Kyoto, Japan -- From birth to death, stars generally slow by 100 to 1000 times their initial rotation rates; in other words, they spin down. The Sun's total angular momentum has declined as material is gradually blown off at the surface as solar wind. By observing this, astronomers have theorized the interaction between magnetic fields and plasma flow to be the most efficient way to spin down stars.

Why and how this happens has long interested astronomers, and recently an observational technique called astroseismology, which measures a star's natural oscillation frequencies, has made it possible to measure the internal rotation rates and magnetic fields of other stars in our galaxy. From this huge population, a picture of how stellar rotation decreases with stellar age has emerged, one that suggests that current theory is insufficient to explain the dramatic decrease in rotation.

Fascinated by astroseismology and by other researchers' 3D simulations of the solar convective zone, a team of researchers at Kyoto University was inspired to investigate how magnetic fields affect rotation inside massive stars..

Synthetic materials rarely mimic the dynamic helicity observed in biological systems like DNA and proteins, often forming fixed structures early in assembly. Inspired by this adaptability, researchers at Chiba University, Keele University, Shizuoka University, Kanazawa University, and Ritsumeikan University developed a chlorophyll-based supramolecular polymer that gradually evolves from nonhelical fibers into helical structures through intermediate stages. This stepwise, cooperative transformation offers a new strategy for designing adaptive materials with tunable optical and electronic properties.

The decline in marriage and fertility rates has emerged as a prominent demographic trend in recent decades, with women’s education being identified as a critical factor. In an insightful study, researchers investigated the causal relationship between women’s education and family formation in Japan and found that education only modestly delays family formation. These findings suggest that other institutional factors deserve greater attention in understanding the demographic trends in East Asia.

Kyoto, Japan --  The Fe Kα line, or iron Kα line, is often used in astronomical research to understand the physical composition of astronomical objects. This line is produced when a K-shell electron of an iron ion in the photosphere -- the gas on the stellar surface -- is ejected by an external process, and has been detected in X-ray spectra of solar and stellar flares. Yet the dominant mechanism behind this ionization process has remained an open question for many years.

Astronomers have proposed two possible mechanisms: photoionization by X-ray photons emitting from hot flare plasma, or collisional ionization by high-energy electrons accelerating at the onset of the flare. With these two possibilities in mind, a team of researchers at Kyoto University set out to uncover the truth behind the iron Kα line.

The team focused on the triple star system UX Arietis, conducting several days of simultaneous ultraviolet and X-ray observations using NICER, NASA's X-ray telescope aboard the International Space Station, and Hisaki, JAXA's ultraviolet space telescope. While Hisaki was developed primarily for observations of planets in the Solar System, the researchers demonstrated that it can also be used to study distant stars.

Interpreting Fermi surface data requires specialized expertise and is vulnerable to noise, creating a bottleneck in materials research. Researchers now demonstrate a machine learning approach that can analyze simulated Fermi surface images of the alloy Co₂MnGa_xGe_1-x and automatically identify compositions where the Fermi surface morphology changes, even in blurred or noisy data. The method reduces the need for manual screening and could accelerate the discovery of advanced electronic materials.

Tokyo, Japan – A scientist from Tokyo Metropolitan University has proposed using safety monitoring at synchrotron facilities to study the properties of dark photons, hypothetical particles proposed to explain dark matter. Calculations showed that the X-ray source at these sites and a Geiger-Muller counter behind safety shielding could be used to propose limits on how strongly dark photons interact with normal photons. The experiment would not involve a dedicated facility and can run alongside other experiments.

Chiral objects are important in fields like drug development because their interactions with biological systems depend on handedness. Researchers from Tokyo University of Science, Institute for Molecular Science, and Seoul National University used light to selectively manipulate nanosized chiral objects. By confining circularly polarized light in an ultra-thin optical fiber, they transported metallic chiral nanoparticles based on handedness, thereby enabling chirality control at near-molecular scales, opening possibilities for applications involving chiral systems, including drug development.

Biodegradable plastics hold potential for reducing marine plastic pollution, but degrade too quickly, limiting their practical use. Researchers from Gunma University now show that crab shell by-products can reduce the breakdown rate of biodegradable plastics in seawater by altering the microbial communities that colonize their surfaces, known as the plastisphere. These findings could help design plastics that stay durable during use and then degrade at an appropriate time once in the ocean.

As is well known, the Earth behaves like a “giant magnet” (that is, it possesses a dipole magnetic field*1), and this magnetic field is thought to be generated by a dynamo process*2 driven by thermal convection of liquid iron in the Earth’s outer core. Paleomagnetism studies have shown that the Earth’s magnetic field reverses its polarity at irregular intervals, ranging from several hundred thousand to about ten million years. However, the physical mechanism responsible for these reversals remains unresolved. In particular, it is still not well understood how the polarity of the magnetic field - northward or southward - is determined.

Focusing on this polarity-determination mechanism, a research team at the National Institute for Fusion Science (NIFS) and the Graduate University for Advanced Studies, SOKENDAI, carried out a detailed study of a convective dynamo arising in a spherical-shell plasma having the same geometry as the Earth’s outer core, using three-dimensional magnetohydrodynamic simulations*3. As a result, they showed for the first time that, in an Earth-like dynamo, the polarity of the magnetic field (northward or southward) is determined randomly, not by the direction of convection, but by extremely weak magnetic perturbations present initially. Moreover, depending on subtle differences in the imposed magnetic perturbations, the system settles into either a northward - or southward- polarity state and remains there (bi-stability of the dipole polarity). Thus, the polarity of the Earth’s magnetic field may likewise have been determined by tiny fluctuations present when the geodynamo first emerged some four billion years ago. That polarity would then be expected to persist, yet in reality the geomagnetic field undergoes repeated reversals. This suggests that geomagnetic reversals may be caused by physical effects not included in the present computational model.