Tag: research

Metallic hydrogen, once theory, becomes reality

Metallic hydrogen, once theory, becomes reality

Image of diamond anvils compressing molecular hydrogen. At higher pressure the sample converts to atomic hydrogen, as shown on the right. Credit: R. Dias and I.F. Silvera

Nearly a century after it was theorized, Harvard scientists have succeeded in creating the rarest – and potentially one of the most valuable – materials on the planet.

The material – atomic  – was created by Thomas D. Cabot Professor of the Natural Sciences Isaac Silvera and post-doctoral fellow Ranga Dias. In addition to helping scientists answer fundamental questions about the nature of matter, the material is theorized to have a wide range of applications, including as a . The creation of the rare material is described in a January 26 paper published in Science.

“This is the holy grail of high-pressure physics,” Silvera said. “It’s the first-ever sample of metallic hydrogen on Earth, so when you’re looking at it, you’re looking at something that’s never existed before.”

To create it, Silvera and Dias squeezed a tiny hydrogen sample at 495 gigapascal, or more than 71.7 million pounds-per-square inch – greater than the pressure at the center of the Earth. At those extreme pressures, Silvera explained, solid molecular hydrogen -which consists of molecules on the lattice sites of the solid – breaks down, and the tightly bound molecules dissociate to transforms into , which is a metal.

While the work offers an important new window into understanding the general properties of hydrogen, it also offers tantalizing hints at potentially revolutionary new .

“One prediction that’s very important is metallic hydrogen is predicted to be meta-stable,” Silvera said. “That means if you take the pressure off, it will stay metallic, similar to the way diamonds form from graphite under intense heat and pressure, but remains a diamond when that pressure and heat is removed.”

Understanding whether the material is stable is important, Silvera said, because predictions suggest metallic hydrogen could act as a superconductor at room temperatures.

“That would be revolutionary,” he said. “As much as 15 percent of energy is lost to dissipation during transmission, so if you could make wires from this material and use them in the electrical grid, it could change that story.”

Among the holy grails of physics, a room temperature superconductor, Dias said, could radically change our transportation system, making magnetic levitation of high-speed trains possible, as well as making electric cars more efficient and improving the performance of many electronic devices.

The material could also provide major improvements in energy production and storage – because superconductors have zero resistance energy could be stored by maintaining currents in superconducting coils, and then be used when needed.

Metallic hydrogen, once theory, becomes reality
Photos of compressed hydrogen transitioning with increasing pressure from transparent molecular to black molecular to atomic metallic hydrogen. The sketches below show a molecular solid being compressed and then dissociated to atomic hydrogen. Credit: R. Dias and I.F. Silvera

Though it has the potential to transform life on Earth, metallic hydrogen could also play a key role in helping humans explore the far reaches of space, as the most powerful rocket propellant yet discovered.

“It takes a tremendous amount of energy to make metallic hydrogen,” Silvera explained. “And if you convert it back to molecular hydrogen, all that energy is released, so it would make it the most powerful rocket propellant known to man, and could revolutionize rocketry.”

The most powerful fuels in use today are characterized by a “specific impulse” – a measure, in seconds, of how fast a propellant is fired from the back of a rocket – of 450 seconds. The specific impulse for metallic hydrogen, by comparison, is theorized to be 1,700 seconds.

“That would easily allow you to explore the outer planets,” Silvera said. “We would be able to put rockets into orbit with only one stage, versus two, and could send up larger payloads, so it could be very important.”

To create the new material, Silvera and Dias turned to one of the hardest materials on Earth – diamond.

But rather than natural diamond, Silvera and Dias used two small pieces of carefully polished synthetic diamond which were then treated to make them even tougher and then mounted opposite each other in a device known as a .

“Diamonds are polished with diamond powder, and that can gouge out carbon from the surface,” Silvera said. “When we looked at the diamond using atomic force microscopy, we found defects, which could cause it to weaken and break.”

The solution, he said, was to use a reactive ion etching process to shave a tiny layer – just five microns thick, or about one-tenth of a human hair – from the diamond’s surface. The diamonds were then coated with a thin layer of alumina to prevent the hydrogen from diffusing into their crystal structure and embrittling them.

After more than four decades of work on metallic hydrogen, and nearly a century after it was first theorized, seeing the material for the first time, Silvera said, was thrilling.

“It was really exciting,” he said. “Ranga was running the experiment, and we thought we might get there, but when he called me and said, ‘The sample is shining,’ I went running down there, and it was metallic hydrogen.

“I immediately said we have to make the measurements to confirm it, so we rearranged the lab…and that’s what we did,” he said. “It’s a tremendous achievement, and even if it only exists in this diamond anvil cell at high pressure, it’s a very fundamental and transformative discovery.”

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Laser pulses help scientists tease apart complex electron interactions

Laser pulses help scientists tease apart complex electron interactions

Microscopic image of one of the bismuth strontium calcium copper oxide samples the scientists studied using a new high-speed imaging technique. Color changes show changes in sample height and curvature to dramatically reveal the layered structure and flatness of the material. Credit: Brookhaven National Laboratory

Scientists studying high temperature superconductors-materials that carry electric current with no energy loss when cooled below a certain temperature-have been searching for ways to study in detail the electron interactions thought to drive this promising property. One big challenge is disentangling the many different types of interactions-for example, separating the effects of electrons interacting with one another from those caused by their interactions with the atoms of the material.

Now a group of scientists including physicists at the U.S. Department of Energy’s Brookhaven National Laboratory has demonstrated a new laser-driven “stop-action” technique for studying complex  under dynamic conditions. As described in a paper just published in Nature Communications, they use one very fast, intense “pump” laser to give  a blast of energy, and a second “probe” laser to measure the electrons’ energy level and direction of movement as they relax back to their normal state.

“By varying the time between the ‘pump’ and ‘probe’ laser pulses we can build up a stroboscopic record of what happens-a movie of what this material looks like from rest through the violent interaction to how it settles back down,” said Brookhaven physicist Jonathan Rameau, one of the lead authors on the paper. “It’s like dropping a bowling ball in a bucket of water to cause a big disruption, and then taking pictures at various times afterward,” he explained.

The technique, known as time-resolved, angle-resolved photoelectron spectroscopy (tr-ARPES), combined with complex theoretical simulations and analysis, allowed the team to tease out the sequence and energy “signatures” of different types of electron interactions. They were able to pick out distinct signals of interactions among  (which happen quickly but don’t dissipate much energy), as well as later-stage random interactions between electrons and the atoms that make up the crystal lattice (which generate friction and lead to gradual energy loss in the form of heat).

But they also discovered another, unexpected signal-which they say represents a distinct form of extremely efficient  at a particular energy level and timescale between the other two.

“We see a very strong and peculiar interaction between the excited electrons and the lattice where the electrons are losing most of their energy very rapidly in a coherent, non-random way,” Rameau said. At this special energy level, he explained, the electrons appear to be interacting with lattice atoms all vibrating at a particular frequency-like a tuning fork emitting a single note. When all of the electrons that have the energy required for this unique interaction have given up most of their energy, they start to cool down more slowly by hitting atoms more randomly without striking the “resonant” frequency, he said.

Laser pulses help scientists tease apart complex electron interactions
Brookhaven Lab physicists Peter Johnson (rear) and Jonathan Rameau. Credit: Brookhaven National Laboratory

The frequency of the special lattice interaction “note” is particularly noteworthy, the scientists say, because its energy level corresponds with a “kink” in the energy signature of the same material in its superconducting state, which was first identified by Brookhaven scientists using a static form of ARPES. Following that discovery, many scientists suggested that the kink might have something to do with the material’s ability to become a superconductor, because it is not readily observed above the superconducting temperature.

But the new time-resolved experiments, which were done on the material well above its superconducting temperature, were able to tease out the subtle signal. These new findings indicate that this special condition exists even when the material is not a superconductor.

“We know now that this interaction doesn’t just switch on when the material becomes a superconductor; it’s actually always there,” Rameau said.

The scientists still believe there is something special about the energy level of the unique tuning-fork-like interaction. Other intriguing phenomena have been observed at this same , which Rameau says has been studied in excruciating detail.

It’s possible, he says, that the one-note lattice interaction plays a role in superconductivity, but requires some still-to-be-determined additional factor to turn the superconductivity on.

“There is clearly something special about this one note,” Rameau said.

Hubble ‘cranes’ in for a closer look at a galaxy

Hubble 'cranes' in for a closer look at a galaxy

IC 5201 sits over 40 million light-years away from us. As with two thirds of all the spirals we see in the universe — including the Milky Way, the galaxy has a bar of stars slicing through its center. Credit: ESA/Hubble & NASA

In 1900, astronomer Joseph Lunt made a discovery: Peering through a telescope at Cape Town Observatory, the British-South African scientist spotted this beautiful sight in the southern constellation of Grus (The Crane): a barred spiral galaxy now named IC 5201.

Over a century later, the galaxy is still of interest to astronomers. For this image, the NASA/ESA Hubble Space Telescope used its Advanced Camera for Surveys (ACS) to produce a beautiful and intricate image of the galaxy. Hubble’s ACS can resolve individual stars within other galaxies, making it an invaluable tool to explore how various populations of stars sprang to life, evolved, and died throughout the cosmos.

IC 5201 sits over 40 million light-years away from us. As with two thirds of all the spirals we see in the Universe—including the Milky Way—the galaxy has a bar of stars slicing through its center.

Verlinde’s new theory of gravity passes first test

Verlindes new theory of gravity passes first test

The gravity of galaxies bends space, such that the light traveling through this space is bent. This bending of light allows astronomers to measure the distribution of gravity around galaxies, even up to distances a hundred times larger than the galaxy itself. Credit: APS/Alan Stonebraker; galaxy images from STScI/AURA, NASA, ESA, and the Hubble Heritage Team

A team led by astronomer Margot Brouwer (Leiden Observatory, The Netherlands) has tested the new theory of theoretical physicist Erik Verlinde (University of Amsterdam) for the first time through the lensing effect of gravity. Brouwer and her team measured the distribution of gravity around more than 33,000 galaxies to put Verlinde’s prediction to the test. She concludes that Verlinde’s theory agrees well with the measured gravity distribution. The results have been accepted for publication in the British journal Monthly Notices of the Royal Astronomical Society.

The gravity of galaxies bends space, such that the light traveling through this space is bent, as through a lens. Background galaxies that are situated far behind a foreground galaxy (the lens), thereby seem slightly distorted. This effect can be measured in order to determine the distribution of gravity around a foreground-galaxy. Astronomers have measured, however, that at distances up to a hundred times the radius of the galaxy, the force of gravity is much stronger than Einstein’s  of gravity predicts. The existing theory only works when invisible particles, the so-called dark matter, are added.

Verlinde now claims that he not only explains the mechanism behind gravity with his alternative to Einstein’s theory, but also the origin of the mysterious extra gravity, which astronomers currently attribute to dark matter. Verlinde’s new theory predicts how much gravity there must be, based only on the mass of the .

Brouwer calculated Verlinde’s prediction for the gravity of 33,613 galaxies, based only on their visible mass. She compared this prediction to the distribution of gravity measured by gravitational lensing, in order to test Verlinde’s theory. Her conclusion is that his prediction agrees well with the observed  distribution, but she emphasizes that dark matter could also explain the extra gravitational force. However, the mass of the dark matter is a free parameter, which must be adjusted to the observation. Verlinde’s theory provides a direct , without free parameters.

The new theory is currently only applicable to isolated, spherical and static systems, while the universe is dynamic and complex. Many observations cannot yet be explained by the new theory, so  is still in the race. Brouwer: “The question now is how the theory develops, and how it can be further tested. But the result of this first test definitely looks interesting.”

Astronomers discover new gas giant exoplanet

Astronomers discover new gas giant alien world

Observed data for event OGLE-2014-BLG-0676/MOA-2014-BLG-175 from the MOA (gray), OGLE (red) and Wise (green) microlensing survey groups along with data from the RoboNET/LCOGT (cyan) and MiNDSTEp (magenta) groups. Also shown is the best-fitting binary lens model light-curve (black line). The epoch when the OGLE collaboration issued an alert for this event is indicated with a black arrow. Data with extremely large errors are omitted. Credit: Nicolas Rattenbury et al., 2016.

Using the gravitational microlensing method, an international team of astronomers has recently detected a new gas giant exoplanet three times more massive than Jupiter. The newly discovered planet received designation OGLE-2014-BLG-0676Lb and is an important addition to the short list of extrasolar worlds detected by the microlensing technique. The discovery was described in a paper published Dec. 12 on arXiv.org.

Unlike other methods of detecting exoplanets, microlensing is most sensitive when it comes to searching for exoworlds that orbit around one to 10 AU away from their host stars. These planets are of special interest for astronomers studying planetary formation theories due to proximity to their parent stars, within the so-called “snow line.” Just beyond this line, the most active planet formation occurs; therefore, understanding the distribution of exoplanets in this region could offer important clues to how planets form.

So far, 47 planets have been discovered by microlensing. Currently, several ground-based observation programs routinely monitor dense stellar fields to search for microlensing events. When a new event is discovered, an alert to the broader scientific community is issued in order to allow follow-up observations. Astronomers are particularly interested in events showing evidence for perturbations that could be due to the presence of a planet, or which are predicted to have a high sensitivity to such perturbations.

OGLE-2014-BLG-0676, discovered in April 2014 by a Polish astronomical project called the Optical Gravitational Lensing Experiment (OGLE), is one of those interesting microlensing events. Recently, a collaboration of researchers consisting of the OGLE group, the Microlensing Observations in Astrophysics (MOA), the Wise Observatory Group and the Microlensing Network for the Detection of Small Terrestrial Exoplanets (MiNDSTEp), has detected an anomalous signal in this event consistent with a planetary lens system.

“The source star passed through the central caustic, with the second caustic crossing being well recorded by the MOA microlensing survey collaboration. Observations at epochs between the unrecorded first caustic crossing and the second caustic crossing were made by the OGLE, Wise and MOA collaborations. (…) All analyses of the light curve data favor a lens system comprising a planetary mass orbiting a host star,” the paper reads.

According to the research, the newly discovered planet has a mass of about 3.1 Jupiter masses and orbits its parent star at a deprojected orbital separation of about 4.4 AU. The host star is approximately 38 percent less massive than our sun and was classified as a K-dwarf. The distance to the  is about 7,200 light years.

Moreover, the team revealed some information about the source star. They revealed that is rather faint and very red, noting that there is a possibility that the source may be blended with a nearby red star, causing an incorrect identification of the source star type.

In conclusion, the scientists emphasize the importance of their discovery, noting that OGLE-2014-BLG-0676Lb could serve as a test bed for planet formation scenarios. “Planet OGLE-2014-BLG-0676Lb can be added to the growing list of planets discovered by microlensing against which planetary formation theories can be tested,” the researchers wrote in the paper.

Researchers report possible solution to a long-standing solar mystery

Researchers report possible solution to a long-standing solar mystery

An image of the sun taken with The Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory spacecraft. HMI is an instrument designed to study oscillations and the magnetic field at the solar surface, or photosphere. HMI observes the full solar disk with a resolution of 1 arcsecond. Credit: NASA

Astronomers from the University of Hawaii Institute for Astronomy (IfA), Brazil, and Stanford University may have solved a long-standing solar mystery.

Two decades ago, scientists discovered that the outer five percent of the sun spins more slowly than the rest of its interior. Now, in a new study, to be published in the journal Physical Review Letters, IfA Maui scientists Ian Cunnyngham, Jeff Kuhn, and Isabelle Scholl, together with Marcelo Emilio (Brazil) and Rock Bush (Stanford), describe the physical mechanism responsible for slowing the sun’s outer layers.

Team leader Jeff Kuhn said “The sun won’t stop spinning anytime soon, but we’ve discovered that the same solar radiation that heats the Earth is ‘braking’ the sun because of Einstein’s Special Relativity, causing it to gradually slow down, starting from its surface.”

The sun rotates on its axis at an average rate of about once per month but that rotation isn’t like, for example, the solid Earth or a spinning disk because the rate varies with solar latitude and distance from the center of the sun.

The team used several years of data from the Helioseismic and Magnetic Imager on NASA’s Solar Dynamics Observatory satellite to measure a sharp down-turn in the sun’s  in its very outer 150km. Kuhn said, “This is a gentle torque that is slowing it down, but over the sun’s 5 billion year lifetime it has had a very noticeable influence on its outer 35,000km.” Their paper describes how this photon-braking effect should be at work in most stars.

This change in rotation at the sun’s surface affects the large-scale  and researchers are now trying to understand how the solar magnetism that extends out into the corona and finally into the Earth’s environment will be affected by this braking.

Gravity sensors might offer earlier warning of earthquakes

earthquake

Ruins from the 1906 San Francisco earthquake, remembered as one of the worst natural disasters in United States history. Credit: Public Domain

A team of researchers from France, the U.S. and Italy has found evidence from the Tohoku-Oki earthquake that sensors that measure changes in gravity might offer a way to warn people of impending disaster faster than traditional methods. In their paper published in the journal Nature Communications, the group describes how they analyzed data from gravity sensors near the epicenter of the Tohoku-Oki quake back in 2011 and found that it was possible to isolate gravitational changes due to the earthquake from the noise of other events.

Current earthquake warning systems rely on a network of seismic —they listen for P-waves below the ground which are generated by an earthquake and send a signal to an alarm if they are heard. Such a system offers those in the vicinity of a quake from a few seconds to perhaps a minute to take safety measures. In this new effort, the researches wondered if it might be possible to detect subtle changes in  near the epicenter of a quake to offer those in harm’s way a little more time to prepare for it—because  waves travel at the speed of light.

Prior research has shown that there are subtle changes in gravitational pull around the epicenter of a quake, due to changes in the density of the rock in the area. But until now, it was not clear if such changes could be picked out from all the other background noise. To find out, the researchers pulled data from gravimeter sensors located approximately 500 kilometers from the epicenter of the Tohoku-Oki quake and compared what they found in the record with data from five  in the same area. They noted also that it took 65 seconds for the P-waves to reach the seismic stations. To find out if the quake data would stand out amongst the noise of other natural events (such as the changing tides) the team looked at measurements taken over the 60 days prior to the quake and then at the data from the day before, the day of, and the day after the quake. In looking at the data, the researchers found that they were able to “see” a small blip—one that stood out enough to confirm a quake had occurred.

More research will have to be done before it can be proven that a network of gravity sensors would truly offer people more time to prepare for a  (depending on how close they are to the ), but the results from this initial study seem promising.