experimental evidence for it: "Superradiance" is the phenomenon of one atom giving off energy in the form of light and causing a large number of other atoms in its immediate vicinity to emit energy as well at the same time. This creates a short, intense flash of light.

Up until now, this phenomenon could only be studied with free atoms (and with the use of special symmetries). Now, at TU Wien (Vienna), it was measured in a solid-state system. The team used nitrogen atoms, built into tiny diamonds that can be coupled with microwave radiation. The results have now been published in the journal Nature Physics.

A bright flash of quantum light

According to the laws of quantum physics, atoms can be in different states. "When the atom absorbs energy, it is shifted into a so-called excited state. When it returns to a lower energy state, the energy is released again in the form of a photon. This usually happens randomly, at completely unpredictable points in time," says Johannes Majer, research group leader at the Institute of Atomic and Subatomic Physics (TU Wien). However, if several atoms are located close to each other, an interesting quantum effect can occur: one of the atoms emits a photon (spontaneously and randomly), thereby affecting all other excited atoms in its neighborhood. Many of them release their excess energy at the same moment, producing an intense flash of quantum light. This phenomenon is called "superradiance."

"Unfortunately, this effect cannot be directly observed with ordinary atoms," says Andreas Angerer, first author of the study. "Super radiance is only possible if you place all the atoms in an area that is significantly smaller than the wavelength of the photons." So you would have to focus the atoms to less than 100 nanometers -- and then, the interactions between the atoms would be so strong that the effect would no longer be possible.

Defects in the diamond lattice

One solution to this problem is using a quantum system that Majer and his team have been researching for years: tiny defects built into diamonds. While ordinary diamonds consist of a regular grid of carbon atoms, lattice defects have been deliberately incorporated into the diamonds in Majer's lab. At certain points, instead of a carbon atom, there is a nitrogen atom, and the adjacent point in the diamond lattice is unoccupied.

These special diamonds with lattice defects were made in Japan by Junichi Isoya and his team at the University of Tsukuba. They have succeeded in producing the world's highest concentration of these desired defects without causing any other damage. The theoretical basis of the effect was developed by Kae Nemoto (National Institute of Informatics) and William Munro (NTT Basic Research Laboratories) in Tokyo, Japan.

Just like ordinary atoms, these diamond defects can also be switched into an excited state -- but this is achieved with photons in the microwave range, with a very large wavelength. "Our system has the decisive advantage that we can work with electromagnetic radiation that has a wavelength of several centimeters -- so it is no problem to concentrate the individual defect sites within the radius of one wavelength," explains Andreas Angerer.

When many diamond defects are switched to an excited state, it can usually take hours for all of them to return to the lower-energy state. Due to the superradiance effect, however, this happens within about 100 nanoseconds. The first photon that is sent out spontaneously causes all other defect sites to emit photons as well.

Similar to lasers

Superradiance is based on the same basic principle as the laser -- in both cases there is a stimulated emission of photons, triggered by a photon hitting energetically excited atoms. Nevertheless, these are two quite different phenomena: In the laser, a permanent background of many photons is needed, constantly stimulating new atoms. In superradiance, a single photon triggers a flash of light all by itself.

Read more at Science Daily

Genetically engineered virus spins gold into beads

Electron microscope image of M13 spheroid-templated spiky gold nanobead with corresponding graphical illustration.

The race is on to find manufacturing techniques capable of arranging molecular and nanoscale objects with precision.

Engineers at the University of California, Riverside, have altered a virus to arrange gold atoms into spheroids measuring a few nanometers in diameter. The finding could make production of some electronic components cheaper, easier, and faster.

"Nature has been assembling complex, highly organized nanostructures for millennia with precision and specificity far superior to the most advanced technological approaches," said Elaine Haberer, a professor of electrical and computer engineering in UCR's Marlin and Rosemary Bourns College of Engineering and senior author of the paper describing the breakthrough. "By understanding and harnessing these capabilities, this extraordinary nanoscale precision can be used to tailor and build highly advanced materials with previously unattainable performance."

Viruses exist in a multitude of shapes and contain a wide range of receptors that bind to molecules. Genetically modifying the receptors to bind to ions of metals used in electronics causes these ions to "stick" to the virus, creating an object of the same size and shape. This procedure has been used to produce nanostructures used in battery electrodes, supercapacitors, sensors, biomedical tools, photocatalytic materials, and photovoltaics.

The virus' natural shape has limited the range of possible metal shapes. Most viruses can change volume under different scenarios, but resist the dramatic alterations to their basic architecture that would permit other forms.

The M13 bacteriophage, however, is more flexible. Bacteriophages are a type of virus that infects bacteria, in this case, gram-negative bacteria, such as Escherichia coli, which is ubiquitous in the digestive tracts of humans and animals. M13 bacteriophages genetically modified to bind with gold are usually used to form long, golden nanowires.

Studies of the infection process of the M13 bacteriophage have shown the virus can be converted to a spheroid upon interaction with water and chloroform. Yet, until now, the M13 spheroid has been completely unexplored as a nanomaterial template.

Haberer's group added a gold ion solution to M13 spheroids, creating gold nanobeads that are spiky and hollow.

"The novelty of our work lies in the optimization and demonstration of a viral template, which overcomes the geometric constraints associated with most other viruses," Haberer said. "We used a simple conversion process to make the M13 virus synthesize inorganic spherical nanoshells tens of nanometers in diameter, as well as nanowires nearly 1 micron in length."

The researchers are using the gold nanobeads to remove pollutants from wastewater through enhanced photocatalytic behavior.

The work enhances the utility of the M13 bacteriophage as a scaffold for nanomaterial synthesis. The researchers believe the M13 bacteriophage template transformation scheme described in the paper can be extended to related bacteriophages.

Read more at Science Daily

Evidence of matter-matter coupling

Rice University scientists observed Dicke cooperativity in a magnetic crystal in which two types of spins, in iron (blue arrows) and erbium (red arrows), interacted with each other. The iron spins were excited to form a wave-like object called a spin wave; the erbium spins precessing in a magnetic field (B) behaved like two-level atoms.

After their recent pioneering experiments to couple light and matter to an extreme degree, Rice University scientists decided to look for a similar effect in matter alone. They didn't expect to find it so soon.

Rice physicist Junichiro Kono, graduate student Xinwei Li and their international colleagues have discovered the first example of Dicke cooperativity in a matter-matter system, a result reported in Science this week.

The discovery could help advance the understanding of spintronics and quantum magnetism, Kono said. On the spintronics side, he said the work will lead to faster information processing with lower power consumption and will contribute to the development of spin-based quantum computing. The team's findings on quantum magnetism will lead to a deeper understanding of the phases of matter induced by many-body interactions at the atomic scale.

Instead of using light to trigger interactions in a quantum well, a system that produced new evidence of ultrastrong light-matter coupling earlier this year, the Kono lab at Rice used a magnetic field to prompt cooperativity among the spins within a crystalline compound made primarily of iron and erbium.

"This is an emerging subject in condensed matter physics," Kono said. "There's a long history in atomic and molecular physics of looking for the phenomenon of ultrastrong cooperative coupling. In our case, we'd already found a way to make light and condensed matter interact and hybridize, but what we're reporting here is more exotic."

Dicke cooperativity, named for physicist Robert Dicke, happens when incoming radiation causes a collection of atomic dipoles to couple, like gears in a motor that don't actually touch. Dicke's early work set the stage for the invention of lasers, the discovery of cosmic background radiation in the universe and the development of lock-in amplifiers used by scientists and engineers.

"Dicke was an unusually productive physicist," Kono said. "He had many high-impact papers and accomplishments in almost all areas of physics. The particular Dicke phenomenon that's relevant to our work is related to superradiance, which he introduced in 1954. The idea is that if you have a collection of atoms, or spins, they can work together in light-matter interaction to make spontaneous emission coherent. This was a very strange idea.

"When you stimulate many atoms within a small volume, one atom produces a photon that immediately interacts with another atom in the excited state," Kono said. "That atom produces another photon. Now you have coherent superposition of two photons.

"This happens between every pair of atoms within the volume and produces macroscopic polarization that eventually leads to a burst of coherent light called superradiance," he said. Taking light out of the equation meant the Kono lab had to find another way to excite the material's dipoles, the compass-like magnetic force inherent in every atom, and prompt them to align. Because the lab is uniquely equipped for such experiments, when the test material showed up, Kono and Li were ready.

"The sample was provided by my colleague (and co-author) Shixun Cao at Shanghai University," Kono said. Characterization tests with a small or no magnetic field performed by another co-author, Dmitry Turchinovich of the University of Duisburg-Essen, drew little response.

"But Dmitry is a good friend, and he knows we have a special experimental setup that combines terahertz spectroscopy, low temperatures and high magnetic field," Kono said. "He was curious to know what would happen if we did the measurements."

"Because we have some experience in this field, we got our initial data, identified some interesting details in it and thought there was something more we could explore in depth," Li added. "But we certainly didn't predict this," Kono said.

Li said that to show cooperativity, the magnetic components of the compound had to mimic the two essential ingredients in a standard light-atom coupling system where Dicke cooperativity was originally proposed: one a species of spins that can be excited into a wave-like object that simulates the light wave, and another with quantum energy levels that would shift with the applied magnetic field and simulate the atoms.

"Within a single orthoferrite compound, on one side the iron ions can be triggered to form a spin wave at a particular frequency," Li said. "On the other side, we used the electron paramagnetic resonance of the erbium ions, which forms a two-level quantum structure that interacts with the spin wave."

While the lab's powerful magnet tuned the energy levels of the erbium ions, as detected by the terahertz spectroscope, it did not initially show strong interactions with the iron spin wave at room temperature. But the interactions started to appear at lower temperatures, seen in a spectroscopic measurement of coupling strength known as vacuum Rabi splitting.

Chemically doping the erbium with yttrium brought it in line with the observation and showed Dicke cooperativity in the magnetic interactions. "The way the coupling strength increased matches in an excellent manner with Dicke's early predictions," Li said. "But here, light is out of the picture and the coupling is matter-matter in nature."

Read more at Science Daily