The study, led by Garima Karki of Kumaun University in Nainital, India, together with Brigitte Schmieder of the Observatoire de Paris and KU Leuven, Ramesh Chandra, Pooja Devi, Pascal Démoulin and Stefaan Poedts, focused on a quiescent filament observed on September 28, 2023. Quiescent filaments are the long-lived, relatively stable cousins of the structures that sometimes erupt as the engines of coronal mass ejections. They consist of dense, cool plasma at chromospheric temperatures, roughly 10,000 kelvin, embedded within the million-degree corona and supported against gravity by magnetic fields. Understanding how plasma enters, circulates within, and drains out of these structures is a central problem in solar physics, because the mass budget of a filament over its lifetime cannot be explained by static conditions alone. Material must be continuously supplied and removed, and the mechanisms responsible remain actively debated.

The key instrument in this investigation was the Télescope Héliographique pour l’Étude du Magnétisme et des Instabilités Solaires, or THEMIS, located on the Canary Island of Tenerife. THEMIS observed the filament in the H-alpha spectral line, the workhorse diagnostic of cool solar plasma, using its Multi-channel Subtractive Double Pass spectrograph in a scanning mode that delivered both high spatial resolution and high spectral resolution. Crucially, the THEMIS field of view happened to be centred on the northern end of the filament at the precise moment when one of a series of repetitive plasma motions swept through it. That coincidence of timing and pointing allowed the team to capture spectra of an elongated cool blob as it fell, and those spectra revealed H-alpha line profiles that were dramatically broadened and shifted, the spectroscopic fingerprints of extremely fast motion.

To convert those distorted line profiles into a velocity, the researchers employed a technique known as the cloud model, a classical method in solar spectroscopy that treats an individual absorbing structure as a uniform slab of plasma with well-defined properties: a source function, a Doppler width, a line-of-sight velocity, and an optical thickness. By fitting synthetic profiles to the observed ones and minimising the root-mean-square difference between model and measurement, the team derived a downflow speed of 89.8 kilometres per second, with a remarkably tight standard deviation of plus or minus 0.25 kilometres per second. For context, the sound speed in the cool filament plasma is on the order of 10 kilometres per second, so the falling material was moving at roughly nine times the local sound speed, unambiguously supersonic. Such speeds are rarely measured with this degree of confidence in quiescent filament structures, and the precision of the cloud-model fit lends the result considerable weight.

The supersonic measurement alone would be noteworthy, but the broader context of the observation makes it genuinely intriguing. Using data from the Global Oscillation Network Group, or GONG, a worldwide network of instruments that monitors the Sun in H-alpha around the clock, the team tracked plasma moving along the filament body toward its northern end. These repetitive motions suggested a conveyor-bear-like flow of material along the filament’s internal magnetic structure. When the flowing plasma reached the region imaged by THEMIS, it appeared to be falling toward the chromosphere. The researchers first considered a ballistic interpretation: material launched or displaced along the filament’s magnetic dips simply falling under gravity along a curved trajectory. A ballistic path could, in principle, account for the observed acceleration and speed, painting a picture of cool plasma draining from the filament body down into the dense lower atmosphere.

However, the team could not rule out a second and arguably more exotic scenario: coronal rain. Coronal rain occurs when plasma trapped in coronal magnetic loops undergoes a thermal instability. Under certain conditions, the delicate balance between heating and radiative cooling in the corona breaks down, and localised pockets of plasma cool catastrophically from millions of kelvin to chromospheric temperatures in a matter of minutes. The resulting condensations become dense and heavy, lose magnetic support, and plummet along the curved field lines of the hosting loop system, often appearing as shimmering showers of dark blobs in H-alpha and other cool-line observations. Coronal rain is now recognised as a ubiquitous phenomenon in the solar corona, and numerical simulations with modern magnetohydrodynamic codes have reproduced its formation in striking detail, including its connection to cycles of heating and cooling in coronal loops.

A crucial clue linking the falling plasma to the hot corona came from the Atmospheric Imaging Assembly, AIA, aboard NASA’s Solar Dynamics Observatory. In AIA’s hot extreme-ultraviolet channels, which sample plasma at temperatures of a million kelvin and above, the team identified a coronal bright point at exactly the same location as the supersonic downflow, with the temperature there reaching approximately 6 million kelvin. Coronal bright points are small, compact regions of enhanced emission associated with magnetic bipoles and frequent small-scale reconnection events. The spatial coincidence between a 6-million-kelvin bright point and a stream of 10,000-kelvin plasma falling at 90 kilometres per second suggests a physical connection: heating and reconnection at the bright point may destabilise nearby coronal plasma, triggering the thermal condensation that then rains down, or alternatively may inject material that subsequently follows a ballistic descent along the filament’s magnetic architecture.

The THEMIS spectra also confirmed a phenomenon that has fascinated solar physicists for decades: counter-streaming flows. Along the fine internal strands of the filament, which the high-resolution observations resolved to widths of less than one arcsecond, plasma was observed flowing in opposite directions simultaneously. Counter-streaming was first documented in prominences in the late 1990s and has since been attributed to various mechanisms, including intermittent heating events at the filament’s footpoints, waves propagating along the strands, and networks of small-scale jets from the chromosphere below. The fact that THEMIS measured these bidirectional flows in individual sub-arcsecond strands, using both imaging and spectroscopy, provides some of the most direct evidence yet that the filament’s fine structure is a dynamically active web of plasma conduits rather than a static reservoir of gas.

What makes this study compelling is the way it stitches together observations across an enormous range of scales and temperatures. A single arcsecond-scale blob of cool plasma, falling at nine times the sound speed, is connected to a million-degree bright point, to repetitive flows threading a filament tens of thousands of kilometres long, and to the grand question of how the Sun’s atmosphere cycles mass between its coolest and hottest layers. Whether the supersonic downflow proves to be ballistic drainage or coronal rain, the measurement demonstrates that quiescent filaments are anything but quiet: they are sites of continuous, violent mass transport that ground-based spectrometers of the THEMIS class are now capable of quantifying with exquisite precision. As solar physicists refine the interplay between thermal instability, magnetic topology and reconnection in these structures, each such observation brings the field closer to understanding not only the life cycle of filaments themselves but also the precursors of the eruptions that can send space weather hurtling toward Earth.

Subject of Research: Supersonic downflows in a quiescent solar filament observed with THEMIS and their relation to a coronal bright point

Article Title: Supersonic Flows Observed by THEMIS Related to a Coronal Bright Point and Filament

Article References: Karki, G., Schmieder, B., Chandra, R., Devi, P., Démoulin, P., & Poedts, S. (2026). Supersonic Flows Observed by THEMIS Related to a Coronal Bright Point and Filament. Solar Physics, 301(9), Article 148. https://doi.org/10.1007/s11207-026-02744-9

Image Credits: AI Generated

DOI: 10.1007/s11207-026-02744-9

Keywords: solar physics, solar filament, prominence, THEMIS, coronal bright point, coronal rain, H-alpha spectroscopy, cloud model, counter-streaming flows, SDO/AIA, GONG, supersonic downflows

The stakes of this question extend far beyond stellar physics. Space telescopes such as Kepler and TESS have revealed that magnetically active stars frequently unleash superflares, explosive releases of magnetic energy exceeding 10^33 erg, roughly the energy of the largest solar flares on record and often much greater. On the Sun, large flares are usually accompanied by CMEs, eruptions that carry billions of tons of plasma into interplanetary space and drive the most severe space weather at Earth. If young solar-type stars behave the same way, their planets would be bathed not only in intense X-ray and ultraviolet radiation but also in dense magnetized plasma, shocks, and energetic particles, conditions that could strip atmospheres, alter chemistry, and influence whether a rocky world can ever become habitable.

Yet confirming a CME on another star is extraordinarily difficult. Unlike the Sun, distant stars cannot be spatially resolved, so astronomers must infer eruptions from disk-integrated spectra and light curves. The most productive technique searches for transient Doppler shifts in chromospheric lines, especially H-alpha. Cool filament or prominence material erupting toward the observer produces a blue-shifted absorption or emission feature, exactly as seen in solar eruptions. Other diagnostics include coronal dimming, a temporary fading of X-ray or ultraviolet emission caused by the evacuation of coronal plasma, and radio bursts such as type-II and type-IV events that trace shocks and energetic electrons. Each method has limitations, and a single signature is rarely enough to prove that material actually escaped the star.

The breakthrough came from dedicated monitoring of two nearby young solar-type stars: EK Draconis, a G1.5V star roughly 50 to 125 million years old, and V889 Herculis, a G0V star only about 30 million years old. Using the KOOLS-IFU spectrograph on the 3.8-meter Seimei Telescope in Okayama, Japan, Namekata and collaborators captured a spectacular event on April 5, 2020, when EK Draconis produced a superflare of about 2 x 10^33 erg accompanied by a clear blue-shifted absorption component in H-alpha, reaching velocities up to 510 kilometers per second. The feature decelerated in a way consistent with the star’s surface gravity, indicating that cool material had been ejected from near the stellar surface, the hallmark of a filament eruption.

A second event on April 10, 2022 revealed the complementary geometry. During a superflare of roughly 1.5 x 10^33 erg, the H-alpha line showed a blue-shifted emission component moving at 400 to 690 kilometers per second, interpreted as a prominence erupting above the stellar limb. Because the feature appeared in emission rather than absorption, and because its velocity was too high to be explained by flare-related line broadening, the natural interpretation is cool material rising beyond the edge of the visible disk. Together, the two events demonstrate that both on-disk filament eruptions and off-limb prominence eruptions can be detected in unresolved stellar spectra, mirroring the two ways solar eruptions are observed.

Critical to these interpretations is the solar-stellar connection. By analyzing solar filament eruptions as if the Sun were an unresolved point of light, the so-called Sun-as-a-star approach, researchers have shown that the disk-integrated H-alpha signature of a solar eruption closely resembles the EK Draconis events, including the blue-shifted absorption and a post-flare dimming-like feature. This calibration provides a powerful check against false positives. Data-driven modeling strengthens the case further: pseudo two-dimensional magnetohydrodynamic simulations reproduce the observed H-alpha dynamic spectra, showing that cool erupting material embedded in an expanding magnetic loop can decelerate under gravity while the surrounding structure continues to expand outward and evolve into a CME.

Do these eruptions actually escape? Several lines of evidence say yes, at least sometimes. The observed velocities approach or exceed the escape velocity of EK Draconis, with velocity dispersions suggesting top speeds of 660 to 1080 kilometers per second. On the Sun, the CME front typically propagates several times faster than its filament core, implying stellar CME fronts of several thousand kilometers per second. Moreover, an empirical solar criterion based on the velocity-length-scale relation, which separates CME-associated from confined filament eruptions, places the EK Draconis events well above the threshold. The inferred masses of the cool erupting material, ranging from about 10^17 to 10^20 grams, are vastly larger than typical present-day solar filament masses and broadly consistent with extrapolations of solar mass-flare energy relations.

Not everything fits the simple solar extrapolation, however. The kinetic energies of the stellar events fall below some naive solar scaling relations, a discrepancy that has two competing explanations. Physically, the strong overlying magnetic fields of active stars may suppress or decelerate eruptions, confining even enormous events. Observationally, H-alpha traces only the cool core of an eruption, whose projected velocity is expected to be slower than the surrounding coronal front, so the inferred kinetic energies should be treated as lower limits. Resolving this controversy is one of the central challenges for the coming decade, and it will require multi-wavelength observations that can trace the hotter, faster components of eruptions.

Frequency matters as much as size. A five-year monitoring campaign of EK Draconis and V889 Herculis detected fifteen H-alpha superflares, including four with blue-shifted signatures of eruptions, yielding a lower-limit association rate of about 27 percent and an eruption frequency of roughly 0.21 events per day for EK Draconis. Combining this rate with the estimated masses gives a CME-driven mass-loss rate of order 10^-13 to 10^-12 solar masses per year, comparable to the expected steady wind of a young solar-type star. If confirmed, transient eruptions would be a major player in the spin-down and angular momentum evolution of young stars, not a curiosity.

The implications for planets are profound. CME impacts can compress magnetospheres, disturb ionospheres, and drive atmospheric escape, particularly on weakly magnetized worlds like early Mars and Venus, while energetic particles from CME-driven shocks can both destroy ozone and synthesize greenhouse gases and prebiotic molecules. Modeling of the young solar analog kappa^1 Ceti suggests that CME impact probabilities for early terrestrial planets may be as high as 30 percent. The review points to a future built on coordinated campaigns spanning optical, X-ray, ultraviolet, and radio wavelengths, with missions such as ESCAPE, LAPYUTA, XRISM, NewAthena, and the SKA poised to fill critical gaps. For the first time, astronomers have an empirical foundation for understanding the space weather that young Earths endured, and perhaps that made life possible.

Subject of Research: Observational evidence for coronal mass ejections from young solar-type stars and their impact on planetary space weather

Article Title: Coronal mass ejections from young Suns: an observational view through the solar–stellar connection

Article References: Namekata, K. (2026). Coronal mass ejections from young Suns: an observational view through the solar–stellar connection. Astrophysics and Space Science, 371(9), Article 110. https://doi.org/10.1007/s10509-026-04641-w

Image Credits: AI Generated

DOI: 10.1007/s10509-026-04641-w

Keywords: coronal mass ejections, superflares, young solar-type stars, EK Draconis, stellar activity, space weather, H-alpha spectroscopy, solar-stellar connection, exoplanets, stellar mass loss, filament eruptions, magnetic fields