From its birth, celestial mechanics has been deeply intertwined with the question of the solar system’s dynamical stability. For the inner planets, this question is now statistically settled: Mercury’s orbit carries a ∼1% chance of destabilization before the Sun leaves the main sequence. The outer solar system has seemed more secure, with its intrinsic dynamical lifetime estimated at ∼1018 yr. Even accounting for the Sun’s mass loss and stellar flybys, the orbital architecture of the giant planets had been expected to persist for ∼100 Gyr. Here we show that these estimates rest on the assumption that solar mass loss is smooth. The recently measured white dwarf recoil demands asymmetric mass loss that is most readily attributed to discrete, independently directed ejections that impulsively perturb stellar motion. As the Sun sheds its envelope in such parcels, the planets’ orbits random-walk with amplitude set by the mass-loss granularity. At a coarseness corresponding to observationally permitted kicks, this stochastic forcing restructures the outer solar system concurrently with the Sun’s death. In particular, our numerical experiments reveal that orbit crossings can commence on the red giant branch, with ∼40% of realizations undergoing disruption or violent scattering before the white dwarf forms and ∼90% self-destructing within 3 Gyr. The outer solar system’s dynamical lifetime thus collapses from 1018 yr to approximately a gigayear after white dwarf formation.
The American Astronomical Society (AAS), established in 1899 and based in Washington, DC, is the major organization of professional astronomers in North America. Its membership of about 7,000 individuals also includes physicists, mathematicians, geologists, engineers, and others whose research and educational interests lie within the broad spectrum of subjects comprising contemporary astronomy. The mission of the AAS is to enhance and share humanity's scientific understanding of the universe.
The Astrophysical Journal Letters is an open access express scientific journal that allows astrophysicists to rapidly publish short notices of significant original research. ApJL articles are timely, high-impact, and broadly understandable.
- The following article is Open accessTerminal Instability of the Solar System Triggered by Stochastic Solar Mass Loss
Konstantin Batygin et al 2026 ApJL 1009 L22
- The following article is Open accessSearching for Embedded Protoplanets with the Keck/NIRC2 Vortex Coronagraph: Confirmation of a Core-accretion Planet in the Narrow Gap of the Elias 2-24 Disk
Andrea Bernardi et al 2026 ApJL 1009 L3
View article, Searching for Embedded Protoplanets with the Keck/NIRC2 Vortex Coronagraph: Confirmation of a Core-accretion Planet in the Narrow Gap of the Elias 2-24 DiskPDF, Searching for Embedded Protoplanets with the Keck/NIRC2 Vortex Coronagraph: Confirmation of a Core-accretion Planet in the Narrow Gap of the Elias 2-24 DiskDownload ePub, Searching for Embedded Protoplanets with the Keck/NIRC2 Vortex Coronagraph: Confirmation of a Core-accretion Planet in the Narrow Gap of the Elias 2-24 DiskWe present high-contrast imaging observations of seven stars obtained with the Keck/NIRC2 vortex coronagraph between 2018 May and June in the
and Ms bands. All targets host protoplanetary disks with substructures such as gaps and cavities, potentially tracing ongoing planet formation. Our aim is to assess whether these embedded planets can be directly detected. We reduced the observations with a custom pipeline based on the VIP Python package. Postprocessed images were obtained using angular differential imaging and reference differential imaging combined with principal component analysis. Finally, 5σ contrast curves and detection limits were derived for all targets. We confirm the planetary candidate around Elias 2-24, previously proposed in the literature, at a separation of 394 ± 31 mas (54.9 ± 4.3 au) and a position angle of 2988 ± 32, within the narrow gap of the protoplanetary disk. Comparing the derived photometry with 1 Myr isochrones, we infer a mass between 1.9 and 4.0 MJup for Elias 2-24 b, without considering accretion effects, in agreement with estimates considering the properties of the gap and planet–disk interactions. For all the systems in the survey, the 5σ detection limits reach sensitivities down to 1–11 MJup at separations ≳025. Since Elias 2-24 b (age ≲1 Myr) is the youngest exoplanet discovered to date, its confirmation has important implications for planet formation timescales and the origin of the gaps observed in very young disks. - The following article is Open accessFirst M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
The Event Horizon Telescope Collaboration et al 2019 ApJL 875 L1
View article, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black HolePDF, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black HoleDownload ePub, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black HoleWhen surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 ± 3 μas, which is circular and encompasses a central depression in brightness with a flux ratio ≳10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5 ± 0.7) × 109 M⊙. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.
- The following article is Open accessLighting Up the Circumgalactic Medium: Strong, Jet-aligned Hα Emission around Radio Galaxies
Namrata Roy et al 2026 ApJL 1009 L34
View article, Lighting Up the Circumgalactic Medium: Strong, Jet-aligned Hα Emission around Radio GalaxiesPDF, Lighting Up the Circumgalactic Medium: Strong, Jet-aligned Hα Emission around Radio GalaxiesDownload ePub, Lighting Up the Circumgalactic Medium: Strong, Jet-aligned Hα Emission around Radio GalaxiesA primary question is how active galactic nuclei (AGN) feedback modifies the circumgalactic medium (CGM). We present a search for faint Hα emission from the cool ionized CGM (T ∼ 104 K) around radio galaxies by stacking background-quasar spectra from Dark Energy Spectroscopic Instrument (DESI) sight lines. We take into account the projected distance and position angle of each quasar sight line relative to the radio-jet axis, and test whether jet–CGM coupling is anisotropic. We detect a strong Hα excess at >5σ along the collimated radio-jet axis (θ < 20∘) with a mean integrated flux of 1.19 × 10−17 erg cm−2 s−1. In contrast, the azimuthally averaged stack over all 324 sight-line angles yields no detection (<2σ), indicating that this excess emission is very localized along the radio jet. We also find that the jet-aligned Hα signal is radially structured, where the strongest emission occurs near the host galaxy just outside the optical half-light radius, and rising again near the projected radio-lobe region. The jet-aligned stacks reveal Hα signal that is roughly 100 times brighter than normal halos. In the same sight lines however, Mg ii absorption shows no difference in incidence between jet-aligned and off-axis directions, with broadly similar equivalent widths, column densities, and line widths. This striking contrast shows that while Mg ii traces the ambient, clumpy cool CGM reservoir, the Hα emission directly captures localized, low-covering-fraction clouds whose density, pressure, or ionization level has been dramatically boosted by the propagating jet. These results deliver clear evidence of localized jet–CGM interaction in radio-jetted AGNs.
- The following article is Open accessDifferential Polarization Calibration: A Consistency Test for Cosmic Birefringence
Anto I. Lonappan et al 2026 ApJL 1009 L12
View article, Differential Polarization Calibration: A Consistency Test for Cosmic BirefringencePDF, Differential Polarization Calibration: A Consistency Test for Cosmic BirefringenceDownload ePub, Differential Polarization Calibration: A Consistency Test for Cosmic BirefringenceThe cosmic microwave background (CMB) birefringence angle β is exactly degenerate with a common instrumental polarization-angle offset. The Minami–Komatsu (MK) likelihood separates these quantities using Galactic foreground polarization, so its inferred detector angles merit a diagnostic that does not reuse the foreground-EB model. We develop a birefringence-blind differential estimator from antisymmetric and symmetric cross spectra and apply it for the first time as an explicit consistency test of a foreground-assisted birefringence analysis. For a map pair, the common rotation cancels identically and the estimator measures Δαij = αi − αj; combining all pairs in a gauge-fixed network reconstructs the observable detector-dependent calibration pattern. Applied to eight Planck NPIPE detector-set maps, the differential reconstruction agrees with the MK pattern, giving χ2 = 8.18 for 7 degrees of freedom (PTE = 0.32), with all shared-data residuals below 1.8σ. Because both reconstructions use the same maps, this is an independent estimator and modeling route rather than an independent-data confirmation. The agreement therefore strengthens confidence in the calibration foundation of the MK-inferred β without providing an independent absolute measurement of it. A conditional common-mode reconstruction gives β = 0
37 ± 012. The differential test uses existing data and can serve as a validation layer for future EB-based birefringence analyses. - The following article is Open accessEvidence for an Atmosphere on the Ultra-short-period Super-Earth HD 3167 b
Brandon Park Coy et al 2026 ApJL 1005 L77
View article, Evidence for an Atmosphere on the Ultra-short-period Super-Earth HD 3167 bPDF, Evidence for an Atmosphere on the Ultra-short-period Super-Earth HD 3167 bDownload ePub, Evidence for an Atmosphere on the Ultra-short-period Super-Earth HD 3167 b“Lava worlds”, Earth-sized planets hot enough (Teq ≳ 1100 K) to melt their dayside silicate surfaces, have emerged as promising candidates for atmospheric detection and characterization. Thermal emission observations show an apparent dichotomy: The hottest lava worlds have colder daysides than the temperature of a maximally emitting bare rock, indicating the likely presence of thick and/or reflective atmospheres, while the coldest ones do not. However, where in instellation flux this potential bifurcation occurs is uncertain. We present a JWST/MIRI Low Resolution Spectrometer eclipse of the ultra-short-period (USP) lava world HD 3167 b (Teq = 1786 K, R = 1.6 R⊕, P = 0.96 day) that helps bridge this gap. We measure the white-light eclipse depth to be 38 ± 11 ppm, more than 5σ lower than the expected eclipse depth of a dark, maximally hot bare rock. We use this to derive a dayside brightness temperature that is best explained by the presence of an atmosphere that cools the dayside by reflecting incoming starlight and/or efficiently redistributing heat to the planet’s nightside. An atmosphere is further compatible with the planet’s slight underdensity compared to an Earth-like composition. The corresponding dayside emission spectrum is not precise enough to constrain atmospheric composition, motivating follow-up spectroscopic observations with JWST/NIRSpec. Lastly, we use our observation and existing data to refine key planetary parameters of the HD 3167 system. HD 3167 b is currently the least irradiated USP super-Earth with evidence for an atmosphere.
- The following article is Open accessCollisional Capture of an Intact Moon Depends on Strength
C. Adeene Denton et al 2026 ApJL 1008 L30
View article, Collisional Capture of an Intact Moon Depends on StrengthPDF, Collisional Capture of an Intact Moon Depends on StrengthDownload ePub, Collisional Capture of an Intact Moon Depends on StrengthThe 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.
- The following article is Open accessThe Population of the Galactic Center Filaments: Position Angle Distribution Reveals a Degree-scale Collimated Outflow from Sgr A* along the Galactic Plane
F. Yusef-Zadeh et al 2023 ApJL 949 L31
View article, The Population of the Galactic Center Filaments: Position Angle Distribution Reveals a Degree-scale Collimated Outflow from Sgr A* along the Galactic PlanePDF, The Population of the Galactic Center Filaments: Position Angle Distribution Reveals a Degree-scale Collimated Outflow from Sgr A* along the Galactic PlaneDownload ePub, The Population of the Galactic Center Filaments: Position Angle Distribution Reveals a Degree-scale Collimated Outflow from Sgr A* along the Galactic PlaneWe have examined the distribution of the position angle (PA) of the Galactic center filaments with lengths L > 66″ and <66″ as well as their length distribution as a function of PA. We find bimodal PA distributions of the filaments, and long and short populations of radio filaments. Our PA study shows the evidence for a distinct population of short filaments with PA close to the Galactic plane. Mainly thermal, short-radio filaments (<66″) have PAs concentrated close to the Galactic plane within 60° < PA < 120°. Remarkably, the short filament PAs are radial with respect to the Galactic center at l < 0° and extend in the direction toward Sgr A*. On a smaller scale, the prominent Sgr E H ii complex G358.7-0.0 provides a vivid example of the nearly radial distribution of short filaments. The bimodal PA distribution suggests a different origin for two distinct filament populations. We argue that the alignment of the short-filament population results from the ram pressure of a degree-scale outflow from Sgr A* that exceeds the internal filament pressure, and aligns them along the Galactic plane. The ram pressure is estimated to be 2 × 106 cm−3 K at a distance of 300 pc, requiring biconical mass outflow rate 10−4M⊙ yr−1 with an opening angle of ∼40°. This outflow aligns not only the magnetized filaments along the Galactic plane but also accelerates thermal material associated with embedded or partially embedded clouds. This places an estimate of ∼6 Myr as the age of the outflow.
- The following article is Open accessFirst Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
Event Horizon Telescope Collaboration et al 2022 ApJL 930 L12
View article, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky WayPDF, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky WayDownload ePub, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky WayWe present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of λ = 1.3 mm. The EHT data resolve a compact emission region with intrahour variability. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of 51.8 ± 2.3 μas (68% credible interval). The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass ∼4 × 106 M⊙, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination (i > 50°), as well as nonspinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of 103–105 gravitational radii to event-horizon-scale images and variability. Furthermore, a comparison with the EHT results for the supermassive black hole M87* shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass.
- The following article is Open accessNew Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI
Nikku Madhusudhan et al 2025 ApJL 983 L40
View article, New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRIPDF, New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRIDownload ePub, New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRIThe sub-Neptune frontier has opened a new window into the rich diversity of planetary environments beyond the solar system. The possibility of hycean worlds, with planet-wide oceans and H2-rich atmospheres, significantly expands and accelerates the search for habitable environments elsewhere. Recent JWST transmission spectroscopy of the candidate hycean world K2-18 b in the near-infrared led to the first detections of the carbon-bearing molecules CH4 and CO2 in its atmosphere, with a composition consistent with predictions for hycean conditions. The observations also provided a tentative hint of dimethyl sulfide (DMS), a possible biosignature gas, but the inference was of low statistical significance. We report a mid-infrared transmission spectrum of K2-18 b obtained using the JWST MIRI LRS instrument in the ∼6–12 μm range. The spectrum shows distinct features and is inconsistent with a featureless spectrum at 3.4σ significance compared to our canonical model. We find that the spectrum cannot be explained by most molecules predicted for K2-18 b, with the exception of DMS and dimethyl disulfide (DMDS), also a potential biosignature gas. We report new independent evidence for DMS and/or DMDS in the atmosphere at 3σ significance, with high abundance (≳10 ppmv) of at least one of the two molecules. More observations are needed to increase the robustness of the findings and resolve the degeneracy between DMS and DMDS. The results also highlight the need for additional experimental and theoretical work to determine accurate cross sections of important biosignature gases and identify potential abiotic sources. We discuss the implications of the present findings for the possibility of biological activity on K2-18 b.
- The following article is Open accessBe Star Formation through Stellar Mergers: V1371 Tau
Rebecca G. Martin et al 2026 ApJL 1011 L5
View article, Be Star Formation through Stellar Mergers: V1371 TauPDF, Be Star Formation through Stellar Mergers: V1371 TauDownload ePub, Be Star Formation through Stellar Mergers: V1371 TauThe origin of the near-critical rotation of classical Be stars remains uncertain. Binary mass transfer provides a formation channel, but it cannot explain Be stars that are observed without a close companion. We investigate V1371 Tau, a hierarchical triple containing an inner B+B binary and an outer Be star. With n-body simulations, we first show that the observed inclination variations of the B+B binary do not require von Zeipel–Lidov–Kozai (ZLK) oscillations, as nodal precession alone can produce substantial changes in inclination relative to the line of sight. We then consider whether V1371 Tau formed from a primordial 2+2 quadruple, in which a progenitor binary of the Be star underwent ZLK-driven eccentricity excitation and merged. We find that mergers occur over a broad range of progenitor binary parameters while leaving the observed B+B binary intact. The merger remnant is expected to retain the orbital angular-momentum direction at the time of merger, producing a potentially observable misalignment between the Be-star spin axis and its orbit around the surviving B+B binary. These results demonstrate that ZLK-driven mergers in higher-order multiple systems provide a viable formation pathway for rapidly rotating Be stars without present-day close companions.
- The following article is Open accessEpisodic Plasma Flows and Coronal Brightenings in an Arch Filament System Observed with Sunrise iii
Sergio Javier González Manrique et al 2026 ApJL 1011 L4
View article, Episodic Plasma Flows and Coronal Brightenings in an Arch Filament System Observed with Sunrise iiiPDF, Episodic Plasma Flows and Coronal Brightenings in an Arch Filament System Observed with Sunrise iiiDownload ePub, Episodic Plasma Flows and Coronal Brightenings in an Arch Filament System Observed with Sunrise iiiEmerging flux regions (EFRs) are key sites of magnetic flux transport and energy release in the solar atmosphere, often hosting arch filament systems (AFSs). We present high-resolution observations of an EFR obtained during the Sunrise III mission, combining spectropolarimetric measurements from the Tunable Magnetograph (TuMag) and Sunrise Chromospheric Infrared Spectro-Polarimeter (SCIP) with complementary observations from the Solar Dynamics Observatory (SDO). The data set provides a continuous view of an AFS over nearly 4 hr. Line-of-sight (LOS) velocities derived from the Mg I b2 line reveal three episodic plasma-flow events characterized by strong downflows reaching up to ∼17 km s−1 at the AFS footpoints and enhanced upflows near the loop tops. Although this pattern agrees with the classical emergence and draining scenario, the strongest upflows and downflows occur nearly simultaneously. Atmospheric Imaging Assembly (AIA) 304 and 171 Å observations reveal transient extreme-UV (EUV) brightenings in the surrounding emerging system; some occur during episodes of enhanced LOS velocities, while others do not, indicating that the temporal correspondence is not systematic. Multiline spectropolarimetric inversions reveal temperatures between ∼4000 and ∼10,000 K and a smooth variation of the magnetic field inclination along a representative AFS loop. Non-force-free-field extrapolations provide the large-scale magnetic context of the low-lying AFS loops and surrounding coronal structures. Together, the observations reveal a spatially and temporally complex evolution of the emerging system without establishing a direct causal connection between the local plasma-flow enhancements and the EUV brightenings.
- The following article is Open accessFallback-triggered Reconnection Drives Coronal Mass Ejections on II Pegasi
Dongtao Cao and Shenghong Gu 2026 ApJL 1011 L3
View article, Fallback-triggered Reconnection Drives Coronal Mass Ejections on II PegasiPDF, Fallback-triggered Reconnection Drives Coronal Mass Ejections on II PegasiDownload ePub, Fallback-triggered Reconnection Drives Coronal Mass Ejections on II PegasiStellar coronal mass ejections (CMEs) play key roles in stellar evolution and planetary habitability. On the Sun, CMEs typically originate from preexisting prominences or filaments, while materials condensed via the evaporation–condensation process have only been observed to remain confined or fall back as rain—never to trigger reconnection or drive eruptions. Here, we present high-resolution spectroscopic observations of II Pegasi (II Peg) obtained by the NARVAL, which captured successive sequences of loop-top condensation, gravitational fallback, and subsequent ejection, associated with stellar flares. Three successive flares originating from the same active region exhibited similar early phase spectral evolution but diverged into distinct final outcomes. Two flares developed to show blueshifted emission in the Hα line, with maximum velocities reaching 1.7 and 1.07 times the stellar surface escape velocity (∼306 km s−1), indicating mass ejections. In contrast, the third flare exhibited a redshifted emission feature in the Hα line, signifying a confined event. We interpret these contrasting behaviors within an impact-triggered magnetic reconnection framework, in which the final trajectory—eruptive or confined—is set by whether the newly reconnected field lines open outward or remain closed. Our studies show that stellar CMEs can arise directly from coronal condensations that fall back, trigger reconnection, and are subsequently ejected, revealing a previously unrecognized eruption pathway.
- The following article is Open accessA Forest of Emission Lines Observed by Sunrise III/SUSI above the Solar Limb
Juan Sebastián Castellanos Durán et al 2026 ApJL 1010 L43
View article, A Forest of Emission Lines Observed by Sunrise III/SUSI above the Solar LimbPDF, A Forest of Emission Lines Observed by Sunrise III/SUSI above the Solar LimbDownload ePub, A Forest of Emission Lines Observed by Sunrise III/SUSI above the Solar LimbWe present off-limb spectroscopy using low-stray-light data from the Sunrise Spectropolarimeter and Imager (SUSI) on board the Sunrise iii stratospheric solar observatory. A spatial scan with SUSI’s slit almost parallel to the local limb reached from within the solar disk to 6.5 Mm off-limb. The wavelength range spanned from 407.6 to 410.25 nm. We detected a total of 174 spectral lines in emission off-limb, a 2.5-fold increase over previous reports. Surprisingly, 122 of these lines begin to appear in emission already on the disk, although close to the limb. In addition, one-fifth of relatively prominent emission lines are due to rare-earth and heavy elements and molecules, where the absorption lines of these transitions are typically weak on-disc.
- The following article is Open accessA Possible Complication of Using the 4.14 μm Band to Assess D/H Ratios on Icy Bodies
Mark J. Loeffler et al 2026 ApJL 1011 L2
View article, A Possible Complication of Using the 4.14 μm Band to Assess D/H Ratios on Icy BodiesPDF, A Possible Complication of Using the 4.14 μm Band to Assess D/H Ratios on Icy BodiesDownload ePub, A Possible Complication of Using the 4.14 μm Band to Assess D/H Ratios on Icy BodiesDetermining isotopic ratios on the surfaces of extraterrestrial objects can provide insight into their formation conditions and evolution. Recently, remote-sensing detections of the 4.14 μm HDO absorption band have enabled astronomers to estimate the D/H ratio on several icy objects in the outer solar system. Here, we quantify how ice phase and radiation processing affect the 4.14 μm absorption band. While the band is visible in H2O-ice samples with a crystalline component, we cannot detect it in amorphous H2O ice. Furthermore, we find that radiation processing, using 10 keV electrons as a proxy, quickly makes this absorption feature undetectable at a rate consistent with the amorphization of an initially crystalline sample. Interestingly, we also find that recrystallizing the irradiated sample causes this band to reappear nearly to its original band depth. For the Saturnian satellite Mimas, we estimate that the HDO feature will decrease by a factor of 2 within ∼1 × 104 yr at typical depths probed by remote sensing spectroscopy. While we suspect that existing methods could still determine the D/H ratio from a surface composed entirely of crystalline H2O ice, deriving it for surfaces with a significant amorphous fraction may lead to severe underestimation of the true D/H ratio. However, given the direct correlation between the amorphous fraction of a sample and the HDO band depth, we propose that one could still estimate the D/H ratio of a surface with mixed phases by determining the crystalline fraction of the surface H2O ice using other absorption features.
- The following article is Open accessA Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s−1 Mpc−1 Uncertainty from the Hubble Space Telescope and the SH0ES Team
Adam G. Riess et al 2022 ApJL 934 L7
View article, A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s−1 Mpc−1 Uncertainty from the Hubble Space Telescope and the SH0ES TeamPDF, A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s−1 Mpc−1 Uncertainty from the Hubble Space Telescope and the SH0ES TeamDownload ePub, A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km s−1 Mpc−1 Uncertainty from the Hubble Space Telescope and the SH0ES TeamWe report observations from the Hubble Space Telescope (HST) of Cepheid variables in the host galaxies of 42 Type Ia supernovae (SNe Ia) used to calibrate the Hubble constant (H0). These include the complete sample of all suitable SNe Ia discovered in the last four decades at redshift z ≤ 0.01, collected and calibrated from ≥1000 HST orbits, more than doubling the sample whose size limits the precision of the direct determination of H0. The Cepheids are calibrated geometrically from Gaia EDR3 parallaxes, masers in NGC 4258 (here tripling that sample of Cepheids), and detached eclipsing binaries in the Large Magellanic Cloud. All Cepheids in these anchors and SN Ia hosts were measured with the same instrument (WFC3) and filters (F555W, F814W, F160W) to negate zero-point errors. We present multiple verifications of Cepheid photometry and six tests of background determinations that show Cepheid measurements are accurate in the presence of crowded backgrounds. The SNe Ia in these hosts calibrate the magnitude–redshift relation from the revised Pantheon+ compilation, accounting here for covariance between all SN data and with host properties and SN surveys matched throughout to negate systematics. We decrease the uncertainty in the local determination of H0 to 1 km s−1 Mpc−1 including systematics. We present results for a comprehensive set of nearly 70 analysis variants to explore the sensitivity of H0 to selections of anchors, SN surveys, redshift ranges, the treatment of Cepheid dust, metallicity, form of the period–luminosity relation, SN color, peculiar-velocity corrections, sample bifurcations, and simultaneous measurement of the expansion history. Our baseline result from the Cepheid–SN Ia sample is H0 = 73.04 ± 1.04 km s−1 Mpc−1, which includes systematic uncertainties and lies near the median of all analysis variants. We demonstrate consistency with measures from HST of the TRGB between SN Ia hosts and NGC 4258, and include them simultaneously to yield 72.53 ± 0.99 km s−1 Mpc−1. The inclusion of high-redshift SNe Ia yields H0 = 73.30 ± 1.04 km s−1 Mpc−1 and q0 = −0.51 ± 0.024. We find a 5σ difference with the prediction of H0 from Planck cosmic microwave background observations under ΛCDM, with no indication that the discrepancy arises from measurement uncertainties or analysis variations considered to date. The source of this now long-standing discrepancy between direct and cosmological routes to determining H0 remains unknown.
- The following article is Open accessFirst Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
Event Horizon Telescope Collaboration et al 2022 ApJL 930 L12
View article, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky WayPDF, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky WayDownload ePub, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky WayWe present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of λ = 1.3 mm. The EHT data resolve a compact emission region with intrahour variability. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of 51.8 ± 2.3 μas (68% credible interval). The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass ∼4 × 106 M⊙, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination (i > 50°), as well as nonspinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of 103–105 gravitational radii to event-horizon-scale images and variability. Furthermore, a comparison with the EHT results for the supermassive black hole M87* shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass.
- The following article is Open accessFirst M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
The Event Horizon Telescope Collaboration et al 2019 ApJL 875 L1
View article, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black HolePDF, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black HoleDownload ePub, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black HoleWhen surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 ± 3 μas, which is circular and encompasses a central depression in brightness with a flux ratio ≳10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5 ± 0.7) × 109 M⊙. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.
- The following article is Open accessThe NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background
Gabriella Agazie et al 2023 ApJL 951 L8
View article, The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave BackgroundPDF, The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave BackgroundDownload ePub, The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave BackgroundWe report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings–Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of 1014, and this same model is favored over an uncorrelated common power-law spectrum model with Bayes factors of 200–1000, depending on spectral modeling choices. We have built a statistical background distribution for the latter Bayes factors using a method that removes interpulsar correlations from our data set, finding p = 10−3 (≈3σ) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of interpulsar correlations yields p = 5 × 10−5 to 1.9 × 10−4 (≈3.5σ–4σ). Assuming a fiducial f−2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is
(median + 90% credible interval) at a reference frequency of 1 yr−1. The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings–Downs correlations points to the gravitational-wave origin of this signal. - PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star Matter
M. C. Miller et al 2019 ApJL 887 L24
View article, PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star MatterPDF, PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star MatterDownload ePub, PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star MatterNeutron stars are not only of astrophysical interest, but are also of great interest to nuclear physicists because their attributes can be used to determine the properties of the dense matter in their cores. One of the most informative approaches for determining the equation of state (EoS) of this dense matter is to measure both a star’s equatorial circumferential radius Re and its gravitational mass M. Here we report estimates of the mass and radius of the isolated 205.53 Hz millisecond pulsar PSR J0030+0451 obtained using a Bayesian inference approach to analyze its energy-dependent thermal X-ray waveform, which was observed using the Neutron Star Interior Composition Explorer (NICER). This approach is thought to be less subject to systematic errors than other approaches for estimating neutron star radii. We explored a variety of emission patterns on the stellar surface. Our best-fit model has three oval, uniform-temperature emitting spots and provides an excellent description of the pulse waveform observed using NICER. The radius and mass estimates given by this model are
km and (68%). The independent analysis reported in the companion paper by Riley et al. explores different emitting spot models, but finds spot shapes and locations and estimates of Re and M that are consistent with those found in this work. We show that our measurements of Re and M for PSR J0030+0451 improve the astrophysical constraints on the EoS of cold, catalyzed matter above nuclear saturation density. - The following article is Open accessSearch for an Isotropic Gravitational-wave Background with the Parkes Pulsar Timing Array
Daniel J. Reardon et al 2023 ApJL 951 L6
View article, Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar Timing ArrayPDF, Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar Timing ArrayDownload ePub, Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar Timing ArrayPulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise process. Represented as a strain spectrum
, we measure and α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3, corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we recover an amplitude of . However, we demonstrate that the apparent signal strength is time-dependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred common-spectrum amplitude using the complete data set. We search for spatial correlations in the observations by hierarchically analyzing individual pulsar pairs, which also allows for significance validation through randomizing pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB, with an estimated false-alarm probability of p ≲ 0.02 (approx. 2σ). The long timing baselines of the PPTA and the access to southern pulsars will continue to play an important role in the International Pulsar Timing Array. - The following article is Open accessThe Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data Set
DES Collaboration: T. M. C. Abbott et al 2024 ApJL 973 L14
View article, The Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data SetPDF, The Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data SetDownload ePub, The Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data SetWe present cosmological constraints from the sample of Type Ia supernovae (SNe Ia) discovered and measured during the full 5 yr of the Dark Energy Survey (DES) SN program. In contrast to most previous cosmological samples, in which SNe are classified based on their spectra, we classify the DES SNe using a machine learning algorithm applied to their light curves in four photometric bands. Spectroscopic redshifts are acquired from a dedicated follow-up survey of the host galaxies. After accounting for the likelihood of each SN being an SN Ia, we find 1635 DES SNe in the redshift range 0.10 < z < 1.13 that pass quality selection criteria sufficient to constrain cosmological parameters. This quintuples the number of high-quality z > 0.5 SNe compared to the previous leading compilation of Pantheon+ and results in the tightest cosmological constraints achieved by any SN data set to date. To derive cosmological constraints, we combine the DES SN data with a high-quality external low-redshift sample consisting of 194 SNe Ia spanning 0.025 < z < 0.10. Using SN data alone and including systematic uncertainties, we find ΩM = 0.352 ± 0.017 in flat ΛCDM. SN data alone now require acceleration (q0 < 0 in ΛCDM) with over 5σ confidence. We find
in flat wCDM. For flat w0waCDM, we find , consistent with a constant equation of state to within ∼2σ. Including Planck cosmic microwave background, Sloan Digital Sky Survey baryon acoustic oscillation, and DES 3 × 2pt data gives (ΩM, w) = (0.321 ± 0.007, −0.941 ± 0.026). In all cases, dark energy is consistent with a cosmological constant to within ∼2σ. Systematic errors on cosmological parameters are subdominant compared to statistical errors; these results thus pave the way for future photometrically classified SN analyses. - The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
M. C. Miller et al 2021 ApJL 918 L28
View article, The Radius of PSR J0740+6620 from NICER and XMM-Newton DataPDF, The Radius of PSR J0740+6620 from NICER and XMM-Newton DataDownload ePub, The Radius of PSR J0740+6620 from NICER and XMM-Newton DataPSR J0740+6620 has a gravitational mass of 2.08 ± 0.07 M⊙, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740+6620 is
km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030+0451, the masses of two other ∼2 M⊙ pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation-of-state modeling, and find consistent results at ∼1.5–5 times nuclear saturation density. For a given framework, when all measurements are included, the radius of a 1.4 M⊙ neutron star is known to ±4% (68% credibility) and the radius of a 2.08 M⊙ neutron star is known to ±5%. The full radius range that spans the ±1σ credible intervals of all the radius estimates in the three frameworks is 12.45 ± 0.65 km for a 1.4 M⊙ neutron star and 12.35 ± 0.75 km for a 2.08 M⊙ neutron star. - The following article is Open accessGravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
B. P. Abbott et al 2017 ApJL 848 L13
View article, Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817APDF, Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817ADownload ePub, Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817AOn 2017 August 17, the gravitational-wave event GW170817 was observed by the Advanced LIGO and Virgo detectors, and the gamma-ray burst (GRB) GRB 170817A was observed independently by the Fermi Gamma-ray Burst Monitor, and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory. The probability of the near-simultaneous temporal and spatial observation of GRB 170817A and GW170817 occurring by chance is
. We therefore confirm binary neutron star mergers as a progenitor of short GRBs. The association of GW170817 and GRB 170817A provides new insight into fundamental physics and the origin of short GRBs. We use the observed time delay of between GRB 170817A and GW170817 to: (i) constrain the difference between the speed of gravity and the speed of light to be between and times the speed of light, (ii) place new bounds on the violation of Lorentz invariance, (iii) present a new test of the equivalence principle by constraining the Shapiro delay between gravitational and electromagnetic radiation. We also use the time delay to constrain the size and bulk Lorentz factor of the region emitting the gamma-rays. GRB 170817A is the closest short GRB with a known distance, but is between 2 and 6 orders of magnitude less energetic than other bursts with measured redshift. A new generation of gamma-ray detectors, and subthreshold searches in existing detectors, will be essential to detect similar short bursts at greater distances. Finally, we predict a joint detection rate for the Fermi Gamma-ray Burst Monitor and the Advanced LIGO and Virgo detectors of 0.1–1.4 per year during the 2018–2019 observing run and 0.3–1.7 per year at design sensitivity. - The following article is Open accessGW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact Object
R. Abbott et al 2020 ApJL 896 L44
View article, GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact ObjectPDF, GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact ObjectDownload ePub, GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact ObjectWe report the observation of a compact binary coalescence involving a 22.2–24.3 M⊙ black hole and a compact object with a mass of 2.50–2.67 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO’s and Virgo’s third observing run on 2019 August 14 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of
Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, , and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to ≤0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1–23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models of the formation and mass distribution of compact-object binaries.
