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    How to spot tiny black holes that might pass through the solar system 

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    Black holes about the size of a hydrogen atom could be careening through the solar system unnoticed. But their days of stealth may be numbered.

    Two teams of researchers propose methods to search for these tiny, hypothetical objects, which would have the mass of an asteroid. Because they would have formed in the universe’s infancy, they are known as primordial black holes.

    If they exist, primordial black holes in this mass range could explain some or all of the universe’s dark matter (SN: 8/7/16). That unknown invisible source of mass exerts gravitational influence on galaxies and, perplexingly, seems to outweigh normal matter by about 6 to 1. Extensive searches for subatomic particles that could explain dark matter have come up empty, putting new focus on primordial black holes (SN: 8/26/24).  More

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      in Space & Astronomy

      Separating science fact from fiction in Netflix’s ‘3 Body Problem’ 

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      The orbits of a trio of stars can be so chaotic that it’s impossible to precisely calculate the stars’ future trajectories. That’s the real science behind the name of the hit Netflix show, 3 Body Problem. Much of the sci-fi show’s action hinges on a variety of other physics concepts. But in service of the plot, some of that science is taken to implausible — or even physically impossible — lengths.

      To get a handle on what’s real and what’s fiction, Science News spoke with cosmologist Jacques Delabrouille of CNRS in Paris and Lawrence Berkeley National Laboratory in California.  More

    • 138 Shares169 Views

      in Heart

      Invisible comet tails of mucus slow sinking flakes of ‘marine snow’

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      WASHINGTON — Tiny, sinking flakes of detritus in the ocean fall more slowly thanks to the goop that surrounds each flake, new observations reveal.

      The invisible mucus makes “comet tails” that surround each flake, physicist Rahul Chajwa of Stanford University reported November 19 at the American Physical Society’s Division of Fluid Dynamics meeting. Those mucus tails slow the speed at which the flakes fall. That could affect the rate at which carbon gets sequestered deep in the oceans, making the physics of this sticky goo important for understanding Earth’s climate.

      Although scientists knew the goo was a component of the “marine snow” that falls in the ocean, they hadn’t previously measured its impact on sinking speed.

      Marine snow is made of dead and living phytoplankton, decaying organic matter, feces, bacteria and other aquatic sundries, all wrapped up in mucus that’s produced by the organisms. Like the gunk known for clogging airways during respiratory virus season, the mucus is what’s called a viscoelastic fluid (SN: 3/17/16). That’s something that flows like a liquid but exhibits elastic behavior as well, springing back after being stretched.

      This underwater blizzard is not easy to study. When observed in the ocean, the particles sink swiftly out of view. In the laboratory, the particles can be viewed for longer periods, but the trek ashore degrades the delicate marine snow and kills the living organisms within it.

      [embedded content]
      Tiny particles (white dots) within a seawater-filled chamber were used to measure the rate at which fluid flows around this flake of marine snow as it falls. The chamber is designed to keep the sinking snowflake in view of the camera.

      So Chajwa and colleagues built a physics lab at sea. Aboard a research vessel in the Gulf of Maine, the team collected marine snow particles in traps 80 meters below the water’s surface. Then they loaded their catch into a device onboard, designed to observe the particles falling.

      Nicknamed “the gravity machine,” it’s a fluid-filled wheel that rotates in order to keep an individual flake in view of a camera. It’s a bit like a hamster wheel for falling debris. As the flake sinks, the wheel turns so as to move the snow in the opposite direction, allowing the snowfall to be observed indefinitely. The gravity machine was itself mounted on a gimbal designed to stave off sloshing from the rocking of the ship.

      “It’s a very nice compromise between the real marine snow that you get in the ocean versus what you can do practically in the lab,” says biophysicist Anupam Sengupta of the University of Luxembourg, who was not involved with the research.

      To observe how the fluid flowed around the particles, the researchers added tiny beads within the fluid in the gravity machine. That revealed the rate of fluid flow around the particles. The speed of fluid flow was slowed in a comet tail–shaped region around the particle, revealing the invisible mucus that sinks along with the particle.

      Marine snow particles (one shown) are surrounded with invisible mucus. Drag the slider to see how fluid flows around the flake as it falls. Slower speeds (yellow) reveal mucus that trails the flake in a comet tail–shape (red dotted line). Left: Rahul Chajwa and Manu Prakash/PrakashLab/Stanford UniversityRight: Rahul Chajwa and Manu Prakash/PrakashLab/Stanford University

      The particles sank at speeds up to 200 meters per day. The mucus played a big role in sinking speed. “The more the mucus, the slower the particles sink,” Chajwa says. On average, the mucus causes the marine snow particles to linger twice as long in the upper 100 meters of the ocean as they otherwise would, Chajwa and colleagues determined.

      If it falls deep enough, marine snow can sequester carbon away from the atmosphere. That’s because living phytoplankton, like plants, take in carbon dioxide and release oxygen. When phytoplankton form marine snow, they take that carbon along with them as they sink. If a flake reaches the ocean floor, it can settle into a scum at the bottom that caches that carbon over long time periods. The faster the particles sink, the more likely they are to make it to the abyss before being eaten by critters (SN: 6/23/22).

      Knowing how fast the particles sink is important for calculating the ocean’s impact on Earth’s climate, and how that might change as the climate warms, the researchers say. The oceans are major players in the planet’s carbon cycle (SN: 12/2/21), and scientists estimate that oceans have taken up roughly 30 percent of the carbon dioxide released by humans since industrialization. Chajwa and colleagues hope that their results can be used to refine climate models, which currently do not take the mucus into account.

      So this mucus is nothing to sneeze at. “We’re talking about microscopic physics,” says Stanford physicist Manu Prakash, a coauthor of the work, which is also reported in a paper submitted October 3 at arXiv.org. “But multiply that by the volume of the ocean … that’s what gives you the scale of the problem.” More

    • 113 Shares99 Views

      in Space & Astronomy

      Vela’s exploded star is the highest-energy pulsar ever seen

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      The sweeping beams of cosmic lighthouses called pulsars are much more energetic than previously thought, calling into question the bulbs that power them.

      A new analysis, from the High Energy Stereoscopic System array in Namibia, reveals a pulsar that radiates at 20 trillion electron volts — making it the most energetic pulsar ever seen. The finding, described October 5 in Nature Astronomy, is challenging scientists’ understanding of how pulsars can emit such extreme radiation.

      The observation is “spectacular,” says Hayk Hakobyan, an astrophysicist at Columbia University who was not part of the study. “This is basically a stress test for our theories.”

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      Pulsars are the dense remnants of exploded stars, emitting beams of light as they twirl up to hundreds of times a second. Pulsars were first discovered in the late 1960s, from a throb of radio waves so consistent that some suggested it was an alien broadcast (SN: 3/8/18).

      As a pulsar rotates, its massive magnetic field rips charged particles from the surface, ejecting them along magnetic field lines and spitting radiation out the pulsar’s poles. Over the decades, scientists have found pulsars that beam radiation at higher energies, topping off at about a trillion electron volts, as observed in the Crab pulsar in 2016.

      In the new study, scientists analyzed 80 hours of data from the Namibian array, which looks for a wake of light given off when high-energy light emitted elsewhere in the universe crashes into molecules in Earth’s atmosphere. The researchers identified 78 super-energetic particles of light that they traced to a pulsar about 1,000 light-years from Earth, in the constellation Vela. That light, the team determined, had at least 20 times higher energy than the Crab pulsar observation.

      The team first spotted hints of the mighty radiation a few years ago and struggled to interpret the data. “This discovery was so unexpected … that it somehow was difficult to understand,” says Arache Djannati-Ataï, an astrophysicist at CNRS in Paris, who led the analysis.

      To reach such high energies, the light is probably boosted by collisions with other speedy, energetic particles such as electrons. But how it becomes so energetic is still up for debate.

      The new finding lends support to the growing idea that, thousands of kilometers from a pulsar’s surface, its magnetic field lines can collide and snap, launching particles to extreme speeds in a process called magnetic reconnection. But the observed radiation is pushing the limit of how much energy the reconnection process can release, and scientists will have to scramble for new explanations if higher-energy pulsar radiation keeps turning up.

      The possibility of extreme pulsar radiation had been looming over theorists, Hakobyan says. “But now, it’s definite. So now, you have to go do something about it.” More

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      in Space & Astronomy

      Julian Muñoz has a ‘ruler’ that could size up the early universe

      by

      Julian Muñoz has come up with a ruler to measure the early universe.

      A theoretical physicist, Muñoz studies the distant, dim period in the universe’s history known as cosmic dawn. That’s when stars first began flickering on, a few hundred million years after the Big Bang, infusing the universe with initial glimmers of starlight and forming the first galaxies.

      Before the first stars, the universe was cold and dark — as Muñoz describes it, “boring.” Then, starlight began to reshape the universe. “It is a very dramatic epoch,” says Muñoz, of the University of Texas at Austin.

      That epoch is also poorly understood. Cosmic dawn is so unexplored that Muñoz compares it to an uncharted area on early maps of Earth. There, Muñoz says, “there could be dragons.” By studying this era, he hopes to reveal the behavior of one dragon of the cosmos, dark matter, the inscrutable substance whose mass binds galaxies.

      But to understand the cosmos, scientists have to be able to measure it. Looking far into space means looking deep into the past. The trouble is our 2-D view of the sky doesn’t readily reveal how far away things are. “When we look at the night sky, we’ve got no depth perception,” says cosmologist Adrian Liu of McGill University in Montreal.

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      Scientists have devised a variety of methods to get a handle on distances, including standard candles and standard rulers — objects of known brightness or length. If you know how bright an object is (compared with how bright it appears) or you know how long a particular feature is on the sky (compared with its apparent length), you can tell how far away it is. A ruler looks smaller from 20 meters away than from 10 meters away, and a 20-watt lightbulb looks dimmer the farther away it is. The same applies over cosmic distances.

      Scientists use certain types of exploding stars, for example, to estimate distances, because the blasts put out a predictable light show (SN: 5/8/12). Standard rulers or standard candles can be used to trace out how far away other objects of interest are and reveal how rapidly the universe has expanded over its history.

      But none of the known standard objects reach back to the cosmic dawn era. That’s where Muñoz’s ruler comes in. “This ability to reach that far back,” Liu says, “that’s the really valuable thing.”

      Sizing up cosmic dawn

      No one has ever seen a conclusive signature of cosmic dawn — the very first galaxies are too distant to observe directly. But there’s another way to spot cosmic dawn’s effects, one that’s been a long-sought target for astronomers. As the first stars formed, their light heated the surrounding hydrogen gas, causing it to absorb light with a wavelength of 21 centimeters, a number that results from the separation between energy levels in hydrogen atoms. Observing that 21-centimeter absorption signal is the aim of the Hydrogen Epoch of Reionization Array, or HERA, collaboration, an effort that Muñoz and Liu both work on, using a radio telescope in South Africa.

      If it can be detected, this absorption signal should have subtle, ring-shaped patterns imprinted in it, Muñoz reported in 2019 in Physical Review Letters.

      Secrets of the universe’s cosmic dawn era are revealed in patterns of the absorption of light with a 21-centimeter wavelength, shown in a computer simulation. Regions with more absorption (red) correspond to denser pockets of stars, compared with sparsely populated regions with less absorption (blue). Sparse areas tend to be separated by distances of about half a billion light-years (arrow indicates one example); the same goes for dense areas.J.B. Muñoz

      Those patterns, the basis of his ruler, result from the differing behavior of dark matter and normal matter during an even earlier period, less than 400,000 years after the Big Bang. Sound waves careening through the plasma at that time would have pushed normal matter to high speeds while leaving dark matter at a standstill.

      This mismatch in velocities affected where galaxies formed during the later cosmic dawn era. To create a galaxy, dark matter must gravitationally reel in normal matter. But where the velocities differed, the normal matter zipped right on by. The early universe was left with sparsely populated regions of the sky, arranged in ring-shaped patterns with a predictable distance scale. The rings, which are too subtle to pick out by eye from the data but show up in statistical analyses, have radii of half a billion light-years – that’s one long measuring stick.

      The new standard ruler could reveal how fast the universe was expanding back then. That information can tell scientists what that youthful universe was made of, revealing the amount of dark matter, normal matter and dark energy, another hidden piece of the cosmic puzzle.

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      A new expansion measurement could also add fuel to one of the fiercest debates in cosmology. Currently, different measurements of the universe’s expansion rate clash with one another, leaving scientists pondering whether there are flaws in our understanding of the cosmos.

      Seeking to understand the unknown, including these shadowy cosmic realms, is “an integral component of human nature — like art and poetry,” Muñoz says. “You could live without it, but I really hope you don’t have to.”

      Looking into dark corners

      Muñoz’s interest in dark matter drew him to the cosmic dawn. The first galaxies grew off a scaffold of dark matter. So information about how and when those galaxies formed can reveal dark matter’s properties. In a report published in 2018 in Nature, for example, Muñoz and colleagues suggested that, if some of the universe’s dark matter had a tiny electric charge, a millionth of an electron’s, that could alter the expected cosmic dawn signal.

      He has also developed important computational tools, like a new technique that allows for lightning-fast simulations of the cosmic dawn, reported in May in Monthly Notices of the Royal Astronomical Society. The time it takes to perform these simulations has previously limited what scientists can study.

      “He’s got an eye for interesting ideas,” says theoretical physicist Marc Kamionkowski of Johns Hopkins University, Muñoz’s Ph.D. adviser. But the cosmic ruler, “that’s probably the most singular idea that he’s had.”

      Becoming a physicist, in itself, was uncharted territory for Muñoz. As a child, he liked science. He recalls being amazed by fossilized shark teeth that were millions of years old — perhaps his first experience grappling with such grand timescales.

      But Muñoz didn’t have a scientific role model; his parents didn’t finish high school. He focused his attention on video games and coding until a high school physics teacher encouraged his scientific streak. He turned to physics, he says, where “it was possible to channel all this nerdy energy for knowledge.” That’s what drives Muñoz to explore the questions that swirl around dark corners of the cosmos. “I do it because I think the answers enrich the human experience.”

      Julian Muñoz is one of this year’s SN 10: Scientists to Watch, our list of 10 early and mid-career scientists who are making extraordinary contributions to their field. We’ll be rolling out the full list throughout 2023.

      Want to nominate someone for the SN 10? Send their name, affiliation and a few sentences about them and their work to sn10@sciencenews.org. More

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      in Physics

      Physicists stored data in quantum holograms made of twisted light

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      Particles of twisted light that have been entangled using quantum mechanics offer a new approach to dense and secure data storage.

      Holograms that produce 3-D images and serve as security features on credit cards are usually made with patterns laid down with beams of laser light. In recent years, physicists have found ways to create holograms with entangled photons instead. Now there is, literally, a new twist to the technology.

      Entangled photons that travel in corkscrew paths have resulted in holograms that offer the possibility of dense and ultrasecure data encryption, researchers report in a study to appear in Physical Review Letters.

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      Light can move in a variety of ways, including the up-and-down and side-to-side patterns of polarized light. But when it carries a type of rotation known as orbital angular momentum, it can also propagate in spirals that resemble twisted rotini pasta.

      Like any other photons, the twisted versions can be entangled so that they essentially act as one entity. Something that affects one of an entangled photon pair instantly affects the other, even if they are very far apart.

      In previous experiments, researchers have sent data through the air in entangled pairs of twisted photons (SN: 8/5/15). The approach should allow high-speed data transmission because light can come with different amounts of twist, with each twist serving as a different channel of communication.

      Now the same approach has been applied to record data in holograms. Instead of transmitting information on multiple, twisted light channels, photon pairs with different amounts of twist create distinct sets of data in a single hologram. The more orbital angular momentum states involved, each with different amounts of twist, the more data researchers can pack into a hologram.

      In addition to cramming more data into holograms, increasing the variety of twists used to record the data boosts security. Anyone who wants to read the information out needs to know, or guess, how the light that recorded it was twisted.

      For a hologram relying on two types of twist, says physicist Xiangdong Zhang of the Beijing Institute of Technology, you would have to pick the right combination of the twists from about 80 possibilities to decode the data. Bumping that up to combinations of seven distinct twists leads to millions of possibilities. That, Zhang says, “should be enough to ensure our quantum holographic encryption system has enough security level.”

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      The researchers demonstrated their technique by encoding words and letters in holograms and reading the data back out again with twisted light. Although the researchers produced images from the holographic data, says physicist Hugo Defienne of the Paris Institute of Nanosciences, the storage itself should not be confused with holographic images.

      Defienne, who was not involved with the new research, says that other quantum holography schemes, such as his efforts with polarized photons, produce direct images of objects including microscopic structures.

      “[Their] idea there is very different . . . from our approach in this sense,” Defrienne says. “They’re using holography to store information,” rather than creating the familiar 3-D images that most people associate with holograms.

      The twisted light data storage that Zhang and his colleagues demonstrated is slow, requiring nearly 20 minutes to decode an image of the acronym “BIT,” for the Beijing Institute of Technology where the experiments were performed. And the security that the researchers have demonstrated is still relatively low because they included only up to six forms of twisted light in their experiments.

      Zhang is confident that both limitations can be overcome with technical improvements. “We think that our technology has potential application in quantum information encryption,” he says, “especially quantum image encryption.” More

    • 138 Shares179 Views

      in Space & Astronomy

      Two black holes merged despite being born far apart in space

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      Signals buried deep in data from gravitational wave observatories imply a collision of two black holes that were clearly born in different places.

      Almost all the spacetime ripples that experiments like the Laser Interferometer Gravitational-Wave Observatory, or LIGO, see come from collisions among black holes and neutron stars that are probably close family members (SN: 1/21/21). They were once pairs of stars born at the same time and in the same place, eventually collapsing to form orbiting black holes or neutron stars in old age.

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      Now, a newly noted marriage of black holes, found in existing data from U.S.–based LIGO and its sister observatory Virgo in Italy, seems to be of an unrelated pair. Evidence for this stems from how they were spinning as they merged into one, researchers report in a paper in press at Physical Review D. Black holes that are born in the same place tend to have their spins aligned, like a pair of toy tops spinning on a table, as they orbit each other. But the pair in this case have no correlation between their respective spins and orbits, implying that they were born in different places.

      “This is telling us we’ve finally found a pair of black holes that must come from the non-grow-old-and-die-together channel,” says Seth Olsen, a physicist at Princeton University.

      Previous events that have turned up in gravitational wave observations show back holes merging that aren’t perfectly aligned, but most are close enough to strongly imply family connections. The new detection, which Olsen and colleagues found by sifting through data that the LIGO-Virgo collaboration released to the public, is different. One of the black holes is effectively spinning upside down.

      That can’t easily happen unless the two black holes come from separate places. They probably met late in their stellar lives, unlike the black hole littermates that seem to make up the bulk of gravitational wave observations.

      In addition to the merger between unrelated black holes, Olsen and his collaborators identified nine other black hole mergers that had slipped through the prior LIGO-Virgo studies (SN: 8/4/21).

      “This is actually the nice thing about this type of analysis,” says LIGO scientific collaboration spokesperson Patrick Brady, a physicist at the University of Wisconsin–Milwaukee who was not affiliated with the new study. “We deliver the data in a format that can be used by other people and then [they] will have access to try out new techniques.”

      To compile so many new signals in data that had already been gone over by other researchers, Olsen’s group lowered the analytical bar a little.

      “Out of the 10 new ones,” Olsen says, “there are about three of them, statistically, that probably come from noise,” rather than being definitive black hole merger detections. Assuming that the merger of black holes strangers is not among the errant signals, it almost certainly tells a tale of black hole histories distinct from the others seen so far.

      “It would be [extremely] unlikely for this to come from two black holes that have been together for their whole lifespan,” Olsen says. “This must have been a capture. That’s cool because we’re finally able to start probing that region of the [black hole] population.”

      Brady notes that “we don’t understand the theory [of black hole mergers] well enough to be able to confidently predict all of these types of things.” But the recent study may point to new and interesting opportunities in gravitational wave astronomy. “Let’s follow this clue to see if it really is reflecting something rare,” he says. “Or if not, well, we’ll learn other things.” More

    • 113 Shares159 Views

      in Physics

      Experiments hint at why bird nests are so sturdy

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      To build its nest, a bird won’t go for any old twig. Somehow, birds pick and choose material that will create a cozy, sturdy nest.

      “That’s just totally mystifying to me,” says physicist Hunter King of the University of Akron in Ohio. Birds seem to have a sense for how the properties of an individual stick will translate to the characteristics of the nest. That relationship “is something we don’t know the first thing about predicting,” King says.

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      A bird’s nest is a special version of a granular material: a substance, such as sand, made up of many smaller objects (SN: 4/30/19). King and colleagues combined laboratory experiments and computer simulations to better understand the quirks of nestlike granular materials, the researchers report in a study to appear in Physical Review Letters.

      In the experiments, a piston repeatedly compressed 460 bamboo rods scattered inside a cylinder. The computer simulations let researchers analyze the points where sticks touched, which is key to understanding the material, the team says.

      The more force the piston applied to the pile, the stiffer the pile became, meaning it resisted further deformation. As the piston bore down, sticks slid against one another, and the contact points between them rearranged. That stiffened the pile by allowing additional contact points to form between sticks, which prevented them from flexing further, the simulations showed.

      Changes in the pile’s stiffness seemed to lag behind the piston’s motion, a phenomenon called hysteresis. That effect caused the pile to be stiffer when the piston pushed in than when the material bounced back as the piston retracted. Simulations suggest that the hysteresis arose because the initial friction between sticks needed to be overcome before the contact points started to rearrange.

      Beyond bird nests, this research could be applied to other materials made of disordered arrangements of long fibers, such as felt. With a better understanding of the physical qualities of such materials, engineers could use them to create new structures designed to protect not only bird eggs, but other cargo that humans consider precious. More

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      in Space & Astronomy

      Gravitational waves gave a new black hole a high-speed ‘kick’

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      This black hole really knows how to kick back.

      Scientists recently observed two black holes that united into one, and in the process got a “kick” that flung the newly formed black hole away at high speed. That black hole zoomed off at about 5 million kilometers per hour, give or take a few million, researchers report in a paper in press in Physical Review Letters. That’s blazingly quick: The speed of light is just 200 times as fast.

      Ripples in spacetime, called gravitational waves, launched the black hole on its breakneck exit. As any two paired-up black holes spiral inward and coalesce, they emit these ripples, which stretch and squeeze space. If those gravitational waves are shot off into the cosmos in one direction preferentially, the black hole will recoil in response.

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      It’s akin to a gun kicking back after shooting a bullet, says astrophysicist Vijay Varma of the Max Planck Institute for Gravitational Physics in Potsdam, Germany.

      Gravitational wave observatories LIGO and Virgo, located in the United States and Italy, detected the black holes’ spacetime ripples when they reached Earth on January 29, 2020. Those waves revealed details of how the black holes merged, hinting that a large kick was probable. As the black holes orbited one another, the plane in which they orbited rotated, or precessed, similar to how a top wobbles as it spins. Precessing black holes are expected to get bigger kicks when they merge.

      So Varma and colleagues delved deeper into the data, gauging whether the black hole got the boot. To estimate the kick velocity, the researchers compared the data with various predicted versions of black hole mergers, created based on computer simulations that solve the equations of general relativity, Einstein’s theory of gravity (SN: 2/3/21). The recoil was so large, the researchers found, that the black hole was probably ejected from its home and kicked to the cosmic curb.

      Dense groups of stars and black holes called globular clusters are one locale where black holes are thought to partner up and merge. The probability that the kicked black hole would stay within a globular cluster home is only about 0.5 percent, the team calculated. For a black hole in another type of dense environment, called a nuclear star cluster, the probability of sticking around was about 8 percent.

      The black hole’s great escape could have big implications. LIGO and Virgo detect mergers of stellar-mass black holes, which form when a star explodes in a supernova and collapses into a black hole. Scientists want to understand if black holes that partner up in crowded clusters could partner up again, going through multiple rounds of melding. If they do, that could help explain some surprisingly bulky black holes previously seen in mergers (SN: 9/2/20). But if merged black holes commonly get rocketed away from home, that would make multiple mergers less likely.

      “Kicks are very important in understanding how heavy stellar-mass black holes form,” Varma says.

      Previously, astronomers have gleaned evidence of gravitational waves giving big kicks to supermassive black holes, the much larger beasts found at the centers of galaxies (SN: 3/28/17). But that conclusion hinges on observations of light, rather than gravitational waves. “Gravitational waves, in a way, are cleaner and easier to interpret,” says astrophysicist Manuela Campanelli of the Rochester Institute of Technology in New York, who was not involved in the new study.

      LIGO and Virgo data had already revealed some evidence of black holes getting small kicks. The new study is the first to report using gravitational waves to spot a black hole on the receiving end of a large kick.

      That big kick isn’t a surprise, Campanelli says. Earlier theoretical predictions by Campanelli and colleagues suggested that such powerful kicks were possible. “It’s always exciting when someone can measure from observations what you predicted from calculations.” More