An asteroid as big as the Rock of Gibraltar will streak past Earth on April 19 at a safe but uncomfortably close distance, according to astronomers.
“Although there is no possibility for the asteroid to collide with our planet, this will be a very close approach for an asteroid this size,” NASA said in a statement.
Dubbed 2014-JO25 and roughly 650 metres (2,000 feet) across, the asteroid will come within 1.8 million kilometres (1.1 million miles) of Earth, less than five times the distance to the Moon.
It will pass closest to our planet after having looped around the Sun. 2014-J25’s will then continue on past Jupiter before heading back toward the centre of our Solar System.
Smaller asteroids whizz by Earth several times a week. But the last time one at least this size came as close was in 2004, when Toutatis—five kilometres (3.1 miles) across—passed within four lunar distances.
The next close encounter with a big rock will not happen before 2027, when the 800-metre (half-mile) wide asteroid 199-AN10 will fly by at just one lunar distance, about 380,000 km (236,000 miles).
The last time 2014-JO25 was in our immediate neighbourhood was 400 years ago, and it’s next brush with Earth won’t happen until sometime after 2600.
The April 19 flyby is an “outstanding opportunity” for astronomers and amateur stargazers, NASA said.
“Astronomers plan to observe it with telescopes around the world to learn as much about it as possible,” the US space agency said.
Besides its size and trajectory, scientists also know that its surface is twice as reflective as that of the Moon.
It should be visible with a small optical telescope for one or two nights before moving out of range.
2014-J25 was discovered in May 2014 by astronomers at the Catalina Sky Survey near Tucson, Arizona.
Also on April 19, a comet known as PanSTARRS will make its closest approach to Earth at a “very safe” distance of 175 million km (109 million miles), according to NASA.
The comet has brightened recently and should be visible in the dawn sky with binoculars or a small telescope.
Asteroids are composed of rocky and metallic material, whereas comets—generally smaller—are more typically made of ice, dust and rocky stuff.
Both were formed early in the history of the Solar System some 4.5 billion years ago.
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 metallic hydrogen – 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 room-temperature superconductor. 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 atomic hydrogen, 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 materials.
“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.
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 diamond anvil cell.
“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.”
Optical fibers are the backbone of modern communications, shuttling information from A to B through thin glass filaments as pulses of light. They are used extensively in telecommunications, allowing information to travel at near the speed of light virtually without loss.
These days, biologists, physicists and other scientists regularly use optical fibers to pipe light around inside their labs. In one recent application, quantum research labs have been reshaping optical fibers, stretching them into tiny tapers (see Nanofibers and designer light traps). For these nanometer-scale tapers, or nanofibers, the injected light still makes its way from A to B, but some of it is forced to travel outside the fiber’s exterior surface. The exterior light, or evanescent field, can capture atoms and then carry information about that light-matter interaction to a detector.
Fine-tuning such evanescent light fields is tricky and requires tools for characterizing both the fiber and the light. To this end, researchers from JQI and the Army Research Laboratory (ARL) have developed a novel method to measure how light propagates through a nanofiber, allowing them to determine the nanofiber’s thickness to a precision less than the width of an atom. The technique, described in the January 20, 2017 issue of the journal Optica , is direct, fast and, unlike the standard imaging method, preserves the integrity of the fiber. As a result, the probe can be used in-situ with the nanofiber fabrication equipment, which will streamline implementation in quantum optics and quantum information experiments. Developing reliable and precise tools for this platform may enable nanofiber technology for sensing and metrology applications.
Light waves have a characteristic size called the wavelength. For visible light, the wavelength is roughly 100 times smaller than a human hair. Light can also have the appearance of different shapes, such a solid circle, ring, clover and more (see image below). Fibers restrict the way light waves can travel and twisting or bending a fiber will alter the light’s characteristics. Nanofibers are made by reshaping a normal fiber into an hourglass-like design, which further affects the guided light waves.
In this experiment, researchers inject a combination of light shapes into a nanofiber. The light passes down a thinning taper, squeezes through a narrow waist, and then exits out the other side of the taper. The changing fiber size distorts the light waves, and multiple patterns emerge from the interfering light shapes (See JQI News on Collecting lost light). This is analogous to musical notes, or sound waves, beating together to form a complex chord.
The researchers make direct measurements of the interference patterns (beats). To do this, they employ a second micron-sized fiber that acts as a non-invasive sensor. The nanofiber is on a moving stage and crosses the probe fiber at an oblique angle. At the touching point, a tiny fraction of nanofiber light evanescently enters the second fiber and travels to a detector. As they scan the probe along the length of the nanofiber, the probe detector collects information about the evolving patterns of nanofiber light. The researchers simultaneously monitor the light transmitting through the nanofiber to ensure that the probe process is harmless.
The team can achieve a high level of precision with this technique because they are not imaging the fiber with a camera, which would have a spatial resolution limited by the collected light’s wavelength. UMD graduate student Pablo Solano explains, “We are actually seeing the different light modes mix together and that sets the limits on determining the fiber waist—in this case sub-angstrom.” A standard tool known as scanning electron microscopy (SEM) can also measure fiber dimensions with nanoscale resolution. This, however, has a comparative disadvantage, says Eliot Fenton, a UMD undergraduate student working on the project, “With our new method, we can avoid using SEM, which destroys the fiber with imaging chemicals and heating.” Other techniques involve collecting randomly scattered light from the fiber, which is less direct and susceptible to errors. Solano summarizes how researchers can benefit from this new tool, “By directly and sensitively measuring the interference (beating) of light without destroying the fiber, we can know exactly the kind of electromagnetic field that we would apply to atoms.”
Astronomers have found a total of 76 new ultra-diffuse galaxies (UDGs) in the massive galaxy cluster designated Abell 2744 (also known as Pandora’s Cluster). The discovery updates the current census of galaxies in this cluster and could help better understand the nature of UDGs in general. The findings were presented in a paper published Dec. 30 on arXiv.org.
UDGs are extremely-low-density galaxies. The largest UDGs have sizes similar the Milky Way but have only about one percent as many stars as our home galaxy. The mystery of UDGs is still baffling scientists as they try explain why these faint but large galaxies are not ripped apart by the tidal field of their host clusters. Furthermore, it is not clear what fraction of UDGs are “failed” giant luminous galaxies, “inflated dwarfs,” or some other phenomenon.
Abell 2744 is a giant galaxy cluster located nearly 4 billion light years away in the Sculptor constellation. It is one of the most massive and most disturbed galaxy clusters known to date. Its intracluster light fraction is high and its stellar population consistent with the disruption of luminous galaxies, which makes it an excellent location to search for UDGs.
That is why a team of researchers led by Steven Janssens of the University of Toronto, Canada, has investigated Abell 2744 using data obtained with the Hubble Space Telescope (HST) Frontier Fields (FF) program. FF is known for producing the deepest images to date of galaxy clusters and gravitational lensing. The analysis of FF data allowed the astronomers to distinguish dozens of new UDGs in this giant galaxy cluster.
“We report the discovery of a large population of ultra-diffuse galaxies in the massive galaxy cluster Abell 2744 (z= 0.308) as observed by the Hubble Frontier Fields program,” the researchers wrote in the paper.
As a result, the team detected 76 new UDGs—41 in the cluster field and 35 in the parallel field. They also estimated the total number of UDGs that Abell 2744 contains. According to the paper, given the fact that the analyzed data from the observations samples only a small portion of the galaxy cluster, there should be approximately 2,100 ultra-diffuse galaxies in Abell 2744. The researchers noted that this is 10 times the number of UDGs that exist in a similar cluster known as Abell 1656 (or Coma Cluster).
“Abell 2744 hosts an estimated 2133±613 UDGs, 10 times the number in Coma,” the paper reads.
The research also allowed the scientists to estimate the number of ultra-compact dwarf (UCD) galaxies in Abell 2744. According to their calculations, there are about 385 UCDs in the galaxy cluster.
The researchers concluded that some UCDs in Abell 2744 may have once been nuclei or satellites of infalling UDGs, noting that the latter are ultimately destroyed by tidal forces.
“As UDGs fall in and dissolve (and, presumably, blend into the intra-cluster light), they leave behind a residue of unbound, but long-lived UCDs,” the team wrote.
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 electron interactions under dynamic conditions. As described in a paper just published in Nature Communications, they use one very fast, intense “pump” laser to give electrons 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 excited electrons (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 energy loss 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.
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 energy level, 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.
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.
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 theory 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 visible matter.
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 gravity 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 prediction, 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 dark matter 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.”