Thanks to the efforts of a citizen science project called Backyard Worlds: Planet 9 and a team of astronomers from around the country, a rare hypervelocity L subdwarf star has been found racing through the Milky Way. More remarkably, this star may be on a trajectory that causes it to leave the Milky Way altogether. The research, led by University of California San Diego Professor of Astronomy and Astrophysics Adam Burgasser, was presented today at a press conference during the 244^th national meeting of the American Astronomical Society (AAS) in Madison, Wisconsin.

The star, charmingly named CWISE J124909+362116.0 (“J1249+36”), was first noticed by some of the over 80,000 citizen science volunteers participating in the Backyard Worlds: Planet 9 project, who comb through enormous reams of data collected over the past 14 years by NASA’s Wide-field Infrared Survey Explorer (WISE) mission. This project capitalizes on the keen ability of humans, who are evolutionarily programmed to look for patterns and spot anomalies in a way that is unmatched by computer technology. Volunteers tag moving objects in data files and when enough volunteers tag the same object, astronomers investigate.

J1249+36 immediately stood out because of the speed at which it is moving across the sky, initially estimated at about 600 kilometers per second (1.3 million miles per hour). At this speed, the star is fast enough to escape the gravity of the Milky Way, making it a potential “hypervelocity” star.

To better understand the nature of this object, Burgasser turned to the W.M. Keck Observatory in Maunakea, Hawaii to measure its infrared spectrum. These data revealed that the object was a rare L subdwarf — a class of stars with very low mass and temperature. Subdwarfs represent the oldest stars in the Milky Way.

The insight into J1249+36’s composition was made possible by a new set of atmosphere models created by UC San Diego alumnus Roman Gerasimov, who worked with UC LEADS scholar Efrain Alvarado III to generate models specifically tuned to study L subdwarfs. “It was exciting to see that our models were able to accurately match the observed spectrum,” said Alvarado, who is presenting his modeling work at the AAS meeting.

The spectral data, along with imaging data from several ground-based telescopes, allowed the team to accurately measure J1249+36’s position and velocity in space, and thereby predict its orbit through the Milky Way. “This is where the source became very interesting, as its speed and trajectory showed that it was moving fast enough to potentially escape the Milky Way,” stated Burgasser.

What gave this star a kick?

Researchers focused on two possible scenarios to explain J1249+36’s unusual trajectory. In the first scenario, J1249+36 was originally the low-mass companion of a white dwarf. White dwarfs are the remnant cores of stars that have depleted their nuclear fuel and died out. When a stellar companion is in a very close orbit with a white dwarf, it can transfer mass, resulting in periodic outbursts called novae. If the white dwarf collects too much mass, it can collapse and explode as a supernova.

“In this kind of supernova, the white dwarf is completely destroyed, so its companion is released and flies off at whatever orbital speed it was originally moving, plus a little bit of a kick from the supernova explosion as well,” said Burgasser. “Our calculations show this scenario works. However, the white dwarf isn’t there anymore and the remnants of the explosion, which likely happened several million years ago, have already dissipated, so we don’t have definitive proof that this is its origin.”

In the second scenario, J1249+36 was originally a member of a globular cluster, a tightly bound cluster of stars, immediately recognizable by its distinct spherical shape. The centers of these clusters are predicted to contain black holes of a wide range of masses. These black holes can also form binaries, and such systems turn out to be great catapults for any stars that happen to wander too close to them.

“When a star encounters a black hole binary, the complex dynamics of this three-body interaction can toss that star right out of the globular cluster,” explained Kyle Kremer, an incoming Assistant Professor in UC San Diego’s Department of Astronomy and Astrophysics. Kremer ran a series of simulations and found that on rare occasions these kinds of interactions can kick a low-mass subdwarf out of a globular cluster and on a trajectory similar to that observed for J1249+36.

“It demonstrates a proof of concept,” said Kremer, “but we don’t actually know what globular cluster this star is from.” Tracing J1249+36 back in time puts it in a very crowded part of the sky that may hide undiscovered clusters.

To determine whether either of these scenarios, or some other mechanism, can explain J1249+36’s trajectory, Burgasser said the team hopes to look more closely at its elemental composition. For example, when a white dwarf explodes, it creates heavy elements that could have “polluted” the atmosphere of J1249+36 as it was escaping. The stars in globular clusters and satellite galaxies of the Milky Way also have distinct abundance patterns that may reveal the origin of J1249+36.

“We’re essentially looking for a chemical fingerprint that would pinpoint what system this star is from,” said Gerasimov, whose modeling work has enabled him to measure the element abundances of cool stars in several globular clusters, work he is also presenting at the AAS meeting.

Whether J1249+36’s speedy journey was because of a supernova, a chance encounter with a black hole binary, or some other scenario, its discovery provides a new opportunity for astronomers to learn more about the history and dynamics of the Milky Way.

“Webb is a supernova discovery machine,” said Christa DeCoursey, a third-year graduate student at the Steward Observatory and the University of Arizona in Tucson. “The sheer number of detections plus the great distances to these supernovae are the two most exciting outcomes from our survey.”

DeCoursey presented these findings at the 244th meeting of the American Astronomical Society in Madison, Wisconsin.

‘A Supernova Discovery Machine’

To make these discoveries, the team analyzed imaging data obtained as part of the JWST Advanced Deep Extragalactic Survey (JADES) program. Webb is ideal for finding extremely distant supernovae because their light is stretched into longer wavelengths — a phenomenon known as cosmological redshift.

Prior to Webb’s launch, only a handful of supernovae had been found above a redshift of 2, which corresponds to when the universe was only 3.3 billion years old — just 25% of its current age. The JADES sample contains many supernovae that exploded even further in the past, when the universe was less than 2 billion years old.

Previously, researchers used NASA’s Hubble Space Telescope to view supernovae from when the universe was in the “young adult” stage. With JADES, scientists are seeing supernovae when the universe was in its “teens” or “pre-teens.” In the future, they hope to look back to the “toddler” or “infant” phase of the universe.

To discover the supernovae, the team compared multiple images taken up to one year apart and looked for sources that disappeared or appeared in those images. These objects that vary in observed brightness over time are called transients, and supernovae are a type of transient. In all, the JADES Transient Survey Sample team uncovered about 80 supernovae in a patch of sky only about the thickness of a grain of rice held at arm’s length.

“This is really our first sample of what the high-redshift universe looks like for transient science,” said teammate Justin Pierel, a NASA Einstein Fellow at the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “We are trying to identify whether distant supernovae are fundamentally different from or very much like what we see in the nearby universe.”

Pierel and other STScI researchers provided expert analysis to determine which transients were actually supernovae and which were not, because often they looked very similar.

The team identified a number of high-redshift supernovae, including the farthest one ever spectroscopically confirmed, at a redshift of 3.6. Its progenitor star exploded when the universe was only 1.8 billion years old. It is a so-called core-collapse supernova, an explosion of a massive star.

Uncovering Distant Type Ia Supernovae

Of particular interest to astrophysicists are Type Ia supernovae. These exploding stars are so predictably bright that they are used to measure far-off cosmic distances and help scientists to calculate the universe’s expansion rate. The team identified at least one Type Ia supernova at a redshift of 2.9. The light from this explosion began traveling to us 11.5 billion years ago when the universe was just 2.3 billion years old. The previous distance record for a spectroscopically confirmed Type Ia supernova was a redshift of 1.95, when the universe was 3.4 billion years old.

Scientists are eager to analyze Type Ia supernovae at high redshifts to see if they all have the same intrinsic brightness, regardless of distance. This is critically important, because if their brightness varies with redshift, they would not be reliable markers for measuring the expansion rate of the universe.

Pierel analyzed this Type Ia supernova found at redshift 2.9 to determine if its intrinsic brightness was different than expected. While this is just the first such object, the results indicate no evidence that Type Ia brightness changes with redshift. More data is needed, but for now, Type Ia supernova-based theories about the universe’s expansion rate and its ultimate fate remain intact. Pierel also presented his findings at the 244th meeting of the American Astronomical Society.

Looking Toward the Future

The early universe was a very different place with extreme environments. Scientists expect to see ancient supernovae that come from stars that contain far fewer heavy chemical elements than stars like our Sun. Comparing these supernovae with those in the local universe will help astrophysicists understand star formation and supernova explosion mechanisms at these early times.

“We’re essentially opening a new window on the transient universe,” said STScI Fellow Matthew Siebert, who is leading the spectroscopic analysis of the JADES supernovae. “Historically, whenever we’ve done that, we’ve found extremely exciting things — things that we didn’t expect.”

“Because Webb is so sensitive, it’s finding supernovae and other transients almost everywhere it’s pointed,” said JADES team member Eiichi Egami, a research professor at the University of Arizona in Tucson. “This is the first significant step toward more extensive surveys of supernovae with Webb.”

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

Oak Ridge National Laboratory’s John Field provided biomass feedstock production expertise to the report focused on the role of the bioeconomy in U.S. decarbonization strategies, which was produced by the Department of Energy’s DECARB program.

The report examined the role of biomass in reducing greenhouse gas emissions across the economy, including opportunities to reach negative emissions. It includes data from the ORNL-led 2016 Billion-Ton Report that identified potential biomass from agricultural and forestry residues, wastes and bioenergy crops.

The latest 2023 Billion-Ton Report identifies up to 1.7 billion tons per year of potential biomass, including winter oilseed crops for jet biofuels.

Carbon-negative bioenergy is expected to be essential to a net-zero emissions economy and could account for 4% to 11% of the nation’s total energy mix by 2050, according to the DECARB report.

Further information: https://www.energy.gov/eere/bioenergy/2023-billion-ton-report-assessment-us-renewable-carbon-resources

Scientists have long been working to understand the Cascadia Subduction Zone’s subterranean structures and mechanics, in order to delineate places most susceptible to quakes, how big they might be and what warning signs they might produce. There is no such thing as predicting an earthquake; rather, scientists try to forecast probabilities of multiple scenarios, hoping to help authorities design building codes and warning systems to minimize the damage when something happens.

A newly published study promises to greatly advance this effort. A research vessel towing an array of the latest geophysical instruments along almost the entire zone has produced the first comprehensive survey of the many complex structures beneath the seafloor. These include the geometry of the down-going ocean plate and overlying sediments, and the makeup of the overriding North American plate. The study was just published in the journal Science Advances.

“The models currently in use by public agencies were based on a limited set of old, low-quality 1980s-era data,” said Suzanne Carbotte, a marine geophysicist at Columbia University’s Lamont-Doherty Earth Observatory, who led the research. “The megathrust has a much more complex geometry than previously assumed. The study provides a new framework for earthquake and tsunami hazard assessment.”

With funding from the U.S. National Science Foundation, the data was gathered during a 41-day cruise in 2021 by Lamont’s research vessel, the Marcus G. Langseth. Researchers aboard the ship penetrated the seafloor with powerful sound pulses and read the echoes, which were then converted into images, somewhat similar to how physicians create interior scans of the human body.

One key finding: the megathrust fault zone is not just one continuous structure, but is divided into at least four segments, each potentially somewhat insulated against movements of the others. Scientists have long debated whether past events, including the 1700 quake, ruptured the entire zone or just part of it — a key question, because the longer the rupture, the bigger the quake.

The data show that the segments are divided by buried features including big faults, where opposing sides slide against each other perpendicular to the shore. This might help buffer against movement on one segment translating to the next. “We can’t say that this definitely means only single segments will rupture, or that definitely the whole thing will go at once,” said Harold Tobin, a geophysicist at the University of Washington and coauthor of the study. “But this does upgrade evidence that there are segmented ruptures.”

The imagery also suggests the causes of the segmentation: the rigid edge of the overriding North American continental plate is composed of many different kinds of rocks, formed at different times over many tens of millions of years, with some being denser than others. This variety in the continental rocks causes the incoming, more pliable oceanic plate to bend and twist to accommodate differences in overlying pressure. In some places, segments go down at relatively steep angles, in others at shallow ones.

The researchers zeroed in on one segment in particular, which runs from southern Vancouver Island alongside Washington state, more or less ending at the Oregon border. The subterranean topography of other segments is relatively rough, with oceanic features like faults and subducted seamounts rubbing up against the upper plate — features that might erode the upper plate and limit how far any quake may propagate within the segment, thus limiting the quake’s size. In contrast, the Vancouver Island to south alongside Washington State segment is quite smooth. This means that it may be more likely to rupture along its entire length at once, making it potentially the most dangerous section.

Also in this segment, the seafloor is subducting under the continental crust at a shallow angle relative to the other segments. In the other segments, most of the earthquake-prone interface between the plates lies offshore, but here the study found the shallow subduction angle means it probably extends directly under Washington’s Olympic Peninsula. This might magnify any shaking on land. “It requires a lot more study, but for places like Tacoma and Seattle, it could mean the difference between alarming and catastrophic,” said Tobin.

With funding from the U.S. Geological Survey, a consortium of state and federal agencies and academic institutions has already been poring over the data since it became available to sort through the implications.

As for tsunami hazard, that is “still a work in progress,” said Kelin Wang, a research scientist at the Geological Survey of Canada who was not involved in the study. Wang’s group is using the data to model features of the seafloor off Vancouver Island that might generate tsunamis. (In general, a tsunami occurs when the deep seafloor moves up or down during a quake, sending a wave to the surface that concentrates its energy and gathers height as it reaches shallower coastal waters.) Wang said his results will go to another group that models tsunamis themselves, and after that to another group that analyzes the hazards on land.

Practical assessments that could affect building codes or other aspects of preparedness may be published as early as next year, say the researchers. “There’s a whole lot more complexity here than was previously inferred,” said Carbotte.

Their study showed that mutating the orco gene in Harpegnathos saltator jumping ants dramatically decreased the number of olfactory neurons, suggesting that Orco is necessary for the development and life of these cells. The findings, published in Science Advances, offer insights into the cellular and molecular basis of how animals socialize.

“Understanding how the nervous system develops is among the most pressing challenges in modern neuroscience,” said Bogdan Sieriebriennikov, a postdoctoral fellow in NYU’s Department of Biology and the study’s first author.

Sensing smell and mutant ants

Ants have evolved approximately 400 smell receptors — a number closer to humans than most other insects — thanks to their use of pheromone communication.

“Ants, like humans, are highly social and display cooperative social behavior, and thus provide an ideal system to study sensory-mediated social behavior,” explained Hua Yan, assistant professor of biology at the University of Florida and the study’s senior author. “Expanded odorant receptor genes allow ants to ‘talk’ to each other in a large society with hundreds, thousands, or up to a million individuals.”

Even for humans, who rely on other senses for communication, smell is essential.

“Loss of function of odorant receptor neurons leads to deficits in olfactory sensing and is often associated with social isolation, neurological disorders such as schizophrenia, and social disorders such as autism,” added Yan.

To better understand how ants’ sense of smell influences their social interactions, NYU researchers previously created the first genetically engineered ants by using CRISPR to edit the orco gene. These “mutant” ants, lacking the Orco protein, experienced changes to their smell organs and had difficulty interacting.

“We found that the antennae — which are the ‘nose’ of the ant — had very few cells. They were almost empty, suggesting that the cells that sense smell were absent from the mutant ants,” said Yan.

Neuron survival depends on Orco

In their new study in Science Advances, the researchers used single-nucleus gene expression profiling of ant antennae and fluorescence microscopy to analyze olfactory cell development. It emerged that mutant insects lacking Orco lose most of their olfactory neurons before adulthood.

“The cells appear to be made normally, and they start developing — growing, changing shape, and switching on certain genes they will need later, such as odorant receptors,” noted Sieriebriennikov. “Once the developing cells turn on the odorant receptors, very soon they start dying in massive amounts.”

This neuronal death may be because of stress. As the odorant receptors in the mutant ants cannot form a complex with Orco to travel to the cell membrane, the newly made receptors clog the organelles, leading to stress and death.

Such neuronal death may also show patterns particular to social insects. “So far, these unique processes have not been found in solitary insects and may provide important evidence of evolution of neural development to adapt to the expansion of odorant receptor genes,” said Kayli Sieber, a doctoral candidate at the University of Florida and the co-first author of the study.

Interestingly, some odorant receptors survived even without Orco. The cells in which they were present also expressed other types of receptors, suggesting that the activity they facilitate is essential for neuronal development.

“Some neurons must periodically ‘fire’ to develop properly. Without Orco, smell cells did not ‘fire’ and complete their development, leading to their death,” said Sieriebriennikov.

The researchers also found that some odorant receptors are present in non-smell cells, such as mechanosensory neurons that detect motion and glia, which wrap around neurons and help them function. This may be due to imperfect regulation of genes, which causes odorant receptors to be accidentally activated by nearby genomic regions that are normally regulating other genes in other cells. Alternatively, the receptors may have a new function in these cells, like the odorant receptors found in the glia of C. elegans worms or human sperm.

“Turning on odorant receptor genes in the cells that are not smell-sensing could be totally useless for the organism — but then again, evolution tends to make use of such mistakes to give existing genes new function, so perhaps there is some exciting new role of odorant receptors in non-smell cells that we will discover in the future,” noted Sieriebriennikov.

“Our findings enhance our understanding of social insects’ sensory systems, including olfactory neural development that establishes a framework for social communication,” said Yan.

Other study authors include Olena Kolumba, Jakub Mlejnek, and Shadi Jafari. This research was supported by the National Institutes of Health (R01-DC020203, T32-DC015994), the National Science Foundation Industry-University Cooperative Research Center for Arthropod Management Technologies (#IIP1821914), and the Human Frontier Science Program (LT000010/2020-L).

Their simulations show that small variations in layers of water ice — too subtle for ground-penetrating radar instruments to resolve — can cause constructive interference between radar waves. Such interference can produce reflections whose intensity and variability match observations to date — not only in the area proposed to be liquid water, but across the so-called south polar layered deposits.

“I can’t say it’s impossible that there’s liquid water down there, but we’re showing that there are much simpler ways to get the same observation without having to stretch that far, using mechanisms and materials that we already know exist there,” said Daniel Lalich, research associate in the Cornell Center for Astrophysics and Planetary Science. “Just through random chance you can create the same observed signal in the radar.”

Lalich is the first author of “Small Variations in Ice Composition and Layer Thickness Explain Bright Reflections Below Martian Polar Cap Without Liquid Water,” published June 7 in Science Advances.

Robotic explorers have provided extensive evidence that water flowed on the surface of ancient Mars, including at a former river delta now under investigation by NASA’s Perseverance rover. Relying on a radar instrument that can probe below the surface to detect water ice and potentially hidden aquifers, members of the European Space Agency-led Mars Express orbiter’s science team in 2018 announced they’d discovered a lake buried below the south polar cap.

The implications were enormous: Where there is liquid water, there could be microbial life.

But while the same bright radar reflections would likely indicate a subglacial lake on Earth, Lalich said, the temperature and pressure conditions on Mars are very different.

Using simpler models, Lalich previously showed that the bright radar signals could be created in the absence of liquid water, but he said assumptions about layers of frozen carbon dioxide below the ice cap likely were incorrect.

The new research tells a more complete story, he said, closing gaps in the radar interference hypothesis with more realistic modeling. The thousands of randomly generated layering scenarios were based only on conditions known to exist at the Martian poles, and varied the ice layers’ composition and spacing in ways that would be expected over tens or hundreds of miles.

Those slight adjustments sometimes produced bright subsurface signals consistent with observations in each of the three frequencies used by the Mars Express orbiter’s MARSIS radar instrument, a partnership between NASA and the Italian Space Agency. Likely for a simple reason, Lalich argues: Radar waves bouncing off layers spaced too closely for the instrument to resolve may be combined, amplifying their peaks and troughs.

“This is the first time we have a hypothesis that explains the entire population of observations below the ice cap, without having to introduce anything unique or odd,” Lalich said. “This result where we get bright reflections scattered all over the place is exactly what you would expect from thin-layer interference in the radar.”

While not ruling out the potential for some future detection by more capable instruments, Lalich said he suspects the story of liquid water and potential life on the red planet ended long ago.

“The idea that there would be liquid water even somewhat near the surface would have been really exciting,” Lalich said. “I just don’t think it’s there.”

The research was supported by NASA.