Physics

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Astronomers think they’ve found a plausible explanation of the Wow! signal

aliens, astronomy, astrophysics, Physics, Science, WOW! signal / /

“I’m not saying it’s aliens…” —

Magnetars could zap clouds of atomic hydrogen, producing focused microwave beams.

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The Wow! signal represented as

Enlarge / The Wow! signal, represented as “6EQUJ5,” was discovered in 1977 by astronomer Jerry Ehman.

Public domain

An unusually bright burst of radio waves—dubbed the Wow! signal—discovered in the 1970s has baffled astronomers ever since, given the tantalizing possibility that it just might be from an alien civilization trying to communicate with us. A team of astronomers think they might have a better explanation, according to a preprint posted to the physics arXiv: clouds of atomic hydrogen that essentially act like a naturally occurring galactic maser, emitting a beam of intense microwave radiation when zapped by a flare from a passing magnetar.

As previously reported, the Wow! signal was detected on August 18, 1977, by The Ohio State University Radio Observatory, known as “Big Ear.” Astronomy professor Jerry Ehman was analyzing Big Ear data in the form of printouts that, to the untrained eye, looked like someone had simply smashed the number row of a typewriter with a preference for lower digits. Numbers and letters in the Big Ear data indicated, essentially, the intensity of the electromagnetic signal picked up by the telescope over time, starting at ones and moving up to letters in the double digits (A was 10, B was 11, and so on). Most of the page was covered in ones and twos, with a stray six or seven sprinkled in.

But that day, Ehman found an anomaly: 6EQUJ5 (sometimes misinterpreted as a message encoded in the radio signal). This signal had started out at an intensity of six—already an outlier on the page—climbed to E, then Q, peaked at U—the highest power signal Big Ear had ever seen—then decreased again. Ehman circled the sequence in red pen and wrote “Wow!” next to it. The signal appeared to be coming from the direction of the Sagittarius constellation, and the entire signal lasted for about 72 seconds. Alas, SETI researchers have never been able to detect the so-called “Wow! Signal” again, despite many tries with radio telescopes around the world.

One reason for the excited reaction is that such a signal had been proposed as a possible communication from extraterrestrial civilizations in a 1959 paper by Cornell University physicists Philip Morrison and Giuseppe Cocconi. Morrison and Cocconi thought that such a civilization might use the 1420 megahertz frequency naturally emitted by hydrogen, the universe’s most abundant element and, therefore, something an alien civilization would be familiar with. In fact, the Big Ear had been reassigned to the SETI project in 1973 specifically to hunt for possible signals. Ehman himself was quite skeptical of the “it could be aliens” hypothesis for several decades, although he admitted in a 2019 interview that “the Wow! signal certainly has the potential of being the first signal from extraterrestrial intelligence.”

Several other alternative hypotheses have been suggested. For instance, Antonio Paris suggested in 2016 that the signal may have come from the hydrogen cloud surrounding a pair of comets, 266P/Christensen and 335P/Gibbs. This was rejected by most astronomers, however, in part because comets don’t emit strongly at the relevant frequencies. Others have suggested the signal was the result of interference from satellites orbiting the Earth, or a signal from Earth reflected off a piece of space debris.

Space maser!

Astrobiologist Abel Mendez of the University of Puerto Rico at Arecibo and his co-authors think they have the strongest astrophysical explanation to date with their cosmic maser hypothesis. The team was actually hunting for habitable exoplanets using signals from red dwarf stars. In some of the last archival data collected at the Arecibo radio telescope (which collapsed in 2020), they noticed several signals that were remarkably similar to the Wow! signal in terms of frequency—just much less intense (bright).

Mendez admitted to Science News that he had always viewed the Wow! signal as just a fluke—he certainly didn’t think it was aliens. But he realized that if the signals they were identifying had blazed brighter, even momentarily, they would be very much like the Wow! signal. As for the mechanism that caused such a brightening, Mendez et al. propose that a magnetar (a highly magnetic neutron star) passing behind a cloud of atomic hydrogen could have flared up with sufficient energy to produce stimulated emission in the form of a tightly focused beam of microwave radiation—a cosmic maser. (Masers are akin to lasers, except they emit microwave radiation rather than visible radiation.)

Proving their working hypothesis will be much more challenging, although there have been rare sightings of such naturally occurring masers from hydrogen molecules in space. But nobody has ever spotted an atomic hydrogen cloud with an associated maser, and that’s what would be needed to explain the intensity of the Wow! signal. That’s why other astronomers are opting for cautious skepticism. “A magnetar is going to produce [short] radio emissions as well. Do you really need this complicated maser stuff happening as well to explain the Wow! signal?” Michael Garrett of the University of Manchester told New Scientist. “Personally, I don’t think so. It just makes a complicated story even more complicated.”

arXiv, 2024. DOI: 10.48550/arXiv.2408.08513  (About DOIs).

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Why cricket’s latest bowling technique is so effective against batters

aerodynamics, cricket game, fluid dynamics, Magnus effect, Physics, Science, sports science / /
Some cricket bowlers favor keeping the arm horizontal during delivery, the better to trick the batsmen.

Enlarge / Some cricket bowlers favor keeping the arm horizontal during delivery, the better to trick the batsmen.

Although the sport of cricket has been around for centuries in some form, the game strategy continues to evolve in the 21st century. Among the newer strategies employed by “bowlers”—the equivalent of the pitcher in baseball—is delivering the ball with the arm horizontally positioned close to the shoulder line, which has proven remarkably effective in “tricking” batsmen in their perception of the ball’s trajectory.

Scientists at Amity University Dubai in the United Arab Emirates were curious about the effectiveness of the approach, so they tested the aerodynamics of cricket balls in wind tunnel experiments. The team concluded that this style of bowling creates a high-speed spinning effect that shifts the ball’s trajectory mid-flight—an effect also seen in certain baseball pitches, according to a new paper published in the journal Physics of Fluids.

“The unique and unorthodox bowling styles demonstrated by cricketers have drawn significant attention, particularly emphasizing their proficiency with a new ball in early stages of a match,” said co-author Kizhakkelan Sudhakaran Siddharth, a mechanical engineer at Amity University Dubai. “Their bowling techniques frequently deceive batsmen, rendering these bowlers effective throughout all phases of a match in almost all formats of the game.”

As previously reported, any moving ball leaves a trail of air as it travels; the inevitable drag slows the ball down. The ball’s trajectory is affected by diameter and speed and by tiny irregularities on the surface. Baseballs, for example, are not completely smooth; they have stitching in a figure-eight pattern. Those stitches are bumpy enough to affect the airflow around the baseball as it’s thrown toward home plate. As a baseball moves, it creates a whirlpool of air around it, commonly known as the Magnus effect. The raised seams churn the air around the ball, creating high-pressure zones in various locations (depending on the pitch type) that can cause deviations in its trajectory.

Physicists have been enthusiastically studying baseballs since the 1940s, when Lyman Briggs became intrigued by whether a curveball actually curves. Initially, he enlisted the aid of the Washington Senators pitching staff at Griffith Stadium to measure the spin of a pitched ball; the idea was to determine how much the curve of a baseball depends on its spin and speed.

Briggs followed up with wind tunnel experiments at the National Bureau of Standards (now the National Institute of Standards and Technology) to make even more precise measurements since he could control most variables. He found that spin rather than speed was the key factor in causing a pitched ball to curve and that a curveball could dip up to 17.5 inches as it travels from the pitcher’s mound to home plate.

The first recorded photo of a cricket match taken on July 25, 1857, by Roger Fenton.

Enlarge / The first recorded photo of a cricket match taken on July 25, 1857, by Roger Fenton.

Public domain

In 2018, we reported on a Utah State University study to explain the fastball’s unexpected twist in experiments using Little League baseballs. The USU scientists fired the balls one by one through a smoke-filled chamber. Two red sensors detected the balls as they zoomed past, triggering lasers that acted as flashbulbs. They then used particle image velocimetry to calculate airflow at any given spot around the ball. Conclusion: It all comes down to spin speed, spin axis, and the orientation of the ball, and there is no meaningful aerodynamical difference between a two-seam fastball and a four-seam fastball.

In 2022, two physicists developed a laser-guided speed measurement system to measure the change in speed of a baseball mid-flight and then used that measurement to calculate the acceleration, the various forces acting on the ball, and the lift and drag. They suggested their approach could also be used for other ball sports like cricket and soccer.

The Armfield C15-15 Wake Survey Rake measured pressure downstream of the ball.

Enlarge / The Armfield C15-15 Wake Survey Rake measured pressure downstream of the ball.

A.B. Faazil et al., 2024

Similarly, golf ball dimples reduce the drag flow by creating a turbulent boundary layer of air, while the ball’s spin generates lift by creating a higher air pressure area on the bottom of the ball than on the top. The surface patterns on volleyballs can also affect their trajectories. Conventional volleyballs have six panels, but more recent designs have eight panels, a hexagonal honeycomb pattern, or dimples. A 2019 study found that the surface panels on conventional volleyballs can give rise to unpredictable trajectories on float serves (which have no spin), and modifying the surface patterns could make for a more consistent flight.

From a physics standpoint, the float serve is similar to throwing a knuckleball in baseball, which is largely unaffected by the Magnus force because it has no spin. Its trajectory is determined entirely by how the seams affect the turbulent airflow around the baseball. The seams of a baseball can change the speed (velocity) of the air near the ball’s surface, speeding the ball up or slowing it down, depending on whether said seams are on the top or the bottom. The panels on conventional volleyballs have a similar effect.

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Pass the mayo: Condiment could help improve fusion energy yields

condiments, fluid dynamics, hydrodynamics, nuclear fusion, nuclear physics, phase transitions, Physics, Rayleigh-Taylor instability, Science / /

Don’t hold the mayo —

Controlling a problematic instability could lead to cheaper internal fusion.

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A jar of homemade mayonnaise

Inertial confinement fusion is one method for generating energy through nuclear fusion, albeit one plagued by all manner of scientific challenges (although progress is being made). Researchers at LeHigh University are attempting to overcome one specific bugbear with this approach by conducting experiments with mayonnaise placed in a rotating figure-eight contraption. They described their most recent findings in a new paper published in the journal Physical Review E with an eye toward increasing energy yields from fusion.

The work builds on prior research in the LeHigh laboratory of mechanical engineer Arindam Banerjee, who focuses on investigating the dynamics of fluids and other materials in response to extremely high acceleration and centrifugal force. In this case, his team was exploring what’s known as the “instability threshold” of elastic/plastic materials. Scientists have debated whether this comes about because of initial conditions, or whether it’s the result of “more local catastrophic processes,” according to Banerjee. The question is relevant to a variety of fields, including geophysics, astrophysics, explosive welding, and yes, inertial confinement fusion.

How exactly does inertial confinement fusion work? As Chris Lee explained for Ars back in 2016:

The idea behind inertial confinement fusion is simple. To get two atoms to fuse together, you need to bring their nuclei into contact with each other. Both nuclei are positively charged, so they repel each other, which means that force is needed to convince two hydrogen nuclei to touch. In a hydrogen bomb, force is generated when a small fission bomb explodes, compressing a core of hydrogen. This fuses to create heavier elements, releasing a huge amount of energy.

Being killjoys, scientists prefer not to detonate nuclear weapons every time they want to study fusion or use it to generate electricity. Which brings us to inertial confinement fusion. In inertial confinement fusion, the hydrogen core consists of a spherical pellet of hydrogen ice inside a heavy metal casing. The casing is illuminated by powerful lasers, which burn off a large portion of the material. The reaction force from the vaporized material exploding outward causes the remaining shell to implode. The resulting shockwave compresses the center of the core of the hydrogen pellet so that it begins to fuse.

If confinement fusion ended there, the amount of energy released would be tiny. But the energy released due to the initial fusion burn in the center generates enough heat for the hydrogen on the outside of the pellet to reach the required temperature and pressure. So, in the end (at least in computer models), all of the hydrogen is consumed in a fiery death, and massive quantities of energy are released.

That’s the idea anyway. The problem is that hydrodynamic instabilities tend to form in the plasma state—Banerjee likens it to “two materials [that] penetrate one another like fingers” in the presence of gravity or any accelerating field—which in turn reduces energy yields. The technical term is a Rayleigh-Taylor instability, which occurs between two materials of different densities, where the density and pressure gradients move in opposite directions. Mayonnaise turns out to be an excellent analog for investigating this instability in accelerated solids, with no need for a lab setup with high temperature and pressure conditions, because it’s a non-Newtonian fluid.

“We use mayonnaise because it behaves like a solid, but when subjected to a pressure gradient, it starts to flow,” said Banerjee. “As with a traditional molten metal, if you put a stress on mayonnaise, it will start to deform, but if you remove the stress, it goes back to its original shape. So there’s an elastic phase followed by a stable plastic phase. The next phase is when it starts flowing, and that’s where the instability kicks in.”

More mayo, please

2019 video showcasing the rotating wheel Rayleigh Taylor instability experiment at Lehigh University.

His team’s 2019 experiments involved pouring Hellman’s Real Mayonnaise—no Miracle Whip for this crew—into a Plexiglass container and then creating wavelike perturbations in the mayo. One experiment involved placing the container on a rotating wheel in the shape of a figure eight and tracking the material with a high-speed camera, using an image processing algorithm to analyze the footage. Their results supported the claim that the instability threshold is dependent on initial conditions, namely amplitude and wavelength.

This latest paper sheds more light on the structural integrity of fusion capsules used in inertial confinement fusion, taking a closer look at the material properties, the amplitude and wavelength conditions, and the acceleration rate of such materials as they hit the Rayleigh-Taylor instability threshold. The more scientists know about the phase transition from the elastic to the stable phase, the better they can control the conditions and maintain either an elastic or plastic phase, avoiding the instability. Banerjee et al. were able to identify the conditions to maintain the elastic phase, which could inform the design of future pellets for inertial confinement fusion.

That said, the mayonnaise experiments are an analog, orders of magnitude away from the real-world conditions of nuclear fusion, which Banerjee readily acknowledges. He is nonetheless hopeful that future research will improve the predictability of just what happens within the pellets in their high-temperature, high-pressure environments. “We’re another cog in this giant wheel of researchers,” he said. “And we’re all working towards making inertial fusion cheaper and therefore, attainable.”

DOI: Physical Review E, 2024. 10.1103/PhysRevE.109.055103 (About DOIs).

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Broadway embraces particle physics with musical about Higgs boson discovery

culture, Higgs boson, Particle Fever, particle physics, Physics, Science, science documentaries / /

Catch the fever —

The 2013 documentary Particle Fever is being turned into a Broadway musical.

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A collision between subatomic particles in the Large Hadron Collider's CMS detector.

A collision between subatomic particles in the Large Hadron Collider’s CMS detector.

Particle physics is poised to hit the bright lights of Broadway with the adaptation into a musical of the 2013 documentary Particle Fever, which charts the journey to detect the Higgs boson at the world’s largest particle accelerator. According to Deadline Hollywood, the creators described their musical as being filled with “heart, humor, and hope,” calling it an “exploration of the very nature of exploration itself… Particle Fever proves that even the very best theories are often no match for reality.”

(Spoiler: Physicists discovered the Higgs boson in 2012.)

Johns Hopkins University’s David Kaplan was a film student turned theoretical physicist when he came up with the idea for a documentary on the search for the Higgs boson—at the time, the last remaining piece of the Standard Model of Particle Physics yet to be detected. The Large Hadron Collider at CERN was designed for that purpose, although the physics community hoped (in vain thus far) to also discover exciting new physics.

Kaplan has said he originally planned to make the film himself, but his Los Angeles-based sister talked him out of it. Mark Levinson (a physicist turned filmmaker) ended up directing, with Oscar winner Walter Murch handling the editing, sifting through nearly 500 hours of footage—including amateur video footage shot by CERN physicists themselves.

Particle Fever.” height=”427″ src=”https://cdn.arstechnica.net/wp-content/uploads/2024/08/particle1-640×427.jpg” width=”640″>

Enlarge / Physicist David Kaplan interviews Fabiola Gianotti, head of one of the two teams that found the Higgs Boson at CERN, in a still from Particle Fever.

Anthos Media

The project took seven years to complete and made its debut at various small film festivals before enjoying a limited US release in March 2015. It received critical acclaim, and for fans of popular physics, it was delightful to see working physicists like Monica Dunford—then a post-doc working on the ATLAS experiment, now a professor at Heidelberg University—and Nima Arkani-Hamed of the Institute for Advanced Study front and center, highlighting the give-and-take between experiment and theory as they sought to detect the elusive Higgs boson.

Kaplan and his crew were there in July 2012 when the momentous discovery was announced, capturing the standing ovation for an emotional Peter Higgs. It was physics in action, right down to the theorists’ disappointment that the Higgs mass turned out to be about 125 GeV, consistent with many models predicting new physics.

Still, it’s hardly the first documentary that comes to mind when one thinks “musical.” But ROCO Films CEO Annie Roney, whose company distributed the film, had that vision. “It’s already infused with the elements that make a musical memorable and desirable,” she told The New York Times. “It has universal themes of humankind trying to understand the meaning of our lives and our place in the universe. The story celebrates the best in humanity—collaboration, curiosity.” And while she liked the explanations of the heady physics concepts in the film, “I thought that the bigger concepts can be best communicated by music nonverbally.”

Roney has been working to bring that vision to life ever since, tapping noted Broadway playwright David Henry Hwang (M. Butterfly) to write, with music and lyrics by Bear McCreary (Battlestar Galactica, Rings of Power) and Zoe Sarnak (Galileo: A Rock Musical). Leigh Silverman, who just won a Tony for the Broadway musical Suffs, will direct. There’s no word on when we’ll be seeing Particle Fever: The Musical on Boardway, but the group just held the first private reading: a basement industry-only performance featuring songs about particle physics.

Trailer for Particle Fever.

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How Kepler’s 400-year-old sunspot sketches helped solve a modern mystery

astronomy, astrophysics, Johannes Kepler, Physics, Science, solar physics, sun spots / /
A naked-eye sunspot group on 11 May 2024

Enlarge / A naked-eye sunspot group on May 11, 2024. There are typically 40,000 to 50,000 sunspots observed in ~11-year solar cycles.

E. T. H. Teague

A team of Japanese and Belgian astronomers has re-examined the sunspot drawings made by 17th century astronomer Johannes Kepler with modern analytical techniques. By doing so, they resolved a long-standing mystery about solar cycles during that period, according to a recent paper published in The Astrophysical Journal Letters.

Precisely who first observed sunspots was a matter of heated debate in the early 17th century. We now know that ancient Chinese astronomers between 364 and 28 BCE observed these features and included them in their official records. A Benedictine monk in 807 thought he’d observed Mercury passing in front of the Sun when, in reality, he had witnessed a sunspot; similar mistaken interpretations were also common in the 12th century. (An English monk made the first known drawings of sunspots in December 1128.)

English astronomer Thomas Harriot made the first telescope observations of sunspots in late 1610 and recorded them in his notebooks, as did Galileo around the same time, although the latter did not publish a scientific paper on sunspots (accompanied by sketches) until 1613. Galileo also argued that the spots were not, as some believed, solar satellites but more like clouds in the atmosphere or the surface of the Sun. But he was not the first to suggest this; that credit belongs to Dutch astronomer Johannes Fabricus, who published his scientific treatise on sunspots in 1611.

Kepler read that particular treatise and admired it, having made his sunspot observations using a camera obscura in 1607 (published in a 1609 treatise), which he initially thought was a transit of Mercury. He retracted that report in 1618, concluding that he had actually seen a group of sunspots. Kepler made his solar drawings based on observations conducted both in his own house and in the workshop of court mechanic Justus Burgi in Prague.  In the first case, he reported “a small spot in the size of a small fly”; in the second, “a small spot of deep darkness toward the center… in size and appearance like a thin flea.”

The earliest datable sunspot drawings based on Kepler's solar observations with camera obscura in May 1607.

Enlarge / The earliest datable sunspot drawings based on Kepler’s solar observations with camera obscura in May 1607.

Public domain

The long-standing debate that is the subject of this latest paper concerns the period from around 1645 to 1715, during which there were very few recorded observations of sunspots despite the best efforts of astronomers. This was a unique event in astronomical history. Despite only observing some 59 sunspots during this time—compared to between 40,000 to 50,000 sunspots over a similar time span in our current age—astronomers were nonetheless able to determine that sunspots seemed to occur in 11-year cycles.

German astronomer Gustav Spörer noted the steep decline in 1887 and 1889 papers, and his British colleagues, Edward and Annie Maunder, expanded on that work to study how the latitudes of sunspots changed over time. That period became known as the “Maunder Minimum.” Spörer also came up with “Spörer’s law,” which holds that spots at the start of a cycle appear at higher latitudes in the Sun’s northern hemisphere, moving to successively lower latitudes in the southern hemisphere as the cycle runs its course until a new cycle of sunspots begins in the higher latitudes.

But precisely how the solar cycle transitioned to the Maunder Minimum has been far from clear. Reconstructions based on tree rings have produced conflicting data. For instance, one such reconstruction concluded that the gradual transition was preceded either by an extremely short solar cycle of about five years or an extremely long solar cycle of about 16 years. Another tree ring reconstruction concluded the solar cycle would have been of normal 11-year duration.

Independent observational records can help resolve the discrepancy. That’s why Hisashi Hayakawa of Nagoya University in Japan and co-authors turned to Kepler’s drawings of sunspots for additional insight, which predate existing telescopic observations by several years.

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Astronomers find first emission spectra in brightest GRB of all time

astronomy, astrophysics, B.O.A.T., Fermi space telescope, Gamma ray bursts, Physics, Science / /

shine on, you beautiful BOAT —

Chance that first detected emission line is a noise fluctuation is one in half a billion.

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A jet of particles moving at nearly light speed emerges from a massive star in this artist’s concept.

Enlarge / A jet of particles moving at nearly light-speed emerges from a massive star in this artist’s concept of the BOAT.

NASA’s Goddard Space Flight Center Conceptual Image Lab

Scientists have been all aflutter since several space-based detectors picked up a powerful gamma-ray burst (GRB) in October 2022—a burst so energetic that astronomers nicknamed it the BOAT (Brightest Of All Time). Now an international team of astronomers has analyzed an unusual energy peak detected by NASA’s Fermi Gamma-ray Space Telescope and concluded that it was an emission spectra, according to a new paper published in the journal Science. Per the authors, it’s the first high-confidence emission line ever seen in 50 years of studying GRBs.

As reported previously, gamma-ray bursts are extremely high-energy explosions in distant galaxies lasting between mere milliseconds to several hours. There are two classes of gamma-ray bursts. Most (70 percent) are long bursts lasting more than two seconds, often with a bright afterglow. These are usually linked to galaxies with rapid star formation. Astronomers think that long bursts are tied to the deaths of massive stars collapsing to form a neutron star or black hole (or, alternatively, a newly formed magnetar). The baby black hole would produce jets of highly energetic particles moving near the speed of light, powerful enough to pierce through the remains of the progenitor star, emitting X-rays and gamma rays.

Those gamma-ray bursts lasting less than two seconds (about 30 percent) are deemed short bursts, usually emitting from regions with very little star formation. Astronomers think these gamma-ray bursts are the result of mergers between two neutron stars, or a neutron star merging with a black hole, comprising a “kilonova.” That hypothesis was confirmed in 2017 when the LIGO collaboration picked up the gravitational wave signal of two neutron stars merging, accompanied by the powerful gamma-ray bursts associated with a kilonova.

Several papers were published last year reporting on the analytical results of all the observational data. Those findings confirmed that GRB 221009A was indeed the BOAT, appearing especially bright because its narrow jet was pointing directly at Earth. But the various analyses also yielded several surprising results that puzzled astronomers. Most notably, a supernova should have occurred a few weeks after the initial burst, but astronomers didn’t detect one, perhaps because it was very faint, and thick dust clouds in that part of the sky were dimming any incoming light.

Earlier this year, astronomers confirmed that the BOAT came from a supernova, thanks to the telltale signatures of key elements like calcium and oxygen that one would expect to find with a supernova. However, they did not find evidence of the expected heavy elements like platinum and gold, which bears on the longstanding question of the origin of such elements in the universe. The BOAT might just be special in that regard; further data will tell us more.

“It gave me goosebumps”

A few minutes after the BOAT erupted, Fermi’s Gamma-ray Burst Monitor recorded an unusual energy peak. Scientists now say this feature is the first high-confidence emission line ever seen in 50 years of studying GRBs.

The newly detected spectral emission line was likely caused by the collision of matter and anti-matter, according to the authors, producing a pair of gamma rays that are blue-shifted toward higher energies because we are looking into the jet. Having a spectral emission associated with a GRB is important because it can shed light on the specific chemicals involved in the interactions. There have been prior studies reporting possible evidence for absorption or emission lines in other GRBs, but they have usually turned out likely to be statistical noise.

That’s not the case with this latest detection, according to co-author Om Sharan Salafia at INAF-Brera Observatory in Milan, Italy, who added that the odds of this turning out to be a statistical fluctuation “are less than one chance in half a billion.” His INAF colleague and co-author, Maria Edvige Ravasio, said that when she first saw the signal, “it gave me goosebumps.”

Why did astronomers take so long to detect it? When the BOAT first erupted in 2022, it saturated most of the space-based gamma-ray detectors, including the Fermi Space Telescope, making them unable to measure the most intense part of that blast. The emission line didn’t appear until a good five minutes after the burst when it had sufficiently dimmed for Fermi to make a measurement. The spectral emission lasted for about 40 seconds and reached a peak energy of about 12 MeV, compared to 2 or 3 MeB for visible light, per the authors.

Science, 2024. DOI: 10.1126/science.adj3638  (About DOIs).

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Scientists unlock more secrets of Rembrandt’s pigments in The Night Watch

art conservation, chemistry, Physics, pigments, rembrandt, Science, The Night Watch / /

More from operation night watch —

Use of arsenic sulfides for yellow, orange/red hues adds to artist’s known pigment palette.

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The Nightwatch, or Militia Company of District II under the Command of Captain Frans Banninck Cocq (1642)

Enlarge / Rembrandt’s The Night Watch underwent many chemical and mechanical alterations over the last 400 years.

Public domain

Since 2019, researchers have been analyzing the chemical composition of the materials used to create Rembrandt’s masterpiece, The Night Watch, as part of the Rijksmuseum’s ongoing Operation Night Watch, devoted to its long-term preservation. Chemists at the Rijksmuseum and the University of Amsterdam have now detected unusual arsenic-based yellow and orange/red pigments used to paint the duff coat of one of the central figures in the painting, according to a recent paper in the journal Heritage Science. It’s a new addition to Rembrandt’s known pigment palette that further adds to our growing body of knowledge about the materials he used.

As previously reported, past analyses of Rembrandt’s paintings identified many pigments the Dutch master used in his work, including lead white, multiple ochres, bone black, vermilion, madder lake, azurite, ultramarine, yellow lake, and lead-tin yellow, among others. The artist rarely used pure blue or green pigments, with Belshazzar’s Feast being a notable exception. (The Rembrandt Database is the best resource for a comprehensive chronicling of the many different investigative reports.)

Early last year, the researchers at Operation Night Watch found rare traces of a compound called lead formate in the painting—surprising in itself, but the team also identified those formates in areas where there was no lead pigment, white or yellow. It’s possible that lead formates disappear fairly quickly, which could explain why they have not been detected in paintings by the Dutch Masters until now. But if that is the case, why didn’t the lead formate disappear in The Night Watch? And where did it come from in the first place?

Hoping to answer these questions, the team whipped up a model of “cooked oils” from a 17th-century recipe and analyzed those model oils with synchrotron radiation. The results supported their hypothesis that the oil used for light parts of the painting was treated with an alkaline lead drier. The fact that The Night Watch was revarnished with an oil-based varnish in the 18th century complicates matters, as this may have provided a fresh source of formic acid, such that different regions of the painting rich in lead formates may have formed at different times in the painting’s history.

Last December, the team turned its attention to the preparatory layers applied to the canvas. It’s known that Rembrandt used a quartz-clay ground for The Night Watch—the first time he had done so, perhaps because the colossal size of the painting “motivated him to look for a cheaper, less heavy and more flexible alternative for the ground layer” than the red earth, lead white, and cerussite he was known to use on earlier paintings.

The Night Watch. (b) Detail of figure’s embroidered gold buff coat. (c) X-ray diffraction image of coat detail showing arsenic. (d) Stereomicroscope image showing arsenic hot spot.” height=”531″ src=”https://cdn.arstechnica.net/wp-content/uploads/2024/07/rembrandt1-640×531.jpg” width=”640″>

Enlarge / (a) Rembrandt’s The Night Watch. (b) Detail of figure’s embroidered gold buff coat. (c) X-ray diffraction image of coat detail showing arsenic. (d) Stereomicroscope image showing arsenic hot spot.

N. De Keyser et al., 2024

They used 3D X-ray methods to capture more detail, revealing the presence of an unknown (and unexpected) lead-containing layer located just underneath the ground layer. This could be due to using a lead compound added to the oil used to prepare the canvas as a drying additive—perhaps to protect the painting from the damaging effects of humidity. (Usually a glue sizing was used before applying the ground layer.) The lead layer discovered last year could be the reason for the unusual lead protrusions in areas of The Night Watch, since there are no other lead-containing compounds in the paint. It’s possible that lead migrated into the painting’s ground layer from the lead-oil preparatory layer below.

An intentional combination

The presence of arsenic sulfides in The Night Watch appears to be an intentional pigment combination by Rembrandt, according to the authors of this latest paper. Artists throughout history have used naturally occurring orpiment and realgar, as well as artificial arsenic sulfide pigments, to get yellow, orange, and red hues in their paints. Orpiment was also used for medicinal purposes, in hair removal creams and oils, in wax seals, yellow ink, bookbinder green (mixed with indigo), and for the treatment or coating of metals like silver.

However, the use of artificial arsenic sulfides has rarely been reported in artworks, although they are mentioned in multiple artists’ treatises dating back to the 15th century. Earlier work using advanced analytical techniques such as Raman spectroscopy and X-ray powder diffraction revealed that Rembrandt used arsenic sulfide pigments (artificial orpiment) in two late paintings: The Jewish Bride (c 1665) and The Man in a Red Cap (c 1665).

For this latest work, Nouchka De Keyser of the Rijksmuseum and co-authors used macroscopic X-ray fluorescence imaging to map The Night Watch, which revealed the presence of arsenic and sulfur in the doublet sleeves and embroidered buff coat worn by Lt. Willem Van Ruytenburch, i.e., the central figure to the right of Captain Frans Bannick Cocq in the painting. The researchers initially assumed that this was due to Rembrandt’s use of orpiment for yellow hues and realgar for red hues.

Ars Vitraria Experimentalis, 1679. (c) Page from the Weimar taxa of 1674 including prices for white, yellow, and red arsenic.” height=”300″ src=”https://cdn.arstechnica.net/wp-content/uploads/2024/07/rembrandt2-640×300.jpg” width=”640″>

Enlarge / (a, b) Pages from Johann Kunckel’s Ars Vitraria Experimentalis, 1679. (c) Page from the Weimar taxa of 1674 including prices for white, yellow, and red arsenic.

N. De Keyser et al., 2024

To learn more, they took tiny samples and analyzed them with light microscopy, micro-Raman spectroscopy, electron microscopy, and X-ray powder diffraction. They found the yellow particles were actually pararealgar while the orange to red particles were semi-amorphous pararealgar. These are more unusual arsenic sulfide components, typically associated with degradation products from either the natural minerals or their artificial equivalents as they age.

But De Keyser et al. concluded that the presence of these components was actually an intentional mixture, based on their perusal of multiple historical sources and catalogs of collection cabinets with long lists of various arsenic sulfides. There was clearly contemporary knowledge of manipulating both natural and artificial arsenic sulfides to get different shades of yellow, orange, and red.

They also found vermilion and lead-tin yellow in the paint mixture; Rembrandt was known to use these to add brightness and intensity to his paintings. In the case of The Night Watch, “Rembrandt clearly aimed for a bright orange tone with a high color strength that allowed him to create an illusion of the gold thread embroidery in Van Ruytenburch’s costume,” the authors wrote. “The artificial orange to red arsenic sulfide might have offered different optical and rheological paint properties as compared to the mineral form of orpiment and realgar.”

In addition, the team examined paint samples from different artists known to use arsenic sulfides—whose works are also part of the Rijksmuseum collection—and found a similar mixture of pigments in a painting by Rembrandt’s contemporary, Willem Kalf. “It is evidence that a variety of natural and artificial arsenic sulfides were manufactured and traded during Rembrandt’s time and were available in Amsterdam,” the authors wrote—most likely imported, since the Dutch Republic did not have considerable mining resources.

Heritage Science, 2024. DOI: 10.1186/s40494-024-01350-x  (About DOIs).

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Researchers build ultralight drone that flies with onboard solar

drone, materials science, Physics, robotics, Science, solar power / /

Where does it go? It goes up! —

Bizarre design uses a solar-powered motor that’s optimized for weight.

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Image of a metallic object composed from top to bottom of a propeller, a large cylinder with metallic panels, a stalk, and a flat slab with solar panels and electronics.

Enlarge / The CoulombFly doing its thing.

On Wednesday, researchers reported that they had developed a drone they’re calling the CoulombFly, which is capable of self-powered hovering for as long as the Sun is shining. The drone, which is shaped like no aerial vehicle you’ve ever seen before, combines solar cells, a voltage converter, and an electrostatic motor to drive a helicopter-like propeller—with all components having been optimized for a balance of efficiency and light weight.

Before people get excited about buying one, the list of caveats is extensive. There’s no onboard control hardware, and the drone isn’t capable of directed flight anyway, meaning it would drift on the breeze if ever set loose outdoors. Lots of the components appear quite fragile, as well. However, the design can be miniaturized, and the researchers built a version that weighs only 9 milligrams.

Built around a motor

One key to this development was the researchers’ recognition that most drones use electromagnetic motors, which involve lots of metal coils that add significant weight to any system. So, the team behind the work decided to focus on developing a lightweight electrostatic motor. These rely on charge attraction and repulsion to power the motor, as opposed to magnetic interactions.

The motor the researchers developed is quite large relative to the size of the drone. It consists of an inner ring of stationary charged plates called the stator. These plates are composed of a thin carbon-fiber plate covered in aluminum foil. When in operation, neighboring plates have opposite charges. A ring of 64 rotating plates surrounds that.

The motor starts operating when the plates in the outer ring are charged. Since one of the nearby plates on the stator will be guaranteed to have the opposite charge, the pull will start the rotating ring turning. When the plates of the stator and rotor reach their closest approach, thin wires will make contact, allowing charges to transfer between them. This ensures that the stator and rotor plates now have the same charge, converting the attraction to a repulsion. This keeps the rotor moving, and guarantees that the rotor’s plate now has the opposite charge from the next stator plate down the line.

These systems typically require very little in the way of amperage to operate. But they do require a large voltage difference between the plates (something we’ll come back to).

When hooked up to a 10-centimeter, eight-bladed propeller, the system could produce a maximum lift of 5.8 grams. This gave the researchers clear weight targets when designing the remaining components.

Ready to hover

The solar power cells were made of a thin film of gallium arsenide, which is far more expensive than other photovoltaic materials, but offers a higher efficiency (30 percent conversion compared to numbers that are typically in the mid-20s). This tends to provide the opposite of what the system needs: reasonable current at a relatively low voltage. So, the system also needed a high-voltage power converter.

Here, the researchers sacrificed efficiency for low weight, arranging a bunch of voltage converters in series to create a system that weighs just 1.13 grams, but steps the voltage up from 4.5 V all the way to 9.0 kV. But it does so with a power conversion efficiency of just 24 percent.

The resulting CoulombFly is dominated by the large cylindrical motor, which is topped by the propeller. Suspended below that is a platform with the solar cells on one side, balanced out by the long, thin power converter on the other.

Meet the CoulombFly.

To test their system, the researchers simply opened a window on a sunny day in Beijing. Starting at noon, the drone took off and hovered for over an hour, and all indications are that it would have continued to do so for as long as the sunlight provided enough power.

The total system required just over half a watt of power to stay aloft. Given a total mass of 4 grams, that works out to a lift-to-power efficiency of 7.6 grams per watt. But a lot of that power is lost during the voltage conversion. If you focus on the motor alone, it only requires 0.14 watts, giving it a lift-to-power efficiency of over 30 grams per watt.

The researchers provide a long list of things they could do to optimize the design, including increasing the motor’s torque and propeller’s lift, placing the solar cells on structural components, and boosting the efficiency of the voltage converter. But one thing they don’t have to optimize is the vehicle’s size since they already built a miniaturized version that’s only 8 millimeters high and weighs just 9 milligrams but is able to generate a milliwatt of power that turns its propeller at over 15,000 rpm.

Again, all this is done without any onboard control circuitry or the hardware needed to move the machine anywhere—they’re basically flying these in cages to keep them from wandering off on the breeze. But there seems to be enough leeway in the weight that some additional hardware should be possible, especially if they manage some of the potential optimizations they mentioned.

Nature, 2024. DOI: 10.1038/s41586-024-07609-4  (About DOIs).

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ITER fusion reactor to see further delays, with operations pushed to 2034

delays, fusion, ITER, Physics, Science / /

Better late than never? —

Full fusion power won’t happen until nearly 2040 on new timeline.

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Image of a large metal vessel with a number of holes cut into it.

Enlarge / One of the components of the reactor during leak testing.

On Tuesday, the people managing the ITER experimental fusion reactor announced that a combination of delays and altered priorities meant that its first-of-its-kind hardware wouldn’t see plasma until 2036, with the full-energy deuterium-tritium fusion pushed back to 2039. The latter represents a four-year delay relative to the previous roadmap. While the former is also a delay, it’s due in part to changing priorities.

COVID and construction delays

ITER is an attempt to build a fusion reactor that’s capable of sustaining plasmas that allow it to operate well beyond the break-even point, where the energy released by fusion reactions significantly exceeds the energy required to create the conditions that enable those reactions. It’s meant to hit that milestone by scaling up a well-understood design called a tokamak.

But the problem has been plagued by delays and cost overruns nearly from its start. At early stages, many of these stemmed from changes in designs necessitated by a better and improved understanding of plasmas held at extreme pressures and temperatures due to better modeling capabilities and a better understanding of the behavior of plasmas in smaller reactions.

The latest delays are due to more prosaic reasons. One of them is the product of the international nature of the collaboration, which sees individual components built by different partner organizations before assembly at the reactor site in France. The pandemic, unsurprisingly, severely disrupted the production of a lot of these components, and the project’s structure meant that alternate suppliers couldn’t be used (assuming alternate suppliers of one-of-a-kind hardware existed in the first place).

The second problem relates to the location of the reactor in France. The country’s nuclear safety regulator had concerns about the assembly of some of the components and halted construction on the reactor.

High energy from the start

During the re-evaluation of the schedule that these delays would necessitate, the organization that manages ITER re-assessed some of its priorities. The previous schedule would have seen getting plasma into the machine prioritized, seeing relatively low-energy hydrogen plasmas put into the machine before all of the final hardware was complete. This would necessitate an extended shutdown after initial experiments before the reactor could be used at progressively higher energies, using more potent deuterium and deuterium/tritium plasmas.

In the previous schedule, the low-energy, hydrogen-only plasmas would have started testing in 2025, a target date that the delays have made completely unrealistic. Instead, they’ll now happen in 2034. However, rather than being a set of brief demonstrations, these experiments will continue for over two years and reach much higher energies. So, while having plasma in the machine will be delayed by nearly a decade, the system’s magnets will reach power only three years later than expected under the previous plan.

Full power operations using a deuterium/tritium fuel mix will be set back by four years. Even if this new schedule is kept, however, that won’t be until 2039.

So, we’re looking at 15 years even if there are no further delays. But the potential for said delays likely went up, as the announcement indicates that ITER will be switching to a different material (from beryllium to tungsten) for the construction of the inner wall that faces the plasma. This will be more relevant since many other projects, including commercial fusion startups, are planning on using tungsten. But it may still add a new suite of technical and manufacturing delays.

The risk for ITER, however, is that all of these delays cause some of the nations that are supporting the project to back out. Or, if some of the commercial fusion startups that have launched would have it, create the risk that fusion will already be here by the time ITER is ready to run.

ITER fusion reactor to see further delays, with operations pushed to 2034 Read More »

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Supermassive black hole roars to life as astronomers watch in real time

active galactic nuclei, astronomy, astrophysics, black holes, Physics, Science, Very Large Telescope / /

Sleeping Beauty —

A similar awakening may one day occur with the Milky Way’s supermassive black hole

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Artist’s animation of the black hole at the center of SDSS1335+0728 awakening in real time—a first for astronomers.

In December 2019, astronomers were surprised to observe a long-quiet galaxy, 300 million light-years away, suddenly come alive, emitting ultraviolet, optical, and infrared light into space. Far from quieting down again, by February of this year, the galaxy had begun emitting X-ray light; it is becoming more active. Astronomers think it is most likely an active galactic nucleus (AGN), which gets its energy from supermassive black holes at the galaxy’s center and/or from the black hole’s spin. That’s the conclusion of a new paper accepted for publication in the journal Astronomy and Astrophysics, although the authors acknowledge the possibility that it might also be some kind of rare tidal disruption event (TDE).

The brightening of SDSS1335_0728 in the constellation Virgo, after decades of quietude, was first detected by the Zwicky Transient Facility telescope. Its supermassive black hole is estimated to be about 1 million solar masses. To get a better understanding of what might be going on, the authors combed through archival data and combined that with data from new observations from various instruments, including the X-shooter, part of the Very Large Telescope (VLT) in Chile’s Atacama Desert.

There are many reasons why a normally quiet galaxy might suddenly brighten, including supernovae or a TDE, in which part of the shredded star’s original mass is ejected violently outward. This, in turn, can form an accretion disk around the black hole that emits powerful X-rays and visible light. But these events don’t last nearly five years—usually not more than a few hundred days.

So the authors concluded that the galaxy has awakened and now has an AGN. First discovered by Carl Seyfert in 1943, the glow is the result of the cold dust and gas surrounding the black hole, which can form orbiting accretion disks. Gravitational forces compress the matter in the disk and heat it to millions of degrees Kelvin, producing radiation across the electromagnetic spectrum.

Alternatively, the activity might be due to an especially long and faint TDE—the longest and faintest yet detected, if so. Or it could be an entirely new phenomenon altogether. So SDSS1335+0728 is a galaxy to watch. Astronomers are already preparing for follow-up observations with the VLT’s Multi Unit Spectroscopic Explorer (MUSE) and Extremely Large Telescope, among others, and perhaps even the Vera Rubin Observatory slated to come online next summer. Its Large Synoptic Survey Telescope (LSST) will be capable of imaging the entire southern sky continuously, potentially capturing even more galaxy awakenings.

“Regardless of the nature of the variations, [this galaxy] provides valuable information on how black holes grow and evolve,” said co-author Paula Sánchez Sáez, an astronomer at the European Southern Observatory in Germany. “We expect that instruments like [these] will be key in understanding [why the galaxy is brightening].”

There is also a supermassive black hole at the center of our Milky Way galaxy (Sgr A*), but there is not yet enough material that has accreted for astronomers to pick up any emitted radiation, even in the infrared. So, its galactic nucleus is deemed inactive. It may have been active in the past, and it’s possible that it will reawaken again in a few million (or even billion) years when the Milky Way merges with the Andromeda Galaxy and their respective supermassive black holes combine. Only much time will tell.

Astronomy and Astrophysics, 2024. DOI: 10.1051/0004-6361/202347957  (About DOIs).

Listing image by ESO/M. Kornmesser

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Polarized light yields fresh insight into mysterious fast radio bursts

astronomy, astrophysics, CHIME, fast radio bursts, Physics, Science / /

CHIME-ing in —

Scientists looked at how polarization changed direction to learn more about origins

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Artist’s rendition of how the angle of polarized light from an FRB changes as it journeys through space.

Enlarge / Artist’s rendition of how the angle of polarized light from a fast radio burst changes as it journeys through space.

CHIME/Dunlap Institute

Astronomers have been puzzling over the origins of mysterious fast radio bursts (FRBs) since the first one was spotted in 2007. Researchers now have their first look at non-repeating FRBs, i.e., those that have only produced a single burst of light to date. The authors of a new paper published in The Astrophysical Journal looked specifically at the properties of polarized light emitting from these FRBs, yielding further insight into the origins of the phenomenon. The analysis supports the hypothesis that there are different origins for repeating and non-repeating FRBs.

“This is a new way to analyze the data we have on FRBs. Instead of just looking at how bright something is, we’re also looking at the angle of the light’s vibrating electromagnetic waves,” said co-author Ayush Pandhi, a graduate student at the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics. “It gives you additional information about how and where that light is produced and what it has passed through on its journey to us over many millions of light years.”

As we’ve reported previously, FRBs involve a sudden blast of radio-frequency radiation that lasts just a few microseconds. Astronomers have over a thousand of them to date; some come from sources that repeatedly emit FRBs, while others seem to burst once and go silent. You can produce this sort of sudden surge of energy by destroying something. But the existence of repeating sources suggests that at least some of them are produced by an object that survives the event. That has led to a focus on compact objects, like neutron stars and black holes—especially a class of neutron stars called magnetars—as likely sources.

There have also been many detected FRBs that don’t seem to repeat at all, suggesting that the conditions that produced them may destroy their source. That’s consistent with a blitzar—a bizarre astronomical event caused by the sudden collapse of an overly massive neutron star. The event is driven by an earlier merger of two neutron stars; this creates an unstable intermediate neutron star, which is kept from collapsing immediately by its rapid spin.

In a blitzar, the strong magnetic fields of the neutron star slow down its spin, causing it to collapse into a black hole several hours after the merger. That collapse suddenly deletes the dynamo powering the magnetic fields, releasing their energy in the form of a fast radio burst.

So the events we’ve been lumping together as FRBs could actually be the product of two different events. The repeating events occur in the environment around a magnetar. The one-shot events are triggered by the death of a highly magnetized neutron star within a few hours of its formation. Astronomers announced the detection of a possible blitzar potentially associated with an FRB last year.

Only about 3 percent of FRBs are of the repeating variety. Per Pandhi, this is the first analysis of the other 97 percent of non-repeating FRBs, using data from Canada’s CHIME instrument (Canadian Hydrogen Intensity Mapping Experiment). CHIME was built for other observations but is sensitive to many of the wavelengths that make up an FRB. Unlike most radio telescopes, which focus on small points in the sky, CHIME scans a huge area, allowing it to pick out FRBs even though they almost never happen in the same place twice.

Pandhi et al. decided to investigate how the direction of the light polarization from 128 non-repeating FRBs changes to learn more about the environments in which they originated. The team found that the polarized light from non-repeating FRBs changes both with time and with different colors of light. They concluded that this particular sample of non-repeating FRBs is either a separate population or more evolved versions of these kinds of FRBs that are part of a population that originated in less extreme environments with lower burst rates. That’s in keeping with the notion that non-repeating FRBs are quite different from their rarer repeating FRBs.

The Astrophysical Journal, 2024. DOI: 10.3847/1538-4357/ad40aa  (About DOIs).

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How you can make cold-brew coffee in under 3 minutes using ultrasound

acoustic cavitation, acoustics, bubbles, chemistry, coffee brewing, cold brew coffee, Food science, Physics, Science, sonochemistry, ultrasound / /

Save yourself a few hours —

A “sonication” time between 1 and 3 minutes is ideal to get the perfect cold brew.

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UNSW Sydney engineers developed a new way to make cold brew coffee in under three minutes without sacrificing taste.

Enlarge / UNSW Sydney engineers developed a new way to make cold brew coffee in under three minutes without sacrificing taste.

University of New South Wales, Sydney

Diehard fans of cold-brew coffee put in a lot of time and effort for their preferred caffeinated beverage. But engineers at the University of New South Wales, Sydney, figured out a nifty hack. They rejiggered an existing espresso machine to accommodate an ultrasonic transducer to administer ultrasonic pulses, thereby reducing the brewing time from 12 to 24 hours to just under three minutes, according to a new paper published in the journal Ultrasonics Sonochemistry.

As previously reported, rather than pouring boiling or near-boiling water over coffee grounds and steeping for a few minutes, the cold-brew method involves mixing coffee grounds with room-temperature water and letting the mixture steep for anywhere from several hours to two days. Then it is strained through a sieve to filter out all the sludge-like solids, followed by filtering. This can be done at home in a Mason jar, or you can get fancy and use a French press or a more elaborate Toddy system. It’s not necessarily served cold (although it can be)—just brewed cold.

The result is coffee that tastes less bitter than traditionally brewed coffee. “There’s nothing like it,” co-author Francisco Trujillo of UNSW Sydney told New Scientist. “The flavor is nice, the aroma is nice and the mouthfeel is more viscous and there’s less bitterness than a regular espresso shot. And it has a level of acidity that people seem to like. It’s now my favorite way to drink coffee.”

While there have been plenty of scientific studies delving into the chemistry of coffee, only a handful have focused specifically on cold-brew coffee. For instance, a 2018 study by scientists at Thomas Jefferson University in Philadelphia involved measuring levels of acidity and antioxidants in batches of cold- and hot-brew coffee. But those experiments only used lightly roasted coffee beans. The degree of roasting (temperature) makes a significant difference when it comes to hot-brew coffee. Might the same be true for cold-brew coffee?

To find out, the same team decided in 2020 to explore the extraction yields of light-, medium-, and dark-roast coffee beans during the cold-brew process. They used the cold-brew recipe from The New York Times for their experiments, with a water-to-coffee ratio of 10:1 for both cold- and hot-brew batches. (Hot brew normally has a water-to-coffee ratio of 20:1, but the team wanted to control variables as much as possible.) They carefully controlled when water was added to the coffee grounds, how long to shake (or stir) the solution, and how best to press the cold-brew coffee.

The team found that for the lighter roasts, caffeine content and antioxidant levels were roughly the same in both the hot- and cold-brew batches. However, there were significant differences between the two methods when medium- and dark-roast coffee beans were used. Specifically, the hot-brew method extracts more antioxidants from the grind; the darker the bean, the greater the difference. Both hot- and cold-brew batches become less acidic the darker the roast.

The new faster cold brew system subjects coffee grounds in the filter basket to ultrasonic sound waves from a transducer, via a specially adapted horn.

Enlarge / The new faster cold brew system subjects coffee grounds in the filter basket to ultrasonic sound waves from a transducer, via a specially adapted horn.

UNSW/Francisco Trujillo

That gives cold brew fans a few handy tips, but the process remains incredibly time-consuming; only true aficionados have the patience required to cold brew their own morning cuppa. Many coffee houses now offer cold brews, but it requires expensive, large semi-industrial brewing units and a good deal of refrigeration space. According to Trujillo, the inspiration for using ultrasound to speed up the process arose from failed research attempts to extract more antioxidants. Those experiments ultimately failed, but the setup produced very good coffee.

Trujillo et al. used a Breville Dual Boiler BES920 espresso machine for their latest experiments, with a few key modifications. They connected a bolt-clawed transducer to the brewing basket with a metal horn. They then used the transducer to inject 38.8 kHz sound waves through the walls at several different points, thereby transforming the filter basket into a powerful ultrasonic reactor.

The team used the machine’s original boiler but set it up to be independently controlled it with an integrated circuit to better manage the temperature of the water. As for the coffee beans, they picked Campos Coffee’s Caramel & Rich Blend (a medium roast). “This blend combines fresh, high-quality specialty coffee beans from Ethiopia, Kenya, and Colombia, and the roasted beans deliver sweet caramel, butterscotch, and milk chocolate flavors,” the authors wrote.

There were three types of samples for the experiments: cold brew hit with ultrasound at room temperature for one minute or for three minutes, and cold brew prepared with the usual 24-hour process. For the ultrasonic brews, the beans were ground into a fine grind typical for espresso, while a slightly coarser grind was used for the traditional cold-brew coffee.

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