There’s more to a galaxy than meets the eye. Galaxies’ bright stars seem to spiral serenely against the dark backdrop of space. But a more careful look reveals a whole lot of mayhem.

“Galaxies are just like you and me,” Jessica Werk, an astronomer at the University of Washington in Seattle, said in January at a meeting of the American Astronomical Society. “They live their lives in a constant state of turmoil.”

Much of that turmoil takes place in a huge, complicated setting called the circumgalactic medium, or CGM. This vast, roiling cloud of dust and gas is a galaxy’s fuel source, waste dump and recycling center all in one. Astronomers think the answers to some of the most pressing galactic mysteries — how galaxies keep forming new stars for billions of years, why star formation abruptly stops — are hidden in a galaxy’s enveloping CGM.
“To understand the galaxies, you have to understand the ecosystem that they’re in,” says astronomer Molly Peeples of the Space Telescope Science Institute in Baltimore.

Yet this galactic atmosphere is so diffuse that it’s invisible — a liter of CGM contains just a single atom. It has taken almost 60 years and an upgrade to the Hubble Space Telescope just to begin probing distant CGMs and figuring out how their constant churning can make or break galaxies.

“Only recently have we been able to really, truly, observationally characterize the relationship between this gaseous cycle and the properties of the galaxy itself,” Werk says.
Armed with the first extragalactic census, astronomers are now piecing together how a CGM controls its galaxy’s life and death. And new theoretical studies hint that galaxies’ stars would be arranged very differently without a medium’s frenetic flows. Plus, new observations show that some CGMs are surprisingly lumpy. A better understanding of CGMs, enabled by new telescopes and computer simulations, could change how scientists think about everything from galaxy collisions to the origins of our own atoms.

“The CGM is the part of the iceberg that’s under the water,” says astrophysicist Kevin Schawinski of ETH Zurich, who studies the more conventional parts of galaxies. “We now have good measurements where we’re sure it’s important.”
Waiting for Hubble
That 2009 Hubble telescope upgrade, which made the CGM census possible, almost didn’t happen.

In a cosmic coincidence, the Hubble telescope’s chief champions were also the first astronomers to figure out how to observe a galaxy’s CGM. Lyman Spitzer of Princeton University and John Bahcall of the Institute for Advanced Study in Princeton, N.J., and other astronomers noticed something strange after the 1963 discovery of quasars (SN Online: 3/21/14), bright beacons now known to be white-hot disks surrounding supermassive black holes in the centers of distant galaxies.

Everywhere astronomers looked, quasars’ spectra — the rainbow created when their light is spread out over all wavelengths — were notched with dark holes. Some wavelengths of light weren’t getting through.

In 1969, Spitzer and Bahcall realized what was going on: The missing light was absorbed by gas at the edges of galaxies, the same stuff that would later be called the CGM. Astronomers had been peering at quasars shining through CGMs like headlights through a fog.

Not much more could be done at the time, though. Earth’s atmosphere also absorbs light in those same wavelengths, making it difficult to tell which light-blocking atoms were in a galaxy’s CGM and which came from closer to home. Knowing that a CGM was there was one thing; taking its measurements would require something extra.

Spitzer and Bahcall knew what they needed: a space telescope that could observe from outside Earth’s atmosphere. The pair were two of the most vocal and consistent champions of the Hubble Space Telescope, which launched in 1990. Spitzer’s colleagues called him Hubble’s “intellectual and political father.”

Bahcall never stopped advocating for Hubble. In February 2005, six months before his death at age 70 from a rare blood disorder, he cowrote an article in the Los Angeles Times urging Congress to restore funding for a mission to fix some aging Hubble instruments, which NASA had canceled after the 2003 Columbia space shuttle disaster.

“What is at stake is not only a piece of stellar technology but our commitment to the most fundamental human quest: understanding the cosmos,” Bahcall and colleagues wrote. “Hubble’s most important discoveries could be in the future.”

His plea was answered: The space shuttle Atlantis brought astronauts to repair Hubble for the last time in May 2009 (SN Online: 5/19/09). During the repair, the astronauts installed the Cosmic Origins Spectrograph, which could pick up diffuse CGM gas with 30 times the sensitivity of any previous instrument. Although earlier spectrographs on Hubble had picked out CGMs a few quasar-beams at a time, the new device let astronomers search around dozens of galaxies, using the light of even dimmer quasars.

“It blew the field wide open,” Werk says.
The circumgalactic census
A team led by Jason Tumlinson of Baltimore’s Space Telescope Science Institute, Hubble’s academic home, made a catalog of 44 galaxies with a quasar sitting behind them from Hubble’s perspective. In a 2011 paper in Science, the researchers reported that every time they looked within 490,000 light-years of a galaxy, they saw spectra dappled with blank spots from atoms absorbing light. That meant that CGMs weren’t odd cloaks worn by just a few galaxies. They were everywhere.

Tumlinson’s team spent the first few years after Hubble’s upgrade like 19th century naturalists describing new species. The group measured the mass and the chemical makeup of the galaxies’ CGMs and found they were huge cisterns of heavy elements. CGMs contain 10 million times the mass of the sun in oxygen alone. In many cases, the mass of a CGM is comparable to the mass of the entire visible part of its galaxy.

The finding offers an answer to a long-standing cosmic mystery: How do galaxies have enough star-forming fuel to keep going for billions of years? Galaxies build stars from collapsing clouds of cool gas at a constant rate; the Milky Way, for example, makes one to two solar masses’ worth of stars every year. But there isn’t enough cool gas within the visible part of a galaxy, the disk containing its stars, to support observed rates of star formation.

“We think that gas probably comes from the CGM,” Werk says. “But exactly how that gas is getting into galaxies, where it gets in, the timescale on which it gets in, are there things that prevent it from getting in? Those are big questions that keep us all awake at night.”

Werk and Peeples realized that all that mass could help solve two other cosmic bookkeeping problems. All elements heavier than helium (which astronomers lump together as “metals”) are forged by nuclear fusion in the hearts of stars. When stars use up their fuel and explode as supernovas, they scatter those metals around to be folded into the next generation of stars.

But if you add up all the metals in the stars, gas and dust in a given galaxy’s disk, it’s not enough to account for all the metals the galaxy has ever made. The mismatch gets even worse if you include the hydrogen, helium, electrons and protons — basically all the ordinary matter that should have collected in the galaxy since the Big Bang. Astronomers call all those bits baryons. Galaxies seem to be missing 70 to 95 percent of that stuff.

So Peeples and Werk led a comprehensive effort to tally all the ordinary matter in about 40 galaxies observed with Hubble’s new spectrometer. The researchers published the results in two 2014 papers in the Astrophysical Journal.

At the time, Werk reported that at least half of galaxies’ missing ordinary matter can be accounted for in their CGMs. In a 2017 update, Werk and colleagues found that the mass of baryons just in the form of cool gas in a galaxy’s CGM could be nearly 90 billion solar masses. “Obviously, this mass could resolve the galactic missing baryons problem,” the team wrote.

“It’s a classic science story,” Schawinski says. The researchers had a hypothesis about where the missing material should be and made predictions. The group made observations to test those predictions and found what it sought.

In a separate study, Peeples showed that although metals are born in galaxies’ starry disks, those metals don’t stay there. Only 20 to 25 percent of the metals a galaxy has ever produced remains in the stars, gas and dust in the disk, where the metals can be incorporated into new stars and planets. The rest probably ends up in the CGM.

“If you look at all the metals the galaxies ever produced in their whole lifetime, more of them are outside the galaxy than are still inside the galaxy,” Tumlinson says, “which was a huge shock.”

Recycling centers
So how did the metals get into the CGM? Quasars’ spectra couldn’t help with that question. Their light shows only a slice through a single galaxy at a single moment in time. But astronomers can track galaxies’ growth and development with computer simulations based on physical rules for how stars and gas behave.

This strategy revealed the churning, ever-changing nature of gas in galaxies’ CGMs. Simulations such as EAGLE, or Evolution and Assembly of GaLaxies and their Environments, which is run out of Leiden University in the Netherlands, showed that metals can reach CGMs through stars’ violent lives: in powerful winds of radiation blowing away from massive young stars, and in the death throes of supernovas spraying metals far and wide.
Once the metals are in the CGM, though, they don’t always stay put. In simulations, galaxies seem to use the same gas over and over again.

“It’s basically just gravity,” Peeples says. “Throw a baseball up, and it’ll come back to the ground.” The same goes for gas flowing out of galaxies: Unless the gas travels fast enough to escape the galaxy’s gravity altogether, those atoms will eventually fall back into the disk — and form new stars.

Some simulations show discrete gas parcels making the trip from a galaxy’s disk out into the CGM and back again several times. Together, CGMs and their galaxies are giant recycling devices.

That means that the atoms that make up planets, plants and people may have taken several trips to circumgalactic space before becoming part of us. Over hundreds of millions of years, the atoms that eventually became part of you traveled hundreds of thousands of light-years.

“This is my favorite thing,” Tumlinson says. “At some point, your carbon, your oxygen, your nitrogen, your iron was out in intergalactic space.”

How galaxies die
But not all galaxies get their CGM gas back. Losing the gas could shut off star formation in a galaxy for good. No one knows how star formation shuts off, or quenches. But the answer is probably in the CGM.

Galaxies come in two main forms: young spiral galaxies that are making stars and old blobby galaxies where star formation is quenched (SN Online: 4/23/18).

“How galaxies quench and why they stay that way is one of the most important questions in galaxy formation generally,” Tumlinson says. “It just has to have something to do with the gas supply.”
One possibility, suggested in a paper posted online February 20 at arXiv.org, is that sprays of supernova-heated gas could get stripped from galaxies. Physicist Chad Bustard of the University of Wisconsin–Madison and colleagues simulated the Large Magellanic Cloud, a satellite galaxy of the Milky Way, and found that the small galaxy’s outflowing gas was swept away by the slight pressure of the galaxy’s movement around the Milky Way.

Alternatively, a dead galaxy’s CGM gas could be too hot to sink into the galaxy and form stars. If so, star-forming galaxies should have CGMs full of cold gas, and dead galaxies should be shrouded in hot gas. Hot gas would stay floating above the galactic disk like a hot air balloon, too buoyant to sink in and form stars.

But Hubble saw the opposite. Star-forming galaxies had CGMs chock-full of oxygen-VI — meaning that the gas was so hot (a million degrees Celsius or more) that oxygen atoms lost five of their original electrons. Dead galaxies had surprisingly little oxygen-VI.

“That was puzzling,” Tumlinson says. “If theory told us anything, it should have gone the other way.”

In 2016, Benjamin Oppenheimer, a computational astrophysicist at the University of Colorado Boulder, suggested a solution: The “dead” galaxies didn’t lack oxygen at all. The gas was just too hot for Hubble to observe. “In fact, there is even more oxygen around those passive galaxies,” Oppenheimer says.

All that hot gas could potentially explain why those galaxies died — except that these galaxies were full of star-forming cold gas, too.

“The dead galaxies have plenty of fuel left in the tank,” Tumlinson says. “We don’t know why they’re not using it. Everybody’s chasing that problem.”

Grabbing at the elephant
The chase comes at a good time. Until recently, observers had no way to map a single galaxy’s CGM. Researchers have had to add up dozens of quasar beams to understand the composition of CGMs on average.

“We’ve been like the three blind people grabbing at the elephant,” says John O’Meara, an observational astronomer at Saint Michael’s College in Colchester, Vt.

Teams using two new spectrographs — KCWI, the Keck Cosmic Web Imager on the Keck telescope in Hawaii, and MUSE, the Multi Unit Spectroscopic Explorer on the Very Large Telescope in Chile — are racing to change that. These instruments, called integral field spectrographs, can read spectra across a full galaxy all at once. Given enough background light, astronomers can now examine a single galaxy’s entire CGM. Finally, astronomers have a way to test theories of how gas circulates into and out of a galaxy.
A Chilean team, led by astronomer Sebastian Lopez of the University of Chile in Santiago and colleagues, used MUSE to observe a small dim galaxy that happens to be sandwiched between a bright, distant galaxy and a massive galaxy cluster closer to Earth. The cluster acts as a gravitational lens, distorting the image of the distant galaxy into a long bright arc (SN: 3/10/12, p. 4). The light from that arc filtered through the CGM of the sandwiched galaxy, which the team called G1, at 56 different points.

Surprisingly, G1’s CGM was lumpy, not smooth as expected, the team reported in the Feb. 22 Nature. “The assumption has been that that gas is distributed homogeneously around every system,” Lopez says. “This is not the case.”
O’Meara is leading a group that is hot on Lopez’s trail. Last year, while KCWI was being installed, O’Meara got an hour of observing time and was able to see hydrogen — which is associated with cool, star-forming gas — in the CGM of another galaxy backlit by a bright lensed arc. He’s not ready to discuss the results in detail yet, but the team is submitting a paper to Science.
Meanwhile, Peeples’ team is revisiting how computers render CGMs. “The resolution of the circumgalactic medium in simulations is, um, bad,” she says. Existing simulations are good at matching the visible properties of galaxies — their stars, the gas between the stars, and the overall shapes and sizes. But they “utterly fail at reproducing the properties of the circumgalactic medium,” she says.
So she’s running a new set of simulations called FOGGIE, which focus on CGMs for the first time. “We’re finding that it changes everything,” she says: The shape, star formation history and even the orientation of the galaxy in space look different.

Together, the new observations and simulations suggest that the CGM’s function in the life cycle of a galaxy has been underestimated. Theorists like Peeples and observers like O’Meara are working together to make new predictions about how the CGM should look. Then the researchers will check real galaxies to see if they match.

“Molly will post a really amazing new render of a simulation on Slack, and I’ll go, ‘Holy crap, that looks weird!’ ” O’Meara says. “I’ll go scampering off to find a similar example in the data, and we get into this positive feedback loop of going ‘Holy crap! Holy crap!’ ”

While future circumgalactic studies will focus on gathering spectra from full CGMs, Tumlinson is hoping to squeeze more information out of Hubble while he still can. Hubble made CGM studies possible, but the telescope is 28 years old, and probably has less than a decade left. Hubble’s spectrograph is still the best at observing certain atoms in CGMs to help reveal the gaseous halos’ secrets. “It’s something we definitely want to do,” he says, “before Hubble ends up in the ocean.”

Deep water reefs are unlikely to be safe harbors for many fish and coral species from shallow reefs threatened by climate change and human activity. Shallow water creatures may have trouble adapting to conditions in the deep, scientists report in the July 20 Science. Plus, deep reefs are facing the same threats that are putting shallower ones at risk.

The study deals a blow to the “deep reef refugia” hypothesis. That’s the idea that species from troubled shallow reefs could simply move to reefs at depths of 30 to 150 meters, called mesophotic reefs because they exist at the limits of where sunlight reaches. Even though individuals of a typical shallow water species may be spotted at a wide range of depths, it doesn’t mean the majority of that species could survive living in deeper waters, says study coauthor Luiz Rocha, a zoologist at the California Academy of Sciences in San Francisco.
“When you start looking into details,” Rocha says, “a lot of these species don’t actually live in these depths.” But there was scant data, partly because seeing these species requires scientists to undergo technical diving training.

Rocha and his team wanted to figure out which, if any, shallow water species can also thrive in deep water reefs. And the only way to do that was to get wet.

The scientists made dozens of dives to depths of up to 150 meters in waters off the Philippines in Asia, the Caribbean island of Curaçao, the mid-Atlantic island of Bermuda and the western Pacific island nation of Micronesia. While cataloging 687 coral species and 1,761 fish species, the team found that deep water ecosystems were strikingly different from surface reefs and had many distinct species evolved to live in darker and colder waters.

While the researchers didn’t quantify the overlap, in some places, it looked like about half of all species were found in both deep and shallow reefs, says coauthor Richard Pyle, a zoologist at the Bishop Museum in Honolulu. The rest were found in only deep water or shallow water.
The team also noted that none of the deep water reefs were pristine. The researchers saw tangled fishing line, broken bottles and coral bleaching, a problem that can be caused by consistently higher water temperatures (SN: 2/3/18, p. 16). These problems were particularly severe in the Philippines reefs.
“One of the things that people assume is that these deep ecosystems are less impacted,” says oceanographer Kimberly Puglise at the National Oceanic and Atmospheric Administration in Silver Spring Md., who was not part of the study. But deep reefs are also susceptible to damage, and yet usually don’t fall within protected areas as shallow reefs do.

The study shows that deep water reef ecosystems are “not just important because they may be able to protect shallow reefs,” Puglise says. “They’re important in their own right.”

This research doesn’t rule out the possibility of species migration to deeper waters. A meta-analysis published in the June 11 Environmental Evidence found that some species do well in both shallow and deep waters, though that work relied on reported depth ranges rather than in-person research.

Coral reef ecologist Tyler Smith at the University of the Virgin Islands in St. Thomas, who was a not a part of either study, says there could be other regions of the world with more depth overlap between reef species. “It might depend on where you’re looking.”

Meghalayan
mehg-a-LAY-an n.
The newly named current geologic age that started 4,200 years ago.

Welcome to the Meghalayan, our geologic here and now. It’s one of three newly designated ages divvying up the Holocene Epoch, a geologic time period kicked off 11,700 years ago by the end of the Ice Age.

First came a warming period, now dubbed the Greenlandian Age. Then, about 8,300 years ago, the Northgrippian Age began with a big chill that gripped Earth for about 4,000 years. Finally, the Meghalayan started 4,200 years ago with a devastating, 200-year worldwide megadrought.
“It marked a quite serious collapse of human agricultural civilizations,” says Phil Gibbard of the International Union of Geological Sciences, which ratified the new ages June 14 and released an updated geologic time scale July 13. The megadrought triggered human crises and migrations ranging from China to the Middle East to India, where the new age’s namesake is located. A stalagmite from a cave in the northeast Indian state of Meghalaya acts as the official time stamp marker for the start of the age. The drought is also recorded in other geologic sediments and at archaeological sites around the world.

The Meghalayan is the first formal geologic time interval in Earth’s 4.6-billion-year history that began at the same time as a global, climate-driven cultural event.

It sounds bonkers that a tick bite might make meat eaters allergic to their steaks and ribs, but it’s true. Now new research has added a potential twist: The source of this tick-related sensitivity to red meat may also be linked to coronary artery disease.

A bite from the lone star tick, Amblyomma americanum, can trigger antibodies to a sugar called alpha-gal, found in many mammals but not humans. For some of the tick-bitten, that produces an allergic reaction to alpha-gal in red meats like beef and pork. A new study also finds that heart patients with the antibodies had more plaque buildup in their artery walls. Of 118 people with coronary artery disease, 31 who tested positive for the antibodies had about 25 percent more plaque in their artery walls than those who were negative, researchers report in the July Arteriosclerosis, Thrombosis and Vascular Biology.
Study participants were aged 30 to 80; the connection between extra gummed-up arteries and the presence of antibodies was strongest in those 65 and younger. For the antibody-positive participants in that group, the plaques penetrating the walls of the arteries were of the sort more likely to rupture and cause a heart attack (SN Online: 5/5/09).

Elevated levels of allergen-targeting antibodies have been previously linked with coronary artery disease, but this study is the first to identify a specific allergen, says cardiologist Coleen McNamara of University of Virginia School of Medicine in Charlottesville. The study also tested for possible links to antibodies to other common allergens such as peanut, ragweed and dust mites but didn’t find a connection. She and her colleagues want to see if the link to alpha-gal antibodies holds up among a larger group.

Eating red meat is associated with an increased risk of heart disease, and the new work adds to the story of why that may be, says biochemist Guo-Ping Shi of Brigham and Women’s Hospital in Boston, who was not involved with the study.

Still, the study only shows an association. To search for a possible mechanism, McNamara’s team plans to study alpha-gal and artery inflammation in mice; inflammatory cells released via the immune system contribute to plaques.

Anxiety can run in families. Key differences in how an anxious monkey’s brain operates can be passed along too, a large study suggests.

By finding a pattern of brain activity linked to anxiety, and by tracing it through generations of monkeys, the results bring researchers closer to understanding the brain characteristics involved in severe anxiety — and how these characteristics can be inherited.

“We can trace how anxiety falls through the family tree,” which parents pass it on to which children, how cousins are affected and so on, says study coauthor Ned Kalin of the University of Wisconsin School of Medicine and Public Health in Madison. The newly identified brain activity pattern takes the same path through the family tree as the anxious behavior, Kalin and colleagues report July 30 in the Journal of Neuroscience.
Kalin and colleagues studied rhesus monkeys that, as youngsters, displayed an anxious temperament. Human children with this trait are often painfully shy, and are at much higher risk of going on to develop anxiety and depression than other children, studies have shown.

Monkeys can behave similarly. Researchers measured anxious temperament by subjecting young monkeys to a stressful situation: An intruder entered their cage and showed only his or her profile to the monkey. “The monkey isn’t sure what is going to happen, because it can’t see the individual’s eyes,” Kalin says. Faced with this potential threat, monkeys freeze and fall silent. By measuring the degree of this response, as well as levels of the stress hormone cortisol, the researchers figured out which monkeys had anxious temperaments.

In addition to collecting these behavioral measures for 378 young monkeys from 2007 to 2011, the researchers subjected the monkeys to brain scans under anesthesia. Monkeys with outsized stress responses to the intruder showed a crucial difference in the extended amygdala — a brain structure and its surroundings known to be heavily involved in fear and threat detection.
Two parts in particular — the central nucleus and the bed nucleus of the stria terminalis — behaved in lockstep. When the activity of one was high, for instance, so was the activity of the other, functional magnetic resonance imaging scans showed. This tight link in activity between those two parts of the brain was also passed down from parents to offspring, along with anxious temperament, family trees revealed.

The study wasn’t designed to show whether the differences in brain behavior actually caused the anxious behavior in the monkeys. To do that, researchers will need to alter the activity of the amygdala and its surrounding parts and see whether changes in anxious behavior result.

Still, the results are “very relevant to the human condition,” says psychiatrist and chief scientific officer Kerry Ressler at McLean Hospital in Belmont, Mass. These same brain structures are also thought to be heavily involved in human anxiety.

This study and others like it are revealing details of how the brain operates to create certain psychiatric disorders — information necessary for designing targeted treatments, Ressler says. Even so, there’s much more work to be done before the results can help people with anxiety. Understanding brain areas involved in anxiety, “while critical, is still many steps away from knowing the best way to intervene,” Ressler cautions.

Kalin and colleagues are performing similar studies on children, though the researchers won’t be able to collect the same sort of data on multiple generations.

When a strong tornado roars through a city, it often leaves behind demolished buildings, broken tree limbs and trails of debris. But a similarly powerful storm touching down over barren, unvegetated land is much harder to spot in the rearview mirror.

Now, satellite imagery has revealed a 60-kilometer-long track of moist earth in Arkansas that was invisible to human eyes. The feature was presumably excavated by a tornado when it stripped away the uppermost layer of the soil, researchers report in the March 28 Geophysical Research Letters. This method of looking for “hidden” tornado tracks is particularly valuable for better understanding storms that strike in the winter, when there’s less vegetation, the researchers suggest. And recent research has shown that wintertime storms are likely to increase in intensity as the climate warms (SN: 12/16/21).
Over 1,000 tornadoes strike the United States each year, according to the National Weather Service. But not all are equally likely to be studied, says Darrel Kingfield, a meteorologist at the National Oceanic and Atmospheric Administration in Boulder, Colo., who was not involved in the research.

For starters, storms that pass over populated areas are more apt to be analyzed. “There’s historically been a pretty big population bias,” Kingfield says. Storms that occur over vegetated regions also tend to be well studied, simply because they leave obvious scars on the landscape. Ripped-up grasses or downed trees function like beacons to indicate the path of a storm, says Kingfield, who has studied forests damaged by tornadoes.

Spring and summer are peak storm seasons in the United States — more than 70 percent of tornadoes strike from March through September, according to NOAA. But on December 10, 2021, a cluster of storms started racing across the central and southern United States. Those tornadoes, which claimed more than 80 lives, swept across cities and also farmland, much of which had already been harvested for the season.

Jingyu Wang, a physical geographer at Nanyang Technological University in Singapore, and his colleagues set out to detect the signatures of those deadly storms in unpopulated, barren landscapes.

Swirling winds, even relatively weak ones, can suction up several centimeters of soil. And since deeper layers of the ground tend to be wetter, a tornado ought to leave behind a telltale signature: a long swath of moister-than-usual soil. Two properties linked with soil moisture level — its texture and temperature — in turn impact how much near-infrared light the soil reflects.

Wang and his collaborators analyzed near-infrared data collected by NASA’s Terra and Aqua satellites and looked for changes in soil moisture consistent with a passing tornado.

When the team looked at data obtained shortly after the 2021 storm outbreak, they noticed a signal in northeastern Arkansas. The feature was consistent with a roughly 60-kilometer-long track of wet soil. Tornadoes had been previously reported in that area — outside the city of Osceola — so it’s likely that this feature was created by a powerful storm, the team concluded.
That makes sense, Kingfield says, and observations like these can reveal tornado signatures that might otherwise be missed. However, it’s important to acknowledge that this new technique works best in places where soils are capable of retaining water, he says. “You need to have clay-rich soils.”

Even so, these results hold promise for analyzing other tornadoes, Kingfield says. It’s always useful to have a new tool for estimating the strength, path and structure of a storm, but many storms go relatively unexamined simply because of where and when they occur, he says. “Now we have this new ground truth.”

No matter how chaotic the train station at rush hour might seem, there’s likely more order than you think in that crowd.

It’s long been observed that in a dense crowd with people headed in opposite directions, multiple parallel lanes emerge. In a recent report in the March 3 Science, mathematicians Tim Rogers and Karol Bacik of the University of Bath in England used a mathematical model to describe how such lanes form and evolve and confirmed the predictions with live experiments.
The results show that, assuming the passageway is wide enough, two groups intersecting head on form multiple lanes roughly two body widths across. If the two groups instead intersect at right angles, they will again form lanes, which migrate like the stripes on a barber pole. (Each person stays in a lane but the lane itself moves to the side.) Even if you tell everyone to pass on the right in a misguided attempt to form just two lanes, you will instead get multiple lanes at an oblique angle to the preferred direction of flow. This slows everybody down.

Apparently, the best thing you can do to control the traffic is … nothing at all. “Anarchy is enough,” Rogers says.
Rogers and Bacik began working on crowds during the pandemic — ironically, at a time when crowds were scarce. “We were working with a local civil engineering firm to design layouts for socially distanced use of spaces, including conference venues,” Rogers says. For example, how do you design a coffee break area so a large volume of people can pass through quickly while staying six feet apart? Although software already existed for simulating pedestrian traffic, it had to be tweaked for a new world in which the definition of a close encounter had changed.

While working on this practical problem, Rogers and Bacik became intrigued by the known phenomenon of spontaneous lane formation. As early as 1991, Dirk Helbing, a physicist now at ETH Zürich, had developed a mathematical model to explain the formation of lanes when two groups flow in opposite directions. Helbing’s “social force” model describes the intended direction of the pedestrians, as well as the way they modify their motion to avoid collisions. It remains a state-of-the-art model, and it was part of the software that Rogers and Bacik were using. The challenge for any such model is to bridge the gap between individual decisions and the patterns of the crowd.

“We rediscovered the various hypotheses that people have had, and we have tried to unify them and show that they are different parts of the big picture,” Bacik says.

In the new report, Rogers and Bacik describe lane formation as a result of two processes: drift and diffusion. As pedestrians are moving across King’s Cross Station in London, for example, they can drift from their planned route either because collisions push them away from regions with a lot of opposing traffic or because they are attracted to pockets that are more open. This drift strongly encourages lane formation: As soon as a stripe of northbound pedestrians starts to form, other northbound pedestrians are attracted to it and southbound pedestrians are pushed away. Diffusion, on the other hand, tends to smooth out fluctuations in pedestrian density, so an excess in one direction has to be fairly large to survive.
Using a mathematical technique called perturbation analysis, Rogers and Bacik showed that fluctuations on the scale of two body widths dominate the formation of lanes and thus explain their width. “It’s a great idea, and I wish I had thought of it myself,” says Nicolas Bain of École Normale Supérieure in Lyon, France, who has also studied lane formation.

Beyond testing head-on traffic, intersecting traffic and passing on the right, Rogers and Bacik also tested two streams crossing in a square vestibule when one or both streams have to funnel through a narrow exit, such as a doorway. Here, a surprise emerged that no one studying lane formation over the past three decades had noticed before: The lanes that form are curved, making the shape of a parabola (if only one exit is narrow) or an ellipse (if both exits are).

Finally, the team tested all of these mathematical predictions in a crowd of 60 to 70 people passing through a 6-meter-by-6-meter arena set up in Katowice, Poland. (Bacik’s father, Bogdan, a biomechanics expert, helped arrange this experiment.) Their video footage confirmed the predictions. “It is the connection between the actual experiments and the simulations which makes the paper top-notch,” says Hartmut Löwen, a physicist at University of Düsseldorf in Germany who was not involved in the research.
While Rogers and Bacik’s recent work focused on pattern formation, pedestrian flow can have real and sometimes tragic consequences. Stampedes or crowd crushes have killed people — more than 150 people celebrating Halloween in Seoul in 2022, for example, and hundreds of pilgrims in Saudi Arabia in 2015. Public spaces can be designed to help prevent such tragedies.

According to Helbing, one sign of trouble is three-way (or more) collisions, where people have no good way to escape, and they get stuck. These collisions can occur particularly at Y-shaped intersections or at four-way intersections. Rogers and Bacik’s models specifically exclude such situations, and civil engineers would be well advised to avoid them too.

“Two pedestrian streams can walk through each other in a surprisingly efficient way,” Helbing says. But, Helbing adds, “When more pedestrian flows intersect, there are typically no stable patterns of motion.” This can lead to turbulent flow or “crowdquakes,” in which people can’t control where they are going. The takeaway: When pedestrians are traveling two ways, trust the wisdom of crowds. When there’s a three-way or four-way intersection, watch out.

Babies exposed to a Zika infection while in the womb are not out of the woods even if they look healthy at birth.

Nearly 1 in 10 of 1,450 babies examined developed neurological or developmental problems, such as seizures, hearing loss, impaired vision or difficulty crawling, a study from the U.S. Centers for Disease Control and Prevention finds. It’s the first tally of the health of children at least 1 year old who were born in Puerto Rico and other U.S. territories and exposed to Zika in utero.
Overall, 14 percent of children exposed to Zika in the womb — about 1 in 7 — were harmed in some way by the virus, the researchers report online August 7 in Morbidity and Mortality Weekly Report. These babies were either born with a birth defect such as microcephaly — a condition in which a baby’s head is significantly smaller than it should be — or developed neurological symptoms that may be related to Zika, or both.

“Congenital Zika virus infection is quite serious, even beyond just the microcephaly,” says Peter Hotez, a pediatrician and microbiologist at Baylor College of Medicine in Houston, who was not involved in the report. “We’re still getting our arms around the full neurologic spectrum of illness” that is related to Zika.

The report also found that 6 percent of babies in the study had at least one birth defect caused by the virus, such as defects of the eye or brain or microcephaly (SN: 10/29/16, p. 14).

That’s fairly consistent with what’s seen in other countries hit by the Zika virus, Margaret Honein, director of CDC’s Division of Congenital and Developmental Disorders, said at a news conference. While a 2016 study suggested higher rates of birth defects in Brazil, “we think there isn’t a geographic difference” but more of a difference in how Zika-related birth defects are defined, she said.
The data come from the U.S. Zika Pregnancy and Infant Registry, set up to monitor pregnant women with Zika virus infection and the health of their babies. The study focuses on those pregnancies reported from Puerto Rico, the U.S. Virgin Islands, American Samoa, the Federated States of Micronesia and the Marshall Islands. The children, all at least a year old, had received some follow-up medical care, such as brain imaging, hearing tests, eye exams or developmental screening. A report on pregnancies from the mainland United States is expected later this year.

Zika ravaged Brazil, Colombia and other countries of the Americas in 2015 and 2016. By 2017, the spread of the virus had slowed to a crawl (SN: 11/11/17, p. 12). But experts expect to see future outbreaks (SN: 12/23/17, p. 30).

“What makes this report unique is that we’re looking at the health of these babies beyond what was observed at birth,” Honein said. “This is really providing us with the first clues about how common some of these neurodevelopmental disabilities might be.”

Researchers suspect that health issues will continue to emerge for children exposed to Zika in the womb as they grow older. “This is why it is so absolutely critical that these babies receive care to identify issues as soon as possible,” Honein said, and that children continue to be monitored over time.

Conventional wisdom states that viruses work as lone soldiers. Scientists now report that some viruses also clump together in vesicles, or membrane-bound sacs, before an invasion. Compared with solo viruses, these viral “Trojan horses” caused more severe infections in mice, researchers report August 8 in Cell Host & Microbe.

Cell biologist Nihal Altan-Bonnet had been involved in discovering in 2015 that polioviruses can cluster together to invade cells in a petri dish. In the new study, Altan-Bonnet and a different group of colleagues find that transmission via virus clumps also occurs naturally with both rotavirus and norovirus, which can cause gastrointestinal illness.
The scientists first identified norovirus cluster vesicles in patients’ stool samples, which was “eye-opening,” says Altan-Bonnet, who works at the National Institutes of Health in Bethesda, Md. “We can see these vesicles everywhere.”

Altan-Bonnet and her team infected live mice with either vesicle-packaged rotavirus or equal amounts of single virus particles. Vesicles were not only more successful in causing infections, they also caused infections that were more severe, the researchers found. In the mice, it took five times the amount of single virus particles to cause the same severity of infection as caused by the clustered viruses. It also took the mice two to four days longer to fight off the cluster-caused infections.
While the mice were sick, the researchers found viral clumps in their feces, showing that the vesicles were able to survive the harsh environment of the GI system unscathed. It’s still unclear, however, if the viruses remain inside the vesicles to invade cells, and if so, how.
The clusters act like a Trojan horse, Altan-Bonnet suggests. “The wooden horse would be the vesicle, and inside it you have all the soldiers.” She has several hypotheses for why viruses behave this way. Vesicles may help the viruses evade the immune system or replicate faster inside cells. “We really have to rethink the way we think about viruses,” she says.

Norovirus and rotavirus, which can be dangerous for children and the elderly, kill a combined total of about 265,000 children each year worldwide, mostly in developing countries (SN: 8/8/15, p. 5). The researchers hope the discovery of vesicle transmission will lead to better prevention methods and treatments, for example, by targeting the membranes containing the virus clusters.

Because the long-standing “dogma in the field” suggested viruses were transmitted individually, it’s not surprising that these vesicles were missed in earlier virus research, says Craig Wilen, a physician at the Yale School of Medicine who recently discovered what cells norovirus targets in mice (SN: 5/12/18, p. 14). “It’s probably been seen and just dismissed.”

Wilen says that there are still questions about viral clusters that need to be answered. For example, he says, “how does the virus escape the vesicle?” Other questions that remain include how the vesicle latches on to a cell’s surface, and what advantage the viruses actually get from packaging themselves together.

Peer pressure can be tough for kids to resist, even if it comes from robots.

School-aged children tend to echo the incorrect but unanimous responses of a group of robots to a simple visual task, a new study finds. In contrast, adults who often go along with the errant judgments of human peers resist such social pressure applied by robots, researchers report August 15 in Science Robotics.

“Rather than seeing a robot as a machine, children may see it as a social character,” says psychologist Anna-Lisa Vollmer of Bielefeld University, Germany. “This might explain why they succumb to peer pressure [applied] by robots.”
Little is known about how either adults or children respond to the behavior of lifelike robots designed to interact with people, for example, as museum tour guides, child-care assistants and teaching aids.

In a preliminary examination of the influence of social robots, Vollmer’s group adapted a 1950s social psychology experiment in which most adults agreed with groups of peers who had been coached to say that lines of different lengths were in fact the same length (SN Online: 5/15/18).

Vollmer’s team observed comparable social conformity in a study of 60 British adults, ages 18 to 69, who judged line lengths after hearing the opinions of three peers who were working with the researchers. Participants usually endorsed peers’ unanimous, inaccurate judgments. Conformity vanished, however, when volunteers performed the task while sitting with three robots that, on some trials, agreed on an incorrect answer.
Each robot was programmed to make periodic movements, such as blinking its eyes and briefly gazing at others. Robots spoke with distinctive, individualized voice pitches when making line judgments.
When children sat with the robots, though, the kids frequently went all-in. The study’s 43 participating British grade-schoolers, aged 7 to 9, agreed with three-quarters of the robots’ unanimous, inaccurate answers. The kids did not participate in conformity experiments with trios of same-age human peers, given the difficulty of getting youngsters to act convincingly according to researchers’ directions.

Still, larger samples of volunteers are needed to confirm that kids usually cave to social pressure from robots. Cultural factors, such as being raised in a society that emphasizes individualism or group values, also may influence how people of all ages perceive and react to social robots.

Three unresolved issues in particular stand out, says psychologist and child development researcher Paul Harris of Harvard University. First, it’s unclear whether some robot behaviors, but not others, triggered conformity in children. A bot’s periodic head turns toward a child, for example, might sway that youngster’s choice more than the same robot’s eye blinks or finger movements. It’s also unclear why adults who bent to human peer pressure reversed course with robots.

Finally, Harris asks, “Would fine-tuning of the robots’ repertoire [of movements and vocalizations] eventually elicit deference even from adults?”