Thursday, May 28, 2026

SPACE/COSMOS

Listening to Sun's 'heart' hints our star could be changing




Royal Astronomical Society

Sun cycle 

image: 

A split image showing an active Sun during solar maximum (on the left, taken in 2014) and a quiet Sun during solar minimum (on the right, taken in 2019).

view more 

Credit: NASA/SDO





The Sun's internal 'biorhythm' – which plays a critical role in the space weather we experience on Earth – has mysteriously changed over the past 40 years, a new study suggests.

Listening to tiny sound waves inside our star's 'heart' led researchers to discover that it may be entering "a different mode of behaviour". They now need to explore what this means.

The research, published today in Monthly Notices of the Royal Astronomical Society, is of particular significance to space weather.

Solar activity rises and falls in 11‑year cycles, producing solar flares, and ejections of highly charged particles and coronal mass ejections that give rise to geomagnetic storms and aurorae.

This activity, and its cyclic variation, has its origins in the Sun's interior, in processes that regenerate and reorganise the Sun's magnetic field.

Understanding what drives the solar cycle is therefore crucial for making predictions of space weather, which can disrupt satellites, communications, GPS systems and power grids on Earth.

Traditional measures of solar activity track these emissions and other surface phenomena like sunspots, but they do not look under the solar surface. However, by 'listening' to tiny sound waves inside the Sun – a technique known as helioseismology – it is possible to do just that. By tracking changes in the otherwise hidden solar interior, the team found a different picture emerged of the Sun's activity over the past few cycles to the one given by the traditional measures.

Using almost 40 years of helioseismic data from six telescopes around the world in the Birmingham Solar Oscillations Network (BiSON), the international team of researchers uncovered a gradual change in structure just beneath the surface that has spanned multiple cycles, with the current solar cycle 25 showing particularly strong signatures of these changes.

They discovered that solar magnetic activity is being squeezed into an increasingly shallow layer just below the visible surface, signposting long-term changes to the Sun's active behaviour.

Lead author Professor Bill Chaplin, from the University of Birmingham, said: "The Sun has its own 'active biorhythm' creating rising and falling magnetic activity that shapes space weather. However, traditional surface measures don't capture the full story – that the Sun may be entering a different mode of behaviour unfolding over decades.

"We have uncovered evidence of systematic changes in the solar activity cycle. Crucially, magnetic activity is becoming more tightly confined near the surface with each cycle. This is the first such discovery and would have been impossible without the long BiSON observations."

The researchers analysed the p-mode oscillations – formed by global sound waves inside the Sun – whose frequencies shift in response to solar magnetic activity. This allowed them to determine how the Sun's internal structure changed across solar cycles 22–25, from 1987 to 2025.

They grouped oscillations into low-, mid-, and high-frequency bands to probe different depths beneath the solar surface. The team then compared these frequency shifts with traditional measures of solar activity to reach three main conclusions:

  • Evidence of changing behaviour – the link between oscillation frequencies and traditional activity measures has shifted significantly since Cycle 23, indicating long-term evolution in the Sun's internal processes.
  • Surface confinement of structural changes – the combined behaviour of low-, mid-, and high-frequency modes shows that solar-cycle-driven structural changes are becoming increasingly confined to shallow layers, within 1,000km of the Sun's surface.
  • Reinterpreting the strength of the latest cycle – Cycle 25 appears weaker in traditional surface indicators but comparably strong when seen in the high-frequency helioseismic data.

Professor Sarbani Basu, from Yale University, said: "We discovered that the relationship between internal solar oscillations and surface activity has evolved over the past few cycles.

"This trend cannot be explained simply by weaker magnetic fields. Instead, it indicates a structural reorganisation of how the Sun's magnetic activity is stored beneath the surface."

Ongoing collection and analysis of BiSON solar data over what remains of Cycle 25 and into the upcoming Cycle 26 will be crucial in determining whether the changes discovered in the Sun's activity point to a sustained, systematic change in solar magnetic behaviour.

ENDS


Images & captions

Solar biorhythm

Caption: As the Sun's activity varies over each 11-year solar cycle – from periods of high activity (solar maxima) to low activity (solar minima) – so the Sun's oscillations, which are due to sound waves in the Sun's interior, increase and decrease in frequency. The oscillations therefore track and probe the Sun's active biorhythm.

Credit: W. J. Chaplin

 

Sun cycle

Caption: A split image showing an active Sun during solar maximum (on the left, taken in 2014) and a quiet Sun during solar minimum (on the right, taken in 2019).

Credit: NASA/SDO


Solar biorhythm 

As the Sun's activity varies over each 11-year solar cycle – from periods of high activity (solar maxima) to low activity (solar minima) – so the Sun's oscillations, which are due to sound waves in the Sun's interior, increase and decrease in frequency. The oscillations therefore track and probe the Sun's active biorhythm.

Credit

W. J. Chaplin


Further information

The paper ‘Subsurface structural changes associated with successive 11-yr solar activity cycles have been progressively more confined near the surface: new helioseismic results on Cycles 22–25 from BiSON’ by Chaplin et al. has been published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stag847.


Notes for editors

About the Royal Astronomical Society

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

The RAS organises scientific meetings, publishes international research journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

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Scientists show how baby stars’ cradles get their radial shape



New 3D simulations show a dying star's last shockwave can weave a star-forming hub into shape




Kyushu University

Observed hub-filament system compared with simulation results 

image: 

The left panel shows a hub-filament system observed in an actual star-forming region; the right shows the structure produced by this study's 3D simulation. Both show multiple elongated filaments of gas radiating toward a dense central hub. The study shows that this characteristic pattern can emerge when a fast interstellar shockwave strikes a molecular cloud with a curved magnetic field.

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Credit: Left: M. S. N. Kumar, ESA/Herschel, NASA/JPL-Caltech (Spitzer); Right: S. Nozaki & S. Inutsuka





Fukuoka, Japan—The universe is full of fascinating structures, and some of the most striking take shape inside the giant clouds where stars are born. There, streams of gas appear to converge from all directions toward a dense central hub, like spokes meeting at the center of a wheel.

Now, researchers from Kyushu University and Nagoya University have used 3D computer simulations to reveal the physics behind these elegant structures. The study was published in March 2026 in The Astrophysical Journal Letters.

“Stars are born inside molecular clouds—vast, cold clouds of gas that drift through space,” says Shingo Nozaki, a doctoral student at Kyushu University's Graduate School of Sciences, and a Research Fellow of the Japan Society for the Promotion of Science (JSPS). “But they only form in the coldest and densest parts of those stellar nurseries, where gas can collapse under its own gravity. In some of these star-forming regions, gas is organized into characteristic hub-and-spoke patterns known as Hub-Filament Systems (HFS).”

How this radial pattern forms, however, has long remained unclear. At a workshop at Kyushu University last summer, Nozaki and Shu-ichiro Inutsuka of Nagoya University began exploring one possible explanation: what happens when an external shock hits a gas cloud with a pinched magnetic field shape?

Using ATERUI III, an astronomy-dedicated supercomputer operated by the National Astronomical Observatory of Japan, they conducted a 3D magnetohydrodynamic simulation, a computational method that models how gas and magnetic fields evolve together over time.

As a rough analogy, Nozaki pictures the initial molecular cloud as a dorayaki—a Japanese pancake that's thick in the middle and thin at the edges. A vertical magnetic field runs through the cloud, while gravity pulls the field inward at the center, bending it into an hourglass shape. The team then introduced a cosmic disturbance into the cloud, mimicking the kind of disturbance triggered by a supernova remnant or by expanding gas around massive stars.

The results show several elongated structures that develop toward a dense central region, closely resembling observed HFSs. As the magnetic field lines curve inward, the shock wave strikes different parts of the cloud at different angles, creating what physicists call oblique shocks. These shocks strengthen parts of the magnetic field, forming invisible channels that guide compressed gas into long, narrow filaments converging toward the center.

The simulation also revealed that gas does not flow uniformly into the hub. Dense gas within the filaments moves steadily inward, accelerating as it approaches the center, while the low-density gas between filaments stays mostly still. This indicates that the main carriers of mass to the central region are the shock-produced dense filaments, not the cloud as a whole, offering insights into why star formation efficiency remains limited to a few percent.

The team notes that this study focused on a geometrically regular type of HFS, while many observed systems are more asymmetric and complex. Next, they plan to systematically vary the shock direction and strength; the cloud’s density structure; and the magnetic field geometry. This will help them connect different cloud environments to the formation of various massive stars and clusters, and more broadly, to understand how star formation proceeds across galaxies.

“There are two main sources of these shock waves: radiation-driven ‘bubbles’ from newly formed massive stars, and expanding supernova remnants formed when a massive star reaches the end of its life,” adds Nozaki. “There is something almost like a life cycle in this. What a star leaves behind can go on to shape the next cradle of stars.”

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For more information about this research, see " An Origin of Radially Aligned Filaments in Hub-filament Systems," Shingo Nozaki and Shu-ichiro Inutsuka, The Astrophysical Journal Letters, https://doi.org/10.3847/2041-8213/ae4c84

About Kyushu University 
Founded in 1911, Kyushu University is one of Japan's leading research-oriented institutions of higher education, consistently ranking as one of the top ten Japanese universities in the Times Higher Education World University Rankings and the QS World Rankings. Located in Fukuoka, on the island of Kyushu—the most southwestern of Japan’s four main islands—Kyushu U sits in a coastal metropolis frequently ranked among the world’s most livable cities and historically known as Japan’s gateway to Asia. Its multiple campuses are home to around 19,000 students and 8,000 faculty and staff. Through its VISION 2030, Kyushu U will “drive social change with integrative knowledge.” By fusing the spectrum of knowledge, from the humanities and arts to engineering and medical sciences, Kyushu U will strengthen its research in the key areas of decarbonization, medicine and health, and environment and food, to tackle society’s most pressing issues.



Observed hub-filament system compared with simulation results [VIDEO] 

The left panel shows a hub-filament system observed in an actual star-forming region; the right shows the structure produced by this study's 3D simulation. Both show multiple elongated filaments of gas radiating toward a dense central hub. The study shows that this characteristic pattern can emerge when a fast interstellar shockwave strikes a molecular cloud with a curved magnetic field.

Credit

Shingo Nozaki / Kyushu University

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