The Biden administration took steps to shield workers from extreme temperatures. The Trump administration is taking a gentler approach with employers.

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The Biden administration took steps to shield workers from extreme temperatures. The Trump administration is taking a gentler approach with employers.

A recent Focus Issue of the Astrophysical Journal Letters describes the fourth version of the catalog of gravitational wave events (GWTC-4.0) from the Laser Interferometer Gravitational Wave Observatory (LIGO), the Virgo interferometer, and the Kamioka Gravitational Wave Detector (KAGRA).

This catalog contains transient gravitational wave events recorded through January 2024, during the observatories’ fourth observing run, which concluded in November 2025. GWTC-4.0 displays the results of significant improvements to our suite of gravitational wave detectors, including higher-powered lasers and reduced quantum noise. A fifth catalog of gravitational wave events was released in Spring 2026, with the accompanying scientific articles being submitted to the Astrophysical Journal and the Astrophysical Journal Letters.

This Monthly Roundup consists of short descriptions of each of the currently published research articles in the LIGO–Virgo–KAGRA Gravitational Wave Transient Catalog (GWTC): Release 4 Focus Issue. Each snippet links to the corresponding research article, and the Focus Issue landing page is linked at the bottom of this post. Be sure to revisit the landing page to catch new articles as they’re published!

Introducing GWTC-4.0

First up, the collaboration orients the reader to many important aspects of the catalog and the articles contained in the Focus Issue. This article describes how four detectors, each with two arms 3–4 kilometers long, monitor gravitational waves from Hanford, Washington; Livingston, Louisiana; Santo Stefano a Macerata, Italy; and Hida, Japan. These detectors work in concert, ready to receive signals from the universe during coordinated observing runs separated by periods of downtime for construction and commissioning. During these pauses, a smaller instrument, the German–British GEO600 gravitational wave detector, has kept an ear out for signals and will continue to do so until the end of 2026.

After these detectors record subtle spacetime squiggles from compact objects colliding millions to billions of light-years away, the collaboration converts the raw signals into the data contained in catalogs like GWTC-4.0. This process involves modeling the gravitational wave signals, filtering them to identify candidate transients, and pinpointing the most significant events.

After collecting and cleaning the signals, the collaboration undertakes a critical step: making their data accessible to researchers and the public. The data are available through the Gravitational Wave Open Science Center, and the Focus Issue article on open data describes how to navigate the online portal, how the datasets archived online are structured, and how the data were calibrated.

Science Results

This fourth version of the gravitational wave transient catalog greatly expands the sample of gravitational wave transients recorded by detectors across the globe. Including events from previous catalogs, GWTC-4.0 brings us to 218 events for which the probability of the source being astrophysical in nature is more than 50% and for which there is little chance of the signal being an instrumental artifact. This represents a more than 100% increase in the number of recorded gravitational wave events fulfilling this criterion, broadening our understanding of colliding compact object pairs. This release also includes some superlative signals, such as the most massive black hole binary with a low false-alarm rate and the highest signal-to-noise ratio for a gravitational wave event thus far.

Detected in November 2023 by both LIGO Hanford and LIGO Livingston, GW231123 is in many ways an exceptional gravitational wave transient. The total mass of the merging components appears to be between 190 and 265 solar masses, and the false-alarm rate for this signal is less than one per year. This makes it the most massive merger event with such a low false-alarm probability. The two components also appear to have high spins, which complicates the interpretation of the signal with existing models. A binary black hole merger in which one or more components lies within the pair-instability mass gap is the likeliest explanation for this signal, but the authors also present alternative scenarios, such as a core-collapse supernova or a gravitationally lensed gravitational wave signal.

GW230814, which was detected only by LIGO Livingston, is the loudest signal in the catalog. This signal is consistent with the collision of two black holes, each of roughly 30 solar masses. During the analysis of this signal, the team discovered potential deviations from the predictions of general relativity in the ringdown phase, when the remnant black hole settles into its final shape. Without a detection from another facility to corroborate this finding, it’s difficult to pinpoint the cause of the deviation, but the team could not rule out statistical noise fluctuations as the source. Surveying merging black holes and neutron stars on the population level, the team analyzed 158 gravitational wave signals from the current catalog. This analysis supported findings from previous transient catalogs, including multiple overdensities in the distribution of merging black hole masses, broadly distributed neutron star masses, and an increase in the merger rate with redshift. The new data strengthened certain previously identified trends, such as an increase in the width of the effective spin distribution with redshift, and weakened others.

The full list of articles in the GWTC-4.0 Focus Issue can be found here.

Citation

“GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog,” A. G. Abac et al 2025 ApJL 995 L18. doi:10.3847/2041-8213/ae0c06

“GWTC-4.0: Methods for Identifying and Characterizing Gravitational-Wave Transients,” A. G. Abac et al 2026 ApJL 1004 L21. doi:10.3847/2041-8213/ae447b

“Open Data from LIGO, Virgo, and KAGRA Through the First Part of the Fourth Observing Run,” A. G. Abac et al 2026 ApJ 1004 232. doi:10.3847/1538-4357/ae211e

“GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO–Virgo–KAGRA Observing Run,” A. G. Abac et al 2026 ApJL 1004 L22. doi:10.3847/2041-8213/ae2c74

“GW231123: A Binary Black Hole Merger with Total Mass 190–265 M_⊙,” A. G. Abac et al 2025 ApJL993 L25. doi:10.3847/2041-8213/ae0c9c

“GW230814: Investigation of a Loud Gravitational-Wave Signal Observed with a Single Detector,” A. G. Abac et al 2026 ApJL 1004 L23. doi:10.3847/2041-8213/ae2ad3

“GWTC-4.0: Population Properties of Merging Compact Binaries,” A. G. Abac et al 2026 ApJL 1005 L51. doi:10.3847/2041-8213/ae771e

The post Monthly Roundup: The Fourth Catalog of Gravitational Wave Events from LIGO, Virgo, and KAGRA appeared first on AAS Nova.

Scientists at the University of California, Riverside have developed a new way to help gravitational-wave observatories see farther

A favorite vacation option may be at risk because of rising temperatures. Even those sticking with their summer plans agree: More air conditioning would help.

New data from NASA’s Juno spacecraft show temperatures spike more than 20 degrees Celsius just a few meters under Io’s surface, providing the first look at what’s happening below the crust of the Solar System’s most volcanic world.

The post Juno’s Microwave Vision Peers beneath Surface of Jupiter’s Volcanic Moon Io appeared first on Sci.News: Breaking Science News.

Scientists from the Salk Institute have determined that brain waves in the visual cortex serve as a computational engine, allowing the brain to construct internal representations of the external world that enhance prediction, reconstruction, and perception capabilities.

While the scientists behind the new study focused their work on the visual cortex, they suspect that similar brain waves washing over other areas of the brain’s surface likely serve a similar role for other sensory systems.

Unraveling the Role of Traveling Brain Waves in the Visual Cortex

The human brain uses electricity to communicate between synapses. Research has shown that this electrical activity can travel in waves across the brain’s surface. Called neural traveling waves, the phenomenon’s role in brain function and consciousness is not completely understood.

Previous studies have established that traveling brain waves play a significant role in behavior and attention. In 2020, Salk neuroscientist John Reynolds, PhD, successfully identified traveling brain waves in the visual systems of animals during a wakeful state.

According to a statement from Reynolds, the senior and co-corresponding author on the new paper, and colleagues, the 2020 research effort also found a direct correlation between traveling brain waves in the visual cortex and an animal’s ability to perceive objects directly in front of them. The authors suggest this discovery explained the “classic conundrum” of searching for something like a pair of keys or a phone that was right in front of you the whole time.

Although the connection between traveling brain waves and an awake animal’s ability to perceive objects seemed solid, Reynolds said he was left wondering why. 

Process is Analogous to LLM’s Like ChatGPT

In their newly proposed theory, Reynolds and colleagues suggest that traveling brain waves are not simply “electrical noise” resulting from the brain’s normal relaying of signals. Instead, the Salk Institute team proposes that the neural connections responsible for the generation of traveling brain waves change their physiological structure, or “synaptic weights,” to more accurately reflect the outside world.

“Each sight, smell, sound, and action of an animal alters the connections that generate these waves, building the neural circuitry that the brain uses to construct an internal representation of the external world,” the team’s statement explains.

In the visual cortex, the part of the brain responsible for receiving and processing visual information, the team proposed that traveling brain waves perform four distinct functions. These include modulating visual perception from moment to moment and turning recent visual sensory inputs into “internal representations” of objects, people, and surroundings.

The team proposes that traveling brain waves also help humans generate short-term predictions about their surroundings, and “store and replay patterns that represent memories of events unfolding in time.” Reynolds said the process laid out by his team is analogous to how ChatGPT and other LLMs translate and interpret data.

“They learn statistical structure from language and use that knowledge to generate meaningful and appropriately structured text that reflects the patterns of language,” the researcher explained. “The brain may be doing something functionally similar—a biological generative model built from the ground up by experience.”

“One Step Closer” to Understanding How Our Brains Compute the World

When detailing the potential impact of their proposed role for traveling brain waves in the visual cortex, the team highlights the contrast between a rich and complex world and its general predictability.

“Objects around you exist in 3D space, you see the world in retinal images that change with your eye and body movements, and the laws of physics and physiology overlay this all,” they explain.

Reynold’s team says that traveling brain waves are merely the brain’s way of internalizing these predictable “regularities” and encoding them in its synapse network. If correct, they said that this encoding would allow the brain to “infer the likely causes of sensory input and construct an internal model of the world.”

“This framing brings us one step closer to understanding how our brains compute the busy, messy world around us, turning a complicated sensory onslaught into behaviors and experiences,” they conclude.

The study “Neural traveling waves in cortex: network mechanisms and potential roles in neural computation” was published in Neuron.

Christopher Plain is a Science Fiction and Fantasy novelist and has spent the last six years as Associate News Editor and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him at christopher@thedebrief.org

Days that are both extremely hot and polluted come with higher risks of respiratory ailments and other health hazards.

Roger Worthington is helping to lead a $50 billion lawsuit against oil producers. This week he’ll face powerful critics in Congress.

© Michael Hanson for The New York Times

Thousands of metres below the ocean’s surface, there are tiny waves moving through the water. Much like breaking waves at the beach, these small waves within the ocean must eventually break. When they do, they create turbulence and mixing, similar to what you feel from a big wave breaking on the beach. This might seem […]

A groundbreaking study unveils how the ARP2/3 complex orchestrates the dynamic behavior of neurites, providing fresh insights into neuronal growth and polarity. Researchers utilized advanced optogenetic tools to manipulate RAC1, an upstream regulator of ARP2/3, revealing spatially distinct roles of actin assembly in neuronal morphology.

By employing photoactivatable RAC1 (PA-RAC1), the team demonstrated that ARP2/3-mediated actin assembly at neurite tips promotes growth cone activation and neurite extension. Local activation of PA-RAC1 triggered robust growth cone dynamics, driving neurite elongation. Conversely, activation of a dominant-negative RAC1 mutant led to collapse of the growth cone and neurite retraction, underscoring ARP2/3’s role in sustaining neurite advancement.

Intriguingly, PA-RAC1 activation at the soma induced lamellipodia formation reminiscent of nascent actin waves, which were associated with neurite retraction events. This phenomenon mirrored intrinsic cellular behaviors where somatic actin waves correspond with retracting neurites. The study elegantly showed that the emergence of these waves reduced somatic actin patch intensity, indicating a tightly regulated cytoskeletal oscillator mechanism.

The authors further explored the effects of ARP2/3 inhibition using CK-666 perfusion at distinct cellular locales. When applied over the soma and proximal neurites, CK-666 induced neurite retraction, whereas neurites outside this region continued growing unabated. Notably, actin waves were initiated in neurites outside the inhibited zone, propagating retrogradely toward the soma but dissipating upon entering CK-666-exposed areas. This highlights a spatial dependence of ARP2/3 activity for wave initiation and propagation.

Remarkably, simultaneous activation of PA-RAC1 at multiple growth cones revealed competitive dynamics in actin assembly, with enhanced growth cone activity limited to one or two sites. This suggests an intrinsic cellular mechanism balancing cytoskeletal resources and neurite growth across the complex neuronal arborization.

Together, these findings articulate a dual role for ARP2/3: driving actin wave initiation at the soma that triggers neurite retraction, and supporting growth cone expansion at neurite tips to promote extension. This oscillatory interplay mediated by ARP2/3 and RAC1 underscores the cytoskeleton’s fundamental role in establishing neuronal polarity.

This study not only provides a mechanistic framework for how neurons spatially regulate growth and retraction but also suggests that intrinsic cytoskeletal oscillators underpin the dynamic remodeling necessary for proper neuronal circuit formation. These insights pave the way for future investigations into cytoskeletal dysregulation in neurodevelopmental disorders and neuronal regeneration strategies.

The precise spatial control of actin dynamics mediated by ARP2/3 complex activity advances our understanding of neuronal development, highlighting how local cytoskeletal modulators can dictate overall neuronal architecture through oscillatory growth behaviors.

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Subject of Research: Neuronal cytoskeletal dynamics and polarity establishment

Article Title: An intrinsic cytoskeletal oscillator establishes neuronal polarity

Article References:
Lin, Tc., Coles, C.H., Alfadil, E. et al. An intrinsic cytoskeletal oscillator establishes neuronal polarity. Nature (2026). https://doi.org/10.1038/s41586-026-10755-6

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-026-10755-6

An unusually early heat wave smashed records across France, Britain and Spain. Temperatures in some areas are starting to soar again.

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The birds are particularly vulnerable to high temperatures, and France’s torrid June took a heavy toll.

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As triple-digit temperatures engulf much of the United States, the Trump administration wants grid managers to require the use of backup power that often goes unused.

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The lawsuit aims to hold fossil fuel companies responsible for a heat wave in Portland five years ago. The industry says the case should be thrown out.

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A scientific analysis concluded that such high temperatures, across so much of the continent, would “not have been possible” without global warming.

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The extreme heat smothering Europe has upended Climate Week in London.

© Pool photo by Yui Mok

The burning of fossil fuels is raising temperatures worldwide, but local factors, on land and at sea, determine which regions warm most rapidly.

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Many philanthropists are backing away from climate giving. But one is writing very big checks.

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Many philanthropists are backing away from climate giving. But one is writing very big checks.