The Astrophysical Journal Letters - IOPscience

The Astrophysical Journal Letters - IOPscience
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.
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The Astrophysical Journal Letters
is an open access express scientific journal that allows astrophysicists to rapidly publish short notices of significant original research.
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The following article is
Open access
Direct Spectroscopic Confirmation of the Young Embedded Protoplanet WISPIT 2c
Chloe Lawlor
et al
2026
ApJL
1000
L38
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, Direct Spectroscopic Confirmation of the Young Embedded Protoplanet WISPIT 2c
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, Direct Spectroscopic Confirmation of the Young Embedded Protoplanet WISPIT 2c
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, Direct Spectroscopic Confirmation of the Young Embedded Protoplanet WISPIT 2c
WISPIT 2 is a nearby young star with a multiringed disk that was recently confirmed to host a ∼4.9
Jup
gas giant planet embedded in a large (60 au) gap at a radial separation of 57 au from the host star. We confirm and characterize a second, close-in planet in the WISPIT 2 system using a combination of new Very Large Telescope/SPHERE
-band dual-polarization imaging and VLTI/GRAVITY
-band interferometric observations of the WISPIT 2 system. The GRAVITY detection is consistent with a point-like source while its extracted
-band spectrum shows CO band-head absorption at 2.3
m and a continuum shape consistent with a young giant planet. From the GRAVITY data, we extract a medium resolution
-band spectrum of the companion and fit atmospheric model grids using the
species
tool with nested sampling to constrain its effective temperature, radius, and luminosity. We infer
eff
of 1500–2600 K, a radius of 0.91–2.2
Jup
, and a luminosity of (−3.47)–(−3.63). Comparison with evolutionary tracks implies a mass range of 8–12
Jup
, approximately twice as massive as the previously confirmed WISPIT 2b. The astrometry rules out a background source and marginally detects orbital motion of WISPIT 2 c, which needs further follow-up observations for confirmation. WISPIT 2 now becomes an analog to PDS 70, offering a second laboratory for studying the formation and early evolution of a multiplanet system within its natal disk.
The following article is
Open access
New 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 MIRI
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, New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI
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, New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI
The 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 H
-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 CH
and CO
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
m range. The spectrum shows distinct features and is inconsistent with a featureless spectrum at 3.4
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 3
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.
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Open access
First 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 Hole
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, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
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, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
When 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
as, 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
= (6.5 ± 0.7) × 10
. 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.
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ALMA Band 9 CO(6–5) Reveals a Warm Ring Structure Associated with the Embedded Protostar in the Cold Dense Core MC 27/L1521F
Kazuki Tokuda
et al
2026
ApJL
1001
L1
View article
, ALMA Band 9 CO(6–5) Reveals a Warm Ring Structure Associated with the Embedded Protostar in the Cold Dense Core MC 27/L1521F
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, ALMA Band 9 CO(6–5) Reveals a Warm Ring Structure Associated with the Embedded Protostar in the Cold Dense Core MC 27/L1521F
ePub
, ALMA Band 9 CO(6–5) Reveals a Warm Ring Structure Associated with the Embedded Protostar in the Cold Dense Core MC 27/L1521F
Infall and outflows, coupled with magnetic fields, rapidly structure the gas around newborn protostars. Shocks from interacting components encode the temperature and density distribution, offering a direct probe of the earliest evolution history. However, interferometric observations characterizing warm envelopes using high-excitation lines remain scarce. We present Atacama Large Millimeter/submillimeter Array Band 9 observations of the Taurus dense core MC 27/L1521F, which hosts a Class 0 protostar, targeting the CO(
= 6–5) line at an angular resolution of ∼2″ (≈300 au). We detect an off-centered ringlike structure with a diameter of ∼1000 au that was not identifiable in previous low-
CO data, where emission close to the systemic velocity is strongly affected by optical depth. The ring shows a typical peak brightness temperature of ∼3 K at our resolution. Excitation considerations indicate that the detected CO(
= 6–5) emission likely arises from relatively warm (
≳ 20 K) and dense (
(H
) ≳ 10
cm
−3
) gas embedded within the surrounding cold, dense core. The morphology and kinematics suggest an energetic and localized shock-heating event, potentially linked to dynamical gas–magnetic-field interactions in the earliest protostellar phase. Our results demonstrate that high-
CO observations provide a powerful new window on warm and dense gas components, enabling a more direct view of the physical processes operating at the onset of star formation.
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Open access
Direct Images of CO
Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk
William O. Balmer
et al
2026
ApJL
1001
L26
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, Direct Images of CO2 Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk
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, Direct Images of CO2 Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk
ePub
, Direct Images of CO2 Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk
It is unclear how directly imaged substellar companions with masses near the deuterium burning limit form, because these objects are rare and their bulk properties are not diagnostic of their formation. In this Letter, we revisit this problem using JWST/NIRCam coronagraphic images of the 29 Cygni (=HIP 99770) system that reveal the recently discovered super-Jovian companion 29 Cyg b at wavelengths covering 4–5
m for the first time. This object has an uncertain mass that straddles the deuterium burning limit (
≃ 15 ± 5
) and a low mass ratio with its early-type host star (
∼ 0.01). Absorption from CO
and CO is apparent at 4.3 and 4.6
m in our images. The strength of the CO
feature relative to CO provides strong evidence, based on empirical comparison with literature observations at these wavelengths and atmospheric modeling, that the companion is enriched in heavier elements compared to the roughly solar abundances of the host (
= 3 ± 2). In addition, we measure the stellar inclination angle with CHARA/PAVO interferometry: the system is consistent with spin–orbit alignment at the 2
level, with Δ
= 12° ± 6°. This ensemble of evidence is suggestive of formation within the protoplanetary disk and the rapid accretion of metal-rich material versus disk fragmentation or capture, like higher-mass-ratio companions. 29 Cyg b shows that planet formation around early-type stars can occur on scales at or exceeding the deuterium burning limit, in agreement with the recently revised planetary mass/metallicity trend that predicts
pl
= 3.3 ± 0.5 at high masses from transiting planet densities.
The following article is
Open access
Gaia-GIC-1: An Evolving Catastrophic Planetesimal Collision Candidate
Anastasios Tzanidakis and James R. A. Davenport 2026
ApJL
1000
L5
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, Gaia-GIC-1: An Evolving Catastrophic Planetesimal Collision Candidate
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, Gaia-GIC-1: An Evolving Catastrophic Planetesimal Collision Candidate
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, Gaia-GIC-1: An Evolving Catastrophic Planetesimal Collision Candidate
We report the discovery of the optical dipper and low-luminosity infrared stellar transient Gaia20ehk (hereafter, Gaia-GIC-1), which is currently undergoing high-amplitude variability due to transiting dusty material. In this work, we identify Gaia-GIC-1 as a likely young F-type star based on the spectral energy distribution before the onset of the high-amplitude optical variability. We detect a significant periodic modulation of 380.5 days in Gaia
band before the onset of the infrared brightening, consistent with a ∼1.1 au orbit assuming circular orbits and a 1.3
star. The system has remained in an infrared-bright state for >4 yr since the last near-infrared detection, confirmed by recent SPHEREx observations, while continuing to undergo large-amplitude irregular optical dimming. We measure the dust temperature from the freshly generated debris to be ∼900 K based on available Wide-field Infrared Survey Explorer photometry, and the dust clump size to have a minimum cross-sectional area of 0.13 au
, and the dust mass 4 × 10
20
kg. Currently, optical follow-up spectroscopy has not revealed any prominent features in the system, likely due to its highly variable nature. We hypothesize that Gaia-GIC-1 represents debris recently formed in a planetary collision, which produced a clumpy dust cloud on a bound orbit, producing the observed dimming events. The ongoing collisional activity in this system presents a unique opportunity for understanding terrestrial planet formation.
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Open access
First 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 Way
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, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
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, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
We 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
= 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
as (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 × 10
, 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 (
> 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 10
–10
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.
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Open access
Multi-messenger Observations of a Binary Neutron Star Merger
B. P. Abbott
et al
2017
ApJL
848
L12
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, Multi-messenger Observations of a Binary Neutron Star Merger
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, Multi-messenger Observations of a Binary Neutron Star Merger
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, Multi-messenger Observations of a Binary Neutron Star Merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The
Fermi
Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of
with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg
at a luminosity distance of
Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26
. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at
) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position
and
days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of
-process nuclei synthesized in the ejecta.
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Open access
Ubiquitous Small-scale Dynamics in the Slow Solar Wind Formation Region Observed by Proba-3/ASPIICS
A. N. Zhukov
et al
2026
ApJL
999
L41
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, Ubiquitous Small-scale Dynamics in the Slow Solar Wind Formation Region Observed by Proba-3/ASPIICS
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, Ubiquitous Small-scale Dynamics in the Slow Solar Wind Formation Region Observed by Proba-3/ASPIICS
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, Ubiquitous Small-scale Dynamics in the Slow Solar Wind Formation Region Observed by Proba-3/ASPIICS
The origin of the slow solar wind remains a subject of ongoing debate. Several mechanisms have been proposed: the large expansion factor of open magnetic field in the corona, interchange reconnection between open and closed field lines in streamers and pseudostreamers, reconnection within the web of separatrices (S-web), and the field line pinch-off at streamer cusps. Many of these mechanisms involve the release of small-scale density inhomogeneities into the solar wind. A significant obstacle to understanding these processes is the difficulty of observing the region between the lower corona (traditionally observed with extreme ultraviolet imagers) and the high corona (traditionally observed with externally occulted coronagraphs), where these small-scale structures are thought to originate. Here, we present for the first time high-cadence (30 s) and high-spatial-resolution (5
6) white-light observations of the solar corona in the range of the radial distances
of 1.1
< 3
taken by the ASPIICS coronagraph on board the formation-flying Proba-3 mission. The ASPIICS data reveal ubiquitous, weak (0.5%–2% of the background brightness), small-scale dynamic features (blobs, outflows, inflows, jets, and waves). Their speeds range from 14 km s
−1
to 520 km s
−1
, with outflowing structures generally propagating faster than the inflowing ones. All these features appear to originate from streamers and pseudostreamers. ASPIICS observations provide important constraints on the role of small-scale dynamics in the formation of the slow solar wind.
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Open access
GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog
A. G. Abac
et al
2025
ApJL
995
L18
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, GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog
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, GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog
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, GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog
The Gravitational-Wave Transient Catalog (GWTC) is a collection of short-duration (transient) gravitational-wave signals identified by the LIGO–Virgo–KAGRA Collaboration in gravitational-wave data produced by the eponymous detectors. The catalog provides information about the identified candidates, such as the arrival time and amplitude of the signal and properties of the signal’s source as inferred from the observational data. GWTC is the data release of this dataset, and version 4.0 extends the catalog to include observations made during the first part of the fourth LIGO–Virgo–KAGRA observing run up until 2024 January 31. This Letter marks an introduction to a collection of articles related to this version of the catalog, GWTC-4.0. The collection of articles accompanying the catalog provides documentation of the methods used to analyze the data, summaries of the catalog of events, observational measurements drawn from the population, and detailed discussions of selected candidates.
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Open access
A Major Geomagnetic Storm in 2024 October Linked to Sympathetic Coronal Mass Ejection–Prominence Eruptions
Rui Wang
et al
2026
ApJL
1002
L23
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, A Major Geomagnetic Storm in 2024 October Linked to Sympathetic Coronal Mass Ejection–Prominence Eruptions
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, A Major Geomagnetic Storm in 2024 October Linked to Sympathetic Coronal Mass Ejection–Prominence Eruptions
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, A Major Geomagnetic Storm in 2024 October Linked to Sympathetic Coronal Mass Ejection–Prominence Eruptions
Improving predictions of the geomagnetic impact of coronal mass ejections (CMEs) requires understanding how solar source properties relate to in situ measurements at Earth. However, major geomagnetic storms frequently arise from interacting CMEs, complicating the link back to their solar origins. We analyze a CME interaction event that caused a major geomagnetic storm in 2024 October 10–11 (
st
∼ −333 nT). Multiviewpoint observations reveal that the storm was related to a sympathetic eruption involving a quiescent filament and an active-region CME. The coronagraph on board the Advanced Space-based Solar Observatory clearly shows that this sympathetic eruption resulted in two distinct CMEs. Due to the overlap of the CMEs in the coronagraph field of view (FOV), a spheroid shock model was used to fit the observed shock. Kinematic analysis indicates that the interacting CMEs had completed their impulsive acceleration phase before entering the coronagraph FOV, with a slow deceleration continuing beyond 100
. In situ measurements indicate that the enhanced southward magnetic fields, arising from compression during CME interactions, were the primary driver of the storm. Compared to photospheric fields, the in situ magnetic fields suggest that the trailing CME maintained flux-rope-like signatures consistent with the source region. In contrast, the compressed leading CME displayed varying magnetic configurations between Wind and STEREO-A, featuring distorted flux-rope signatures and inconsistent inferred axis orientations. Our study bridges solar source dynamics to in situ multipoint measurements, providing key insights for space weather prediction. Nevertheless, the direct linkage between source-region magnetic field configurations and these measurements remains tentative and requires further investigation.
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Open access
Measurement of the Full Shape of the Thermal Sunyaev–Zel’dovich Power Spectrum from the South Pole Telescope and Herschel–SPIRE Observations
S. Raghunathan
et al
2026
ApJL
1002
L22
View article
, Measurement of the Full Shape of the Thermal Sunyaev–Zel’dovich Power Spectrum from the South Pole Telescope and Herschel–SPIRE Observations
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, Measurement of the Full Shape of the Thermal Sunyaev–Zel’dovich Power Spectrum from the South Pole Telescope and Herschel–SPIRE Observations
ePub
, Measurement of the Full Shape of the Thermal Sunyaev–Zel’dovich Power Spectrum from the South Pole Telescope and Herschel–SPIRE Observations
We present a measurement of the full shape of the power spectrum of the thermal Sunyaev–Zel’dovich (tSZ) effect down to arcminute scales using cosmic microwave background (CMB) data from the South Pole Telescope (SPT) over a roughly 100 deg
field. The analysis incorporates data from the 2019–2020 seasons of the SPT-3G survey in bands centered at 95, 150, and 220 GHz; from the full SPTpol dataset at 150 GHz; and from the Herschel–SPIRE survey in bands centered at 600 and 857 GHz. We combine data from all the above bands using linear combination (LC) techniques to produce a tSZ or Compton-
map. We modify the LC weights to produce multiple versions of the Compton-
map, including minimum-variance (MV) and foreground-minimized (-min) maps. We measure the auto- and cross-power spectra of a subset of these maps in the range
∈ [500, 5000]. While this power spectrum includes contributions from signals other than tSZ, we present numerous checks to show that the most challenging foreground signal, the cosmic infrared background (CIB), is much lower than the desired tSZ signal in the scales of interest in this work. The final tSZ power spectrum is measured at 9.3
with both the MV and CIB-min maps. Our results are consistent with those reported in other CMB surveys across the literature. Using the difference in the tSZ power spectrum from the MV and CIB-min maps, we reconstruct the scale-dependent tSZ–CIB cross correlation
, finding 3.1
evidence for a nonzero correlation coefficient that is positive on large scales and approaches zero for
> 2500. This result represents the deepest tSZ maps ever produced and provides new constraints that can help refine astrophysical feedback mechanisms and models of the intracluster medium.
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A Tale of Two Jets: Double Relativistic Outflows from Close Binary Gamma-Ray Burst Progenitors
He Gao 2026
ApJL
1002
L21
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, A Tale of Two Jets: Double Relativistic Outflows from Close Binary Gamma-Ray Burst Progenitors
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, A Tale of Two Jets: Double Relativistic Outflows from Close Binary Gamma-Ray Burst Progenitors
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, A Tale of Two Jets: Double Relativistic Outflows from Close Binary Gamma-Ray Burst Progenitors
Gravitational-wave astronomy has revealed that close binaries with compact companions are widespread. Long gamma-ray bursts (LGRBs) from massive star collapse face persistent challenges in achieving the rapid core rotation required by the collapsar model. Binary interaction via tidal spin-up offers a natural solution; recent population synthesis studies suggest a substantial fraction of LGRBs may originate from close binaries with a compact companion. In this scenario, supernova ejecta from the primary can be accreted by the companion, potentially launching a second relativistic jet after a delay set by the binary separation. We develop a comprehensive model for these double-jet systems, analyzing the dynamics of the second jet and its interaction with the first. The resulting observational signatures depend critically on the Lorentz factor ratio, the alignment angle, and the time delay. For aligned jets, two regimes arise: a fast second jet producing multiple gamma-ray triggers with distinct spectral/polarization evolution, and a slow second jet where its emission appears as an X-ray flare followed by an afterglow plateau from energy injection. For misaligned jets, the observed signal ranges from normal gamma-ray bursts (GRBs) with late-time radio structures to fast X-ray transients followed by off-axis rebrightening. These features have observational parallels in existing GRB data. High-resolution radio interferometry with SKA, time-resolved polarimetry with eXTP, and multiwavelength surveys with Einstein Probe and SVOM will test these predictions, providing constraints on the evolution of close massive binaries as progenitors of GRBs and gravitational-wave sources.
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Toward Early-type Eclipsing Binaries as Extragalactic Milestones: First Calibration of the SBCR from O- and B-type Stars in Detached Eclipsing Binaries
Mónica Taormina
et al
2026
ApJL
1002
L20
View article
, Toward Early-type Eclipsing Binaries as Extragalactic Milestones: First Calibration of the SBCR from O- and B-type Stars in Detached Eclipsing Binaries
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, Toward Early-type Eclipsing Binaries as Extragalactic Milestones: First Calibration of the SBCR from O- and B-type Stars in Detached Eclipsing Binaries
ePub
, Toward Early-type Eclipsing Binaries as Extragalactic Milestones: First Calibration of the SBCR from O- and B-type Stars in Detached Eclipsing Binaries
To measure precise distances beyond the Magellanic Clouds and determine an accurate value of the Hubble constant, eclipsing binary systems composed of early-type stars can play a crucial role. However, it is fundamental to first obtain a reliable empirical surface brightness–color relation (SBCR) for the hottest possible stars. Based on our previous study of six detached eclipsing binaries composed of O- and B-type stars in the Large Magellanic Cloud, we calibrated the SBCR using 12 stars with
< –0.6 mag. We found a significant difference between O-type and B-type stars in SBCRs, which are clearly separated in mass. The relation based on B-type stars is consistent with the relation for redder stars from the literature. This allowed us to provide a combined relation valid for stars less massive than ∼16
in the wide color range −0.9 <
< 2.1 mag, with
= 0.025 mag. Such a relation can provide extragalactic distances precise to as high as ∼1.2% given the sufficient quality and number of target objects. The relation for O-type stars (
= 0.055 mag) remains uncertain due to its strong dependence on the method used to determine reddening and requires further study. However, we tested it on the only known eclipsing system in M33 and obtained distance modulus DM = 24.90 ± 0.17 mag, which perfectly agrees with the published distance to the system.
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A Kiloparsec-scale Stellar Cavity in the Center of A402-BCG May Be Caused by Dynamic Interactions with an Ultramassive Black Hole
Michael McDonald
et al
2026
ApJL
1002
L19
View article
, A Kiloparsec-scale Stellar Cavity in the Center of A402-BCG May Be Caused by Dynamic Interactions with an Ultramassive Black Hole
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, A Kiloparsec-scale Stellar Cavity in the Center of A402-BCG May Be Caused by Dynamic Interactions with an Ultramassive Black Hole
ePub
, A Kiloparsec-scale Stellar Cavity in the Center of A402-BCG May Be Caused by Dynamic Interactions with an Ultramassive Black Hole
We present new observations from JWST that reveal a striking kiloparsec-wide cavity in the stellar distribution of the central galaxy in the cluster A402. Supporting data from the Hubble Space Telescope (HST) allow us to rule out extinction due to dust as an explanation, and instead, suggest that this is a localized depression in the stellar density field corresponding to ∼2 × 10
in missing stars within a volume of 0.5 kpc
. On larger scales, both the JWST and HST data show evidence for a 2.2 kpc flattened core in the stellar distribution (on which the smaller-scale cavity is superimposed), which implies the presence of a central ultramassive black hole with
BH
∼ 5 × 10
10
. We report evidence for a mid-IR-bright point source at one edge of the cavity, suggesting that this black hole is actively accreting. MUSE spectroscopy reveals that this source is a low-ionization nuclear emission-line region active galactic nucleus (AGN) and that there is a second candidate AGN on the opposite side of the cavity with a relative velocity of 370 km s
−1
—if real, this implies the presence of a kiloparsec-separation dual AGN with a total binary mass of 6 ± 2 × 10
10
, which would make this the most massive binary black hole system discovered to date. We propose that this unique stellar cavity is the result of a short-lived dynamical interaction between at least one supermassive black hole and the background stellar density field, caused either by three-body scattering during binary hardening or the induction of a dipole instability in the stellar density field.
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Open access
First 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 Hole
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, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
ePub
, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
When 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
as, 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
= (6.5 ± 0.7) × 10
. 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.
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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 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 Team
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, 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 Team
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 Team
We 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 (
). These include the complete sample of all suitable SNe Ia discovered in the last four decades at redshift
≤ 0.01, collected and calibrated from ≥1000 HST orbits, more than doubling the sample whose size limits the precision of the direct determination of
. 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
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
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
= 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
= 73.30 ± 1.04 km s
−1
Mpc
−1
and
= −0.51 ± 0.024. We find a 5
difference with the prediction of
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
remains unknown.
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First 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 Way
PDF
, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
ePub
, First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
We 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
= 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
as (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 × 10
, 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 (
> 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 10
–10
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.
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Open access
The 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 Background
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, The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background
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, The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background
We 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 10
14
, 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
= 10
−3
(≈3
) 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
= 5 × 10
−5
to 1.9 × 10
−4
(≈3.5
–4
). Assuming a fiducial
−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.
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Open access
Search 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 Array
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, Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar Timing Array
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, Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar Timing Array
Pulsar 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
= −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of
= −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
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
= −2/3, we measure spatial correlations consistent with a GWB, with an estimated false-alarm probability of
≲ 0.02 (approx. 2
). 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.
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 Matter
PDF
, PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star Matter
ePub
, PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star Matter
Neutron 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
and its gravitational mass
. 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
and
that are consistent with those found in this work. We show that our measurements of
and
for PSR J0030+0451 improve the astrophysical constraints on the EoS of cold, catalyzed matter above nuclear saturation density.
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 Data
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, The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
ePub
, The Radius of PSR J0740+6620 from NICER and XMM-Newton Data
PSR J0740+6620 has a gravitational mass of 2.08 ± 0.07
, 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
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
neutron star is known to ±4% (68% credibility) and the radius of a 2.08
neutron star is known to ±5%. The full radius range that spans the ±1
credible intervals of all the radius estimates in the three frameworks is 12.45 ± 0.65 km for a 1.4
neutron star and 12.35 ± 0.75 km for a 2.08
neutron star.
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Open access
Gravitational 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 170817A
PDF
, Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
ePub
, Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A
On 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.
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Open access
GW190814: 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 Object
PDF
, GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact Object
ePub
, GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact Object
We report the observation of a compact binary coalescence involving a 22.2–24.3
black hole and a compact object with a mass of 2.50–2.67
(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 deg
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.
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Open access
The 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 Set
PDF
, The Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data Set
ePub
, The Dark Energy Survey: Cosmology Results with ∼1500 New High-redshift Type Ia Supernovae Using the Full 5 yr Data Set
We 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 <
< 1.13 that pass quality selection criteria sufficient to constrain cosmological parameters. This quintuples the number of high-quality
> 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 <
< 0.10. Using SN data alone and including systematic uncertainties, we find Ω
= 0.352 ± 0.017 in flat ΛCDM. SN data alone now require acceleration (
< 0 in ΛCDM) with over 5
confidence. We find
in flat
CDM. For flat
CDM, we find
, consistent with a constant equation of state to within ∼2
. Including Planck cosmic microwave background, Sloan Digital Sky Survey baryon acoustic oscillation, and DES 3 × 2pt data gives (Ω
) = (0.321 ± 0.007, −0.941 ± 0.026). In all cases, dark energy is consistent with a cosmological constant to within ∼2
. Systematic errors on cosmological parameters are subdominant compared to statistical errors; these results thus pave the way for future photometrically classified SN analyses.
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