Highly eccentric black hole merger discovered

For the first time, scientists believe they have detected a merger of two black holes with eccentric orbits. According to a paper published in Nature Astronomy by researchers from Rochester Institute of Technology's Center for Computational Relativity and Gravitation and the University of Florida, this can help explain how some of the black hole mergers detected by LIGO Scientific Collaboration and the Virgo Collaboration are much heavier than previously thought possible.

Eccentric orbits are a sign that black holes could be repeatedly gobbling up others during chance encounters in areas densely populated with black holes such as galactic nuclei. The scientists studied the most massive gravitational wave binary observed to date, GW190521, to determine if the merger had eccentric orbits.

"The estimated masses of the black holes are more than 70 times the size of our sun each, placing them well above the estimated maximum mass predicted currently by stellar evolution theory," said Carlos Lousto, a professor in the School of Mathematical Sciences and a member of the CCRG. "This makes an interesting case to study as a second generation binary black hole system and opens up to new possibilities of formation scenarios of black holes in dense star clusters."

A team of RIT researchers including Lousto, Research Associate James Healy, Jacob Lange '20 Ph.D. (astrophysical sciences and technology), Professor and CCRG Director Manuela Campanelli, Associate Professor Richard O'Shaughnessy, and collaborators from the University of Florida formed to give a fresh look at the data to see if the black holes had highly eccentric orbits before they merged. They found the merger is best explained by a high-eccentricity, precessing model. To achieve this, the team performed hundreds of new full numerical simulations in local and national lab supercomputers, taking nearly a year to complete.

"This represents a major advancement in our understanding of how black holes merge," said Campanelli. "Through our sophisticated supercomputer simulations and the wealth of new data provided by LIGO and Virgo's rapidly advancing detectors, we are making new discoveries about the universe at astonishing rates."

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Novel nanoantibiotics kill bacteria without harming healthy cells

The Centers for Disease Control and Prevention estimates that more than 2.8 million Americans experience antibiotic-resistant infections each year; more than 35,000 die from those infections.

To address this critical and worldwide public health issue, a team of researchers led by Hongjun (Henry) Liang, Ph.D., from the Texas Tech University Health Sciences Center (TTUHSC) Department of Cell Physiology and Molecular Biophysics, recently investigated whether or not a series of novel nanoparticles can kill some of the pathogens that lead to human infection without affecting healthy cells.

The study, "Hydrophilic Nanoparticles that Kill Bacteria while Sparing Mammalian Cells Reveal the Antibiotic Role of Nanostructures," was published Jan. 11 by Nature Communications. Other study members of the Liang team, all from TTUHSC, included Yunjiang Jiang, Ph.D., Wan Zheng, Ph.D., Keith Tran, Elizabeth Kamilar, Jitender Bariwal, Ph.D., and Hairong Ma, Ph.D.

Past research has shown that hydrophobicity (a molecule's ability to repel water) and hydrophilicity (a molecule's ability to attract and dissolve in water) affects cells; the more hydrophobic a substance is, the more adverse the reaction it will cause. However, Liang said, there is no quantitative standard for how much hydrophobicity is acceptable.

"Basically, you can kill bacteria when you increase hydrophobicity," Liang said. "But it will also kill healthy cells, and we don't want that."

For their study, the Liang team used novel hydrophilic nanoparticles known as nanoantibiotics that were developed by Liang's laboratory. Structurally speaking, these novel nanoantibiotics resemble tiny hairy spheres, each composed of many hydrophilic polymer brushes grafted onto silica nanoparticles of different sizes.

These synthetic compounds, which Liang's lab produces, are designed to kill bacteria via membrane disruptions like antimicrobial peptides do, but through a different mode of membrane remodeling that damages bacterial membranes and not mammalian cells. Antimicrobial peptides are a diverse class of amphipathic molecules (partially hydrophilic-partially hydrophobic), which occur naturally and serve as the first line of defense for all multicellular organisms. The direct use of antimicrobial peptides as antibiotics is limited by their stability and toxicity.

There have been other studies in which researchers grafted amphipathic molecules onto nanoparticles, and they too kill bacteria. However, Liang said the primary issue in using amphipathic molecules is that it becomes very difficult to strike the right balance between their hydrophobicity and hydrophilicity so that the toxicity of these molecules to our own cells is significantly reduced.

"In our case, we remove that uncertainty from the equation because we started with a hydrophilic polymer," Liang pointed out. "The cytotoxicity of hydrophobic moieties is not a concern anymore. Those hydrophilic polymers by themselves, or the silica nanoparticles alone don't kill bacteria; they have to be grafted onto the nanostructure to be able to kill bacteria. And so, this is the first important discovery."

The Liang team also discovered that the degree of antibiotic activity is affected by the size of the hairy spheres, which according to Liang is the second important discovery of this research. Those measuring 50 nanometers and below appear to be much more active than those whose size exceeds 50 nanometers. Liang said those measuring approximately 10 nanometers appear to be the most active. (Using synchrotron small angle x-ray scattering and other methods, the Liang team is able to interpret the molecular mechanism of the size-dependent antibiotic activity.)

These discoveries are important because using nanoantibiotics to kill bacteria evades all known mechanisms of bacterial resistance unless bacteria completely revamp their pathways for making cell membranes, which Liang said is unlikely.

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Consistent asteroid showers rock previous thinking on Mars craters

New Curtin University research has confirmed the frequency of asteroid collisions that formed impact craters on Mars has been consistent over the past 600 million years.

The study, published in Earth and Planetary Science Letters, analysed the formation of more than 500 large Martian craters using a crater detection algorithm previously developed at Curtin, which automatically counts the visible impact craters from a high-resolution image.

Despite previous studies suggesting spikes in the frequency of asteroid collisions, lead researcher Dr Anthony Lagain, from Curtin's School of Earth and Planetary Sciences, said his research had found they did not vary much at all for many millions of years.

Dr Lagain said counting impact craters on a planetary surface was the only way to accurately date geological events, such as canyons, rivers and volcanoes, and to predict when, and how big, future collisions would be.

"On Earth, the erosion of plate tectonics erases the history of our planet. Studying planetary bodies of our Solar System that still conserve their early geological history, such as Mars, helps us to understand the evolution of our planet," Dr Lagain said.

"The crater detection algorithm provides us with a thorough understanding of the formation of impact craters including their size and quantity, and the timing and frequency of the asteroid collisions that made them."

Past studies had suggested that there was a spike in the timing and frequency of asteroid collisions due to the production of debris, Dr Lagain said.

"When big bodies smash into each other, they break into pieces or debris, which is thought to have an effect on the creation of impact craters," Dr Lagain said.

"Our study shows it is unlikely that debris resulted in any changes to the formation of impact craters on planetary surfaces."

Co-author and leader of the team that created the algorithm, Professor Gretchen Benedix, said the algorithm could also be adapted to work on other planetary surfaces, including the Moon.

"The formation of thousands of lunar craters can now be dated automatically, and their formation frequency analysed at a higher resolution to investigate their evolution," Professor Benedix said.

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Using ice to boil water: Researcher makes heat transfer discovery that expands on 18th century principle

Associate Professor Jonathan Boreyko and graduate fellow Mojtaba Edalatpour have made a discovery about the properties of water that could provide an exciting addendum to a phenomenon established over two centuries ago. The discovery also holds interesting possibilities for cooling devices and processes in industrial applications using only the basic properties of water. Their work was published on Jan. 21 in the journal Physical Review Fluids.

Water can exist in three phases: a frozen solid, a liquid, and a gas. When heat is applied to a frozen solid, it becomes a liquid. When applied to the liquid, it becomes vapor. This elementary principle is familiar to anyone who has observed a glass of iced tea on a hot day, or boiled a pot of water to make spaghetti.

When the heat source is hot enough, the water's behavior changes dramatically. According to Boreyko, a water droplet deposited onto an aluminum plate heated to 150 degrees Celsius (302 degrees Fahrenheit) or above will no longer boil. Instead, the vapor that forms when the droplet approaches the surface will become trapped beneath the droplet, creating a cushion that prevents the liquid from making direct contact with the surface. The trapped vapor causes the liquid to levitate, sliding around the heated surface like an air hockey puck. This phenomenon is known as the Leidenfrost effect, named for the German doctor and theologian who first described it in a 1751 publication.

This commonly accepted scientific principle applies to water as a liquid, floating on a bed of vapor. Boreyko's team found themselves wondering: Could ice perform in the same way?

"There are so many papers out there about levitating liquid, we wanted to ask the question about levitating ice," said Boreyko. "It started as a curiosity project. What drove our research was the question of whether or not it was possible to have a three-phase Leidenfrost effect with solid, liquid, and vapor."

Going into the ice

Curiosity sparked the first investigation in Boreyko's lab some five years ago in the form of a research project by then-undergraduate student Daniel Cusumano. What he observed was fascinating. Even when the aluminum was heated above 150 C, the ice did not levitate on vapor as liquid does. Cusumano continued raising the temperature, observing the behavior of the ice as the heat increased. What he found was that the threshold for levitation was dramatically higher: 550 C (1022 F) rather than 150 C. Up until that threshold, the meltwater beneath the ice continued to boil in direct contact with the surface, rather than exhibit the Leidenfrost effect.

What was going on underneath the ice that prolonged the boiling? The project was picked back up by graduate student Mojtaba Edalatpour a short time later, to solve the mystery. Edalatpour had been working with Boreyko to develop novel methods of heat transfer and put that knowledge to work in approaching this problem. The answer turned out to be the temperature differential in the meltwater layer beneath the ice. The meltwater layer has two different extremes: Its bottom is boiling, which fixes the temperature at about 100 C, but its top is adhered to the remaining ice, which fixes it at about 0 C. Edalatpour's model revealed that the maintenance of this extreme temperature differential consumes most of the surface's heat, explaining why levitation was more difficult for ice.

Boreyko elaborated. "The temperature differential the ice is uniquely creating across the water layer has changed what happens in the water itself, because now most of the heat from the hot plate has to go across the water to maintain that extreme differential. So only a tiny fraction of the energy can be used to produce vapor anymore."

The elevated temperature of 550 degrees Celsius for the icy Leidenfrost effect is practically important. Boiling water is optimally transporting heat away from the substrate, which is why you feel ample heat rising from a pot of water that is boiling, but not from a pot of water that is merely hot. This means that the difficulty in levitating ice is actually a good thing, as the larger temperature window for boiling will result in better heat transfer compared to using a liquid alone.

"It is much harder to levitate the ice than it was to levitate the water droplet," said Boreyko. "Heat transfer plummets as soon as levitation begins, because when liquid levitates, it doesn't boil anymore. It's floating over the surface rather than touching, and touching is what causes it to boil the heat away. So, for heat transfer, levitation is terrible. Boiling is incredible."

Using ice for heat transfer

As the team explored possibilities for practical application, they looked to their existing work. Since Edalatpour had extensive research in heat transfer, that topic became a logical fit.

Heat transfer comes most into play for cooling off things like computer servers or car engines. It requires a substance or mechanism that can move energy away from a hot surface, redistributing heat quickly to reduce the wear and tear on metal parts. In nuclear power plants, the application of ice to induce rapid cooling could become an easily-deployed emergency measure if power fails, or a regular practice for servicing power plant parts.

There are also potential applications for metallurgy. To produce alloys, it is necessary to quench the heat from metals that have been shaped in a narrow window of time, making the metal stronger and less brittle. If ice were applied, it would allow heat to be offloaded rapidly through the three water phases, quickly cooling the metal.

Boreyko also foresees a potential for applications in firefighting.

"You could imagine having a specially made hose that is spraying ice chips as opposed to a jet of water," he said. "This is not science fiction. I visited an aerospace company that has an icing tunnel and they already have this technology where a nozzle sprays out ice particles as opposed to water droplets."

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Muscular study provides new information about how the largest dinosaurs moved and evolved

New research led by the University of Bristol has revealed how giant 50-tonne sauropod dinosaurs, like Diplodocus, evolved from much smaller ancestors, like the wolf-sized Thecodontosaurus.

In a new study published today in the journal Royal Society Open Science, researchers present a reconstruction of the limb muscles of Thecodontosaurus, detailing the anatomy of the most important muscles involved in movement.

Thecodontosaurus was a small to medium sized two-legged dinosaur that roamed around what today is the United Kingdom during the Triassic period (around 205 million years ago).

This dinosaur was one of the first ever to be discovered and named by scientists, in 1836, but it still surprises scientists with new information about how the earliest dinosaurs lived and evolved.

Antonio Ballell, PhD student in Bristol's School of Earth Sciences and lead author of the study, said: "The University of Bristol houses a huge collection of beautifully preserved Thecodontosaurus fossils that were discovered around Bristol. The amazing thing about these fossilised bones is that many preserve the scars and rugosities that the limb musculature left on them with its attachment."

These features are extremely valuable in scientific terms to infer the shape and direction of the limb muscles. Reconstructing muscles in extinct species requires this kind of exceptional preservation of fossils, but also a good understanding of the muscle anatomy of living, closely related species.

Antonio Ballell added: "In the case of dinosaurs, we have to look at modern crocodilians and birds, that form a group that we call archosaurs, meaning 'ruling reptiles'. Dinosaurs are extinct members of this lineage, and due to evolutionary resemblance, we can compare the muscle anatomy in crocodiles and birds and study the scars that they leave on bones to identify and reconstruct the position of those muscles in dinosaurs."

Professor Emily Rayfield, co-author of the study, said: "These kinds of muscular reconstructions are fundamental to understand functional aspects of the life of extinct organisms. We can use this information to simulate how these animals walked and ran with computational tools."

From the size and orientation of its limb muscles, the authors argue that Thecodontosaurus was quite agile and probably used its forelimbs to grasp objects instead of walking.

This contrasts with its later relatives, the giant sauropods, which partly achieved these huge body sizes by shifting to a quadrupedal posture. The muscular anatomy of Thecodontosaurus seems to indicate that key features of later sauropod-line dinosaurs had already evolved in this early species.

Professor Mike Benton, another co-author, said: "From an evolutionary perspective, our study adds more pieces to the puzzle of how the locomotion and posture changed during the evolution of dinosaurs and in the line to the giant sauropods.

"How were limb muscles modified in the evolution of multi-ton quadrupeds from tiny bipeds? Reconstructing the limb muscles of Thecodontosaurus gives us new information of the early stages of that important evolutionary transition."

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Scientists find previously unknown jumping behavior in insects

A team of researchers has discovered a jumping behavior that is entirely new to insect larvae, and there is evidence that it is occurring in a range of species -- we just haven't noticed it before.

The previously unrecorded behavior occurs in the larvae of a species of lined flat bark beetle (Laemophloeus biguttatus). Specifically, the larvae are able to spring into the air, with each larva curling itself into a loop as it leaps forward. What makes these leaps unique is how the larvae are able to pull it off.

"Jumping at all is exceedingly rare in the larvae of beetle species, and the mechanism they use to execute their leaps is -- as far as we can tell -- previously unrecorded in any insect larvae," says Matt Bertone, corresponding author of a paper on the discovery and director of North Carolina State University's Plant Disease and Insect Clinic.

While there are other insect species that are capable of making prodigious leaps, they rely on something called a "latch-mediated spring actuation mechanism." This means that they essentially have two parts of their body latch onto each other while the insect exerts force, building up a significant amount of energy. The insect then unlatches the two parts, releasing all of that energy at once, allowing it to spring off the ground.

"What makes the L. biguttatus so remarkable is that it makes these leaps without latching two parts of its body together," Bertone says. "Instead, it uses claws on its legs to grip the ground while it builds up that potential energy -- and once those claws release their hold on the ground, that potential energy is converted into kinetic energy, launching it skyward."

The discovery of the behavior was somewhat serendipitous. Bertone had collected a variety of insect samples from a rotting tree near his lab in order to photograph them when he noticed that these beetle larvae appeared to be hopping.

Bertone and paper co-author Adrian Smith then decided to film the behavior in order to get a better look at what was going on. That's when they began to understand just how peculiar the behavior was. Smith is a research assistant professor of biological sciences at NC State and head of the Evolutionary Biology & Behavior Research Lab at the North Carolina Museum of Natural Sciences.

"The way these larvae were jumping was impressive at first, but we didn't immediately understand how unique it was," Bertone says. "We then shared it with a number of beetle experts around the country, and none of them had seen the jumping behavior before. That's when we realized we needed to take a closer look at just how the larvae was doing what it was doing."

To determine how L. biguttatus was able to execute its acrobatics, the researchers filmed the jumps at speeds of up to 60,000 frames per second. This allowed them to capture all of the external movements associated with the jumps, and suggested that the legs were essentially creating a latching mechanism with the ground.

The researchers also conducted a muscle mass assessment to determine whether it was possible for the larvae to make their leaps using just their muscles, as opposed to using a latch mechanism to store energy. They found that the larvae lacked sufficient muscle to hurl themselves into the air as far or as fast as they had been filmed jumping. Ergo, latching onto the ground was the only way the larvae could pull off their aerial feats.

Meanwhile, in an unrelated video about jumping maggots, Smith had included a short clip of the jumping behavior in L. biguttatus. That video was seen by a researcher in Japan named Takahiro Yoshida, who had witnessed similar jumps in the larvae of another beetle species called Placonotus testaceus, but had not published anything related to the behavior.

"We don't have high-speed footage of P. testaceus, but the video evidence we do have from Yoshida's lab suggests that this previously unknown behavior is found in two different genera which are not even closely related," Bertone says.

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Hubble finds a black hole igniting star formation in a dwarf galaxy

Often portrayed as destructive monsters that hold light captive, black holes take on a less villainous role in the latest research from NASA's Hubble Space Telescope. A black hole at the heart of the dwarf galaxy Henize 2-10 is creating stars rather than gobbling them up. The black hole is apparently contributing to the firestorm of new star formation taking place in the galaxy. The dwarf galaxy lies 30 million light-years away, in the southern constellation Pyxis.

A decade ago this small galaxy set off debate among astronomers as to whether dwarf galaxies were home to black holes proportional to the supermassive behemoths found in the hearts of larger galaxies. This new discovery has little Henize 2-10, containing only one-tenth the number of stars found in our Milky Way, poised to play a big part in solving the mystery of where supermassive black holes came from in the first place.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

"Ten years ago, as a graduate student thinking I would spend my career on star formation, I looked at the data from Henize 2-10 and everything changed," said Amy Reines, who published the first evidence for a black hole in the galaxy in 2011 and is the principal investigator on the new Hubble observations, published in the January 19 issue of Nature.

"From the beginning I knew something unusual and special was happening in Henize 2-10, and now Hubble has provided a very clear picture of the connection between the black hole and a neighboring star forming region located 230 light-years from the black hole," Reines said.

That connection is an outflow of gas stretching across space like an umbilical cord to a bright stellar nursery. The region was already home to a dense cocoon of gas when the low-velocity outflow arrived. Hubble spectroscopy shows the outflow was moving about 1 million miles per hour, slamming into the dense gas like a garden hose hitting a pile of dirt and spreading out. Newborn star clusters dot the path of the outflow's spread, their ages also calculated by Hubble.

This is the opposite effect of what's seen in larger galaxies, where material falling toward the black hole is whisked away by surrounding magnetic fields, forming blazing jets of plasma moving at close to the speed of light. Gas clouds caught in the jets' path would be heated far beyond their ability to cool back down and form stars. But with the less-massive black hole in Henize 2-10, and its gentler outflow, gas was compressed just enough to precipitate new star formation.

"At only 30 million light-years away, Henize 2-10 is close enough that Hubble was able to capture both images and spectroscopic evidence of a black hole outflow very clearly. The additional surprise was that, rather than suppressing star formation, the outflow was triggering the birth of new stars," said Zachary Schutte, Reines' graduate student and lead author of the new study.

Ever since her first discovery of distinctive radio and X-ray emissions in Henize 2-10, Reines has thought they likely came from a massive black hole, but not as supermassive as those seen in larger galaxies. Other astronomers, however, thought that the radiation was more likely being emitted by a supernova remnant, which would be a familiar occurrence in a galaxy that is rapidly pumping out massive stars that quickly explode.

"Hubble's amazing resolution clearly shows a corkscrew-like pattern in the velocities of the gas, which we can fit to the model of a precessing, or wobbling, outflow from a black hole. A supernova remnant would not have that pattern, and so it is effectively our smoking-gun proof that this is a black hole," Reines said.

Reines expects that even more research will be directed at dwarf galaxy black holes in the future, with the aim of using them as clues to the mystery of how supermassive black holes came to be in the early universe. It's a persistent puzzle for astronomers. The relationship between the mass of the galaxy and its black hole can provide clues. The black hole in Henize 2-10 is around 1 million solar masses. In larger galaxies, black holes can be more than 1 billion times our Sun's mass. The more massive the host galaxy, the more massive the central black hole.

Current theories on the origin of supermassive black holes break down into three categories: 1) they formed just like smaller stellar-mass black holes, from the implosion of stars, and somehow gathered enough material to grow supermassive, 2) special conditions in the early universe allowed for the formation of supermassive stars, which collapsed to form massive black hole "seeds" right off the bat, or 3) the seeds of future supermassive black holes were born in dense star clusters, where the cluster's overall mass would have been enough to somehow create them from gravitational collapse.

So far, none of these black hole seeding theories has taken the lead. Dwarf galaxies like Henize 2-10 offer promising potential clues, because they have remained small over cosmic time, rather than undergoing the growth and mergers of large galaxies like the Milky Way. Astronomers think that dwarf galaxy black holes could serve as an analog for black holes in the early universe, when they were just beginning to form and grow.

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Haunted-house experience scares up interesting insights on the body’s reaction to threats

The so-called fight-or-flight response is evolution's way of preparing the body to defend itself or flee from a real or perceived threat, like a lion in the tall grass or -- in modern times -- an overdue performance review.

Scientists have struggled to study the effects of genuine threats on people's mental and physical state because of ethical and practical constraints of human lab experiments.

In new research published in the journal Psychological Science, researchers used a haunted-house experience to study participants' subjective and physiological responses to perceived threats in a safe yet immersive environment.

In this haunted-house setting, which included 17 rooms with various threats that formed an uninterrupted experience, the researchers examined how the body responds to threats differently depending on the social context (whether friends were around), features of the threats (whether they were expected), and emotions (whether individuals felt afraid).

"There are a lot of factors that influence how human bodies respond to threat," said Sarah M. Tashjian, of the Division of Humanities and Social Sciences at the California Institute of Technology and lead author of the study. "We found that friend-related emotional contagion, threat predictability, and subjective feelings of fear were all relevant for the body mounting a response."

All of these factors help increase a person's ability to survive when under threat, but in the study, each had slightly different influences, which demonstrate the dynamic nature of the sympathetic nervous system.

To study the effects of frightening experiences, previous studies used scary images, mild electric shocks, or loud noises. In the current study, 156 participants went through the haunted house in small groups. During the 30-minute experience, they encountered situations that mimicked the threat of suffocation, an oncoming speeding car, and a volley of shots (with pellets) from a firing squad.

Participants wore real-time physiological-monitoring wristbands to measure their electrodermal activity, or sweat-induced changes in the skin's electrical characteristics, including skin conductance level and skin conductance response.

Before visiting the haunted house, participants rated their expected fear on a scale from 1 to 10. Afterward, they rated their experienced fear level on the same scale. From these data, four factors were examined, including group composition, threat imminence, intrapersonal factors of fear, and a "baseline orienting response," or the participant's sensitivity to threats.

Results showed a positive association between the number of friends in a group and tonic arousal, which reflects the body's overall physical response to stress or emotion. On average, the more friends that participants had with them while touring the haunted house, the higher their physical response.

"We interpreted this to reflect fear contagion -- if your friends are around, your body picks up on their signals and has a higher level of arousal even in the absence of specific scares or startles," Tashjian said. "In the lab, it is difficult to study the effects of groups on physiology."

Studies usually involve testing one person at a time or, at most, pairs of friends. In this study, the researchers had the unique opportunity to study how being in groups with different mixes of friends and strangers affected people's perceptions of threat.

The researchers also noted positive associations between unexpected attacks, subjective fear, and phasic frequency. Phasic effects are rapid changes the body experiences as it responds to an event. Individuals who felt the most afraid during the haunted house had more peaks in these responses. "If your body is more cued-in to the threatening event, you also psychologically feel more fear," Tashjian said.

Other findings revealed that participants with an initially strong response to the first room of the haunted house showed increased responses as they visited other rooms. Participants with more frequent responses in the first room showed decreased responses over time.

"From a results perspective, this study is distinct because we measure multiple aspects of skin conductance, including slow responding, rapid responding, frequency of responses, and level of responses," Tashjian explained. "Most studies use just one of these measures, which limits our understanding of how dynamic the sympathetic nervous system is and how different factors exert different influences on biology."

She added that the research is a "major advance for cognitive and social psychology," because it furthers the understanding of how "naturalistic contexts," such as the immersive haunted house experience, influence the body's response to threats. Also significant is the finding that friends amplify the physical response.

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COVID-19 vaccines do not cause infertility, study finds

COVID-19 vaccination in either partner does not appear to affect fertility, according to new research led by Boston University School of Public Health (BUSPH) investigators.

Published in the American Journal of Epidemiology, the prospective study of couples trying to conceive found no association between COVID-19 vaccination and fecundability -- the probability of conception per menstrual cycle -- in female or male partners who received the Pfizer-BioNTech, Moderna, or Johnson & Johnson vaccines.

In contrast, the findings indicate that COVID-19 infection among males may temporarily reduce fertility -- an outcome that could be avoidable through vaccination.

"Many reproductive-aged individuals have cited concerns about fertility as a reason for remaining unvaccinated," says study lead author Dr. Amelia Wesselink, research assistant professor of epidemiology at BUSPH. "Our study shows for the first time that COVID-19 vaccination in either partner is unrelated to fertility among couples trying to conceive through intercourse. Time-to-pregnancy was very similar regardless of vaccination status."

Wesselink and colleagues analyzed survey data on COVID-19 vaccination and infection, and fecundability, among female and male participants in the BUSPH-based Pregnancy Study Online (PRESTO), an ongoing NIH-funded study that enrolls women trying to conceive, and follows them from preconception through six months after delivery. Participants included 2,126 women in the US and Canada who provided information on sociodemographics, lifestyle, medical factors, and characteristics of their partners from December 2020 to September 2021, and the participants were followed in the study through November 2021.

The researchers calculated the per menstrual cycle probability of conception using self-reported dates of participants' last menstrual period, typical menstrual cycle length, and pregnancy status. Fertility rates among female participants who received at least one dose of a vaccine were nearly identical to unvaccinated female participants. Fecundability was also similar for male partners who had received at least one dose of a COVID-19 vaccine compared with unvaccinated male participants. Additional analyses that considered the number of vaccine doses, brand of vaccine, infertility history, occupation, and geographic region also indicated no effect of vaccination on fertility.

While COVID-19 infection was not strongly associated with fertility, men who tested positive for COVID within 60 days of a given cycle had reduced fertility compared to men who never tested positive, or men who tested positive at least 60 days prior. This data supports previous research that has linked COVID-19 infection in men with poor sperm quality and other reproductive dysfunction.

"These data provide reassuring evidence that COVID vaccination in either partner does not affect fertility among couples trying to conceive," says study senior author Dr. Lauren Wise, professor of epidemiology at BUSPH. "The prospective study design, large sample size, and geographically heterogeneous study population are study strengths, as was our control for many variables such as age, socioeconomic status, preexisting health conditions, occupation, and stress levels."

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Babies can tell who has close relationships based on one clue: Saliva

Learning to navigate social relationships is a skill that is critical for surviving in human societies. For babies and young children, that means learning who they can count on to take care of them.

MIT neuroscientists have now identified a specific signal that young children and even babies use to determine whether two people have a strong relationship and a mutual obligation to help each other: whether those two people kiss, share food, or have other interactions that involve sharing saliva.

In a new study, the researchers showed that babies expect people who share saliva to come to one another's aid when one person is in distress, much more so than when people share toys or interact in other ways that do not involve saliva exchange. The findings suggest that babies can use these cues to try to figure out who around them is most likely to offer help, the researchers say.

"Babies don't know in advance which relationships are the close and morally obligating ones, so they have to have some way of learning this by looking at what happens around them," says Rebecca Saxe, the John W. Jarve Professor of Brain and Cognitive Sciences, a member of MIT's McGovern Institute for Brain Research, and the senior author of the new study.

MIT postdoc Ashley Thomas is the lead author of the study, which appears today in Science. Brandon Woo, a Harvard University graduate student; Daniel Nettle, a professor of behavioral science at Newcastle University; and Elizabeth Spelke, a professor of psychology at Harvard, are also authors of the paper.

Sharing saliva

In human societies, people typically distinguish between "thick" and "thin" relationships. Thick relationships, usually found between family members, feature strong levels of attachment, obligation, and mutual responsiveness. Anthropologists have also observed that people in thick relationships are more willing to share bodily fluids such as saliva.

"That inspired both the question of whether infants distinguish between those types of relationships, and whether saliva sharing might be a really good cue they could use to recognize them," Thomas says.

To study those questions, the researchers observed toddlers (16.5 to 18.5 months) and babies (8.5 to 10 months) as they watched interactions between human actors and puppets. In the first set of experiments, a puppet shared an orange with one actor, then tossed a ball back and forth with a different actor.

After the children watched these initial interactions, the researchers observed the children's reactions when the puppet showed distress while sitting between the two actors. Based on an earlier study of nonhuman primates, the researchers hypothesized that babies would look first at the person whom they expected to help. That study showed that when baby monkeys cry, other members of the troop look to the baby's parents, as if expecting them to step in.

The MIT team found that the children were more likely to look toward the actor who had shared food with the puppet, not the one who had shared a toy, when the puppet was in distress.

In a second set of experiments, designed to focus more specifically on saliva, the actor either placed her finger in her mouth and then into the mouth of the puppet, or placed her finger on her forehead and then onto the forehead of the puppet. Later, when the actor expressed distress while standing between the two puppets, children watching the video were more likely to look toward the puppet with whom she had shared saliva.

Social cues

The findings suggest that saliva sharing is likely an important cue that helps infants to learn about their own social relationships and those of people around them, the researchers say.

"The general skill of learning about social relationships is very useful," Thomas says. "One reason why this distinction between thick and thin might be important for infants in particular, especially human infants, who depend on adults for longer than many other species, is that it might be a good way to figure out who else can provide the support that they depend on to survive."

The researchers did their first set of studies shortly before Covid-19 lockdowns began, with babies who came to the lab with their families. Later experiments were done over Zoom. The results that the researchers saw were similar before and after the pandemic, confirming that pandemic-related hygiene concerns did not affect the outcome.

"We actually know the results would have been similar if it hadn't been for the pandemic," Saxe says. "You might wonder, did kids start to think very differently about sharing saliva when suddenly everybody was talking about hygiene all the time? So, for that question, it's very useful that we had an initial data set collected before the pandemic."

Doing the second set of studies on Zoom also allowed the researchers to recruit a much more diverse group of children because the subjects were not limited to families who could come to the lab in Cambridge during normal working hours.

In future work, the researchers hope to perform similar studies with infants in cultures that have different types of family structures. In adult subjects, they plan to use functional magnetic resonance imaging (fMRI) to study what parts of the brain are involved in making saliva-based assessments about social relationships.

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