Six years ago, tour guide Brenden Miles was traveling down the Kinabatangan River in the Malaysian part of Borneo, when he spotted an odd-looking primate he had never seen before. He snapped a few pictures of the strange monkey and, on reaching home, checked his images.

“At first, I thought it could be a morph of the silvered leaf monkey,” meaning a member of the species with rare color variation, Miles says. But then he noticed other little details. “Its nose was long like that of a proboscis monkey, and its tail was thicker than that of a silvered leaf [monkey],” he says. He posted a picture of the animal on Facebook and forgot all about it.

Now, an analysis of that photo and others suggests that the “mystery monkey” is a hybrid of two distantly related primate species that share the same fragmented habitat.
The putative offspring was produced when a male proboscis monkey (Nasalis larvatus) mated with a female silvered leaf monkey (Trachypithecus cristatus), researchers suggest April 26 in the International Journal of Primatology. And that conclusion has the scientists worried about the creature’s parent species.

Hybridization between closely related organisms has been observed in captivity and occasionally in the wild (SN: 7/23/21). “But hybridization across genera, that’s very rare,” says conservation practitioner Ramesh Boonratana, the regional vice-chair for Southeast Asia for the International Union for Conservation of Nature’s primate specialist group.

Severe habitat loss, fragmentation and degradation caused by expanding palm oil plantations along the Kinabatangan River could explain how the possible hybrid came to be, says primatologist Nadine Ruppert.

“Different species — even from the same genus — when they share a habitat, they may interact with each other, but they may usually not mate. This kind of cross-genera hybridization happens only when there is some ecological pressure,” says Ruppert, of the Universiti Sains Malaysia in Penang Island.

The state of Sabah, where Kinabatangan River is located, lost about 40 percent of its forest cover from 1973 to 2010, with logging and palm oil plantations being the main drivers of deforestation, a study in 2014 found.
“In certain areas, both [monkey] species are confined to small forest fragments along the river,” Ruppert says. This leads to competition for food, mates and other resources. “The animals cannot disperse and, in this case, the male of the larger species — the proboscis monkey — can easily displace the male silvered leaf monkey.”

Since 2016, there have been some more documented sightings of the mystery monkey, though these have been sporadic. The infrequent sightings and the COVID-19 pandemic has, for now, prevented researchers from gathering fecal samples for genetic analysis to reveal the monkey’s identity. Instead, Ruppert and colleagues compared images of the possible hybrid with those of the parent species, both visually as well as by using limb ratios. “If the individual was from one of the two parent species, all its measurements would be similar to that of one species,” Ruppert says. “But that is not the case with this animal.”

A photograph of a male proboscis monkey mating with a female silvered leaf monkey, along with anecdotes from boat operators and tour guides about a single male proboscis monkey hanging around a troop of female silvered leaf monkeys, has added further weight to the researchers’ conclusion.

The mystery monkey is generating a lot of excitement in the area, but Ruppert is concerned for the welfare of both proposed parent species. The International Union for Conservation of Nature classifies proboscis monkeys as endangered and silvered leaf monkeys as vulnerable. “The hybrid is gorgeous, but we don’t want to see more of them,” Ruppert says. “Both species should have a large enough habitat, dispersal opportunities and enough food to conduct their natural behaviors in the long term.”

Increasing habitat loss or fragmentation in Borneo and elsewhere as a result of changing land uses or climate change could lead to more instances of mating — or at least, attempts at mating — between species or even genera, Boonratana says.

The mystery monkey was last photographed in September of 2020 with swollen breasts and holding a baby, suggesting that the animal is a fertile female. That’s another surprising development, the researchers say, because most hybrids tend to be sterile.

When a star gets too close to a black hole, sparks fly. And, potentially, so do subatomic particles called neutrinos.

A dramatic light show results when a supermassive black hole rips apart a wayward star. Now, for the second time, a high-energy neutrino has been spotted that may have come from one of these “tidal disruption events,” researchers report in a study accepted in Physical Review Letters.

These lightweight particles, which have no electric charge, careen across the cosmos and can be detected upon their arrival at Earth. The origins of such zippy neutrinos are a big mystery in physics. To create them, conditions must be just right to drastically accelerate charged particles, which would then produce neutrinos. Scientists have begun lining up likely candidates for cosmic particle accelerators. In 2020, researchers reported the first neutrino linked to a tidal disruption event (SN: 5/26/20). Other neutrinos have been tied to active galactic nuclei, bright regions at the centers of some galaxies (SN: 7/12/18).
Discovered in 2019, the tidal disruption event reported in the new study stood out. “It was extraordinarily bright; it’s really one of the brightest transients ever seen,” says astroparticle physicist Marek Kowalski of Deutsches Elektronen-Synchrotron, or DESY, in Zeuthen, Germany.

Transients are short-lived flares in the sky, such as tidal disruption events and exploding stars called supernovas. Further observations of the brilliant outburst revealed that it shone in infrared, X-rays and other wavelengths of light.

Roughly a year after the flare’s discovery, the Antarctic neutrino observatory IceCube spotted a high-energy neutrino. By tracing the particle’s path backward, researchers determined that the neutrino came from the flare’s vicinity.

The matchup between the two events could be a coincidence. But when combined with the previous neutrino that was tied to a tidal disruption event, the case gets stronger. The probability of finding two such associations by chance is only about 0.034 percent, the researchers say.

It’s still not clear how tidal disruption events would produce high-energy neutrinos. In one proposed scenario, a jet of particles flung away from the black hole could accelerate protons, which could interact with surrounding radiation to produce the speedy neutrinos.

‘We need more data … in order to say that these are real neutrino sources or not,” says astrophysicist Kohta Murase of Penn State University, a coauthor of the new study. If the link between the neutrinos and tidal disruption events is real, he’s optimistic that researchers won’t have to wait too long. “If this is the case, we will see more.”

But scientists don’t all agree that the flare was a tidal disruption event. Instead, it could have been an especially bright type of supernova, astrophysicist Irene Tamborra and colleagues suggest in the April 20 Astrophysical Journal.

In such a supernova, it’s clear how energetic neutrinos could be produced, says Tamborra, of the Niels Bohr Institute at the University of Copenhagen. Protons accelerated by the supernova’s shock wave could collide with protons in the medium that surrounds the star, producing other particles that could decay to make neutrinos.

It’s only recently that observations of high-energy neutrinos and transients have improved enough to enable scientists to find potential links between the two. “It’s exciting,” Tamborra says. But as the debate over the newly detected neutrino’s origin shows, “at the same time, it’s uncovering many things that we don’t know.

The pandemic has entered a murky stage, and social norms are quickly shifting, something I’ve thought a lot about lately. Many people are testing at home, or not at all. Here in Vermont, where I live, you can pick up a type of PCR test that can be taken at home. But state officials both here and elsewhere are no longer carefully monitoring the results of these tests, which means that the actual spread of coronavirus in the U.S. population remains unclear (SN: 4/22/22).

For a few weeks, rumors of a stealth COVID-19 wave have been circulating both in the media and on my Twitter feed. Now cases and hospitalizations are rising, as are the levels of coronavirus in wastewater. That suggests that more cases, and ultimately deaths, could follow.
Even with rising caseloads and a vaccination rate that has flatlined at about 66 percent of the eligible population, the American public has largely begun to move on from the COVID-19 crisis. People are shedding their masks, eating out, attending concerts, traveling to far-flung locations, having large, indoor weddings and doing all the social things that people tend to do when left to their own devices.

The 2,600-person White House Correspondents’ Association dinner late last month is a case in point. Just as host Trevor Noah prophesied, many of those in attendance have since tested positive for COVID-19, including U.S. Secretary of State Antony Blinken and reporters from NBC, ABC, the Washington Post, Politico and other media outlets. And those who almost certainly knew better — cue White House Coronavirus Response Coordinator Ashish Jha — nonetheless made an appearance.

Myriad quirks related to human behavior undoubtedly underpin these arguably poor choices. The Decision Lab website has a list of the biases and mental shortcuts people use to make decisions. The one that caught my eye is social norms. This particular quirk outlines what behaviors people deem appropriate in a given situation.

I started thinking about social norms while writing a feature on how to get people in the United States to eat less meat when the practice is so, well, normal (SN: 5/11/22). Social norms, my research informed me, vary with the group one is hanging out with and one’s environs. “We rapidly switch our perspective depending on the context of the situation we find ourselves in,” writes marketing expert John Laurence on the Decision Lab site.

I might have found this idea of rapid switching suspect had I not recently experienced the phenomenon. My husband’s Disney-phile brother and his wife had been planning a family reunion in Disney World in Florida since the start of the pandemic. And I, a curmudgeonly sort not prone to feeling the magic, long ago agreed to go on the condition that other people do all the planning. And so it was, after multiple COVID-related postponements, that my kids, my husband and I landed in Orlando on a blisteringly hot April day.

Disney normal, I soon learned, bore little resemblance to Vermont normal. This was obvious immediately from people’s attire. All around me parents and kids dressed in coordinated outfits and matching Mickey Mouse ears. (Apologies to my kids — your mom missed the fashion memo.)
Social norms almost certainly arose to foster cohesion among our earliest ancestors, who needed solidarity to hunt large prey, share limited resources and ward off predators and enemy tribes. In-group norms also provide humans with a sense of belonging, which research suggests is vital for our overall health. A meta-analysis of more than 3.4 million people followed for an average of seven years showed that the likelihood of dying during the study period increased by 26 percent for participants who reported feeling alone (SN: 3/29/20).

Not surprisingly, then, one of the strongest drivers of human behavior is to seek out belonging. At Disney, that quest means blocking out the reality that exists just outside the fiefdom. Wars, climate crises, political fighting and the like have no place within those magical walls. Nor do reminders of a global health crisis that, according to the latest World Health Organization estimates, has thus far killed nearly 15 million people worldwide.

Within Disney’s walls, throngs of mostly maskless tourists packed onto iconic rides and into restaurants. When halfway through our trip, a Florida judge ruled that masks could not be mandated on public transit, nary a mask was to be seen on buses shuttling people to the Magic Kingdom and Epcot Center. And everywhere, all the time, people seemed to be coughing, sniffling or blowing their noses.

As a science reporter covering COVID-19, I certainly knew that I should keep my mask on. And yet, my resolve soon faltered. My kids pointed out that no one else was masking, not even my typically rule-following relatives. Donning my mask meant confessing that I was not reveling in the sparkle and glitz and magic and making all too obvious to my beloved extended family that I did not, in fact, belong. I kept my face covering in my pocket.

Humans’ tendency toward conformity is not all bad. In a now classic study from the 1980s, researchers investigated how to reduce water consumption in drought-prone California. Signs at the University of California, Santa Cruz asking students to turn off the shower while soaping up led to only 6 percent compliance. So researchers recruited male students to serve as norm-setting role models. These role models would hang out in the communal shower until they heard another student come in, and then soap up with the water off. When one role model soaped with the shower off, roughly half of the unwitting students also began turning off their faucets at soaping time. Compliance jumped to 67 percent when two role models followed the sign.

But conformity can also distort how we make decisions. For instance, in the summer of 2020, when the pandemic was still new, researchers asked 23,000 people in Mexico to predict how a fictional woman named Mariana would decide whether or not to attend a birthday party. Most participants believed Mariana should not attend. But when they read a sentence suggesting her friends would attend or that others approved of the party, their predictions that Mariana would also go increased by 25 percent, researchers reported in PLOS ONE.

My decision to conform to Disney normal ended predictably — with a positive COVID-19 test. After weeks of coughing and sleepless nights, though, my frustration is less directed at myself than at political leaders who so blithely ignore both epidemiology and human behavior research and tell us to live like it’s 2019. It’s not. Nor is it 2020 or 2021. It’s the murky year known as 2022. And the rules of behavior that bolster our social norms — such as role models who refrain from large, indoor, unmasked gatherings, and leaders who uphold mask mandates on public transit to protect the most vulnerable — should reflect this liminal space.

A molar tooth from Southeast Asia probably belonged to a member of a cryptic group of Stone Age hominids called Denisovans, researchers say.

If so, this relatively large tooth joins only a handful of fossils from Denisovans, who are known from ancient DNA pegging them as close Neandertal relatives.

Analyses of the tooth’s internal structure and protein makeup indicate that the molar came from a girl in the Homo genus. She died between the ages of 3½ and 8½, paleoanthropologist Fabrice Demeter of the University of Copenhagen and colleagues say.
A Denisovan molar that dates to at least 160,000 years ago was previously found on the Tibetan Plateau (SN: 12/16/19). The newly discovered tooth strongly resembles that other molar, indicating that the new find is probably Denisovan too, the team reports May 17 in Nature Communications. Before the Tibetan Plateau tooth, all known fossils from the mysterious hominids had been found in Siberia.

Estimated ages of sediment and fossil animal bones in Tam Ngu Hao 2, or Cobra Cave, in Laos place the tooth found there between 164,000 and 131,000 years old.

It’s possible that the Cobra Cave tooth represents a Neandertal or someone with Denisovan and Neandertal ancestry (SN: 8/22/18), Demeter says. His group hopes to extract DNA from the fossil, which could clarify its evolutionary status.

It now appears that at least five Homo species, including Denisovans, inhabited Southeast Asia between roughly 150,000 and 40,000 years ago, Demeter says. Others include Homo sapiens, Homo erectus (SN: 12/18/19), Homo luzonensis (SN: 4/10/19) and Homo floresiensis (SN: 3/30/16), also known as hobbits, he contends.

Still, some researchers regard Denisovans as one of several closely related, ancient Homo populations rather than a distinct species (SN: 6/25/21). Whatever evolutionary ID Denisovans actually held, the Cobra Cave tooth adds to suspicions that the hominids inhabited Southeast Asia’s tropical forests as well as Central Asia’s cold mountain ranges and Siberia.

One million deaths. That is now roughly the toll of COVID-19 in the United States. And that official milestone is almost certainly an undercount. The World Health Organization’s data suggest that this country hit a million deaths early in the year.

Whatever the precise dates and numbers, the crisis is enormous. The disease has taken the lives of more than 6 million people worldwide. Yet our minds cannot grasp such large numbers. Instead, as we go further out on a mental number line, our intuitive understanding of quantities, or number sense, gets fuzzier. Numbers simply start to feel big. Consequently, people’s emotions do not grow stronger as crises escalate. “The more who die, the less we care,” psychologists Paul Slovic and Daniel Västfjäll wrote in 2014.
But even as our brains struggle to grasp big numbers, the modern world is awash in such figures. Demographic information, funding for infrastructure and schools, taxes and national deficits are all calculated in the millions, billions and even trillions. So, too, are the human and financial losses from global crises, including the pandemic, war, famines and climate change. We clearly have a need to conceptualize big numbers. Unfortunately, the slow drumbeat of evolution means our brains have yet to catch up with the times.

Our brains think 5 or 6 is big.
Numbers start to feel big surprisingly fast, says educational neuroscientist Lindsey Hasak of Stanford University. “The brain seems to consider anything larger than five a large number.”

Other scientists peg that value at four. Regardless of the precise pivot from small to big, researchers agree that humans, along with fish, birds, nonhuman primates and other species, do remarkably well at identifying really, really small quantities. That’s because there’s no counting involved. Instead, we and other species quickly recognize these minute quantities through a process called “subitizing” — that is, we look and we immediately see how many.

“You see one apple, you see three apples, you would never mistake that. Many species can do this,” says cognitive scientist Rafael Núñez of the University of California, San Diego.

When the numbers exceed subitizing range — about four or five for humans in most cultures — species across the biological spectrum can still compare approximate quantities, says cognitive scientist Tyler Marghetis of the University of California, Merced.

Imagine a hungry fish eyeing two clumps of similarly sized algae. Because both of those options will make “awesome feasts,” Marghetis says, the fish doesn’t need to waste limited cognitive resources to differentiate between them. But now imagine that one clump contains 900 leaves and the other 1,200 leaves. “It would make evolutionary sense for the fish to try to make that approximate comparison,” Marghetis says.
Scientists call this fuzzy quantification ability an “approximate number sense.” Having the wherewithal to estimate and compare quantities gives animals a survival edge beyond just finding food, researchers wrote in a 2021 review in the Journal of Experimental Biology. For example, when fish find themselves in unfamiliar environments, they consistently join the larger of two schools of fish.

The approximate number system falls short, however, when the quantities being compared are relatively similar, relatively large or both. Comparing two piles, one with five coins and the other with nine coins, is easy. But scale those piles up to 900,005 coins and 900,009 coins, and the task becomes impossible. The same goes for when the U.S. death toll from COVID-19 goes from 999,995 to 999,999.

We can improve our number sense — to a point.
The bridge between fuzzy approximation and precision math appears to be language, Núñez says.

Because the ability to approximate numbers is universal, every known language has words and phrases to describe inexact quantities, such as a lot, a little and a gazillion. “For example, if a boy is said to have a ‘few’ oranges and a girl ‘many’ oranges, a safe inference — without the need of exact calculations — is that the girl has more oranges than the boy,” Núñez writes in the June 1, 2017 Trends in Cognitive Science.

And most cultures have symbols or words for values in the subitizing range, but not necessarily beyond that point, Núñez says. For instance, across 193 languages in hunting and gathering communities, just 8 percent of Australian languages and 39 percent of African languages have symbols or words beyond five, researchers reported in the 2012 Linguistic Typology.
The origin of counting beyond subitizing range, and the complex math that follows, such as algebra and calculus, remains unclear. Núñez and others suspect that cultural practices and preoccupations, such as keeping track of agricultural products and raw materials for trade, gave rise to more complex numerical abilities. As math abilities developed, people became adept at conceptualizing numbers up to 1,000 due to lived experience, says cognitive scientist David Landy. Those experiences could include getting older, traveling long distances or counting large quantities of money.

Regular experiences, however, rarely hit the really big number range, says Landy, a senior data scientist at Netflix in San Francisco. Most people, he says, “get no experience like that for a million.”

Numbers that exceed our experience perplex us.
When big numbers exceed our lived experiences, or move into the abstract, our minds struggle to cope. For instance, with number sense and language so deeply intertwined, those seemingly benign commas in big numbers and linguistic transitions from thousands to millions or millions to billions, can trip us up in surprising ways.

When Landy and his team ask participants, often undergraduates or adults recruited online, to place numbers along a number line, they find that people are very accurate at placing numbers between 1 and 1,000. They also perform well from 1 million to 900 million. But when they change the number line endpoints to, say, 1,000 and 1 billion, people struggle at the 1 million point, Landy and colleagues reported in the March 2017 Cognitive Science.

“Half the people are putting 1 million closer to 500 million than 1,000,” Landy says. “They just don’t know how big a million is.”
Landy believes that as people transition from their lived experiences in the thousands to the more abstract world of 1 million, they reset their mental number lines. In other words, 1 million feels akin to one, 2 million to two and so on.

Changing our notations might prevent that reset, Landy says. “You might be better off writing ‘a thousand thousand’ than ‘1 million’ because that’s easier to compare to 900,000.” The British used to do this with what people in the U.S. now call a trillion, which they called a million million.

Without comprehension, extreme numbers foster apathy.
Our inability to grasp big numbers means that stories featuring a single victim, often a child, are more likely to grab our attention than a massive crisis — a phenomenon known as the identifiable victim effect.

For instance, on September 2, 2015, Aylan Kurdi, a 2-year-old refugee of the Syrian Civil War, was on a boat with his family crossing the Mediterranean Sea. Conservative estimates at the time put the war’s death toll at around 250,000 people. Kurdi’s family was trying to escape, but when their overcrowded boat capsized, the boy drowned, along with his brother and mother. The next day a picture of the infant lying dead on a Turkish beach hit the front pages of newspapers around the world.

No death up until that point had elicited public outcry. That photograph of a single innocent victim, however, proved a catalyst for action. Charitable contributions to the Swedish Red Cross, which had created a fund for Syrian refugees in August 2015, skyrocketed. In the week leading up to the photo’s appearance, daily donations averaged 30,000 Swedish krona, or roughly $3,000 today; in the week after the photo appeared, daily donations averaged 2 million Swedish krona, or roughly $198,500. Paul Slovic, of the University of Oregon, Eugene, Daniel Västfjäll, of Linköping University, Sweden, and colleagues reported those results in 2017 in Proceedings of the National Academy of Sciences.
Earlier research shows that charitable giving, essentially a proxy for compassion, decreases even when the number of victims goes from one to two. The flip side, however, is that psychologists and others can use humans’ tendency to latch onto iconic victims to reframe large tragedies, says Deborah Small, a psychologist at the University of Pennsylvania.

Some research suggests that this power of one need not focus on a single individual. For instance, when people were asked to make hypothetical donations to save 200,000 birds or a flock of 200,000 birds, people gave more money to the flock than the individual birds, researchers reported in the 2011 E-European Advances in Consumer Research.

Framing the current tragedy in terms of a single unit likewise makes sense, Västfjäll says. Many people react differently, he says, to hearing ‘1 million U.S. citizens dead of COVID’ vs. ‘1 million people, roughly the equivalent of the entire city of San José, Calif., have died from COVID.’

Milestones do still matter, even if we can’t feel them.
Kurdi’s photo sparked an outpouring of empathy. But six weeks after it was published, donations had dropped to prephoto levels — what Västfjäll calls “the half-life of empathy.”

That fade to apathy over time exemplifies a phenomenon known as hedonic adaptation, or humans’ ability to eventually adjust to any situation, no matter how dire. We see this adaptation with the pandemic, Small says. A virus that seemed terrifying in March 2020 now exists in the background. In the United States, masks have come off and people are again going out to dinner and attending large social events (SN: 5/17/22).

One of the things that can penetrate this apathy, however, is humans’ tendency to latch onto milestones — like 1 million dead from COVID-19, Landy says. “We have lots of experience with small quantities carrying emotional impact. They are meaningful in our lives. But in order to think about big numbers, we have to go to a more milestone frame of mind.” That’s because our minds have not caught up to this moment in time where big numbers are everywhere.

And even if we cannot feel that 1 million milestone, or mourn the more than 6 million dead worldwide, the fact that we even have the language for numbers beyond just 4 or 5 is a feat of human imagination, Marghetis says. “Maybe we are not having an emotional response to [that number], but at least we can call it out. That’s an amazing power that language gives us.”

Two mysterious galaxies, devoid of dark matter, could have a smashing origin story.

About 8 billion years ago, researchers propose, two dwarf galaxies slammed into one another. That cosmic crash caused the gas within those two galaxies to split up and form multiple new dwarf galaxies, including the two dark matter–free ones.

A newfound row of dwarf galaxies, more than 6 million light-years long, could have formed in the aftermath of the hypothesized crash, researchers report in the May 19 Nature. If correct, the finding could help solve the mystery of how such unusual dark matter–free galaxies form, and reveal new details about the nature of dark matter.

But other scientists are skeptical that there’s enough evidence to support this backstory. “If this is true, I think it would be really exciting. I just don’t think the bar has been met,” says astronomer Michelle Collins of the University of Surrey in Guildford, England.

In 2018, Yale University astronomer Pieter van Dokkum and colleagues reported a dwarf galaxy with no dark matter (SN: 3/28/18). The invisible, mysterious substance is typically detectable in galaxies via its gravitational effects on stars. When a second dark matter–free dwarf galaxy was found in the vicinity in 2019, it raised an obvious question: How did the two oddball galaxies form? Dark matter is generally thought to form the foundation of all galaxies, gravitationally attracting the gas that eventually forms stars. So some process must have separated the dark matter from the galaxies’ gas.

Scientists have previously seen dark matter and normal matter separate on a very large scale in the Bullet Cluster, which formed when two clusters of galaxies rammed into one another (SN: 8/23/06). Other researchers had proposed that something similar might happen with colliding dwarf galaxies, what van Dokkum and colleagues call “bullet dwarfs.”

In such a collision, the dwarf galaxies’ ethereal dark matter would continue on unperturbed, because the dark matter doesn’t interact with other matter. But the gas from the two galaxies would slam together, eventually forming multiple clumps that would each become its own galaxy, free of dark matter.

Now, van Dokkum and colleagues say that the bullet dwarf idea explains the two previously reported dark matter–free galaxies — and several other galaxies nearby. The two galaxies are moving away from each other as if they had come from the same spot, the researchers say. What’s more, the two galaxies are part of a chain of 11 galaxies aligned in a row, a structure that could have formed in the aftermath of a bullet dwarf collision.
“It’s super satisfying to finally have an explanation for these weird objects,” van Dokkum says.

But, Collins says, “there could be much more done to make it convincing.” For example, she says, the scientists didn’t measure the distances of all the galaxies from Earth. That means some of the galaxies could be much farther away than others, and it could be a coincidence that the galaxies appear to be lined up from our viewpoint.

And the researchers haven’t yet measured the velocities of all the galaxies in the trail or determined whether those galaxies are also missing their dark matter, which would help confirm whether the scenario is correct.

Other scientists are more optimistic. “The origin story is very plausible in my opinion,” says astrophysicist Eun-jin Shin of Seoul National University in South Korea. Shin cowrote a perspective article on the discovery with astrophysicist Ji-hoon Kim, also of Seoul National University, that was also published in Nature.

Computer simulations performed by Shin, Kim and others have shown that bullet dwarfs can produce such dark matter–free galaxies. If confirmed, the bullet dwarf idea could help pin down dark matter’s properties, in particular whether dark matter interacts with itself (SN: 4/5/18).

Van Dokkum and colleagues are planning additional measurements that could confirm or refute the case. But so far, he says, “It has, to me, the ring of truth.”

A speck of gold dancing to a pipe organ’s tune has helped solve a long-standing mystery: why certain wind instruments violate a mathematical formula that should describe their sound.

In 1860, physicist Hermann von Helmholtz — famous for his law of the conservation of energy — devised an equation relating the wavelength of a pipe’s fundamental tone (the lowest frequency at which it resonates) to pipe length (SN: 3/31/28). Generally, the longer a pipe is, the lower its fundamental tone will be.

But the equation doesn’t work in practice. A pipe’s fundamental tone always sounds lower than the pipe’s length suggests it should according to Helmholtz’s formula. Fixing this problem requires adding an “end correction” to the equation. In the case of open-ended pipes such as flutes and those of organs, the end correction is 0.6 times the radius of the pipe. Why this was, nobody could figure out.

A break in the case came in 2010. Instrument builder and restorer Bernhardt Edskes of Wohlen, Switzerland was tuning an organ when he spotted a piece of gold that had come loose from a pipe’s gilded lip. Air pumping through the pipe should have carried away the gold. Instead, it seemed to be trapped in a vortex just above the pipe’s upper rim.

Edskes told his friend, physicist Leo van Hemmen of the Technical University of Munich, about the observation. Together with colleagues from Munich and Wageningen University in the Netherlands, they studied how air moves through playing organ pipes using cigarette smoke.

When an organ pipe sounds, a vortex indeed forms over the pipe’s rim, the team reported March 14 in Chicago at a meeting of the American Physical Society. What’s more, this vortex is capped by a hemisphere of resonating air.
This vibrating air cap, van Hemmen says, is the long-sought explanation for the “end correction.” The cap effectively lengthens the organ pipe by the exact amount that must be tacked on to Helmholtz’s formula to explain the pipe’s fundamental tone.