U.S. millennials are rejecting suburbia and moving back to the city. That was a prevailing idea in 2019, when I started as the social sciences reporter at Science News. But when I began digging into a possible story on the phenomenon, I encountered an incoherent mess. Some research showed that suburbs were growing, others that suburbs were shrinking and yet others showed growth in both suburbs and cities.

Unable to make sense of that maze of findings, I shelved the story idea. Then, several months later, I stumbled across a Harvard University white paper explaining that disagreement in the field stems from competing definitions of what distinguishes a city from a suburb. Some researchers define the suburbs as areas falling outside census-designated cities. Others look only for markers of suburbanism, such as a wealth of single-family houses and car-based commutes, the researchers wrote.
I have encountered this type of fuzziness around definitions of all sorts of terms and concepts in the years I’ve covered the social sciences. Sometimes researchers simply assume that their definition of a key concept is the definition. Or they nod briefly at other definitions, and then go forth with whichever one they choose, without much explanation why. Other times, researchers in one subfield choose one definition, and researchers in another subfield choose a different one — each without ever knowing of the other’s existence. It’s enough to drive any reporter to tear their hair out.

“If you look … you will find this morass of definitions and measurements” in the social sciences, says quantitative psychologist Jessica Flake of McGill University in Montreal. My experience was a common one, she assured me.

Definitional morasses exist in other scientific fields too. Biologists frequently disagree about how best to define the word “species” (SN: 11/1/17). Virologists squabble over what counts as “alive” when it comes to viruses (SN: 11/1/21). And not all astronomers are happy with the decision to define the word “planet” in a way that left Pluto out in the cold as a mere dwarf planet (SN: 8/24/21).

But the social sciences have some special challenges, Flake says. The field is a youngster compared with a discipline like astronomy, so has had less time to sort out its definitions. And social science concepts are often inherently subjective. Describing abstract ideas like motivation or feelings can be squishier than describing, say, a meteorite.

It’s tempting to assume, as I did until I began researching this column, that a single, imperfect definition for individual concepts is preferable to this definitional cacophony. And some researchers encourage this approach. “While no suburban definition will be perfect, standardization would increase understanding of how suburban studies relate to each other,” the Harvard researchers wrote in that suburbia paper.

But a recent study taking aim at how we define the middle class showed me how alternative definitions can lead to a shift in perspective.

While most researchers use income as a proxy for class, these researchers used people’s buying patterns. That revealed that a fraction of people who appear middle class by income struggle to pay for basic necessities, such as housing, child care and groceries, the team reported in July in Social Indicators Research. That is, they live as if they are working class.

What’s more, that vulnerable group skews Black and Hispanic, a disparity that arises, in part, because these families of color often lack the generational wealth of white families, says Melissa Haller, a geographer at Binghamton University in New York. So when calamity strikes, families without that financial cushion can struggle to recover. Yet a government or nonprofit organization looking to direct aid toward the neediest families, and relying solely on income-based metrics, would overlook this vulnerable group.

“Depending on what definition you start with, you will see different facts,” says Anna Alexandrova, a philosopher of science at the University of Cambridge. A standardized definition of middle class, for example, could obscure some of those key facts.

In the social sciences, what’s needed instead of conceptual unity, Alexandrova says, is conceptual clarity.

Though social scientists disagree about how to go about solving this problem of clarity, Flake says that failure to tackle the issue jeopardizes the field as much as other crises rocking the discipline (SN: 8/27/18). That’s because how a topic is defined determines the scales, surveys and other instruments used to study that concept. And that in turn shapes how researchers crunch numbers and arrive at conclusions.

Defining one’s key terms and then selecting the right tool is somewhat straightforward when relying on large, external datasets. For instance, instead of using national income databases, as is common in the study of the middle class, Haller and her team turned to the federal government’s Consumer Expenditure Surveys to understand people’s daily and emergency purchases.

But often social scientists, particularly psychologists, develop their own scales and surveys to quantify subjective concepts, such as self-esteem, mood or well-being. Definitions of those terms — and the instruments used to study them — can take on a life of their own, Flake says.

She and her team recently showed how this process plays out in the May-June American Psychologist. They combed through the 100 original studies and 100 replications included in a massive reproducibility project in psychology. The researchers zoomed in on 97 multi-item scales — measuring concepts such as gratitude, motivation and self-esteem — used in the original studies, and found that 54 of those scales had no citations to show where the scales originated. That suggests that the original authors defined their idea, and the tool used to measure that idea, on the fly, Flake says. Research teams then attempted to replicate 29 of those studies without digging into the scales’ sources, calling into question the meaning of their results.

For Flake, the way to achieve conceptual clarity is straightforward, if unlikely. Researchers must hit the brakes on generating new ideas, or replicating old ideas, and instead interrogate the morass of old ones.

She points to one promising, if labor-intensive, effort: the Psychological Science Accelerator, a collaboration of over 1,300 researchers in 84 countries. The project aims to identify big ideas in psychology, such as face perception and gender prejudice, and accumulate all the instruments and resulting data used to make sense of those ideas in order to discard, refine or combine existing definitions and tools.

“Instead of running replications, why don’t we use [this] massive team of researchers who represent a lot of perspectives around the world and review concepts first,” Flake says. “We need to stop replicating garbage.”

I couldn’t agree more.

Wind turbines could offer a double whammy in the fight against climate change.

Besides harnessing wind to generate clean energy, turbines may help to funnel carbon dioxide to systems that pull the greenhouse gas out of the air (SN: 8/10/21). Researchers say their simulations show that wind turbines can drag dirty air from above a city or a smokestack into the turbines’ wakes. That boosts the amount of CO2 that makes it to machines that can remove it from the atmosphere. The researchers plan to describe their simulations and a wind tunnel test of a scaled-down system at a meeting of the American Physical Society’s Division of Fluid Dynamics in Indianapolis on November 21.
Addressing climate change will require dramatic reductions in the amount of carbon dioxide that humans put into the air — but that alone won’t be enough (SN: 3/10/22). One part of the solution could be direct air capture systems that remove some CO2 from the atmosphere (SN: 9/9/22).

But the large amounts of CO2 produced by factories, power plants and cities are often concentrated at heights that put it out of reach of machinery on the ground that can remove it. “We’re looking into the fluid dynamics benefits of utilizing the wake of the wind turbine to redirect higher concentrations” down to carbon capture systems, says mechanical engineer Clarice Nelson of Purdue University in West Lafayette, Ind.

As large, power-generating wind turbines rotate, they cause turbulence that pulls air down into the wakes behind them, says mechanical engineer Luciano Castillo, also of Purdue. It’s an effect that can concentrate carbon dioxide enough to make capture feasible, particularly near large cities like Chicago.

“The beauty is that [around Chicago], you have one of the best wind resources in the region, so you can use the wind turbine to take some of the dirty air in the city and capture it,” Castillo says. Wind turbines don’t require the cooling that nuclear and fossil fuel plants need. “So not only are you producing clean energy,” he says, “you are not using water.”

Running the capture systems from energy produced by the wind turbines can also address the financial burden that often goes along with removing CO2 from the air. “Even with tax credits and potentially selling the CO2, there’s a huge gap between the value that you can get from capturing it and the actual cost” that comes with powering capture with energy that comes from other sources, Nelson says. “Our method would be a no-cost added benefit” to wind turbine farms.

There are probably lots of factors that will impact CO2 transport by real-world turbines, including the interactions the turbine wakes have with water, plants and the ground, says Nicholas Hamilton, a mechanical engineer at the National Renewable Energy Laboratory in Golden, Colo., who was not involved with the new studies. “I’m interested to see how this group scaled their experiment for wind tunnel investigation.”

You might feel a spark when you talk to your crush, but living things don’t require romance to make electricity. A study published October 24 in iScience suggests that the electricity naturally produced by swarming insects like honeybees and locusts is an unappreciated contributor to the overall electric charge of the atmosphere.

“Particles in the atmosphere easily charge up,” says Joseph Dwyer, a physicist at the University of New Hampshire in Durham who was not involved with the study. “Insects are little particles moving around the atmosphere.” Despite this, the potential that insect-induced static electricity plays a role in the atmosphere’s electric field, which influences how water droplets form, dust particles move and lightning strikes brew, hasn’t been considered before, he says.
Scientists have known about the minuscule electric charge carried by living things, such as insects, for a long time. However, the idea that an electric bug-aloo could alter the charge in the air on a large scale came to researchers through sheer chance.

“We were actually interested in understanding how atmospheric electricity influences biology,” says Ellard Hunting, a biologist at the University of Bristol in England. But when a swarm of honeybees passed over a sensor meant to pick up background atmospheric electricity at the team’s field station, the scientists began to suspect that the influence could flow the other way too.

Hunting and colleagues, including biologists and physicists, measured the change in the strength of electric charge when other honeybee swarms passed over the sensor, revealing an average voltage increase of 100 volts per meter. The denser the insect swarm, the greater the charge produced.

This inspired the team to think about even larger insect swarms, like the biblical hordes of locusts that plagued Egypt in antiquity (and, in 2021, Las Vegas (SN: 3/30/21)). Flying objects, from animals to airplanes, build up static electricity as they move through the air. The team measured the charges of individual desert locusts (Schistocerca gregaria) as they flew in a wind tunnel powered by a computer fan. Taking data on locust density from other studies, the team then used a computer simulation based on the honeybee swarm data to scale up these single locust measurements into electric charge estimates for an entire locust swarm. Clouds of locusts could produce electricity on a per-meter basis on par with that in storm clouds, the scientists report.

Hunting says the results highlight the need to explore the unknown lives of airborne animals, which can sometimes reach much greater heights than honeybees or locusts. Spiders, for example, can soar kilometers above Earth when “ballooning” on silk threads to reach new habitats (SN: 7/5/18). “There’s a lot of biology in the sky,” he says, from insects and birds to microorganisms. “Everything adds up.”

Though some insect swarms can be immense, Dwyer says that electrically charged flying animals are unlikely to ever reach the density required to produce lightning like storm clouds do. But their presence could interfere with our efforts to watch for looming strikes that could hurt people or damage property.

“If you have something messing up our electric field measurements, that could cause a false alarm,” he says, “or it could make you miss something that’s actually important.” While the full effect that insects and other animals have on atmospheric electricity remains to be deduced, Dwyer says these results are “an interesting first look” into the phenomenon.

Hunting says this initial step into an exciting new area of research shows that working with scientists from different fields can spark shocking findings. “Being really interdisciplinary,” he says, “allows for these kinds of serendipitous moments.”

Aye-ayes are true champions of nose picking.

A new video offers the first evidence that these nocturnal lemurs of Madagascar stick their fingers up their noses and lick off the mucus. They don’t use just any finger for the job, either. The primates go spelunking for snot with the ultralong, witchy middle finger they typically use to find and fish grubs out of tree bark.

A reconstruction of the inside of an aye-aye’s head based on CT scans shows that this spindly digit probably pokes all the way through the animal’s nasal passages to reach its throat, researchers report online October 26 in the Journal of Zoology.
“This is a brilliant example of how science can serve human curiosity,” says Michael Haslam, a primate archaeologist based in London who was not involved in the new work. “My first take was that it’s a cool — and a bit creepy — video, but [the researchers] have gone beyond that initial reaction of ‘What on Earth?’ to actually explore what’s happening inside the animal.”

The new footage stars Kali, a female aye-aye (Daubentonia madagascariensis) at the Duke Lemur Center in Durham, N.C. “The aye-aye stopped eating and started to pick its nose, and I was really surprised,” says evolutionary biologist Anne-Claire Fabre, who filmed the video. “I was wondering where the finger was going.” An aye-aye is about as big as a house cat, but its clawed middle finger is some 8 centimeters long. And Kali was plunging almost the entire digit up her snout to sample her own snot with dainty licks.

“There is one moment where the camera is [shaking], and I was giggling,” says Fabre, of the Natural History Museum of Bern in Switzerland. Afterward, she asked her colleagues if they had ever seen an aye-aye picking its nose. “The ones that were working a lot with aye-ayes would tell me, ‘Oh, yeah, it’s happening really often,’” says Fabre, who later witnessed the behavior in several other aye-ayes.
This got Fabre and her colleagues curious about how many other primate species have been caught with their fingers in their nostrils. The researchers scoured the literature for past studies and the internet for other videos documenting the behavior.

Unfortunately, “most of the literature that we were finding were jokes,” Fabre says. “I was really surprised, because there is a lot of literature on other types of pretty gross behaviors, such as coprophagy,” or poo eating, among animals (SN: 7/19/21). But between all the bogus articles, the team did find some real reports of primate nose picking, including research done by Jane Goodall in the 1970s.

Aye-ayes are now the 12th known species of primate, including humans, to pick their noses and snack on the snot, the researchers found. Others include gorillas, chimpanzees, bonobos, orangutans and macaques. Nose pickers tend to be primates that have especially good dexterity and use tools.

“The team [has] given us the first map of nose picking across our primate family tree, which immediately raises questions about just how much of this behavior is happening out there, unseen or unreported,” Haslam says. He remembers once seeing a capuchin monkey using a twig or stem to pick its nose (SN: 9/6/15).

“I’m surprised that there aren’t more reports on nose picking, especially from zoos where animals are watched every day,” Haslam adds. “Perhaps our own social stigma around it means that scientists are less likely to want to report nose-picking animals, or it may even be seen as too common to be interesting.”
The fact that so many primate species have been spotted picking their noses and eating the boogers makes Fabre’s team and Haslam wonder whether this seemingly nasty habit has some unknown advantage. Perhaps eating germ-laden boogers boosts the immune system.

For now, untangling the evolutionary origins and potential perks of nose picking will require a more complete census of what species — primate or otherwise — mine and munch on their own mucus.

It’s official: The number of planets known beyond our solar system has just passed 5,000.

The exoplanet census surpassed this milestone with a recent batch of 60 confirmed exoplanets. These additional worlds were found in data from NASA’s now-defunct K2 mission, the “second life” of the prolific Kepler space telescope, and confirmed with new observations, researchers report March 4 at arXiv.org.

As of March 21, these finds put NASA’s official tally of exoplanets at 5,005.

It’s been 30 years since scientists discovered the first planets orbiting another star — an unlikely pair of small worlds huddled around a pulsar (SN: 1/11/92). Today, exoplanets are so common that astronomers expect most stars host at least one (SN: 1/11/12), says astronomer Aurora Kesseli of Caltech.
“One of the most exciting things that I think has happened in the last 30 years is that we’ve really started to be able to fill out the diversity of exoplanets,” Kesseli says

Some look like Jupiter, some look — perhaps — like Earth and some look like nothing familiar. The 5,005 confirmed exoplanets include nearly 1,500 giant gassy planets, roughly 200 that are small and rocky and almost 1,600 “super-Earths,” which are larger than our solar system’s rocky planets and smaller than Neptune (SN: 8/11/15).
Astronomers can’t say much about those worlds beyond diameters, masses and densities. But several projects, like the James Webb Space Telescope, are working on that, Kesseli says (SN: 1/24/22). “Not only are we going to find tons and tons more exoplanets, but we’re also going to start to be able to actually characterize the planets,” she says.

And the search is far from over. NASA’s newest exoplanet hunter, the TESS mission, has confirmed more than 200 planets, with thousands more yet to verify, Kesseli says (SN: 12/2/21). Ongoing searches from ground-based telescopes keep adding to the count as well.

“There’s tons of exoplanets out there,” Kesseli says, “and even more waiting to be discovered.”

Some asteroids can barely hold it together.

Rather than solid lumps of rock, ‘rubble pile’ asteroids are loose collections of material, which can split apart as they rotate (SN: 3/16/20). To understand the inner workings of such asteroids, one team of scientists turned to levitating plastic beads. The beads clump together, forming collections that can spin and break up, physicist Melody Lim of the University of Chicago reported March 15 at a meeting of the American Physical Society in Chicago.

It’s an elegant dance that mimics the physics of asteroid formation, which happens too slowly to observe in real-life space rocks. “These ‘tabletop asteroids’ compress phenomena that take place over kilometers [and] over hundreds of thousands of years to just centimeters and seconds in the lab,” Lim said. The results are also reported in a paper accepted in Physical Review X.
Lim and colleagues used sound waves to levitate the plastic beads, which arranged themselves into two-dimensional clumps. Acoustic forces attract the beads to one another, mimicking the gravitational attraction between bits of debris in space. Separate clumps then coalesced similarly to how asteroids are thought to glom onto one another to grow.
When the experimenters gave the structures a spin using the sound waves, the clumps changed shape above a certain speed, becoming elongated. That could help scientists understand why ‘rubble pile’ asteroids, can have odd structures, such as the ‘spinning tops’ formed by asteroids Bennu and Ryugu (SN: 12/18/18).

Eventually, the fast-spinning clumps broke apart. This observation could help explain why asteroids are typically seen to spin up to a certain rate, but not beyond: Speed demons get split up.

Since Russia’s invasion of Ukraine in late February, people around the world have watched the war play out in jarring detail — at least, in countries with open access to social media platforms such as Twitter, Facebook, TikTok and the messaging app Telegram.

“The way that social media has brought the war into the living rooms of people is quite astounding,” says Joan Donovan, the research director of the Shorenstein Center on Media, Politics and Public Policy at Harvard University. Fighting and explosions play out nearly in real time, and video messages from embattled Ukrainian president Volodymyr Zelenskyy have stirred support across the West.

But that’s not all. Social media is actually changing the way wars are fought today, says political scientist Thomas Zeitzoff of American University in Washington, D.C., who is an expert on political violence.
The platforms have become important places to recruit fighters, organize action, spread news and propaganda and — for social scientists — to gather data on conflicts as they unfold.

As social platforms have become more powerful, governments and politicians have stepped up efforts to use them — or ban them, as in Russia’s recent blocking of Facebook, Twitter and Instagram. And in a first, the White House held a special briefing on the Ukraine war with TikTok stars such as 18-year-old Ellie Zeiler, who has more than 10 million followers. The administration hopes to shape the messages of young influencers who are already important sources of news and information for their audiences.

The Ukraine war is shining a spotlight on social media’s role as a political tool, says Donovan, whose Technology and Social Change Project team has been following the spread of disinformation in the conflict. “This is a huge moment in internet history where we’re starting to see the power of these tech companies play out against the power of the state.” And that, she says, “is actually going to change the internet forever.”

Science News interviewed Donovan and Zeitzoff about social media’s influence on the conflict and vice versa. The following conversations have been edited for length and clarity.

SN: When did social media start to play a role in conflicts?

Zeitzoff: Some people would say the Zapatista uprising in Mexico, way back in the 1990s, because the Zapatistas used the internet [to spread their political message]. But I think the failed Green Revolution in Iran in 2007 and 2008 was one of the first, and especially the Arab Spring in the early 2010s. There was this idea that social media would be a “liberation technology” that allows people to hold truth to power.

But as the Arab Spring gave way to the Arab Winter [and its resurgence of authoritarianism], people started challenging that notion. Yes, it makes it easy to get a bunch of people out on the street [to protest], but it also makes it easier for governments to track these folks.
SN: How do you see social media being used in the Ukrainian conflict, and what’s different now?
Donovan: Some of the platforms that are more well-known, like Facebook and Twitter, are not as consequential as newer platforms like Telegram and TikTok. For instance, Ukrainian groups on Facebook started to build other channels for communication right before the Russian invasion because they felt that Facebook might get compromised. So Telegram has been a very important space for getting information and sharing news.

Telegram has also become a hot zone for propaganda and misinformation, where newer tactics are emerging such as fake debunked videos. These are videos that look like they’re news debunks showing that Ukraine is participating in media manipulation efforts, but they’re actually manufactured by Russia to make Ukraine look bad.

Zeitzoff: I think social media has probably afforded the Ukrainians an easier ability to communicate to their diaspora communities, whether in Canada, the United States or across Europe. It’s also increasingly affording unprecedented battlefield views.

But I think the bigger thing is to think about what these new suites of technology allow, like Volodymyr Zelenskyy holding live videos that basically allow him to show proof of life, and also put pressure on European leaders.

SN: Despite Russia’s big investments in disinformation, is Ukraine winning the social media war?

Zeitzoff: Up to the beginning of the conflict, many Ukrainians were skeptical of Zelenskyy’s ability to lead. But you look back at his presidential campaign, and he was doing Facebook videos where he would talk into the camera, in a very sort of intimate style of campaigning. So he knew how to use social media beforehand. And I think that has allowed Ukraine to communicate to Western audiences, basically, ‘give me money, give me weapons,’ and that has helped. There is an alternative scenario where perhaps if Russia’s military were slightly better organized and had a better social media campaign, it would become very difficult for Ukraine to hold.

And I would say that Russia’s propaganda has been sloppier. It’s not as good of a story. Ukraine already has the underdog sympathy, and they’ve been very good at capitalizing on it. They show their battlefield successes and highlight atrocities committed by Russians.

And the other thing is that social media has helped to organize foreign fighters and folks who have volunteered to go to Ukraine.

SN: Social media is also an enormous source of misinformation and disinformation. How is that playing out?

Donovan: We’re seeing recontextualized media [on TikTok and elsewhere], which is the reuse of content in a new context. And it usually also misrepresents the time and place of the content.

For instance, we’ve seen repurposed video game footage as if it was the war in Ukraine. While we [in the United States] don’t need real-time information to understand what’s happening in Ukraine, we do need access to the truth. Recontextualized media gets in the way of our right to truth.

And we want to make sure the information getting to people in Ukraine is as true and correct and vetted as possible, because they’re going to make a life-or-death decision that day about going out in search of food or trying to flee a certain area. So those people do need real-time accurate information.

There’s one other story about the way in which hope and morale can be decimated by disinformation. Among Ukrainians, there’s a lot of talk about when or if the United States or NATO will send planes. And there were these videos going around suggesting that the United States had already sent planes, and showing paratroopers jumping out. People were sharing these until they got to a reputable news source and heard the news that NATO was still not sending planes. So it can be something as innocent as a video that provides a massive amount of hope to people who share it, and then it’s all snatched away.

SN: What aren’t we seeing on social media?

Donovan: There’s a missing piece, which is that many social media algorithms are set to remove things that are torturous or gory. And so the very violent and vicious aftermath of war is something that the platforms are suppressing, just by virtue of their design.

So in order to get a complete picture of what has happened in Ukraine, people are going to have to see those videos [from other news sources] and be a global witness to the atrocity.

SN: Where is this all heading?

Zeitzoff: I think the biggest thing that’s changing is this decoupling of social media networks across great powers. So you have the Great Firewall [that censors the internet] in China, and I think Russia will be doing something very similar. And how does that influence the free flow of information?

Donovan: We try to understand how information warfare plays out as kind of a chess match between different actors. And what’s been incredible about the situation in Russia is you have this immense titan, the tech industry, pushing back on Russia by removing state media from their platforms. And then Russia counters by removing Facebook and Instagram in Russia.

This is the first time that we’ve seen these companies take action based on the request of other governments. In particular, Nick Clegg [the president of global affairs at Meta, the parent company of Facebook, Instagram and the messaging service WhatsApp] said that they were complying with Ukrainian asks. That means that they are taking some responsibility for the content that is being aired on their platforms. Whatever outcome happens over the next month, I don’t think the internet is going to be as global as it once was.

A new analysis of nearly a quarter million stars puts firm ages on the most momentous pages from our galaxy’s life story.

Far grander than most of its neighbors, the Milky Way arose long ago, as lesser galaxies smashed together. Its thick disk — a pancake-shaped population of old stars — originated remarkably soon after the Big Bang and well before most of the stellar halo that envelops the galaxy’s disk, astronomers report March 23 in Nature.

“We are now able to provide a very clear timeline of what happened in the earliest time of our Milky Way,” says astronomer Maosheng Xiang.
He and Hans-Walter Rix, both at the Max Planck Institute for Astronomy in Heidelberg, Germany, studied almost 250,000 subgiants — stars that are growing larger and cooler after using up the hydrogen fuel at their centers. The temperatures and luminosities of these stars reveal their ages, letting the researchers track how different epochs in galactic history spawned stars with different chemical compositions and orbits around the Milky Way’s center.

“There’s just an incredible amount of information here,” says Rosemary Wyse, an astrophysicist at Johns Hopkins University who was not involved with the study. “We really want to understand how our galaxy came to be the way it is,” she says. “When were the chemical elements of which we are made created?”

Xiang and Rix discovered that the Milky Way’s thick disk got its start about 13 billion years ago. That’s just 800 million years after the universe’s birth. The thick disk, which measures 6,000 light-years from top to bottom in the sun’s vicinity, kept forming stars for a long time, until about 8 billion years ago.

During this period, the thick disk’s iron content shot up 30-fold as exploding stars enriched its star-forming gas, the team found. At the dawn of the thick disk era, a newborn star had only a tenth as much iron, relative to hydrogen, as the sun; by the end, 5 billion years later, a thick disk star was three times richer in iron than the sun.

Xiang and Rix also found a tight relation between a thick disk star’s age and iron content. This means gas was thoroughly mixed throughout the thick disk: As time went on, newborn stars inherited steadily higher amounts of iron, no matter whether the stars formed close to or far from the galactic center.

But that’s not all that was happening. As other researchers reported in 2018, another galaxy once hit our own, giving the Milky Way most of the stars in its halo, which engulfs the disk (SN: 11/1/18). Halo stars have little iron.

The new work revises the date of this great galactic encounter: “We found that the merger happened 11 billion years ago,” Xiang says, a billion years earlier than thought. As the intruder’s gas crashed into the Milky Way’s gas, it triggered the creation of so many new stars that our galaxy’s star formation rate reached a record high 11 billion years ago.

The merger also splashed some thick disk stars up into the halo, which Xiang and Rix identified from the stars’ higher iron abundances. These “splash” stars, the researchers found, are at least 11 billion years old, confirming the date of the merger.

The thick disk ran out of gas 8 billion years ago and stopped making stars. Fresh gas around the Milky Way then settled into a thinner disk, which has given birth to stars ever since — including the 4.6-billion-year-old sun and most of its stellar neighbors. The thin disk is about 2,000 light-years thick in our part of the galaxy.

“The Milky Way has been quite quiet for the last 8 billion years,” Xiang says, experiencing no further encounters with big galaxies. That makes it different from most of its peers.

If the thick disk really existed 13 billion years ago, Xiang says, then the new James Webb Space Telescope (SN: 1/24/22) may discern similar disks in galaxies 13 billion light-years from Earth — portraits of the Milky Way as a young galaxy.

A fierce group of predatory dinosaurs may have done much of their hunting in the water.

An analysis of the bone density of several sharp-toothed spinosaurs suggests that several members of this dino group were predominantly aquatic, researchers report March 23 in Nature.

That finding is the latest salvo in an ongoing challenge to the prevailing view that all dinosaurs were land-based animals that left the realms of water and air to marine reptiles such as Mosasaurus and flying reptiles such as Pteranodon. But, other researchers say, it still doesn’t prove that Spinosaurus and its kin actually swam.
Back in 2014, Nizar Ibrahim, a vertebrate paleontologist now at the University of Portsmouth in England, and colleagues pieced together the fossil of a 15-meter-long Spinosaurus from what’s now Morocco. The dinosaur’s odd collection of features — a massive sail-like structure on its back, short and muscular legs, nostrils set well back from its snout and needlelike teeth seemingly designed for snagging fish — suggested to the researchers that the predator might have been a swimmer (SN: 9/11/14). In particular, it had very dense leg bones, a feature of some aquatic creatures like manatees that need the bones for ballast to stay submerged.

In the new study, Ibrahim and his team returned to that question of bone density to assess whether it’s a reliable proxy for how much time a creature spends in the water. The team assembled “a massive dataset” of femur and dorsal rib bone densities from “an incredible menagerie of extinct and living animals, reaching out to museum curators all around the world,” Ibrahim says.

That menagerie includes spinosaurs like showy, sail-backed Spinosaurus as well as its equally sharp-toothed cousins Baryonyx and Suchomimus. It also includes other groups of dinosaurs, extinct marine reptiles, pterosaurs, birds, modern crocodiles and marine mammals.

The team then compared these bone analyses with the water-dwelling habits of the various creatures in the study. That work confirms that density is “an excellent indicator” for species in the early stages of a transition from land-dwelling to water-dwelling, the team reports. Those compact bones can aid such transitional creatures, which might not yet have features like fins or flippers to help them maneuver in the water more easily, in hunting underwater — what the team calls “subaqueous foraging.”

The analyses also show that not only did Spinosaurus have very dense bones, but Baryonyx did too. That suggests that both of these dinos were subaqueous foragers, the team says. That idea builds on previous work by Ibrahim and colleagues that proposed that Spinosaurus didn’t just spend much of its time in the water, but could actually swim in pursuit of prey, thanks to its odd, paddle-shaped tail (SN: 4/29/20).
The idea of a swimming Spinosaurus hasn’t been convincing to all. In 2021, a study in Palaeontologia Electronica examined Spinosaurus’ anatomy in detail and came to a different conclusion. The dinosaur was not a highly specialized aquatic predator, wrote David Hone, a zoologist and paleobiologist at Queen Mary University of London, and Thomas Holtz Jr., a vertebrate paleontologist at the University of Maryland in College Park. Instead, Spinosaurus may have just waded in the shallows, heronlike, to do its fishing.

The new study has not convinced those skeptics. Spinosaurus has “clearly got very dense bones. This is really good evidence that they’re hanging around in water — but we kind of knew that,” Hone says. “It’s not clear what they’re doing in the water. That’s the contentious part.”

Take hippos, which spend much of their time mostly submerged, Hone says. “Hippos have bone densities entirely comparable to Spinosaurus and Baryonyx, but they don’t eat in the water” and they don’t swim, he adds.

“Everyone has been in agreement that Spinosaurus was more aquatic than other big theropods” like Tyrannosaurus rex, Holtz says. That Baryonyx also had dense bones was a bit of an interesting surprise, he adds.

But dense bones or not, Holtz says, “it still doesn’t turn them into aquatic hunters.” He describes several anatomical features — Spinosaurus’ long slender neck, tilted head and arrangement of neck muscles that suggest a downward striking motion — that point more to a wading creature that hunted from above the water surface than one that chased its prey underwater.

Kiersten Formoso, a vertebrate paleobiologist at the University of Southern California in Los Angeles, says that the new comparison of bone densities among a wide variety of creatures is a valuable addition, one that she anticipates referring to in her own work studying the transition of ancient creatures from land to water. But she too is not convinced that it proves that Spinosaurus and Baryonyx could actually swim.

“I would never detach Spinosaurus from the water,” Formoso says. But, she adds, more work needs to be done on its biomechanics — how it might have moved — to understand how adroitly aquatic the dinosaur might have been.

Smoke rings are being seen in a new light.

Doughnut-shaped structures called vortex rings are sometimes seen swirling through fluids. Smokers can form them with their mouths, volcanoes can spit them out during eruptions and dolphins can blow them as bubble rings. Now, scientists can create the rings with light.

A standard vortex is an eddy in a liquid or gas, like a whirlpool (SN: 3/5/13). Imagine taking that swirling eddy, stretching it out and bending it into a circle and attaching it end-to-end. That’s a vortex ring. These rings travel through the liquid or gas as they swirl — for example, smoke rings float through the air away from a smoker’s head. In the new vortex rings, described June 2 in Nature Photonics, light behaves similarly: The flow of energy swirls as the ring moves.
Optics researcher Qiwen Zhan and colleagues started from a vortex tube, a hurricanelike structure they already knew how to create using laser light. The team used optics techniques to bend the tube into a circular shape, creating a vortex ring.

The light rings aren’t that different from smoke or bubble rings, says Zhan, of the University of Shanghai for Science and Technology. “That’s kind of cool.”

Zhan is interested in seeing whether scientists could create vortex rings out of electric current or a magnetic field. And further study of the light rings might help scientists better understand how topology — the geometry of doughnuts, knots and similar shapes — affects light and how it interacts with matter.