Full 3-D view of binary star-planet system

By precisely tracing a small, almost imperceptible, wobble in a nearby star's motion through space, astronomers have discovered a Jupiter-like planet orbiting that star, which is one of a binary pair. Their work, using the National Science Foundation's Very Long Baseline Array (VLBA), produced the first-ever determination of the complete, 3-dimensional structure of the orbits of a binary pair of stars and a planet orbiting one of them. This achievement, the astronomers said, can provide valuable new insights on the process of planet formation.

Though more than 5,000 extrasolar planets have been discovered so far, only three have been discovered using the technique -- called astrometry -- that produced this discovery. However, the feat of determining the 3-D architecture of a binary-star system that includes a planet "cannot be achieved with other exoplanet discovery methods," said Salvador Curiel, of the National Autonomous University of Mexico (UNAM).

"Since most stars are in binary or multiple systems, being able to understand systems such as this one will help us understand planet formation in general," Curiel said.

The two stars, which together are called GJ 896AB, are about 20 light-years from Earth -- close neighbors by astronomical standards. They are red dwarf stars, the most common type in our Milky Way galaxy. The larger one, around which the planet orbits, has about 44 percent of the mass of our Sun, while the smaller is about 17 percent as massive as the Sun. They are separated by about the distance of Neptune from the Sun, and orbit each other once every 229 years.

For their study of GJ 896AB, the astronomers combined data from optical observations of the system made between 1941 and 2017 with data from VLBA observations between 2006 and 2011. They then made new VLBA observations in 2020. The continent-wide VLBA's supersharp resolution -- ability to see fine detail -- produced extremely precise measurements of the stars' positions over time. The astronomers performed extensive analysis of the data that revealed the stars' orbital motions as well as their common motion through space.

Detailed tracing of the larger star's motion showed a slight wobble that revealed the existence of the planet. The wobble is caused by the planet's gravitational effect on the star. The star and planet orbit a location between them that represents their common center of mass. When that location, called the barycenter, is sufficiently far from the star, the star's motion around it can be detectable.

The astronomers calculated that the planet has about twice the mass of Jupiter and orbits the star every 284 days. Its distance from the star is slightly less than Venus' distance from the Sun. The planet's orbit is inclined roughly 148 degrees from the orbits of the two stars.

"This means that the planet moves around the main star in the opposite direction to that of the secondary star around the main star," said Gisela Ortiz-León, of UNAM and the Max Planck Institute for Radioastronomy. "This is the first time that such dynamical structure has been observed in a planet associated with a compact binary system that presumably was formed in the same protoplanetary disk," she added.

"Additional detailed studies of this and similar systems can help us gain important insights into how planets are formed in binary systems. There are alternate theories for the formation mechanism, and more data can possibly indicate which is most likely," said Joel Sanchez-Bermudez, of UNAM. "In particular, current models indicate that such a large planet is very unlikely as a companion to such a small star, so maybe those models need to be adjusted," he added.

The astrometric technique will be a valuable tool for characterizing more planetary systems, the astronomers said. "We can do much more work like this with the planned Next Generation VLA (ngVLA)," said Amy Mioduszewski, of the National Radio Astronomy Observatory. "With it, we may be able to find planets as small as the Earth."

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How the gut may help to drive COVID-19

New findings from Flinders University have demonstrated a molecular link between COVID-19 and serotonin cells in the gut.

The research could help provide further clues to what could be driving COVID-19 infection and disease severity and supports previous evidence that antidepressants, known as selective serotonin reuptake inhibitors (SSRIs), could reduce the severity of COVID symptoms.

COVID-19 displays an array of symptoms, which can regularly include gastrointestinal issues such as diarrhoea. Recent research has indicated that these gut symptoms in COVID-19 patients worsen with the severity of the disease, and this is linked to heightened gut-derived serotonin, released to cause gut dysfunction, increasing the body's immune response and potentially worsening patient outcomes.

Published in the world's leading gastrointestinal research journal Gut, this new collaborative study involved three Flinders research teams, including teams led by ARC DECRA Fellow Dr Alyce Martin and FAME Director of Bioinformatics and Human-Microbe Interactions, Professor Robert Edwards.

"Our study endeavoured to understand whether the gut could be a site of disease transmission and what genes might be associated with the virus entering the cells lining the gut wall," says study senior author Professor Damien Keating, Deputy Director of the Flinders Health and Medical Research Institute and Head of the Gut Sensory Systems research group.

The researchers looked at gene expression amongst the different cell types that line the gut wall, analysing whole genome sequences from thousands of individual cells from within the intestine.

They found specialised cells within the gut that synthesised and released serotonin had a highly enriched expression of a particular SARS-CoV-2 receptor and were the only type of cell that expressed all the genes associated with COVID-19.

"Many genes linked to COVID-19 were found expressed in the different cell types lining the gut wall but only serotonin cells expressed all three receptors for the virus," says Professor Keating.

"Expression of all three SARS-CoV-2 receptors triples the rate of cell infectivity, compared to expression of only two receptors."

With the exact sites of infection and the primary drivers of COVID-19 disease severity not yet fully understood, the authors say this study provides important information on the gut's role in the virus.

"Our study adds further evidence that COVID-19 is far more likely to infect cells in the gut and increase serotonin levels through direct effects on specific gut cells, potentially worsening disease outcomes," says Professor Keating.

"It also provides further support to emerging clinical evidence that antidepressant drugs, which block serotonin transport around the body, may serve as a beneficial treatment.

"As COVID-19 continues to circulate, further research will be required to advance our understanding of the gut's role in this virus and continue to find treatment options to work alongside vaccinations."

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NASA's Webb takes its first-ever direct image of distant world

For the first time, astronomers have used NASA's James Webb Space Telescope to take a direct image of a planet outside our solar system. The exoplanet is a gas giant, meaning it has no rocky surface and could not be habitable.

The image, as seen through four different light filters, shows how Webb's powerful infrared gaze can easily capture worlds beyond our solar system, pointing the way to future observations that will reveal more information than ever before about exoplanets.

"This is a transformative moment, not only for Webb but also for astronomy generally," said Sasha Hinkley, associate professor of physics and astronomy at the University of Exeter in the United Kingdom, who led these observations with a large international collaboration. Webb is an international mission led by NASA in collaboration with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

The exoplanet in Webb's image, called HIP 65426 b, is about six to 12 times the mass of Jupiter, and these observations could help narrow that down even further. It is young as planets go -- about 15 to 20 million years old, compared to our 4.5-billion-year-old Earth.

Astronomers discovered the planet in 2017 using the SPHERE instrument on the European Southern Observatory's Very Large Telescope in Chile and took images of it using short infrared wavelengths of light. Webb's view, at longer infrared wavelengths, reveals new details that ground-based telescopes would not be able to detect because of the intrinsic infrared glow of Earth's atmosphere.

Researchers have been analyzing the data from these observations and are preparing a paper they will submit to journals for peer review. But Webb's first capture of an exoplanet already hints at future possibilities for studying distant worlds.

Since HIP 65426 b is about 100 times farther from its host star than Earth is from the Sun, it is sufficiently distant from the star that Webb can easily separate the planet from the star in the image.

Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) are both equipped with coronagraphs, which are sets of tiny masks that block out starlight, enabling Webb to take direct images of certain exoplanets like this one. NASA's Nancy Grace Roman Space Telescope, slated to launch later this decade, will demonstrate an even more advanced coronagraph.

"It was really impressive how well the Webb coronagraphs worked to suppress the light of the host star," Hinkley said.

Taking direct images of exoplanets is challenging because stars are so much brighter than planets. The HIP 65426 b planet is more than 10,000 times fainter than its host star in the near-infrared, and a few thousand times fainter in the mid-infrared.

In each filter image, the planet appears as a slightly differently shaped blob of light. That is because of the particulars of Webb's optical system and how it translates light through the different optics.

"Obtaining this image felt like digging for space treasure," said Aarynn Carter, a postdoctoral researcher at the University of California, Santa Cruz, who led the analysis of the images. "At first all I could see was light from the star, but with careful image processing I was able to remove that light and uncover the planet."

While this is not the first direct image of an exoplanet taken from space -- the Hubble Space Telescope has captured direct exoplanet images previously -- HIP 65426 b points the way forward for Webb's exoplanet exploration.

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SU(N) matter is about 3 billion times colder than deep space

Japanese and U.S. physicists have used atoms about 3 billion times colder than interstellar space to open a portal to an unexplored realm of quantum magnetism.

"Unless an alien civilization is doing experiments like these right now, anytime this experiment is running at Kyoto University it is making the coldest fermions in the universe," said Rice University's Kaden Hazzard, corresponding theory author of a studypublished today in Nature Physics. "Fermions are not rare particles. They include things like electrons and are one of two types of particles that all matter is made of."

A Kyoto team led by study author Yoshiro Takahashi used lasers to cool its fermions, atoms of ytterbium, within about one-billionth of a degree of absolute zero, the unattainable temperature where all motion stops. That's about 3 billion times colder than interstellar space, which is still warmed by the afterglow from the Big Bang.

"The payoff of getting this cold is that the physics really changes," Hazzard said. "The physics starts to become more quantum mechanical, and it lets you see new phenomena."

Atoms are subject to the laws of quantum dynamics just like electrons and photons, but their quantum behaviors only become evident when they are cooled within a fraction of a degree of absolute zero. Physicists have used laser cooling to study the quantum properties of ultracold atoms for more than a quarter century. Lasers are used to both cool the atoms and restrict their movements to optical lattices, 1D, 2D or 3D channels of light that can serve as quantum simulators capable of solving complex problems beyond the reach of conventional computers.

Takahashi's lab used optical lattices to simulate a Hubbard model, an oft-used quantum model created in 1963 by theoretical physicist John Hubbard. Physicists use Hubbard models to investigate the magnetic and superconducting behavior of materials, especially those where interactions between electrons produce collective behavior, somewhat like the collective interactions of cheering sports fans who perform "the wave" in crowded stadiums.

"The thermometer they use in Kyoto is one of the important things provided by our theory," said Hazzard, associate professor of physics and astronomy and a member of the Rice Quantum Initiative. "Comparing their measurements to our calculations, we can determine the temperature. The record-setting temperature is achieved thanks to fun new physics that has to do with the very high symmetry of the system."

The Hubbard model simulated in Kyoto has special symmetry known as SU(N), where SU stands for special unitary group -- a mathematical way of describing the symmetry -- and N denotes the possible spin states of particles in the model. The greater the value of N, the greater the model's symmetry and the complexity of magnetic behaviors it describes. Ytterbium atoms have six possible spin states, and the Kyoto simulator is the first to reveal magnetic correlations in an SU(6) Hubbard model, which are impossible to calculate on a computer.

"That's the real reason to do this experiment," Hazzard said. "Because we're dying to know the physics of this SU(N) Hubbard model."

Study co-author Eduardo Ibarra-García-Padilla, a graduate student in Hazzard's research group, said the Hubbard model aims to capture the minimal ingredients to understand why solid materials become metals, insulators, magnets or superconductors.

"One of the fascinating questions that experiments can explore is the role of symmetry," Ibarra-García-Padilla said. "To have the capability to engineer it in a laboratory is extraordinary. If we can understand this, it may guide us to making real materials with new, desired properties."

Takahashi's team showed it could trap up to 300,000 atoms in its 3D lattice. Hazzard said accurately calculating the behavior of even a dozen particles in an SU(6) Hubbard model is beyond the reach of the most powerful supercomputers. The Kyoto experiments offer physicists a chance to learn how these complex quantum systems operate by watching them in action.

The results are a major step in this direction, and include the first observations of particle coordination in an SU(6) Hubbard model, Hazzard said.

"Right now this coordination is short-ranged, but as the particles are cooled even further, subtler and more exotic phases of matter can appear," he said. "One of the interesting things about some of these exotic phases is that they are not ordered in an obvious pattern, and they are also not random. There are correlations, but if you look at two atoms and ask, 'Are they correlated?' you won't see them. They are much more subtle. You can't look at two or three or even 100 atoms. You kind of have to look at the whole system."

Physicists don't yet have tools capable of measuring such behavior in the Kyoto experiment. But Hazzard said work is already underway to create the tools, and the Kyoto team's success will spur those efforts.

"These systems are pretty exotic and special, but the hope is that by studying and understanding them, we can identify the key ingredients that need to be there in real materials," he said.

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Motion of DNA linked to its damage response, ability to repair itself

A multidisciplinary team of Indiana University researchers have discovered that the motion of chromatin, the material that DNA is made of, can help facilitate effective repair of DNA damage in the human nucleus -- a finding that could lead to improved cancer diagnosis and treatment. Their findings were recently published in the Proceedings of the National Academy of Sciences.

DNA damage happens naturally in human body and most of the damage can be repaired by the cell itself. However, unsuccessful repair could lead to cancer.

"DNA in the nucleus is always moving, not static. The motion of its high-order complex, chromatin, has a direct role in influencing DNA repair," said Jing Liu, an assistant professor of physics in the School of Science at IUPUI. "In yeast, past research shows that DNA damage promotes chromatin motion, and the high mobility of it also facilitates the DNA repair. However, in human cells this relationship is more complicated."

Liu and his colleagues found that chromatin on the site of DNA damage moves much faster than those away from the DNA damage. They also found that the chromatin in cell nuclei is not moving randomly. It's a coherent movement, with the DNA moving as a group over a short distance.

The researchers also found evidence that DNA damage may affect the DNA's group movement by reducing the coherence. These findings indicate that chromatin motion is under tight control when DNA is damaged. This is important to prevent the damaged DNA from harmful contact and to improve the accuracy and efficacy of DNA repair, Liu said.

"Our findings reveal a fundamental role of the chromatin motion in DNA damage response and DNA repair," Liu said. "These findings can help to understand the mechanism of DNA repair in human cells and cancer initiation in humans. Practically, we can use these findings as the metrics for the drug response of many different drugs used to treat cancer. We can test different drugs to see if the chromatin motion can be modified to enhance DNA repair."

In order to conduct this research, Liu and his colleagues had to develop the computational tools necessary for analyzing massive amounts of data. With data sizes as large as a terabyte in some cases, Liu and his colleagues worked with IU's University Information Technology Services to establish the Scalable Data Archive of highly dynamic cell images, which centralizes data storage, data transfer, and data processing.

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People generate their own oxidation field and change the indoor air chemistry around them

People typically spend 90 percent of their lives inside, at home, at work, or in transport. Within these enclosed spaces, occupants are exposed to a multitude of chemicals from various sources, including outdoor pollutants penetrating indoors, gaseous emissions from building materials and furnishings, and products of our own activities such as cooking and cleaning. In addition, we are ourselves potent mobile emission sources of chemicals that enter the indoor air from our breath and skin.

But how do the chemicals disappear again? In the atmosphere outdoors, this happens to a certain extent naturally by itself, when it rains and through chemical oxidation. Hydroxyl (OH) radicals are largely responsible for this chemical cleaning. These very reactive molecules are also called the detergents of the atmosphere and they are primarily formed when UV light from the sun interacts with ozone and water vapor.

Indoors, on the other hand, the air is of course far less affected by direct sunlight and rain. Since UV rays are largely filtered out by glass windows it has been generally assumed that the concentration of OH radicals is substantially lower indoors than outdoors and that ozone, leaking in from outdoors, is the major oxidant of indoor airborne chemical pollutants.

OH radicals are formed from ozone and skin oils

However, now it has been discovered that high levels of OH radicals can be generated indoors, simply due to the presence of people and ozone. This has been shown by a team led by the Max Planck Institute for Chemistry in cooperation with researchers from the USA and Denmark.

"The discovery that we humans are not only a source of reactive chemicals, but we are also able to transform these chemicals ourselves was very surprising to us," says Nora Zannoni, first author of the study published in the research magazine Science, and now at the Institute of Atmospheric Sciences and Climate in Bologna, Italy. "The strength and shape of the oxidation field are determined by how much ozone is present, where it infiltrates, and how the ventilation of the indoor space is configured," adds the scientist from Jonathan Williams' team. The levels the scientists found were even comparable to outside daytime OH concentrations levels.

The oxidation field is generated by the reaction of ozone with oils and fats on our skin, especially the unsaturated triterpene squalene, which constitutes about 10 percent of the skin lipids that protect our skin and keep it supple. The reaction releases a host of gas phase chemicals containing double bonds that react further in the air with ozone to generate substantial levels of OH radicals. These squalene degradation products were characterized and quantified individually using Proton Transfer reaction Mass Spectrometry and fast gas chromatograph-mass spectrometry systems. In addition, the total OH reactivity was determined in parallel enabling the OH levels to be quantified empirically.

The experiments were conducted at the Technical University of Denmark (DTU) in Copenhagen. Four test subjects stayed in a special climate-controlled chamber under standardized conditions. Ozone was added to the chamber air inflow in a quantity that was not harmful to humans but representative of higher indoor levels. The team determined the OH values before and during the volunteers' stay both with and without ozone present.

In order to understand how the human-generated OH field looked like in space and time during the experiments, results from a detailed multiphase chemical kinetic model from the University of California, Irvine were combined with a computational fluid dynamics model from Pennsylvania State University, both based in the USA. After validating the models against the experimental results, the modeling team examined how the human-generated OH field varied under different conditions of ventilation and ozone, beyond those tested in the laboratory. From the results, it was clear that the OH radicals were present, abundant, and forming strong spatial gradients.

"Our modeling team is the first and currently the only group that can integrate chemical processes between the skin and indoor air, from molecular scales to room scales," said Manabu Shiraiwa, a professor at UC Irvine who led the modeling part of the new work. "The model makes sense of the measurements -- why OH is generated from the reaction with the skin."

Shiraiwa added that there remain unanswered questions, like the way humidity levels impact the reactions the team traced. "I think this study opens up a new avenue for indoor air research," he said.

Adapt test methods for furniture and building materials

"We need to rethink indoor chemistry in occupied spaces because the oxidation field we create will transform many of the chemicals in our immediate vicinity. OH can oxidize many more species than ozone, creating a multitude of products directly in our breathing zone with as yet unknown health impacts." This oxidation field will also impact the chemical signals we emit and receive," says project leader Jonathan Williams, "and possibly help explain the recent finding that our sense of smell is generally more sensitive to molecules that react faster with OH."

The new finding also has implications for our health: Currently, chemical emissions of many materials and furnishings are being tested in isolation before they are approved for sale. However, it would be advisable to also conduct tests in the presence of people and ozone, says atmospheric chemist Williams. This is because oxidation processes can lead to the generation of respiratory irritants such as 4-oxopentanal (4-OPA) and other OH radical-generated oxygenated species, and small particles in the immediate vicinity of the respiratory tract. These can have adverse effects, especially in children and the infirm.

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MOXIE experiment reliably produces oxygen on Mars

On the red and dusty surface of Mars, nearly 100 million miles from Earth, an instrument the size of a lunchbox is proving it can reliably do the work of a small tree.

The MIT-led Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, has been successfully making oxygen from the Red Planet's carbon-dioxide-rich atmosphere since February 2021, when it touched down on the Martian surface as part of NASA's Perseverance rover mission.

In a study published in the journal Science Advances, researchers report that, by the end of 2021, MOXIE was able to produce oxygen on seven experimental runs, in a variety of atmospheric conditions, including during the day and night, and through different Martian seasons. In each run, the instrument reached its target of producing six grams of oxygen per hour -- about the rate of a modest tree on Earth.

Researchers envision that a scaled-up version of MOXIE could be sent to Mars ahead of a human mission, to continuously produce oxygen at the rate of several hundred trees. At that capacity, the system should generate enough oxygen to both sustain humans once they arrive, and fuel a rocket for returning astronauts back to Earth.

So far, MOXIE's steady output is a promising first step toward that goal.

"We have learned a tremendous amount that will inform future systems at a larger scale," says Michael Hecht, principal investigator of the MOXIE mission at MIT's Haystack Observatory.

MOXIE's oxygen production on Mars also represents the first demonstration of "in-situ resource utilization," which is the idea of harvesting and using a planet's materials (in this case, carbon dioxide on Mars) to make resources (such as oxygen) that would otherwise have to be transported from Earth.

"This is the first demonstration of actually using resources on the surface of another planetary body, and transforming them chemically into something that would be useful for a human mission," says MOXIE deputy principal investigator Jeffrey Hoffman, a professor of the practice in MIT's Department of Aeronautics and Astronautics. "It's historic in that sense."

Hoffman and Hecht's MIT co-authors include MOXIE team members Jason SooHoo, Andrew Liu, Eric Hinterman, Maya Nasr, Shravan Hariharan, and Kyle Horn, along with collaborators from multiple institutions including NASA's Jet Propulsion Laboratory, which managed MOXIE's development, flight software, packaging, and testing prior to launch.

Seasonal air

The current version of MOXIE is small by design, in order to fit aboard the Perseverance rover, and is built to run for short periods, starting up and shutting down with each run, depending on the rover's exploration schedule and mission responsibilities. In contrast, a full-scale oxygen factory would include larger units that would ideally run continuously.

Despite the necessary compromises in MOXIE's current design, the instrument has shown it can reliably and efficiently convert Mars' atmosphere into pure oxygen. It does so by first drawing the Martian air in through a filter that cleans it of contaminants. The air is then pressurized, and sent through the Solid OXide Electrolyzer (SOXE), an instrument developed and built by OxEon Energy, that electrochemically splits the carbon dioxide-rich air into oxygen ions and carbon monoxide.

The oxygen ions are then isolated and recombined to form breathable, molecular oxygen, or O2, which MOXIE then measures for quantity and purity before releasing it harmlessly back into the air, along with carbon monoxide and other atmospheric gases.

Since the rover's landing in February 2021, MOXIE engineers have started up the instrument seven times throughout the Martian year, each time taking a few hours to warm up, then another hour to make oxygen before powering back down. Each run was scheduled for a different time of day or night, and in different seasons, to see whether MOXIE could accommodate shifts in the planet's atmospheric conditions.

"The atmosphere of Mars is far more variable than Earth," Hoffman notes. "The density of the air can vary by a factor of two through the year, and the temperature can vary by 100 degrees. One objective is to show we can run in all seasons."

So far, MOXIE has shown that it can make oxygen at almost any time of the Martian day and year.

"The only thing we have not demonstrated is running at dawn or dusk, when the temperature is changing substantially," Hecht says. "We do have an ace up our sleeve that will let us do that, and once we test that in the lab, we can reach that last milestone to show we can really run any time."

Ahead of the game

As MOXIE continues to churn out oxygen on Mars, engineers plan to push its capacity, and increase its production, particularly in the Martian spring, when atmospheric density and carbon dioxide levels are high.

"The next run coming up will be during the highest density of the year, and we just want to make as much oxygen as we can," Hecht says. "So we'll set everything as high as we dare, and let it run as long as we can."

They will also monitor the system for signs of wear and tear. As MOXIE is just one experiment among several aboard the Perseverance rover, it cannot run continuously as a full-scale system would. Instead, the instrument must start up and shut down with each run -- a thermal stress that can degrade the system over time.

If MOXIE can operate successfully despite repeatedly turning on and off, this would suggest that a full-scale system, designed to run continuously, could do so for thousands of hours.

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Signs of saturation emerge from particle collisions at RHIC

Nuclear physicists studying particle collisions at the Relativistic Heavy Ion Collider (RHIC) -- a U.S. Department of Energy Office of Science user facility at DOE's Brookhaven National Laboratory -- have new evidence that particles called gluons reach a steady "saturated" state inside the speeding ions. The evidence is suppression of back-to-back pairs of particles emerging from collisions between protons and heavier ions (the nuclei of atoms), as tracked by RHIC's STAR detector. In a paper just published in Physical Review Letters, the STAR collaboration shows that the bigger the nucleus the proton collides with, the larger the suppression in this key signature, as predicted by theoretical models of gluon saturation.

"We varied the species of the colliding ion beam because theorists predicted that this sign of saturation would be easier to observe in heavier nuclei," explained Brookhaven Lab physicist Xiaoxuan Chu, a member of the STAR collaboration who led the analysis. "The good thing is RHIC, the world's most flexible collider, can accelerate different species of ion beams. In our analysis, we used collisions of protons with other protons, aluminum, and gold."

Saturation should be easier to see in aluminum, and even easier in gold, when compared to simpler protons, Chu explained, because these bigger nuclei have more protons and neutrons, each made up of quarks and gluons.

Previous experiments have shown that when ions are accelerated to high energies, gluons split, one into two, to multiply to very high numbers. But scientists suspect that gluon multiplication can't go on forever. Instead, in nuclei moving close to the speed of light, where relativistic motion flattens the nuclei into speeding gluon "pancakes," overlapping gluons should start to recombine.

"If the rate of two gluons recombining into one balances out the rate of single gluons splitting, gluon density reaches a steady state, or plateau, where it is not going up or going down. That is saturation," Chu said. "Because there are more gluons and more overlapping gluons in larger nuclei, these bigger ions should show signs of recombination and saturation more readily than smaller ones," she added.

Scanning for back-to-back pairs

To search for those signs, the STAR scientists scanned data collected in 2015 for collisions where a pair of "pi zero" particles hit STAR's forward meson spectrometer in a back-to-back configuration. In this case, back-to-back means 180 degrees from one another around a circular target at the end of the detector in the forward-going direction of the probing proton beam. These collisions select for interactions between a single high-energy quark from the probing proton with a single low-momentum gluon in the target ion (proton, aluminum, or gold).

"We use the quark from the proton like a tool, or probe, to study the gluon inside the other ion," Chu said.

The team was particularly interested in the "low momentum fraction" gluons -- the multitude of gluons that each carry a tiny fraction of the overall momentum of the nucleus. Experiments at the HERA accelerator in Germany (1992-2007) have shown that, at high energy, protons and all nuclei are dominated by these low-momentum-fraction gluons.

In the proton-proton collisions, the quark-gluon interactions are very straightforward, Chu explained. "The two particles -- quark and gluon -- hit each other and generate two pi zero particles back-to-back," she said.

But when a quark from the proton strikes a gluon in a larger flattened-out nucleus, where many gluons overlap, the interactions can be more complex. The quark -- or the struck gluon -- might strike multiple additional gluons. Or the gluon might recombine with another gluon, losing all "memory" of its original tendency to emit a pi zero.

Both processes -- multiple scatterings and gluon recombination -- should "smear" the back-to-back pi zero signal, explained Elke Aschenauer, the leader of Brookhaven Lab's "Cold QCD" experimental group, which explores details of quantum chromodynamics (QCD), the theory governing the interactions of quarks and gluons in protons and nuclei.

"So, the proton-proton collisions give us a baseline," said Chu. "In these collisions we don't have saturation because there aren't enough gluons and not enough overlap. To look for saturation, we compare the observable of the two-particle correlation across the three collision systems."

Results match theory prediction

The results came out just as the theories predicted, with the physicists observing the fewest back-to-back correlated particles striking the detector in the proton-gold collisions, an intermediate level in proton-aluminum collisions, and the highest correlation in the baseline proton-proton collisions.

The suppression of the pi zero correlation in the larger nuclei, and the fact that the suppression gets stronger the larger the nucleus gets, are clear evidence, the scientists say, of gluon recombination needed to reach gluon saturation.

"STAR will follow up these measurements by collecting additional data in 2024 using recently upgraded forward detector components, tracking other observables that should also be sensitive to saturation," explained Brookhaven Lab physicist Akio Ogawa, a member of the STAR collaboration and a key player in building the new forward STAR detector systems.

Together, the RHIC results will also be an important basis for very similar measurements at the future Electron-Ion Collider (EIC), being built at Brookhaven to collide electrons with ions.

According to Aschenauer, one of the physicists laying out the plans for research at that facility, "If we measure this now at RHIC, at a collision energy of 200 billion electron volts (GeV), that is very similar to the collision energy we will get at the EIC. That means we can use the same observable at the EIC to test whether recombination and saturation are universal properties of the nuclei, as predicted by the saturation models."

Seeing the same result at both facilities, "would prove that these properties don't depend on structure and type of the probe we use to study them," she said.

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What you know changes how you see things

Researchers at the George Washington University have gained important insight into how the human brain processes an object in the visual system and where in the brain this processing takes place. Their study, "Mugs and Plants: Object Semantic Knowledge Alters Perceptual Processing with Behavioral Ramifications," shows people perceive objects differently depending on their prior knowledge and experience with that object.

The findings could have important implications in applied settings such as medical displays, cognitive assistants, and product and environmental design, according to the researchers.

"Since the way we perceive objects determines how we interact with them, it is important to visually process them quickly and with high detail" Sarah Shomstein, a professor of cognitive neuroscience at GW said. "However, the way our eyes perceive and process an object can be different depending on what we know about this object. Our study shows, for the first time, that if we recognize an object as a tool, we perceive it faster but with less detail. If we recognize an object as a non-tool, we perceive it slower but with higher detail."

To determine how the human brain processes an object visually, Shomstein and Dick Dubbelde, a recent PhD graduate at GW and co-author on the study, showed participants several images of objects that can be easily manipulated by hand such as a coffee mug, snow shovel or screwdriver, and several images of objects that are infrequently manipulated by hand, such as a potted plant, a picture frame or a fire hydrant. For half of the experiment, a small gap could be cut out of the bottom of each object. For the other half of the experiment, the objects could flicker on the screen. The team asked participants to report the presence or absence of a gap or the flicker, which helped the researchers figure out the speed and detail of object processing, and also which regions of the brain were being used to process the object.

Researchers found that objects usually manipulated by your hands are perceived faster than non-manipulable objects, making it easier to see the flickering. Alternatively, objects that we usually do not manipulate are perceived with greater detail than manipulable objects, making it easier to see the small gaps.

"The differences in perception between 'mugs' and 'plants' in both speed and detail of perception means that these objects are sorted by the visual system for processing in different brain regions," Dubbelde said. "In other words, your knowledge of the object's purpose actually determines where in the brain object processing will occur and how well you will perceive it."

The study also showed that if you interfere with object recognition by making it harder to recognize an object as either manipulable or not manipulable -- for example, by turning it upside down -- then the differences in the speed and detail perception of the objects disappear.

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Corals pass mutations acquired during their lifetimes to offspring

In a discovery that challenges over a century of evolutionary conventional wisdom, corals have been shown to pass somatic mutations -- changes to the DNA sequence that occur in non-reproductive cells -- to their offspring. The finding, by an international team of scientists led by Penn State biologists, demonstrates a potential new route for the generation of genetic diversity, which is the raw material for evolutionary adaptation, and could be vital for allowing endangered corals to adapt to rapidly changing environmental conditions.

"For a trait, such as growth rate, to evolve, the genetic basis of that trait must be passed from generation to generation," said Iliana Baums, professor of biology at Penn State and leader of the research team. "For most animals, a new genetic mutation can only contribute to evolutionary change if it occurs in a germline or reproductive cell, for example in an egg or sperm cell. Mutations that occur in the rest of the body, in the somatic cells, were thought to be evolutionarily irrelevant because they do not get passed on to offspring. However, corals appear to have a way around this barrier that seems to allow them to break this evolutionary rule."

Since the time of Darwin, our understanding of evolution has become ever more detailed. We now know that an organism's traits are heavily determined by the sequence of their DNA. Individuals in a population vary in their DNA sequence, and this genetic variation can lead to the variation in traits, such as body size, that could give an individual a reproductive advantage. Only rarely does a new genetic mutation occur that gives an individual such a reproductive advantage and evolution can only proceed further if -- and this is the key -- the individual can pass the change to its offspring.

"In most animals, reproductive cells are segregated from body cells early in development," said Kate Vasquez Kuntz, a graduate student at Penn State and the co-lead author of the study. "So only genetic mutations that occur in the reproductive cells have the potential to contribute to the evolution of the species. This slow process of waiting for rare mutations in a particular set of cells can be particularly problematic given the rapid nature of climate change. However, for some organisms, like corals, the segregation of reproductive cells from all other cells may occur later in development or may never occur at all, allowing a path for genetic mutations to travel from a parent's body to its offspring. This would increase genetic variation and potentially even serve as a 'pre-screening' system for advantageous mutations."

Corals can reproduce both asexually (through budding and colony fragmentation) and sexually, by producing egg and sperm cells. For the Elkhorn corals studied here, which broadcast their egg and sperm cells into the water in spawning events, eggs from one coral colony are usually fertilized by sperm from a neighboring colony. However, the research team found that some Elkhorn coral eggs developed into viable offspring without a second coral being involved, a kind of single-parent sexual reproduction.

"This single-parent reproduction allowed us to more easily search for potential somatic mutations from the parent coral and track them into the offspring by simplifying the total number of genetic possibilities that could occur in the offspring," said Sheila Kitchen, co-lead author of the study, a postdoctoral researcher at Penn State and the California Institute of Technology co-lead author of the study.

The research team genotyped samples -- using a high-resolution molecular tool called a microarray to investigate DNA differences between the samples -- from ten different locations on a large Elkhorn coral colony that had produced single-parent offspring, and samples from five neighboring colonies at nearly 20,000 genetic locations. The results showed that all six of the separate coral colonies belonged to the same original coral genotype (known as a "genet"), meaning essentially that they were clones derived from a single original colony through asexual reproduction and colony fragmentation. Thus, any genetic variation found in these corals would have been the result of somatic mutation. The team found a total of 268 somatic mutations in the samples, with each coral sample harboring between 2 and 149 somatic mutations.

The team then looked at the single-parent offspring from the parent Elkhorn coral colony and found that 50% of the somatic mutations had been inherited. The exact mechanism of how the somatic mutations make their way into germline cells in the corals is still unknown, but the researchers suspect that the segregation between body and germline cells in corals may be incomplete and some body cells may retain the capacity to form germ cells, allowing somatic mutations to make their way into offspring. They also found evidence for the inheritance of somatic mutations in some offspring from the mating of two separate coral parents but will need additional studies to confirm this.

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