Motivated by the possibility that the laws of physics could be different in other regions of space-time, we consider nuclear processes in universes where the weak interaction is either stronger or ...weaker than observed. We focus on the physics of both Big Bang Nucleosynthesis (BBN) and stellar evolution. For sufficiently ineffective weak interactions, neutrons do not decay during BBN, and the baryon-to-photon ratio \(\eta\) must be smaller in order for protons to survive without becoming incorporated into larger nuclei. For stronger weak interactions, neutrons decay before the onset of BBN, and the early universe is left with nearly a pure hydrogen composition. We then consider stellar structure and evolution for the different nuclear compositions resulting from BBN, a wide range of weak force strengths, and the full range of stellar masses for a given universe. We delineate the range of this parameter space that supports working stars, along with a determination of the dominant nuclear reactions over the different regimes. Deuterium burning dominates the energy generation in stars when the weak force is sufficiently weak, whereas proton-proton burning into helium-3 dominates for the regime where the weak force is much stronger than in our universe. Although stars in these universes are somewhat different, they have comparable surface temperatures, luminosities, radii, and lifetimes, so that a wide range of such universes remain potentially habitable.
We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a \(<\)20 M\(_\mathrm{Jup}\) widely separated (\(\sim\)8\arcsec, a = 150 au), young, planetary-mass ...companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799 c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color-magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256~b with \textit{JWST}'s NIRSpec IFU and MIRI MRS modes for coverage from 1 \(\mu\)m to 20 \(\mu\)m at resolutions of \(\sim\)1,000 - 3,700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the \textit{JWST} spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.
We investigate a class of universes in which the weak interaction is not in operation. We consider how astrophysical processes are altered in the absence of weak forces, including Big Bang ...Nucleosynthesis (BBN), galaxy formation, molecular cloud assembly, star formation, and stellar evolution. Without weak interactions, neutrons no longer decay, and the universe emerges from its early epochs with a mixture of protons, neutrons, deuterium, and helium. The baryon-to-photon ratio must be smaller than the canonical value in our universe to allow free nucleons to survive the BBN epoch without being incorporated into heavier nuclei. At later times, the free neutrons readily combine with protons to make deuterium in sufficiently dense parts of the interstellar medium, and provide a power source before they are incorporated into stars. Almost all of the neutrons are incorporated into deuterium nuclei before stars are formed. As a result, stellar evolution proceeds primarily through strong interactions, with deuterium first burning into helium, and then helium fusing into carbon. Low-mass deuterium-burning stars can be long-lived, and higher mass stars can synthesize the heavier elements necessary for life. Although somewhat different from our own, such universes remain potentially habitable.
The unprecedented medium-resolution (R~1500-3500) near- and mid-infrared (1-18um) spectrum provided by JWST for the young (140+/-20Myr) low-mass (12-20MJup) L-T transition (L7) companion VHS1256b ...gives access to a catalogue of molecular absorptions. In this study, we present a comprehensive analysis of this dataset utilizing a forward modelling approach, applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: Teff, log(g), M/H, C/O, gamma, fsed, and R. Our findings reveal that each parameter's estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS1256b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a Teff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances M/H and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST's data for VHS1256b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.
We construct models of the structural evolution of super-Earth- and mini-Neptune-type exoplanets with hydrogen-helium envelopes, incorporating radiative cooling and XUV-driven mass loss. We conduct a ...parameter study of these models, focusing on initial mass, radius, and envelope mass fractions, as well as orbital distance, metallicity, and the specific prescription for mass loss. From these calculations, we investigate how the observed masses and radii of exoplanets today relate to the distribution of their initial conditions. Orbital distance and initial envelope mass fraction are the most important factors determining planetary evolution, particular radius evolution. Initial mass also becomes important below a "turnoff mass," which varies with orbital distance, with mass-radius curves being approximately flat for higher masses. Initial radius is the least important parameter we study, with very little difference between the hot start and cold start limits after an age of 100 Myr. Model sets with no mass loss fail to produce results consistent with observations, but a plausible range of mass loss scenarios is allowed. In addition, we present scenarios for the formation of the Kepler-11 planets. Our best fit to observations Kepler-11b and Kepler-11c involves formation beyond the snow line, after which they moved inward, circularized, and underwent a reduced degree mass loss.
IMPORTANCE: Functional impairment and pain are common indications for the initiation of lumbar spine surgery, but information about expected improvement in these patient-reported outcome (PRO) ...domains is not readily available to most patients and clinicians considering this type of surgery. OBJECTIVE: To assess population-level PRO response after lumbar spine surgery, and develop/validate a prediction tool for PRO improvement. DESIGN, SETTING, AND PARTICIPANTS: This statewide multicenter cohort was based at 15 Washington state hospitals representing approximately 75% of the state’s spine fusion procedures. The Spine Surgical Care and Outcomes Assessment Program and the survey center at the Comparative Effectiveness Translational Network prospectively collected clinical and PRO data from adult candidates for lumbar surgery, preoperatively and postoperatively, between 2012 and 2016. Prediction models were derived for PRO improvement 1 year after lumbar fusion surgeries on a random sample of 85% of the data and were validated in the remaining 15%. Surgical candidates from 2012 through 2015 were included; follow-up surveying continued until December 31, 2016, and data analysis was completed from July 2016 to April 2017. MAIN OUTCOMES AND MEASURES: Functional improvement, defined as a reduction in Oswestry Disability Index score of 15 points or more; and back pain and leg pain improvement, defined a reduction in Numeric Rating Scale score of 2 points or more. RESULTS: A total of 1965 adult lumbar surgical candidates (mean SD age, 61.3 12.5 years; 944 59.6% female) completed baseline surveys before surgery and at least 1 postoperative follow-up survey within 3 years. Of these, 1583 (80.6%) underwent elective lumbar fusion procedures; 1223 (77.3%) had stenosis, and 1033 (65.3%) had spondylolisthesis. Twelve-month follow-up participation rates for each outcome were between 66% and 70%. Improvements were reported in function, back pain, and leg pain at 12 months by 306 of 528 surgical patients (58.0%), 616 of 899 patients (68.5%), and 355 of 464 patients (76.5%), respectively, whose baseline scores indicated moderate to severe symptoms. Among nonoperative patients, 35 (43.8%), 47 (53.4%), and 53 (63.9%) reported improvements in function, back pain, and leg pain, respectively. Demographic and clinical characteristics included in the final prediction models were age, sex, race, insurance status, American Society of Anesthesiologists score, smoking status, diagnoses, prior surgery, prescription opioid use, asthma, and baseline PRO scores. The models had good predictive performance in the validation cohort (concordance statistic, 0.66-0.79) and were incorporated into a patient-facing, web-based interactive tool (https://becertain.shinyapps.io/lumbar_fusion_calculator). CONCLUSIONS AND RELEVANCE: The PRO response prediction tool, informed by population-level data, explained most of the variability in pain reduction and functional improvement after surgery. Giving patients accurate information about their likelihood of outcomes may be a helpful component in surgery decision making.
We provide an example of an analysis to explore the optimization of observations of transiting hot jupiters with JWST to characterize their atmospheres, based on a simple three-parameter forward ...model. We construct expansive forward model sets for eleven hot jupiters, ten of which are relatively well-characterized, exploring a range of parameters such as equilibrium temperature and metallicity, as well as considering host stars over a wide range in brightness. We compute posterior distributions of our model parameters for each planet with all of the available JWST spectroscopic modes and several programs of combined observations and compute their effectiveness using the metric of estimated mutual information per degree of freedom. From these simulations, clear trends emerge that provide guidelines for designing a JWST observing program. We demonstrate that these guidelines apply over a wide range of planet parameters and target brightnesses for our simple forward model.
The Oort Cloud remains one of the most poorly explored regions of the Solar System. We propose that its properties can be constrained by studying a population of dust grains produced in collisions of ...comets in the outer Solar System. We explore the dynamics of micron-size grains outside the heliosphere (beyond ~250 AU), which are affected predominantly by the magnetic field of the interstellar medium (ISM) flow past the Sun. We derive analytic models for the production and motion of small particles as a function of their birth location in the Cloud and calculate the particle flux and velocity distribution in the inner Solar System. These models are verified by direct numerical simulations. We show that grains originating in the Oort Cloud have a unique distribution of arrival directions, which should easily distinguish them from both interplanetary and interstellar dust populations. We also demonstrate that the distribution of particle arrival velocities is uniquely determined the mass distribution and dust production rate in the Cloud. Cometary collisions within the Cloud produce a flux of micron-size grains in the inner Solar System of up to several per square meter per year. The next-generation dust detectors may be sensitive enough to detect and constrain this dust population, which will illuminate us about the Oort Cloud's properties. We also show that the recently-detected mysterious population of large (micron-size) unbound particles, which seems to arrive with the ISM flow is unlikely to be generated by collisions of comets in the Oort Cloud.
We present JWST Early Release Science (ERS) coronagraphic observations of the
super-Jupiter exoplanet, HIP 65426 b, with the Near-Infrared Camera (NIRCam)
from 2-5 $\mu$m, and with the Mid-Infrared ...Instrument (MIRI) from 11-16 $\mu$m.
At a separation of $\sim$0.82" (86$^{+116}_{-31}$ au), HIP 65426 b is clearly
detected in all seven of our observational filters, representing the first
images of an exoplanet to be obtained by JWST, and the first ever direct
detection of an exoplanet beyond 5 $\mu$m. These observations demonstrate that
JWST is exceeding its nominal predicted performance by up to a factor of 10,
depending on separation and subtraction method, with measured 5$\sigma$
contrast limits of $\sim$1$\times10^{-5}$ and $\sim$2$\times10^{-4}$ at 1" for
NIRCam at 4.4 $\mu$m and MIRI at 11.3 $\mu$m, respectively. These contrast
limits provide sensitivity to sub-Jupiter companions with masses as low as
0.3$M_\mathrm{Jup}$ beyond separations of $\sim$100 au. Together with existing
ground-based near-infrared data, the JWST photometry are well fit by a BT-SETTL
atmospheric model from 1-16 $\mu$m, and span $\sim$97% of HIP 65426 b's
luminous range. Independent of the choice of model atmosphere we measure an
empirical bolometric luminosity that is tightly constrained between
$\mathrm{log}\!\left(L_\mathrm{bol}/L_{\odot}\right)$=-4.31 to $-$4.14, which
in turn provides a robust mass constraint of 7.1$\pm$1.2 $M_\mathrm{Jup}$. In
totality, these observations confirm that JWST presents a powerful and exciting
opportunity to characterise the population of exoplanets amenable to
high-contrast imaging in greater detail.
We present new calculations of transit spectra of super-Earths that allow for atmospheres with arbitrary proportions of common molecular species and haze. We test this method with generic spectra, ...reproducing the expected systematics and absorption features, then apply it to the nearby super-Earth GJ 1214b, which has produced conflicting observational data, leaving the questions of a hydrogen-rich versus hydrogen-poor atmosphere and the water content of the atmosphere ambiguous. We present representative transit spectra for a range of classes of atmosphere models for GJ 1214b. Our analysis supports a hydrogen-rich atmosphere with a cloud or haze layer, although a hydrogen-poor model with less than 10% water is not ruled out. Several classes of models are ruled out, however, including hydrogen-rich atmospheres with no haze, hydrogen-rich atmospheres with a haze of about 0.01-micron tholin particles, and hydrogen-poor atmospheres with major sources of absorption other than water. We propose an observational test to distinguish hydrogen-rich from hydrogen-poor atmospheres. Finally, we provide a library of theoretical transit spectra for super-Earths with a broad range of parameters to facilitate future comparison with anticipated data.
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