Shock breakout (SBO) occurs when a radiation-mediated shock wave, formed during a core-collapse supernova (SN) explosion, breaks out from the stellar surface of the progenitor or from the circumstellar material (CSM), if the CSM is optically thick. The X-ray outburst XRO 080109, associated with Type Ib/c SN SN 2008D, has been suggested to be an SBO event from a regular supernova. The recent detection of EP260321a, associated with broad-lined Type Ic SN SN 2026gzf, by the Einstein Probe adds a new SBO event. However, the two SBO events differ markedly in their spectra, energetics, late-time radio emission, and early optical emission within the first day. We show that the nondetections in radio follow-up observations of EP260321a imply a shock velocity ≲0.1 c , whereas the radio data of XRO 080109 suggest a shock velocity of ≃0.2 c . These velocities are consistent with those inferred from the properties of the X-ray outbursts and explain the difference in their X-ray spectra. The X-ray energy and duration of EP260321a indicate that the shock breaks out from the CSM at a radius of ∼2 × 10 ^13 cm. Its bright optical emission at t ≲ 1 day can be explained by cooling emission from a dense, extended CSM shell heated by the radiation-mediated shock, requiring a total CSM mass of ∼0.06 M _⊙ , substantially larger than that inferred for XRO 080109. Finally, the lower shock velocity and larger CSM mass can be unified in a picture in which a more massive CSM decelerates the radiation-mediated shock more significantly before it breaks out.
During their evolution, stars follow a distinct path in luminosity–temperature space. Low-mass stars that have exhausted hydrogen in their core follow the so-called red-giant branch which is predominantly in the direction of increasing luminosity and decreasing surface temperature. The luminosity bump is a temporary decrease in luminosity against this otherwise increasing trend. The bump is present in both observations and stellar evolution models. However, with canonical physics included in the models, the bump in computed evolutionary tracks appears at higher luminosities than the observed bump. To understand why the bump appears later in the models than in observations, the physics of the bump needs to be unravelled. The end point of the bump is well-understood; however, the onset of the bump is still an enigma. Here, we report on the physical origin of the onset of the luminosity bump. We show that the difference in specific entropy at the mean molecular weight discontinuity decreases due to the discontinuity moving in. This decrease is attributed to the decrease in the ratio of the temperature to the pressure at smaller radii. Upon reaching a critical value the specific entropy difference at the mean molecular weight discontinuity is reduced sufficiently to reduce the specific entropy in the convective envelope. The latter is a key signature of the bump. Hence the evolution of the specific entropy at the mean molecular weight discontinuity provides a viable description for the onset of the bump.
Using high-resolution observations from the TuMag instrument aboard the Sunrise iii solar observatory balloon mission, we investigate solar vortices in the lower atmosphere. First, we identify vortices by extracting coherent dynamical patterns from intensity data using morphological analysis combined with spectral proper orthogonal decomposition applied to Mg I time series that probe the photosphere and lower chromosphere. We found that ∼8.5 × 10 ^4 vortices may be present on the Sun at any given time, with an average lifetime of $\tau \approx 27\,\mathrm{minutes}$ . To investigate vortex-mediated cross-layer coupling, we apply Granger causality (GC), which tests whether past fluctuations in one atmospheric layer carry statistically significant predictive power for future fluctuations in another, serving as a statistical proxy for directed dynamical coupling potentially associated with energy and momentum transfer. A pixel-to-pixel GC analysis reveals enhanced and spatially organized lower-atmospheric coupling within vortices, with statistically dominant photosphere-to-chromosphere influence in some locations and the reverse in others. This locally enhanced bidirectional spatial pattern of influence presents morphology consistent with the vortex-driven vertical Poynting flux distribution predicted by numerical simulations, suggesting that the coupling inferred from GC traces dynamical interactions associated with vortex-driven energy transport across atmospheric layers. On average, the directional asymmetry favors photosphere-to-chromosphere predictive coupling. Within vortex regions, past photospheric fluctuations provide ≈53% stronger predictive power for future chromospheric fluctuations than in nonvortex regions over a lag of 4.5 minutes. These results provide the first observational evidence of enhanced information transfer between atmospheric layers associated with solar vortices.
Einstein’s General Relativity (GR), which has been precisely tested on galaxy and solar system scales, is still poorly constrained in extremely weak gravitational fields (with dimensionless Newtonian potentials of Φ ∼ 10 ^−8 ). In this Letter, we propose a new method to probe such a weak-field regime of gravity and measure the spatial curvature generated per unit mass. Specifically, binary microlensing events provide a laboratory to measure the parameterized post-Newtonian (PPN) parameter ( γ ), by combining the lensing mass ( ${M}_{{\rm{lens}}}^{{\rm{GR}}}$ ) inferred from microlensing with the dynamical mass ( M _dyn ) determined from interferometric astrometry. Astrometric tracking of binary lenses was previously hindered by their faintness and minuscule angular separations (typically a few milliarcseconds). This limitation has been alleviated by the deployment of GRAVITY+, which pushes the instrument’s sensitivity and astrometric precision to unprecedented heights. Based on astrometric simulations of the binary microlensing event ASASSN-22av, we directly estimate γ at the precision of ∼23%. Such testing of GR in the extremely weak-field regime can be further improved to a much higher precision (∼3%), based on more binary microlensing events with precise determination of the dynamical/lens mass.
The canonical giant impact hypothesis suggests that the proto-Earth’s collision with a differentiated Mars-sized planet, Theia, produced an iron-poor debris disk that accreted to form the Moon. Here, we revisit that hypothesis, for the first time using smoothed-particle hydrodynamics (SPH) simulations with realistic strength. Although negligible compared to stresses in the deep interior, strength in the outer hundreds of kilometers of Theia is shown to hinder its deformation, which alters the transfer of momentum, leading to fundamental differences in Moon formation. For one set of otherwise identical canonical impact parameters, a hot but solid Theia produces an intact Moon, whereas a colder, stronger Theia—i.e., a later Moon-formation scenario—produces a classic protolunar disk. These completely different scenarios arise from different mechanical responses due to temperature and establish an important new connection between giant impact dynamics and the timing and geochemistry of lunar formation.
Ion-scale waves are believed to play an important role in heating of the solar corona and wind, though their generation mechanism remains unclear. Based on Parker Solar Probe observations, this Letter investigates the occurrence of ion-scale waves in the near-Sun solar wind with heliocentric distances between 0.1 and 0.2 au. Results show that the occurrence rate of left-handed polarized waves significantly depends on the plasma beta (β) and cross helicity (σ_c). The occurrence rate rapidly increases with decreasing β and increasing σ_c. Overall, the occurrence rate exceeds 45% when β<0.2 and σ_c > 0.7 are satisfied. These observations are consistent with the direct predictions of the helicity barrier theory that suggests the generation of ion cyclotron waves via imbalanced magnetized turbulence.
Stellar obliquity ( λ ) and orbital eccentricity ( e ) trace the dynamical histories of close-in giant planets, but the current observational picture is assembled from heterogeneous analyses that have obscured population-level trends. In this work, we homogeneously refit systems with Rossiter–McLaughlin (RM) measurements by performing a joint global fit to spectral energy distributions, transit light curves, mid-transit times, and out-of-transit and in-transit radial velocities, yielding self-consistent posterior distributions for the physical and orbital parameters of both stars and planets across 256 systems. Restricting to 146 single-star systems with reliable planet-mass measurements, we uncover pronounced structure in the e – λ plane that depends on planet mass: (i) sub-Saturns ( M _p ≤ ∼0.3 M _J ) can be both eccentric and misaligned; (ii) Jupiters (∼0.3 M _J < M _p ≤ ∼3 M _J ) are misaligned only on circular orbits; and (iii) super Jupiters and brown dwarfs ( M _p > ∼3 M _J ) are aligned across the full eccentricity range. A two-dimensional Kolmogorov–Smirnov test shows that the joint ( e , λ ) distributions differ significantly among these three mass regimes. These trends demonstrate that λ depends jointly on eccentricity and planet mass, implying that obliquity alone is not a unique tracer of evolutionary history and underscoring the need for a unified framework for the origins of spin–orbit misalignment.
We present Zwicky Transient Facility observations of the interstellar comet 3I/ATLAS to characterize its dust-activity evolution before and after perihelion. Before perihelion, the effective scattering cross section C _e brightened across the inner 2 × 10 ^4 km as ${C}_{{\rm{e}}}\propto {r}_{{\rm{H}}}^{-\gamma }$ , with γ increasing from 1.63 ± 0.14 to 1.88 ± 0.34 with aperture size. After perihelion, the heliocentric index decreased from 2.44 ± 0.09 in the 5 × 10 ^3 km aperture to 1.54 ± 0.09 in the 8 × 10 ^4 km aperture, indicating faster fading of the inner coma. Under adopted grain-size and residence-time assumptions, the implied dust mass-loss rates are ∼123–203 kg s ^−1 before perihelion and ∼596–1412 kg s ^−1 after perihelion. The morphology yields a sunward ejection-speed scale of ${v}_{{\rm{ej}}}\sim (190\pm 3){a}_{\mu {\rm{m}}}^{-1/2}\,{\rm{m}}\,{{\rm{s}}}^{-1}$ and an effective perpendicular velocity of ${v}_{\perp }=(79\pm 6){a}_{\mu {\rm{m}}}^{-1/2}\,{\rm{m}}\,{{\rm{s}}}^{-1}$ . Postperihelion surface-brightness profiles transiently steepened to k ∼ −2.7 in late November and early December, then became shallower and approached k = −1.5 by January. Matched g − r profiles show that this phase coincided with an anomalously blue outer coma that disappeared by January. We characterize the fading component with a projected destruction length of ℓ _DE ∼ (6.4–7.2) × 10 ^4 km. Thermophysical sublimation calculations indicate that this scale, together with the order of magnitude of the water production near the main imaging epoch, is consistent with a _0 ∼ 5–10 μ m icy grains containing a small absorbing carbonaceous fraction of f _C ∼ 0.1%. These results suggest that the early postperihelion coma likely contained a short-lived, volatile-bearing, icy-grain component whose fading contributed to the outer-coma brightness and color evolution.
Classical pebble and core accretion theories face a severe challenge: they struggle to produce giant planets around low-mass M dwarfs, whose protoplanetary disks contain insufficient material. Yet, discoveries of such systems continue to mount. We propose flyby-induced second accretion (FISA), a new formation channel in which an M dwarf already hosting a terrestrial planet flies through a younger star’s protoplanetary disk, capturing gas and dust to build a second-generation disk. The preexisting planet then undergoes renewed pebble and gas accretion within this replenished reservoir and migrates inward to become a close-in giant. We performed hydrodynamic and core-accretion simulations to show that, under favorable encounter geometries, protoplanets around M dwarfs can grow into gas giants via this two-stage process. We apply the FISA framework to TOI-6894 b, a 0.168 Jupiter-mass planet orbiting a 0.207 solar-mass star at just 0.026 au, showing that it is a plausible outcome of such a flyby. An order-of-magnitude estimation shows that the probability for a close-in gas giant to form in an M dwarf system via the proposed disk-flyby mechanism is roughly 3 × 10 ^−5 .
Magnetic flux ropes are twisted magnetic field lines that are commonly observed in space and astrophysical plasmas. At Mars, these structures are especially interesting because the planet does not have a global magnetic field like Earth, but instead has remanent magnetic fields preserved in its crust. In this study, we report a close conjunction observation by MAVEN and Tianwen-1 of a magnetic flux rope within the Martian ionosphere. The two spacecraft observed closely related magnetic signatures at near-identical locations and altitudes, allowing us to examine the spatial structure of the event. Our analysis suggests that the observed flux rope may have a loop-like geometry, with magnetic-field lines connected to the Martian dayside ionosphere at both ends. This structure may have formed or evolved through ionospheric instabilities under unusually low solar-wind dynamic pressure or internal reconnection between neighboring crustal magnetic fields. This event shows that Mars may produce a loop-like magnetic flux rope that resembles, in geometry, twisted magnetic loops seen in the solar atmosphere, providing a useful connection between planetary and solar plasma processes.
Retrograde S-type planets have been observed in several binary systems, yet their formation pathway remains poorly understood. With high-resolution hydrodynamic simulations, we demonstrate that a polar circumbinary disk around an eccentric, unequal-mass binary can form and sustain a retrograde mini disk around the primary star. This provides a direct in-situ formation channel for retrograde S-type planets. The mini disk forms via a sub-Keplerian accretion stream that is slightly misaligned from the polar disk. The mini disk initially undergoes von Zeipel-Kozai-Lidov (ZKL) oscillations, driving coupled eccentricity and inclination evolution. Rather than oscillating indefinitely, the inner mini disk evolves past the critical ZKL inclination, decouples from the outer disk, and settles into a stable retrograde orbit. This evolution is sensitive to numerical resolution: the retrograde configuration is absent in previous lower-resolution simulations, where the mini disk accretion timescale is too short to sustain ZKL-driven evolution. For a higher disk viscosity, the mini disk remains near-polar due to a shorter accretion timescale. Since protoplanetary disks typically have low viscosity, our results suggest that retrograde S-type planets can form in-situ from retrograde mini disks around polar circumbinary disks, and their occurrence rate may be higher than currently estimated.
Stellar activity complicates exoplanet transmission spectra, particularly for smaller planets around M dwarfs with JWST. The transit light source (TLS) effect, the imprinting of spectral differences between the average stellar disk and the occulted transit chord onto the transmission spectrum, makes it challenging to directly use the out-of-transit spectrum to correct for stellar contamination. Theory and observations suggest that spots may concentrate towards higher latitudes when the Coriolis force is substantial relative to buoyancy, leaving the equatorial region relatively quiet. Here, we evaluate how the latitudinal distribution of active regions shapes the strength of the TLS effect for planets spanning a range of impact parameters (b), using TRAPPIST-1 as a testbed. We first construct a fiducial model to illustrate two distribution regimes. With our model, the moderate-b outer TRAPPIST-1 planets (f, g, h) occult a more typical region of the stellar disk than the inner planets and are thereby less affected by the TLS effect, though their bias may vary more from visit-to-visit as these active regions evolve with time. More generally, our results imply an impact parameter "sweet spot" for atmospheric characterization, independent of the sign of the active region temperature contrast, whose location depends on the distribution of active regions. The distribution may be revealed by transit residuals as multiple planets probe different latitudes, while longitudes are sampled in time, such that the variance and frequency of the correlated scatter could constrain active-region filling factors, sizes, and separations.
This Letter presents JWST MIRI/Medium-Resolution Spectrometer (MRS) observations of the central r ≈ 40–240 pc regions of five active galactic nuclei (AGN) spanning a wide range of luminosities (log L _bol /erg s ^−1 ≈ 39.8–43.8). Combining multiphase diagnostics from polycyclic aromatic hydrocarbons (PAHs), molecular hydrogen (H _2 ), and ionized gas at spatial scales of ∼4–24 pc, this study presents a spatially resolved investigation into the effects of the two distinct AGN feedback modes—radiative and kinetic—on the surrounding medium. The results indicate that these two feedback modes, associated with AGN irradiation and shock processing, respectively, collectively drive the relative suppression of PAH emission in the nuclear regions of the targets studied here. Moreover, the coexistence of these two AGN feedback modes, especially the shock processing associated with either jets or outflows, in the central regions of AGN naturally explains both the bimodal distribution of PAH band ratios observed in the targets studied here and the seemingly disparate results reported in the literature. Although based on a limited sample, these findings provide new insights into calibrating star formation rates from PAH emission in AGN and, more importantly, lay the groundwork for a practical framework to diagnose and quantify AGN feedback in the JWST era.
We report JWST spectra and photometry of the underluminous SN Iax 2024vjm obtained 202.8 restframe days post-explosion. The spectrum exhibits a rich set of forbidden lines from low-ionization, intermediate-mass, and iron-group elements, notably the [Ni II] 6.64 micron resonance line, which is a direct indicator of stable nickel. Strong CO and SiO emission is detected alongside a warm dust continuum; the spectral properties are consistent with pre-existing rather than newly formed dust. Synthetic spectra were computed with the generalized stellar atmospheres code PHOENIX/1D using simplified ejecta models. The models reproduce the overall spectral energy distribution and the molecular emission features reasonably well, but substantially underestimate the strength of the mid-infrared atomic forbidden lines, leaving the synthetic spectrum dominated by molecular emission. Experiments in which the molecular opacity is suppressed do not recover the forbidden lines; instead, the emission peak migrates to Co and Fe transitions near 2 microns. We attribute this discrepancy to poorly constrained collisional rates and possibly to an excess of iron-group material in the current ejecta models. A prominent feature at 12.8 microns is not well accounted for by the [Ne II] 12.81 micron line, indicating that the 12.8 micron feature may be largely due to [Fe III]. The presence of CO, SiO, and stable nickel together with the non-detection of neon places tight constraints on the total ejecta mass and the nucleosynthetic yields of SNe Iax progenitor systems.
We propose a novel approach for the timing of pulsars orbiting a supermassive black hole, which implements the fully relativistic calculations of the photon travel time into a robust timing model. We generate realistic mock catalogues of pulsar times-of-arrival for several putative pulsars on tight orbits around the Galactic Center supermassive black hole, Sagittarius A* (Sgr A*). Then, we perform a proof-of-concept sensitivity analysis to forecast the accuracy that future observational facilities, like the Squared Kilometer Array, will achieve in the characterization of the parameters of our timing model. Our analysis shows how the observation of pulsars at the Galactic Center will open an incredibly promising avenue for the characterization of the physical properties of Sgr A*, which can improve by at least three orders of magnitude the current constraints on the black hole's mass achieved with the S-stars and event-horizon scale observations.
Constraining the sulfur reservoirs of interstellar objects provides essential clues to the nature of sulfur species in protoplanetary disks and interstellar molecular clouds and a potential solution to the cosmic sulfur depletion problem. Observations of interstellar objects, chemical messengers from these systems, allow us sensitive probes of their volatile and refractory content and, when placed in context with recent developments in laboratory astrophysics, allow us to propose hypotheses for their formation and initial conditions. We present Hubble Space Telescope Observations of the interstellar object 3I/ATLAS, taken in 2025 December and 2026 January, that show fluorescence emissions from the CO Fourth Positive Group that are well fit by production rates of 3.8 × 10 ^27 and 1.1 × 10 ^27 molec. s ^−1 , respectively. We also place stringent upper limits on the atomic sulfur column and show that 3I/ATLAS’s comae is significantly depleted in sulfur, with S/O 3 σ upper limits of 0.4% and 0.1% for the 2025 December and 2026 January epochs, respectively. We hypothesize that this sulfur depletion is the result of a physical and chemical formation environment that was extremely cold, UV-shielded, and/or sulfur-depleted and therefore not conducive to the formation of H _2 S or SO/SO _2 while still effectively forming OCS and depleting the H _2 S reservoir, with substantial material inherited from the dense interstellar cloud. That same process would also sequester sulfur into FeS and S _6 –S _8 allotropes, which would be refractory at the observed heliocentric distances and would not contribute to the atomic sulfur coma. These species, which are often highlighted as potential solutions to the cosmic sulfur depletion problem, are also theorized to be the source of excess atomic sulfur seen in solar system comets.
Diffusive shock acceleration, at shocks from coronal mass ejections to supernova-remnant blast waves, presupposes a scattering wave field that the accelerated particles themselves maintain. This self-regulation has not been resolved in situ. We report Parker Solar Probe observations of a fast ( 2800 km/s), near-parallel interplanetary shock at 0.24 AU on 2023 March 13 and separate its upstream wave field into four families, a classification not made before at a fast shock near the Sun. Right-hand and left-hand circularly polarized families over a common wavenumber band, with a field-aligned linearly polarized family, are cyclotron-resonant with the suprathermal-to-MeV protons streaming from the shock: the beam drives the field that scatters it, and the measured mean free path, half the precursor scale, leaves the beam anisotropic enough to sustain the drive. Outside this loop lies a weak, oblique, linearly polarized component, a few per cent of the wave power, resolved here for the first time at an in situ foreshock. Its in-phase density and field-magnitude fluctuations identify the compressive part as fast magnetosonic and shift the cyclotron-resonance energies of the resonant families by up to 13
NGC 1275 is the central galaxy in the Perseus Cluster. The active galactic nucleus (AGN) within NGC 1275 is notable for its strong and variable radio activity, tied to the production of radio jets that inflate large bubbles in the hot intracluster medium (ICM). High spatial resolution X-ray imaging can separate the AGN from the bright ICM, but monitoring the mass accretion rate onto the black hole and establishing disk-jet connections in NGC 1275 requires a high cadence. Here, we report on X-ray monitoring of NGC 1275 using data taken over 20 years with the Neil Gehrels Swift Observatory. Modeling the temporally constant ICM in each observation allows X-ray emission from accretion onto the black hole to be traced reliably, with typical flux errors of ∼ 3%. X-ray flaring by a factor of ∼2 over mere days is detected starting on MJD 59956 (2023 Feb. 21). The flares imply an emission region consistent with r ≤ 870 (10^8 M_⊙/M_BH) GM/c^2. The profile of the flaring is inconsistent with simple predictions for tidal disruption events. A flare appears roughly 300 days later in radio monitoring data at 43 GHz. Overall, our results indicate that coordinated, moderate-resolution X-ray imaging and radio monitoring could potentially trace disk-jet connections in the AGN that most vividly impact large-scale structure, and be extended to other sources that impact their hosts.
Quasi-periodic eruptions (QPEs) are quasi-periodic X-ray bursts observed in the nucleus of a galaxy. Multiple pieces of observational evidence link QPEs to tidal disruption events (TDEs), which occur when stars are disrupted after approaching a supermassive black hole too closely. Post-starburst galaxies are overrepresented among the host galaxies of both TDEs and QPEs, though the mechanism causing this overrepresentation is unknown. While their physical origin is unclear, the delay time distribution (DTD) of QPEs, or rate of QPEs as a function of time since a burst of star formation, can constrain what mechanisms influence the QPE rate and possible QPE formation channels. We compile a catalog of 10 QPE host galaxies with optical spectra, model the stellar populations with Bagpipes, and retrieve the age of the most recent burst of star formation to construct the DTD of QPEs. We find that the QPE rate increases with post-burst age to reach a peak at 1 Gyr relative to a control sample, similar to the observational TDE DTD, though we cannot rule out a flat distribution of burst ages relative to a control sample. However, the fraction of QPE host galaxies with high (>1
Filaments are cool and dense plasmas suspended in the hot corona of the Sun and other stars. Accurately estimating their masses is of great significance for understanding subsequent eruptions and induced space weather effects, but it remains hindered by their intrinsic geometric uncertainties, particularly in spatially unresolved stellar observations. To test and calibrate the methods for estimating the masses of stellar filaments, we conduct a statistical Sun-as-a-star analysis of solar filaments, utilizing full-disk Hα spectroscopic observations from the Chinese Hα Solar Explorer (CHASE). A total of 1346 filaments, covering a period from January 2024 to October 2025, are identified via a machine-learning segmentation model. We construct their virtual sun-as-a-star spectra by spatially integrating the filament regions and then obtain their optical parameters by cloud-model fitting. Upon correcting projection effects, we establish a representative three-dimensional morphological scaling of length, apparent width, and line-of-sight depth (L:W_ app:D_ LOS≈ 4.5:1:1.7), with a median filament depth of about 8000 km. Interestingly, the Sun-as-a-star estimated mass shows high consistency with the resolved intrinsic mass across the full sample, with a log-space regression slope of 1.07. As the first large-sample Sun-as-a-star study of solar filaments, our results provide empirical constraints on filament geometries and masses, offering a critical reference for estimating stellar filament masses based on Hα spectroscopy.
