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A Sun-like star orbiting a black hole
No full textWe report discovery of a bright, nearby (G = 13.8; d = 480 pc) Sun-like star orbiting a dark object. We identified the system as a black hole candidate via its astrometric orbital solution from the Gaia mission. Radial velocities validated and refined the Gaia solution, and spectroscopy ruled out significant light contributions from another star. Joint modelling of radial velocities and astrometry constrains the companion mass of M₂ = 9.62 ± 0.18 M_⊙. The spectroscopic orbit alone sets a minimum companion mass of M₂ > 5 M_⊙; if the companion were a 5 M_⊙ star, it would be 500 times more luminous than the entire system. These constraints are insensitive to the mass of the luminous star, which appears as a slowly rotating G dwarf (T_(eff) = 5850 K, log g = 4.5, M = 0.93 M_⊙), with near-solar metallicity ([Fe/H] = −0.2) and an unremarkable abundance pattern. We find no plausible astrophysical scenario that can explain the orbit and does not involve a black hole. The orbital period, P_(orb) = 185.6 d, is longer than that of any known stellar-mass black hole binary. The system’s modest eccentricity (e = 0.45), high metallicity, and thin-disc Galactic orbit suggest that it was born in the Milky Way disc with at most a weak natal kick. How the system formed is uncertain. Common envelope evolution can only produce the system’s wide orbit under extreme and likely unphysical assumptions. Formation models involving triples or dynamical assembly in an open cluster may be more promising. This is the nearest known black hole by a factor of 3, and its discovery suggests the existence of a sizable population of dormant black holes in binaries. Future Gaia releases will likely facilitate the discovery of dozens more
Spectroscopic Confirmation of a Population of Isolated, Intermediate-mass Young Stellar Objects
No full textWide-field searches for young stellar objects (YSOs) can place useful constraints on the prevalence of clustered versus distributed star formation. The Spitzer/IRAC Candidate YSO (SPICY) catalog is one of the largest compilations of such objects (∼120,000 candidates in the Galactic midplane). Many SPICY candidates are spatially clustered, but, perhaps surprisingly, approximately half the candidates appear spatially distributed. To better characterize this unexpected population and confirm its nature, we obtained Palomar/DBSP spectroscopy for 26 of the optically bright (G < 15 mag) "isolated" YSO candidates. We confirm the YSO classifications of all 26 sources based on their positions on the Hertzsprung–Russell diagram, H and Ca ɪɪ line emission from over half the sample, and robust detection of infrared excesses. This implies a contamination rate of <10% for SPICY stars that meet our optical selection criteria. Spectral types range from B4 to K3, with A-type stars being the most common. Spectral energy distributions, diffuse interstellar bands, and Galactic extinction maps indicate moderate-to-high extinction. Stellar masses range from ∼1 to 7 M_⊙, and the estimated accretion rates, ranging from 3 × 10⁻⁸ to 3 × 10⁻⁷ M_⊙ yr⁻¹, are typical for YSOs in this mass range. The 3D spatial distribution of these stars, based on Gaia astrometry, reveals that the "isolated" YSOs are not evenly distributed in the Solar neighborhood but are concentrated in kiloparsec-scale dusty Galactic structures that also contain the majority of the SPICY YSO clusters. Thus, the processes that produce large Galactic star-forming structures may yield nearly as many distributed as clustered YSOs
Impacts of Organic Ice Condensation on the Optical Properties of Haze on Pluto
No full textThe flyby of the New Horizons spacecraft in 2015 July revealed an unexpected cold atmosphere of Pluto and confirmed the existence of its atmospheric haze. The observed and simulated vertical profiles of chemical species and microphysical processes suggest that the haze particles in Pluto’s middle and lower atmosphere may contain organic ice condensation. Such organic ice components can potentially affect Pluto’s haze chemistry and optical properties, as well as its energy budget. This study investigates the influence of the ice components on the scattering properties of Pluto’s haze by comparing New Horizons observations and simulated particle scattering properties. Comprehensive tests are performed for various haze particle parameters, including their size, chemical component, ice content, and morphology. Scattering properties of these ice-bearing haze particles are calculated by a discrete dipole approximation method and compared to multispectral observations obtained by four New Horizons instruments in spectral regions ranging from the ultraviolet to the near-infrared. The results indicate that the inclusion of the organic ice component leads to higher ratios of backscattering in the visible to extinction in the ultraviolet and provides better agreement with observations compared to monodispersed homogeneous aggregates. But it alone is not sufficient to explain the observed forward scattering values in the visible and near-infrared. Therefore, other scattering sources and/or mechanisms are still required to explain the full set of scattering observations. Further observations, as well as laboratory measurements and numerical tests, are anticipated to improve our understanding of the morphology and ice content of Pluto’s haze
Kepler-80 Revisited: Assessing the Participation of a Newly Discovered Planet in the Resonant Chain
No full textIn this paper, we consider the chain of resonances in the Kepler-80 system and evaluate the impact that the additional member of the resonant chain discovered by Shallue & Vanderburg has on the dynamics of the system and the physical parameters that can be recovered by a fit to the transit timing variations (TTVs). Ultimately, we calculate the mass of Kepler-80 g to be 0.8 ± 0.3 M_⊕ when assuming all planets have zero eccentricity, and 1.0 ± 0.3 M_⊕ when relaxing that assumption. We show that the outer five planets are in successive three-body mean-motion resonances (MMRs). We assess the current state of two-body MMRs in the system and find that the planets do not appear to be in two-body MMRs. We find that while the existence of the additional member of the resonant chain does not significantly alter the character of the Kepler-80 three-body MMRs, it can alter the physical parameters derived from the TTVs, suggesting caution should be applied when drawing conclusions from TTVs for potentially incomplete systems. We also compare our results to those of MacDonald et al., who perform a similar analysis on the same system with a different method. Although the results of this work and MacDonald et al. show that different fit methodologies and underlying assumptions can result in different measured orbital parameters, the most secure conclusion is that which holds true across all lines of analysis: Kepler-80 contains a chain of planets in three-body MMRs but not in two-body MMRs
TESS Discovery of Twin Planets near 2:1 Resonance around Early M Dwarf TOI 4342
No full textWith data from the Transiting Exoplanet Survey Satellite (TESS), we showcase improvements to the MIT Quick Look Pipeline (QLP) through the discovery and validation of a multiplanet system around M dwarf TOI 4342 (T_(mag) = 11.032, M_⋆ = 0.63 M_⊙, R_⋆ = 0.60 R_⊙, T_(eff) = 3900 K, d = 61.54 pc). With updates to QLP, including a new multiplanet search, as well as faster cadence data from TESS’s First Extended Mission, we discovered two sub-Neptunes (R_b = 2.266_(0.040)^(0.043) R_⊕ and R꜀ = 2.415_(−0.040)^(+0.043) R_⊕; P_b = 5.538 days and P꜀ = 10.689 days) and validated them with ground-based photometry, spectra, and speckle imaging. Both planets notably have high transmission spectroscopy metrics of 36 and 32, making TOI 4342 one of the best systems for comparative atmospheric studies. This system demonstrates how improvements to QLP, along with faster cadence full-frame images, can lead to the discovery of new multiplanet systems
Performance of NIRCam on JWST in Flight
No full textThe Near Infrared Camera for the James Webb Space Telescope (JWST) is delivering the imagery that astronomers have hoped for ever since JWST was proposed back in the 1990s. In the Commissioning Period that extended from right after launch to early 2022 July, NIRCam has been subjected to a number of performance tests and operational checks. The camera is exceeding prelaunch expectations in virtually all areas, with very few surprises discovered in flight. NIRCam also delivered the imagery needed by the Wavefront Sensing Team for use in aligning the telescope mirror segments
Detecting Exomoons from Radial Velocity Measurements of Self-luminous Planets: Application to Observations of HR 7672 B and Future Prospects
No full textThe detection of satellites around extrasolar planets, so called exomoons, remains a largely unexplored territory. In this work, we study the potential of detecting these elusive objects from radial velocity monitoring of self-luminous, directly imaged planets. This technique is now possible thanks to the development of dedicated instruments combining the power of high-resolution spectroscopy and high-contrast imaging. First, we demonstrate a sensitivity to satellites with a mass ratio of 1%–4% at separations similar to the Galilean moons from observations of a brown-dwarf companion (HR 7672 B; K_(mag) = 13; 0.″7 separation) with the Keck Planet Imager and Characterizer (R ∼ 35,000 in the K band) at the W. M. Keck Observatory. Current instrumentation is therefore already sensitive to large unresolved satellites that could be forming from gravitational instability akin to binary star formation. Using end-to-end simulations, we then estimate that future instruments such as the Multi-Object Diffraction-limited High-resolution Infrared Spectrograph, planned for the Thirty Meter Telescope, should be sensitive to satellites with mass ratios of ∼10−4. Such small moons would likely form in a circumplanetary disk similar to the Jovian satellites in the solar system. Looking for the Rossiter–McLaughlin effect could also be an interesting pathway to detecting the smallest moons on short orbital periods. Future exomoon discoveries will allow precise mass measurements of the substellar companions that they orbit and provide key insight into the formation of exoplanets. They would also help constrain the population of habitable Earth-sized moons orbiting gas giants in the habitable zone of their stars
FIRE-3: updated stellar evolution models, yields, and microphysics and fitting functions for applications in galaxy simulations
No full textIncreasingly, uncertainties in predictions from galaxy formation simulations (at sub-Milky Way masses) are dominated by uncertainties in stellar evolution inputs. In this paper, we present the full set of updates from the Feedback In Realistic Environment (FIRE)-2 version of the FIRE project code, to the next version, FIRE-3. While the transition from FIRE-1 to FIRE-2 focused on improving numerical methods, here we update the stellar evolution tracks used to determine stellar feedback inputs, e.g. stellar mass-loss (O/B and AGB), spectra (luminosities and ionization rates), and supernova rates (core-collapse and Ia), as well as detailed mass-dependent yields. We also update the low-temperature cooling and chemistry, to enable improved accuracy at T ≲ 10⁴ K and densities n ≫ 1 cm⁻³, and the meta-galactic ionizing background. All of these synthesize newer empirical constraints on these quantities and updated stellar evolution and yield models from a number of groups, addressing different aspects of stellar evolution. To make the updated models as accessible as possible, we provide fitting functions for all of the relevant updated tracks, yields, etc, in a form specifically designed so they can be directly 'plugged in' to existing galaxy formation simulations. We also summarize the default FIRE-3 implementations of 'optional' physics, including spectrally resolved cosmic rays and supermassive black hole growth and feedback
Non-invasive photoacoustic computed tomography of rat heart anatomy and function
No full textComplementary to mainstream cardiac imaging modalities for preclinical research, photoacoustic computed tomography (PACT) can provide functional optical contrast with high imaging speed and resolution. However, PACT has not been demonstrated to reveal the dynamics of whole cardiac anatomy or vascular system without surgical procedure (thoracotomy) for tissue penetration. Here, we achieved non-invasive imaging of rat hearts using the recently developed three-dimensional PACT (3D-PACT) platform, demonstrating the regulated illumination and detection schemes to reduce the effects of optical attenuation and acoustic distortion through the chest wall; thereby, enabling unimpeded visualization of the cardiac anatomy and intracardiac hemodynamics following rapidly scanning the heart within 10 s. We further applied 3D-PACT to reveal distinct cardiac structural and functional changes among the healthy, hypertensive, and obese rats, with optical contrast to uncover differences in cardiac chamber size, wall thickness, and hemodynamics. Accordingly, 3D-PACT provides high imaging speed and nonionizing penetration to capture the whole heart for diagnosing the animal models, holding promises for clinical translation to cardiac imaging of human neonates
Prospects of Gravitational-wave Follow-up through a Wide-field Ultraviolet Satellite: A Dorado Case Study
No full textThe detection of gravitational waves from the binary neuron star merger GW170817 and electromagnetic counterparts GRB170817A and AT2017gfo kick-started the field of gravitational-wave multimessenger astronomy. The optically red to near-infrared emission (“red” component) of AT2017gfo was readily explained as produced by the decay of newly created nuclei produced by rapid neutron capture (a kilonova). However, the ultraviolet to optically blue emission (“blue” component) that was dominant at early times (up to 1.5 days) received no consensus regarding its driving physics. Among many explanations, two leading contenders are kilonova radiation from a lanthanide-poor ejecta component and shock interaction (cocoon emission). In this work, we simulate AT2017gfo-like light curves and perform a Bayesian analysis to study whether an ultraviolet satellite capable of rapid gravitational-wave follow-up, could distinguish between physical processes driving the early “blue” component. We find that ultraviolet data starting at 1.2 hr distinguishes the two early radiation models up to 160 Mpc, implying that an ultraviolet mission like Dorado would significantly contribute to insights into the driving emission physics of the postmerger system. While the same ultraviolet data and optical data starting at 12 hr have limited ability to constrain model parameters separately, the combination of the two unlocks tight constraints for all but one parameter of the kilonova model up to 160 Mpc. We further find that a Dorado-like ultraviolet satellite can distinguish the early radiation models up to at least 130 (60) Mpc if data collection starts within 3.2 (5.2) hr for AT2017gfo-like light curves