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    New ‘vortex beams’ of atoms and molecules are the first of their kind

    Like soft serve ice cream, beams of atoms and molecules now come with a swirl.

    Scientists already knew how to dish up spiraling beams of light or electrons, known as vortex beams (SN: 1/14/11). Now, the first vortex beams of atoms and molecules are on the menu, researchers report in the Sept. 3 Science.

    Vortex beams made of light or electrons have shown promise for making special types of microscope images and for transmitting information using quantum physics (SN: 8/5/15). But vortex beams of larger particles such as atoms or molecules are so new that the possible applications aren’t yet clear, says physicist Sonja Franke-Arnold of the University of Glasgow in Scotland, who was not involved with the research. “It’s maybe too early to really know what we can do with it.”

    In quantum physics, particles are described by a wave function, a wavelike pattern that allows scientists to calculate the probability of finding a particle in a particular place (SN: 6/8/11). But vortex beams’ waves don’t slosh up and down like ripples on water. Instead, the beams’ particles have wave functions that move in a corkscrewing motion as a beam travels through space. That means the beam carries a rotational oomph known as orbital angular momentum. “This is something really very strange, very nonintuitive,” says physicist Edvardas Narevicius of the Weizmann Institute of Science in Rehovot, Israel.

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    Narevicius and colleagues created the new beams by passing helium atoms through a grid of specially shaped slit patterns, each just 600 nanometers wide. The team detected a hallmark of vortex beams: a row of doughnut-shaped rings imprinted on a detector by the atoms, in which each doughnut corresponds to a beam with a different orbital angular momentum.

    Another set of doughnuts revealed the presence of vortex beams of helium excimers, molecules created when a helium atom in an excited, or energized, state pairs up with another helium atom.

    A pattern of rings reveals the presence of vortex beams of atoms and molecules. Each doughnut shape corresponds to a beam of helium atoms with a different angular momentum. Two hard-to-see circles from helium molecules sit in between the center dot and the first two doughnuts left and right of the center.A. Luski et al/Science 2021

    A pattern of rings reveals the presence of vortex beams of atoms and molecules. Each doughnut shape corresponds to a beam of helium atoms with a different angular momentum. Two hard-to-see circles from helium molecules sit in between the center dot and the first two doughnuts left and right of the center.A. Luski et al/Science 2021

    Next, scientists might investigate what happens when vortex beams of molecules or atoms collide with light, electrons or other atoms or molecules. Such collisions are well-understood for normal particle beams, but not for those with orbital angular momentum. Similar vortex beams made with protons might also serve as a method for probing the subatomic particle’s mysterious innards (SN: 4/18/17).

    In physics, “most important things are achieved when we are revisiting known phenomena with a fresh perspective,” says physicist Ivan Madan of EPFL, the Swiss Federal Institute of Technology in Lausanne, who was not involved with the research. “And, for sure, this experiment allows us to do that.” More

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    Windbreaks, surprisingly, could help wind farms boost power output

    Windbreaks may sound like a counterintuitive idea for boosting the performance of a wind turbine. But physicists report that low walls that block wind could actually help wind farms produce more power.

    Scientists already knew that the output of a single wind turbine could be improved with a windbreak. While windbreaks slow wind speed close to the ground, above the height of the windbreak, wind speeds actually increase as air rushes over the top. But for large wind farms, there’s a drawback. A windbreak’s wake slows the flow of air as it travels farther through the rows of turbines. That could suggest that windbreaks would be a wash for wind farms with many turbines.

    But by striking a balance between these competing effects, windbreaks placed in front of each turbine can increase power output, new computer simulations suggest. It comes down to the windbreaks’ dimensions. Squat, wide barriers are the way to go, according to a simulated wind farm with six rows of turbines. To optimize performance, windbreaks should be a tenth the height of the turbine and at least five times the width of the blades, physicists report July 30 in Physical Review Fluids. Such an arrangement could increase the total power by about 10 percent, the researchers found. That’s the equivalent of adding an additional turbine, on average, for every 10 in a wind farm.

    In the simulations, the wind always came from the same direction, suggesting the technique might be useful in locations where wind tends to blow one way, such as coastal regions. Future studies could investigate how this technique might apply in places where wind direction varies.

    In a computer simulation of a wind farm with 24 turbines, scientists found that windbreaks (red) improved the overall power output. Wakes created by the windbreaks appear in dark blue, and wakes of the turbines are light blue.L. Liu and R.J.A.M. Stevens/Physical Review Fluids 2021, Visualizations by Srinidhi N. Gadde More

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    A bounty of potential gravitational wave events hints at exciting possibilities

    A new crew of potential ripples in spacetime has just debuted — emphasis on the word “potential.”

    By loosening the criteria for what qualifies as evidence for gravitational waves, physicists identified 1,201 possible tremors. Most are probably fakes, spurious jitters in the data that can mimic the cosmic vibrations, the team reports August 2 at arXiv.org. But by allowing in more false alarms, the new tally may also include some weak but genuine signals that would otherwise be missed, potentially revealing exciting new information about the sources of gravitational waves.

    Scientists can now look for signs that may corroborate some of the uncertain detections, such as flashes of light in the sky that flared from the cosmic smashups that set off the ripples. Gravitational waves are typically spawned by collisions of dense, massive objects, such as black holes or neutron stars, the remnants of dead stars (SN: 1/21/21).

    To come up with the new census, physicists reanalyzed six months of data from the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, and Virgo gravitational wave observatories. Scientists had already identified 39 of the events as likely gravitational waves in earlier analyses.

    Eight events that hadn’t been previously identified stand a solid chance of being legitimate — with greater than a 50 percent probability of coming from an actual collision.

    The physicists analyzed the data from those eight events to see how they might have occurred. In one, two black holes may have slammed together, melding into a whopper black hole with about 180 times the mass of the sun, which would make it the biggest black hole merger seen yet (SN: 9/2/20). Another event could be a rare sighting of a black hole swallowing a neutron star (SN: 6/29/21). More

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    Black holes born with magnetic fields quickly shed them

    Like a shaggy dog in springtime, some black holes have to shed. New computer simulations reveal how black holes might discard their magnetic fields.

    Unlike dogs with their varied fur coats, isolated black holes are mostly identical. They are characterized by only their mass, spin and electric charge. According to a rule known as the no-hair theorem, any other distinguishing characteristics, or “hair,” are quickly cast off. That includes magnetic fields.

    The rule applies to black holes in a vacuum, where magnetic fields can simply slip away. But, says astrophysicist Ashley Bransgrove of Columbia University, “what we were thinking about is what happens in a more realistic scenario.” A magnetized black hole would typically be surrounded by electrically charged matter called plasma, and scientists didn’t know how — or even if — such black holes would undergo hair loss.

    Black holes can be born with magnetic fields or gain them later, for example by swallowing a neutron star, a highly magnetic dead star (SN: 6/29/21). When Bransgrove and colleagues simulated the plasma surrounding a magnetized black hole, they found that a process called magnetic reconnection allows the magnetic field to escape the black hole. The magnetic field lines that map out the field’s direction break apart and reconnect. Loops of magnetic field form around blobs of plasma, some of which blast outward, while others fall into the black hole. That process eliminates the black hole’s magnetic field, the researchers report in the July 30 Physical Review Letters.

    Magnetic reconnection in balding black holes could spew X-rays that astronomers could detect. So scientists may one day glimpse a black hole losing its hair. More

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    Gravitational waves reveal the first known mergers of a black hole and neutron star

    Caught in a fatal inward spiral, a neutron star met its end when a black hole swallowed it whole. Gravitational ripples from that collision spread outward through the cosmos, eventually reaching Earth. The detection of those waves marks the first reported sighting of a black hole engulfing the dense remnant of dead star. And in a surprise twist, scientists spotted a second such merger just days after the first.

    Until now, all identified sources of gravitational waves were twos of a kind: either two black holes or two neutron stars, spiraling around one another before colliding and coalescing (SN: 1/21/21). The violent cosmic collisions create waves that stretch and squeeze the fabric of spacetime, undulations that can be sussed out by sensitive detectors.

    The mismatched pairing of a black hole and neutron star was the final type of merger that scientists expected to find with current gravitational wave observatories. By pure coincidence, researchers spotted two of these events within 10 days of one another, the LIGO, Virgo and KAGRA collaborations report in the July 1 Astrophysical Journal Letters.

    Not only have unions between black holes and neutron stars not been seen before via gravitational waves, the smashups have also never been spotted at all by any other means.

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    “This is an absolute first look,” says theoretical physicist Susan Scott of the Australian National University in Canberra, a member of the LIGO collaboration.

    The result adds another tick mark to the tally of new discoveries made with gravitational waves. “That’s worth celebration,” says astrophysicist Cole Miller of the University of Maryland in College Park, who was not involved with the research. Since the first gravitational waves were detected in 2015, the observatories keep revealing new secrets. “It’s fantastic new things; it’s not just the same old, same old,” he says.

    Signs of the black hole-neutron star collisions registered in the LIGO and Virgo gravitational wave observatories in 2020, on January 5 and January 15. The first merger consisted of a black hole about 8.9 times the mass of the sun and a neutron star about 1.9 times the sun’s mass. The second merger had a 5.7 solar mass black hole and a 1.5 solar mass neutron star. Both collisions occurred more than 900 million light-years from Earth, the scientists estimate.

    To form detectable gravitational waves, the objects that coalesce must be extremely dense, with identities that can be pinned down by their masses. Anything with a mass above five solar masses could only be a black hole, scientists think. Anything less than about three solar masses must be a neutron star.

    One earlier gravitational wave detection involved a black hole merging with an object that couldn’t be identified, as its mass seemed to fall in between the cutoffs that separate black holes and neutron stars (SN: 6/23/20). Another previous merger may have resulted from a black hole melding with a neutron star, but the signal from that event wasn’t strong enough for scientists to be certain that the detection was the real deal. The two new detections clinch the case for black hole and neutron star meetups.

    One of the new events is more convincing than the other. The Jan. 5 merger was seen in just one of LIGO’s two gravitational wave detectors, and the signal has a relatively high probability of being a false alarm, Miller says. “If this were the only event, then you would not be as confident.” The Jan. 15 event, however, “seems pretty solid,” he says.

    Epic rendezvous between neutron stars and black holes happen regularly throughout the cosmos, the detections suggest. Based on the pace of detections, the researchers estimate that these events take place about once a month within 1 billion light-years of Earth.

    [embedded content]
    In a newly reported class of cosmic smashup, a neutron star (apparent in orange in this computer simulation, after the video zooms in) and black hole (dark gray) spiral inward, producing gravitational waves (blue) in a dance that ends when the black hole swallows the neutron star.

    Scientists don’t yet know how neutron stars and black holes come to meet up. They might form together, as two stars that orbit one another until both run out of fuel and die, with one collapsing into a black hole and the other forming a neutron star. Or the two objects might have formed separately and met up in a crowded region packed with many neutron stars and black holes.

    As a black hole and neutron star spiral inward and merge, scientists expect that the black hole could rip the neutron star to shreds, producing a light show that could be observed with telescopes. But astronomers found no fireworks in the aftermath of the two newly reported encounters, nor any evidence that the black holes deformed the neutron stars.

    That could be because in both cases the black hole was significantly larger than the neutron star, suggesting that the black hole gulped down the neutron star whole in a meal worthy of Pac-Man, Scott says.

    If scientists could spot a black hole shredding a neutron star in the future, that could help researchers pin down the properties of the ultradense, neutron-rich material that makes up the dead stars (SN: 4/20/21).

    In past detections of gravitational waves, the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, based in the United States, has teamed up with Virgo, in Italy. The new observations are the first to include members of a third observatory, KAGRA, in Japan (SN: 1/18/19). But the KAGRA detector itself didn’t contribute to the results, as scientists were still preparing it to detect gravitational waves at the time. LIGO, Virgo and KAGRA are all currently offline while scientists tinker with the detectors, and will resume their communal search for cosmic collisions in 2022. More

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    Dark matter may slow the rotation of the Milky Way’s central bar of stars

    Dark matter can be a real drag. The pull of that unidentified, invisible matter in the Milky Way may be slowing down the rotating bar of stars at the galaxy’s heart.

    Based on a technique that re-creates the history of the slowdown in a manner akin to analyzing a tree’s rings, the bar’s speed has decreased by at least 24 percent since it formed billions of years ago, researchers report in the August Monthly Notices of the Royal Astronomical Society.

    That slowdown is “another indirect but important piece of evidence that dark matter is a thing, not just a conjecture, because this can’t happen without it,” says astrophysicist Martin Weinberg of the University of Massachusetts Amherst, who was not involved with the study.

    Many spiral galaxies, including the Milky Way, contain a central bar-shaped region densely packed with stars and surrounded by the galaxy’s pinwheeling arms. The bar also has some groupies: a crew of stars trapped by the bar’s gravitational influence. Those stars orbit a gravitationally stable point located alongside the bar and farther from the galaxy’s center, known as a Lagrange point (SN: 2/26/21). 

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    If the bar’s rotation slows, it will grow in length, and the bar’s tagalongs will also move outward. As that happens, that cohort of hangers-on will gather additional stars. According to computer simulations of the process, those additional stars should arrange themselves in layers on the outside of the group, says astrophysicist Ralph Schönrich of University College London. The layers of stars imprint a record of the group’s growth. “It’s actually like a tree that you can cut up in your own galaxy,” he says.

    Schönrich and astrophysicist Rimpei Chiba of the University of Oxford studied how the composition of stars in the group changed from its outer edge to its deeper layers. Data from the European Space Agency’s Gaia spacecraft revealed that stars in the outer layers of the bar tended to be less enriched in elements heavier than helium than were stars in the inner layers. That’s evidence for the group of stars moving outward, as a result of the bar slowing, the researchers say. That’s because stars in the center of the galaxy — which would have glommed on to the group in the more distant past — tend to be more enriched in heavier elements than those farther out.

    The bar’s slowdown hints that a gravitational force is acting on it, namely, the pull of dark matter in the galaxy. Normal matter alone wouldn’t be enough to reduce the bar’s speed. “If there is no dark matter, the bar will not slow down,” Chiba says.

    But the results have drawn some skepticism. “Unfortunately, this is not yet convincing to me,” says astrophysicist Isaac Shlosman of the University of Kentucky in Lexington. For example, he doubts that the tree ring layering would really occur. It is “hard to believe that this is the case in a realistic system” as opposed to in a simplified computer simulation, he says.

    Weinberg, on the other hand, says that although the study relies on a variety of assumptions, he suspects it’s correct. “It’s got the right smell.” More

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    Gravitational waves confirm a black hole law predicted by Stephen Hawking

    Despite their mysterious nature, black holes are thought to follow certain simple rules. Now, one of the most famous black hole laws, predicted by physicist Stephen Hawking, has been confirmed with gravitational waves.

    According to the black hole area theorem, developed by Hawking in the early 1970s, black holes can’t decrease in surface area over time. The area theorem fascinates physicists because it mirrors a well-known physics rule that disorder, or entropy, can’t decrease over time. Instead, entropy consistently increases (SN: 7/10/15).

    That’s “an exciting hint that black hole areas are something fundamental and important,” says astrophysicist Will Farr of Stony Brook University in New York and the Flatiron Institute in New York City.

    The surface area of a lone black hole won’t change — after all, nothing can escape from within. However, if you throw something into a black hole, it will gain more mass, increasing its surface area. But the incoming object could also make the black hole spin, which decreases the surface area. The area law says that the increase in surface area due to additional mass will always outweigh the decrease in surface area due to added spin.

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    To test this area rule, MIT astrophysicist Maximiliano Isi, Farr and others used ripples in spacetime stirred up by two black holes that spiraled inward and merged into one bigger black hole. A black hole’s surface area is defined by its event horizon — the boundary from within which it’s impossible to escape. According to the area theorem, the area of the newly formed black hole’s event horizon should be at least as big as the areas of the event horizons of the two original black holes combined.

    The team analyzed data from the first gravitational waves ever spotted, which were detected by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, in 2015 (SN: 2/11/16). The researchers split the gravitational wave data into two time segments, before and after the merger, and calculated the surface areas of the black holes in each period. The surface area of the newly formed black hole was greater than that of the two initial black holes combined, upholding the area law with a 95 percent confidence level, the team reports in a paper to appear in Physical Review Letters.

    “It’s the first time that we can put a number on this,” Isi says.

    The area theorem is a result of the general theory of relativity, which describes the physics of black holes and gravitational waves. Previous analyses of gravitational waves have agreed with predictions of general relativity, and thus already hinted that the area law can’t be wildly off. But the new study “is a more explicit confirmation,” of the area law, says physicist Cecilia Chirenti of the University of Maryland in College Park, who was not involved with the research.

    So far, general relativity describes black holes well. But scientists don’t fully understand what happens where general relativity — which typically applies to large objects like black holes — meets quantum mechanics, which describes small stuff like atoms and subatomic particles. In that quantum realm, strange things can happen.

    For example, black holes can release a faint mist of particles called Hawking radiation, another idea developed by Hawking in the 1970s. That effect could allow black holes to shrink, violating the area law, but only over extremely long periods of time, so it wouldn’t have affected the relatively quick merger of black holes that LIGO saw.

    Physicists are looking for an improved theory that will combine the two disciplines into one new, improved theory of quantum gravity. Any failure of black holes to abide by the rules of general relativity could point physicists in the right direction to find that new theory.

    So physicists tend to be grumpy about the enduring success of general relativity, Farr says. “We’re like, ‘aw, it was right again.’” More

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    A newfound quasicrystal formed in the first atomic bomb test

    In an instant, the bomb obliterated everything.

    The tower it sat on and the copper wires strung around it: vaporized. The desert sand below: melted.

    In the aftermath of the first test of an atomic bomb, in July 1945, all this debris fused together, leaving the ground of the New Mexico test site coated with a glassy substance now called trinitite. High temperatures and pressures helped forge an unusual structure within one piece of trinitite, in a grain of the material just 10 micrometers across — a bit longer than a red blood cell.

    That grain contains a rare form of matter called a quasicrystal, born the moment the nuclear age began, scientists report May 17 in Proceedings of the National Academy of Sciences.

    Normal crystals are made of atoms locked in a lattice that repeats in a regular pattern. Quasicrystals have a structure that is orderly like a normal crystal but that doesn’t repeat. This means quasicrystals can have properties that are forbidden for normal crystals. First discovered in the lab in 1980s, quasicrystals also appear in nature in meteorites (SN: 12/8/16).

    Penrose tilings (one shown) are an example of a structure that is ordered but does not repeat. Quasicrystals are a three-dimensional version of this idea.Inductiveload/Wikimedia Commons

    The newly discovered quasicrystal from the New Mexico test site is the oldest one known that was made by humans.

    Trinitite takes its moniker from the nuclear test, named Trinity, in which the material was created in abundance (SN: 4/8/21). “You can still buy lots of it on eBay,” says geophysicist Terry Wallace, a coauthor of the study and emeritus director of Los Alamos National Laboratory in New Mexico.

    But, he notes, the trinitite the team studied was a rarer variety, called red trinitite. Most trinitite has a greenish tinge, but red trinitite contains copper, remnants of the wires that stretched from the ground to the bomb. Quasicrystals tend to be found in materials that have experienced a violent impact and usually involve metals. Red trinitite fit both criteria.

    But first the team had to find some.

    “I was asking around for months looking for red trinitite,” says theoretical physicist Paul Steinhardt of Princeton University. But Steinhardt, who is known for trekking to Siberia to seek out quasicrystals, wasn’t deterred (SN: 2/19/19). Eventually he and his colleagues got some from an expert in trinitite who began collaborating with the team. Then, the painstaking work started, “looking through every little microscopic speck” of the trinitite sample, says Steinhardt. Finally, the researchers extracted the tiny grain. By scattering X-rays through it, the researchers revealed that the material had a type of symmetry found only in quasicrystals.

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    The new quasicrystal, formed of silicon, copper, calcium and iron, is “brand new to science,” says mineralogist Chi Ma of Caltech, who was not involved with the study. “It’s a quite cool and exciting discovery,” he says.

    Future searches for quasicrystals could examine other materials that experienced a punishing blow, such as impact craters or fulgurites, fused structures formed when lightning strikes soil (SN: 3/16/21).

    The study shows that artifacts from the birth of the atomic age are still of scientific interest, says materials scientist Miriam Hiebert of the University of Maryland in College Park, who has analyzed materials from other pivotal moments in nuclear history (SN: 5/1/19). “Historic objects and materials are not just curiosities in collectors’ cabinets but can be of real scientific value,” she says. More