Proxima Centauri (Cen) has been the subject of many flaring studies due to its proximity and potential to host habitable planets. The discovery of millimeter flares from this M dwarf with Atacama Large Millimeter/submillimeter Array (ALMA) has opened a new window into the flaring process and the space-weather environments of exoplanets like Proxima b. Using a total of ~50 hr of ALMA observations of Proxima Cen at 1.3 mm (233 GHz), we add a new piece to the stellar flaring picture and report the first cumulative flare frequency distribution (FFD) at millimeter wavelengths of any M dwarf. We detect 463 flares ranging from energies 10²⁴ to 10²⁷ erg. The brightest and most energetic flare in our sample reached a flux density of 119 ± 7 mJy, increasing by a factor of 1000× the quiescent flux, and reaching an energy of 10²⁷ erg in the ALMA bandpass, with t_1/2 ≈ 16 s. From a log–log linear regression fit to the FFD, we obtain a power-law index of α_FFD = 2.92 ± 0.02, much steeper than α_FFD values (~2) observed at X-ray to optical wavelengths. If millimeter flare rates are predictive of flare rates at extreme-UV wavelengths, the contribution of small flares to the radiation environment of Proxima b may be much higher than expected based on the shallower power-law slopes observed at optical wavelengths.

We present JWST-NIRCam narrowband, 4.05 μm Br α images of the Sgr C H ii region, located in the central molecular zone (CMZ) of the Galaxy. Unlike any H ii region in the solar vicinity, the Sgr C plasma is dominated by filamentary structure in both Br α and the radio continuum. Some bright filaments, which form a fractured arc with a radius of about 1.85 pc centered on the Sgr C star-forming molecular clump, likely trace ionization fronts. The brightest filaments form a "π-shaped" structure in the center of the H ii region. Fainter filaments radiate away from the surface of the Sgr C molecular cloud. The filaments are emitting optically thin free–free emission, as revealed by spectral index measurements from 1.28 GHz (MeerKAT) to 97 GHz (Atacama Large Millimeter/submillimeter Array). But, the negative in-band 1 to 2 GHz spectral index in the MeerKAT data alone reveals the presence of a nonthermal component across the entire Sgr C H ii region. We argue that the plasma flow in Sgr C is controlled by magnetic fields, which confine the plasma to ropelike filaments or sheets. This results in the measured nonthermal component of low-frequency radio emission plasma, as well as a plasma β (thermal pressure divided by magnetic pressure) below 1, even in the densest regions. We speculate that all mature H ii regions in the CMZ, and galactic nuclei in general, evolve in a magnetically dominated, low plasma β regime.

This study conducts mineralogical and chemical investigations on the oldest achondrite, Erg Chech 002 (∼4565 million yr old). This meteorite exhibits a disequilibrium igneous texture characterized by high-Mg-number (atomic Mg/(Mg + Fe²⁺)) orthopyroxene xenocrysts (Mg number = 60–80) embedded in an andesitic groundmass. Our research reveals that these xenocrysts were early formed crystals, loosely accumulated or scattered in the short-period magma ocean on the parent body. Subsequently, these crystals underwent agitation due to the influx of external materials. The assimilation of these materials enriched the ¹⁶O component of the magma ocean and induced a relatively reduced state. Furthermore, this process significantly cooled the magma ocean and inhibited the evaporation of alkali elements, leading to elevated concentrations of Na and K within the meteorite. Our findings suggest that the introduced materials are probably sourced from the reservoirs of CR clan meteorites, indicating extensive transport and mixing of materials within the early solar system.

The subluminous red nova (SLRN) Zwicky Transient Facility (ZTF) SLRN-2020 is the most compelling direct detection of a planet being consumed by its host star, a scenario known as a planetary engulfment event. We present JWST spectroscopy of ZTF SLRN-2020 taken +830 days after its optical emission peak using the NIRSpec fixed-slit 3–5 μm high-resolution grating and the MIRI 5–12 μm low-resolution spectrometer. NIRSpec reveals the ¹²CO fundamental band (ν = 1–0) in emission at ∼4.7 μm, Brackett-α emission, and the potential detection of PH₃ in emission at ∼4.3 μm. The JWST spectra are consistent with the claim that ZTF SLRN-2020 arose from a planetary engulfment event. We utilize DUSTY to model the late-time ∼1–12 μm spectral energy distribution (SED) of ZTF SLRN-2020, where the best-fit parameters indicate the presence of warm, $72{0}_{-50}^{+80}$ K, circumstellar dust with a total dust mass of Log $\left(\tfrac{{M}_{{\rm{d}}}}{{M}_{\odot }}\right)=-10.6{1}_{-0.16}^{+0.08}$ M_⊙. We also fit a DUSTY model to archival photometry taken +320 days after the peak that suggested the presence of a cooler, ${T}_{{\rm{d}}}=28{0}_{-20}^{+450}$ K, and more massive, Log $\left(\tfrac{{M}_{{\rm{d}}}}{{M}_{\odot }}\right)=-5.8{9}_{-3.21}^{+0.29}$, circumstellar dust component. Assuming the cool component originates from the ZTF SLRN-2020 ejecta, we interpret the warm component as fallback from the ejecta. From the late-time SED model, we measure a luminosity of ${L}_{* }=0.2{9}_{-0.06}^{+0.03}$ L_⊙ for the remnant host star, which is consistent with a ∼0.7 M_⊙ K-type star that should not yet have evolved off the main sequence. If ZTF SLRN-2020 was not triggered by stellar evolution, we suggest that the planetary engulfment was due to orbital decay from tidal interactions between the planet and the host star.

This study presents observations of a large pseudostreamer solar eruption and, in particular, the post-eruption relaxation phase, as captured by Metis, on board the Solar Orbiter, on 2022 October 12, during its perihelion passage. Utilizing total-brightness data, we observe the outward propagation of helical features up to 3 solar radii along a radial column that appears to correspond to the stalk of the pseudostreamer. The helical structures persisted for more than 3 hr following a jet-like coronal mass ejection associated with a polar crown prominence eruption. A notable trend is revealed: the inclination of these features decreases as their polar angle and height increase. Additionally, we measured their helix pitch. Despite the 2 minute time cadence limiting direct correspondence among filamentary structures in consecutive frames, we find that the Metis helical structure may be interpreted as a consequence of twist (nonlinear torsional Alfvén waves) and plasma liberated by interchange reconnection. A comparison was performed between the helix parameters as outlined by fine-scale outflow features and those obtained from synthetic white-light images derived from the high-resolution magnetohydrodynamics simulation of interchange reconnection in a pseudostreamer topology by P. F. Wyper et al. A remarkable similarity between the simulation-derived images and the observations was found. We conjecture that these Metis observations may represent the upper ends of the spatial and energy scales of the interchange reconnection process that has been proposed recently as the origin of the Alfvénic solar wind.

We report the spectroscopic discovery of a massive quiescent galaxy at z_spec = 7.29 ± 0.01, just  ∼700 Myr after the big bang. RUBIES-UDS-QG-z7 was selected from public JWST/NIRCam and MIRI imaging from the PRIMER survey and observed with JWST/NIRSpec as part of RUBIES. The NIRSpec/PRISM spectrum reveals one of the strongest Balmer breaks observed thus far at z > 6, with no emission lines but tentative Balmer and Ca absorption features, as well as a Lyman break. Simultaneous modeling of the NIRSpec/PRISM spectrum and NIRCam and MIRI photometry (spanning 0.9–18 μm) shows that the galaxy formed a stellar mass of log$({M}_{* }/{M}_{\odot })=10.2{3}_{-0.04}^{+0.04}$ before z ∼ 8 and ceased forming stars 50–100 Myr prior to the time of observation, resulting in $\mathrm{log}({{\rm{sSFR/Gyr}}}^{-1})\lt -1$. We measure a small physical size of $20{9}_{-24}^{+33}\,{\rm{pc}}$, which implies a high stellar-mass surface density within the effective radius of $\mathrm{log}({{\rm{\Sigma }}}_{* ,{\rm{e}}}/{M}_{\odot }\,{{\rm{kpc}}}^{-2})=10.8{5}_{-0.12}^{+0.11}$, comparable to the highest densities measured in quiescent galaxies at z ∼ 2–5. The 3D stellar-mass density profile of RUBIES-UDS-QG-z7 is remarkably similar to the central densities of local massive ellipticals, suggesting that at least some of their cores may have already been in place at z > 7. The discovery of RUBIES-UDS-QG-z7 has strong implications for galaxy formation models: the estimated number density of quiescent galaxies at z ∼ 7 is  >100 ×  larger than predicted from any model to date, indicating that quiescent galaxies have formed earlier than previously expected.

We present James Webb Space Telescope (JWST) Near Infrared Camera observations of the massive star-forming molecular cloud Sagittarius C (Sgr C) in the Central Molecular Zone (CMZ). In conjunction with ancillary mid-IR and far-IR data, we characterize the two most massive protostars in Sgr C via spectral energy distribution (SED) fitting, estimating that they each have current masses of m_* ∼ 20 M_⊙ and surrounding envelope masses of ∼100 M_⊙. We report a census of lower-mass protostars in Sgr C via a search for infrared counterparts to millimeter continuum dust cores found with the Atacama Large Millimeter/submillimeter Array (ALMA). We identify 88 molecular hydrogen outflow knot candidates originating from outflows from protostars in Sgr C, the first such unambiguous detections in the infrared in the CMZ. About a quarter of these are associated with flows from the two massive protostars in Sgr C; these extend for over 1 pc and are associated with outflows detected in ALMA SiO line data. An additional ∼40 features likely trace shocks in outflows powered by lower-mass protostars throughout the cloud. We report the discovery of a new star-forming region hosting two prominent bow shocks and several other line-emitting features driven by at least two protostars. We infer that one of these is forming a high-mass star given an SED-derived mass of m_* ∼ 9 M_⊙ and associated massive (∼90 M_⊙) millimeter core and water maser. Finally, we identify a population of miscellaneous molecular hydrogen objects that do not appear to be associated with protostellar outflows.

A new model is proposed in which typical galaxies form most of their stellar mass in a phase with an intrinsically red stellar population. In the standard picture, galaxies with intrinsically red stellar populations are believed to have old stellar populations, so that only galaxies with blue stellar populations have significant star formation, and subsequent changes to the stellar population come predominantly from aging and merging populations that have already formed. However, several observational puzzles have developed that are difficult to reconcile with this standard scenario. The most massive blue star-forming galaxies, presumed to be at the end of their stellar mass growth, are ∼1 dex less massive, have a ∼1 dex lower M_*/M_BH ratio, and have a bottom-lighter IMF than local quiescent galaxies. Here, a new solution is proposed: at low temperature and high metallicity, galaxies can continue to form stars efficiently without being able to form O and B stars. These red star-forming galaxies would have many of the same properties of the population currently described as post-starburst galaxies, allowing a new interpretation of their origin. Finally, additional falsifiable observational predictions of this model are also discussed.

We examine ³He-rich solar energetic particles (SEPs) detected on 2023 October 24–25 by Solar Orbiter at 0.47 au. Measurements reveal that heavy-ion enhancements increase irregularly with mass, peaking at S. C, and especially N, Si, and S, stand out in the enhancement pattern with large abundances. Except for ³He, heavy-ion spectra can only be measured below 0.5 MeV nucleon⁻¹. At 0.386 MeV nucleon⁻¹, the event shows a huge ³He/⁴He ratio of 75.2 ± 33.9, larger than previously observed. Solar Dynamics Observatory extreme-ultraviolet data show a minifilament eruption at the solar source of ³He-rich SEPs that triggered a straight tiny jet. Located at the boundary of a low-latitude coronal hole, the jet base is a bright, small-scale region with a supergranulation scale size. The emission measure (EM) provides relatively cold source temperatures of 1.5–1.7 MK between the filament eruption and nonthermal type III radio burst onset. Analysis suggests that the EM distribution of temperature in the solar source could be a factor that affects the preferential selection of heavy ions for heating or acceleration, thus shaping the observed enhancement pattern. Including previously reported similar events indicates that the eruption of the minifilament is a common feature of events with heavy-ion enhancement not ordered by mass. Surprisingly, sources with weak magnetic fields show extreme ³He enrichment in these events. Moreover, the energy attained by heavy ions seems to be influenced by the size and form of the jets.

The diffuse interstellar bands (DIBs) have remained a mystery in astronomy since their discovery over a century ago. The only currently known carrier is ${{\rm{C}}}_{60}^{+}$, responsible for five DIBs, while more than 550 are yet to be interpreted. The spectra of short carbon chain cations ${({\rm{C}}}_{n}^{+})$, which are considered one of the most promising classes of species for the role of carriers of DIBs, are successfully recorded using He-tagging spectroscopy. The comparison of laboratory spectra with observations demonstrates a close match of two absorption bands of ${{\rm{C}}}_{4}^{+}$ with the broad DIB at 503.9 nm. This defines a high abundance of these ions in the interstellar medium (ISM), which should exceed those of other similar-sized carbon chain cations. It is anticipated that all other short carbon chain cations will exhibit linear geometry and, as a consequence, will have a long vibrational progression. However, the distinctive cyclic geometry of ${{\rm{C}}}_{4}^{+}$ is postulated to underpin the elevated abundance of these ions in the ISM, as well as the distinctive spectrum of this ion, which displays a single, strong, relatively narrow absorption band that exceeds in intensity all other absorption bands in the visible range.

We present the first systematic investigation of off-axis jets in gamma-ray bursts based on rising optical afterglows. As a pilot study, we selected eight well-observed bright optical afterglows and performed a Bayesian inference using two different jet models: a Gaussian-structured jet and a homogeneous top-hat jet. Assuming an adiabatic evolution of the fireball through a constant-density ambient medium, we derived the key afterglow parameters: viewing angle (θ_v), jet opening angle (θ_j for top-hat jets) or characteristic angle (θ_c for Gaussian jets), ambient medium number density n₀, and _B measuring the downstream magnetic field strength. The inferred viewing angles of the sample range from 0.4° to 9.7°. Our results identify delayed optical peaks (occurring hundreds to thousands of seconds postburst) and low luminosity as key signatures of misaligned jets, with slow rises to peak suggesting structured jets. We further observe a correlation between the rest-frame peak time and the degree of misalignment in optical light curves. A larger sample size is required to confirm this.

The composition of protoplanetary disks, and hence the initial conditions of planet formation, may be strongly influenced by the infall and thermal processing of material during the protostellar phase. The composition of dust and ice in protostellar envelopes, shaped by energetic processes driven by the protostar, serves as the fundamental building material for planets and complex organic molecules. As part of the JWST General Observers program, "Investigating Protostellar Accretion," we observed an intermediate-mass protostar HOPS 370 (OMC2-FIR3) using NIRSpec integral field unit and Mid-Infrared Instrument medium-resolution spectroscopy. This study presents the gas and ice phase chemical inventory revealed with the JWST in the spectral range of ∼2.9–28 μm and explores the spatial variation of volatile ice species in the protostellar envelope. We find evidence for the thermal processing of ice species throughout the inner envelope. We present the first high-spatial resolution (∼80 au) maps of key volatile ice species H₂O, CO₂, ¹³CO₂, CO, and OCN⁻, which reveal a highly structured and inhomogeneous density distribution of the protostellar envelope, with a deficiency of ice column density that coincides with the jet/outflow shocked knots. Further, we observe high relative crystallinity of H₂O ice around the shocked knot seen in the H₂ and OH wind/outflow, which can be explained by a lack of outer colder material in the envelope along the line of sight due to the irregular structure of the envelope. These observations show clear evidence of thermal processing of the ices in the inner envelope, close to the outflow cavity walls, heated by the luminous protostar.

We report on the intriguing properties of a variable X-ray source projected at the outskirts of the elliptical galaxy NGC 6099 (d ≈ 139 Mpc). If truly located near NGC 6099, this is a hyperluminous X-ray source that reached an X-ray luminosity L_X ≈ a few times 10⁴² erg s⁻¹ in 2012 February (XMM-Newton data), about 50–100 times brighter than in 2009 May (Chandra) and 2023 August (XMM-Newton). The X-ray spectrum was soft at all three epochs, with a thermal component at kT ≈ 0.2 keV and a power-law photon index >3. Such properties make it a strong candidate for an intermediate-mass black hole (IMBH). We also discovered a point-like, blue optical counterpart (m_g,Vega ≈ 24.7 mag, M_g,Vega ≈ −11.2 mag), from images taken by the Canada–France–Hawaii Telescope and later confirmed with Hubble Space Telescope observations. The optical continuum can be modeled as stellar emission from a compact star cluster or an X-ray-irradiated accretion disk, consistent with the IMBH scenario. We discuss alternative explanations for the nature of this system. A possible scenario is tidal stripping of an orbiting star, with repeated X-ray outbursts every few years. An alternative possibility is that the thermal X-ray emission seen in 2009 was from shocked gas in the self-intersecting tidal stream during the rising phase of a tidal disruption event, while the 2012 and 2023 emissions were from the fully formed accretion disk.

Solar quiet regions are divided into coronal hole regions (CH) and quiet-Sun regions (QS). The global magnetic field in CH is considered open to interplanetary space, while that in QS is closed. To constrain the solar atmosphere and solar wind model, we statistically compared CH and QS in the chromosphere by quantitatively analyzing all available high-resolution spectral data sets of polar off-limb regions taken from the entire catalog of the Interface Region Imaging Spectrograph (IRIS) satellite. We extracted the characteristic quantities from the Mg ii h and k line profiles and compared the dependence of those quantities on the height from the photospheric limb. The main findings are as follows. First, the integrated intensities in the Mg ii k line show a steeper decrease with height in QS while they remain bright at higher altitudes in CH. Second, the unsigned line-of-sight velocities in the Mg ii k line generally increase with height in both regions, although the unsigned velocities increase with height more strongly in QS than in CH. Third, the Mg ii k line widths increase just above the limb and then decrease with height in both CH and QS, but are overall larger for CH than for QS, especially at the lower altitudes. Finally, we found the ratio of the Mg ii k and h lines to show a two-step increase with height in both regions. The results suggest the spicules are higher in CH, and the CH chromosphere exhibits faster motions than the QS.

Ion cyclotron waves (ICWs) are prevalent in the near-Sun solar wind and play a significant role in the nonadiabatic heating of plasma. Recent observations from the Parker Solar Probe have revealed the simultaneous presence of antisunward and sunward ICWs in the vicinity of the Alfvén surface. However, single-satellite observations cannot effectively trace the generation and evolution of these observed waves. To address this limitation, we employ kinetic-hybrid simulations to replicate the generation and evolution of counterpropagating ICWs under typical plasma conditions in the near-Sun solar wind. Following the linear growth phase, the simulated waves exhibit amplitude and polarization characteristics that closely match the observations. Additionally, our simulation illustrates proton scattering induced by the counterpropagating waves. These results underscore the significance of locally generated ICWs in influencing solar wind ion dynamics.