Hasil untuk "Astrophysics"

R. Somerville, R. Dav'e

Modeling galaxy formation in a cosmological context presents one of the greatest challenges in astrophysics today due to the vast range of scales and numerous physical processes involved. Here we review the current status of models that employ two leading techniques to simulate the physics of galaxy formation: semianalytic models and numerical hydrodynamic simulations. We focus on a set of observational targets that describe the evolution of the global and structural properties of galaxies from roughly cosmic high noon (z ∼ 2–3) to the present. Although minor discrepancies remain, overall, models show remarkable convergence among different methods and make predictions that are in qualitative agreement with observations. Modelers have converged on a core set of physical processes that are critical for shaping galaxy properties. This core set includes cosmological accretion, strong stellar-driven winds that are more efficient at low masses, black hole feedback that preferentially suppresses star formation a...

Gregory M. Harry

D. Koch, W. Borucki, G. Basri et al.

The Kepler Mission, launched on 2009 March 6, was designed with the explicit capability to detect Earth-size planets in the habitable zone of solar-like stars using the transit photometry method. Results from just 43 days of data along with ground-based follow-up observations have identified five new transiting planets with measurements of their masses, radii, and orbital periods. Many aspects of stellar astrophysics also benefit from the unique, precise, extended, and nearly continuous data set for a large number and variety of stars. Early results for classical variables and eclipsing stars show great promise. To fully understand the methodology, processes, and eventually the results from the mission, we present the underlying rationale that ultimately led to the flight and ground system designs used to achieve the exquisite photometric performance. As an example of the initial photometric results, we present variability measurements that can be used to distinguish dwarf stars from red giants.

H. Rein, Shangfei Liu

REBOUND is a new multi-purpose N-body code which is freely available under an open-source license. It was designed for collisional dynamics such as planetary rings but can also solve the classical N-body problem. It is highly modular and can be customized easily to work on a wide variety of different problems in astrophysics and beyond. REBOUND comes with three symplectic integrators: leap-frog, the symplectic epicycle integrator (SEI) and a Wisdom-Holman mapping (WH). It supports open, periodic and shearing-sheet boundary conditions. REBOUND can use a Barnes-Hut tree to calculate both self-gravity and collisions. These modules are fully parallelized with MPI as well as OpenMP. The former makes use of a static domain decomposition and a distributed essential tree. Two new collision detection modules based on a plane-sweep algorithm are also implemented. The performance of the plane-sweep algorithm is superior to a tree code for simulations in which one dimension is much longer than the other two and in simulations which are quasi-two dimensional with less than one million particles. In this work, we discuss the different algorithms implemented in REBOUND, the philosophy behind the code's structure as well as implementation specific details of the different modules. We present results of accuracy and scaling tests which show that the code can run efficiently on both desktop machines and large computing clusters.

A. Koning, S. Hilaire, S. Goriely

Yejing Zhan, Di Wang, Shuang-Xi Yi et al.

Gravitational waves (GWs) accompanied by electromagnetic counterparts, known as bright sirens, provide a novel methodology to measure the Hubble constant ( H _0 ). However, the rarity of such multimessenger events limits the precision of the H _0 constraint. Recently, the newly discovered class of nuclear transient, quasiperiodic eruptions (QPEs), shows intriguing evidence of a stellar-mass companion captured by a supermassive black hole in an extreme/intermediate mass ratio inspiral, which is the most promising source of space-based GW detectors, such as LISA. Here, we model the secular orbital evolution of known QPE systems using two frameworks: a stripping scenario in which periodic mass transfer at periapsis drives the evolution, and an orbiter–disk collision scenario in which the companion interacts with a misaligned accretion disk, modulated by coupled orbiter–disk precession. For each framework, we assess detectability by LISA, together with the resulting constraints on H _0 . Our principal findings are (i) in the stripping scenario, no currently known QPE reaches detectability within a four-year LISA mission; (ii) in the orbiter–disk scenario, two sources—eRO-QPE2 and eRO-QPE4—are detectable with signal-to-noise ratios ≃8.5–28.8 and constrain H _0 with a fractional uncertainty of 6.7%–14.9%. QPE systems remain uncertain on the decade-long secular evolution. Therefore, they motivate continued time-domain monitoring of QPE candidates.

Mernier F., Fukushima K., Simionescu A. et al.

Context. Hot, X-ray emitting atmospheres pervading galaxy clusters (and groups) are rich in metals, which have been synthesised and released by asymptotic giant branch (AGB) stars, core-collapse supernovae (SNcc), and Type Ia supernovae (SNIa) over cosmic history. This makes the intracluster medium (ICM) an ideal astrophysical system to constrain its chemical composition, and hence ultimately understand metal production and enrichment on megaparsec scales. Aims. In this work, we take advantage of the unprecedented ∼5 eV resolution offered by the Resolve instrument on board the XRISM observatory to measure the chemical composition of the core of the bright, nearby, and metal-rich Centaurus cluster with unprecedented accuracy. We use these measurements to provide constraints on the stellar populations having enriched the cluster core. Methods. Through a deep (287 ks) Resolve full-array spectral analysis of Centaurus, we derived the Fe abundance and its relative Si/Fe, S/Fe, Ar/Fe, Ca/Fe, Cr/Fe, Mn/Fe, and Ni/Fe ratios. We completed this high-resolution view with N/Fe, O/Fe, Ne/Fe, and Mg/Fe ratios obtained with XMM-Newton/RGS archival data. This abundance pattern was then fitted with various combinations of AGBs, SNcc and SNIa nucleosynthesis yields with the aim of constraining their explosion and/or progenitor models. Results. Similarly to the core of Perseus (from previous Hitomi/SXS results), we find that nine out of our 11 measured abundance ratios are formally consistent with the chemical composition of our Solar System (within uncertainties of the latter). However, the (super-solar) N/Fe and (half-solar) Mg/Fe ratios significantly differ from Perseus and/or other systems, and thus they provide tension with the picture of a fully solar composition ubiquitous to all systems. In addition, possible uncertainties in O/Fe and Ne/Fe with atomic codes highlight the need for studying more systems at high spectral resolution to assess (or rule out) the universality of the ICM composition in clusters’ cool cores. Combinations of (AGB+)SNcc+SNIa yield models can reproduce our observed X/Fe ratios in all cases. However, whether two distinct populations of SNIa are needed depends on the weight of our RGS measurements. We also briefly discuss the possibility of a multi-metallicity gas phase in this respect.

Allen R. C., Ho G. C., Mason G. M. et al.

Investigations of solar energetic particles (SEPs) have long utilized the dispersive nature of onset times, as in, the earlier arrival of higher-energy particles compared to lower-energy particles, to infer information such as the path length to the acceleration site at the time of initial particle release. However, recent observations by Solar Orbiter and Parker Solar Probe have begun to characterize SEP events with an apparent delay in arrival times of the higher energy portion of the particle distribution, above a critical energy separating the delayed particles from that of the typical velocity dispersion signature at lower energies. Features of these delayed maximum energy (DME) SEP events, sometimes referred to as “inverse velocity dispersion” events, could provide new insight into the impacts of magnetic connectivity to locations along an expanding coronal mass ejection-driven (CME-driven) shock wave, variations of acceleration along the shock surface, and transport effects in the inner heliosphere. This study focuses on the occurrence rate and characteristics of DME events observed by Solar Orbiter relative to their footpoint locations with respect to the initial flare site. These DME events show a bias in occurrence rate towards events when the observer’s footpoints were westward of the associated flare location. Additionally, estimated locations at which the highest-energy particles of DME events are released into the flux tube suggest continued release of increasingly higher-energy particles from the CME-driven shock into the connected flux tube well into the inner heliosphere. This indicates that DME events could be attributed to inner heliospheric effects and are not actually coronal in origin. This finding is consistent with previous observations and interpretations of SEP events connected westward of the associated flare.

Pierre Chanial, Simon Biquard, Wassim Kabalan et al.

The Framework for Unified and Robust data Analysis with JAX (Furax) is an open-source Python framework for modeling data acquisition systems and solving inverse problems in astrophysics and cosmology. Built on JAX, Furax provides composable building blocks in the form of general-purpose and domain-specific linear operators, along with preconditioners and solvers for their numerical inversion. Domain-specific tools are provided for astrophysical and cosmic microwave background (CMB) data analysis$-$including map-making, instrument modeling, and astrophysical component separation$-$with a modular architecture designed to extend to other fields.

Suping Zhao, Chenghang Wang, Alejandro Gutierrez–Giles et al.

Unmanned aerial manipulators (UAMs), composed of unmanned aerial vehicles (UAVs) and manipulators, have great application potential in aerial manipulation like precision inspection, disaster rescue, etc. However, strong dynamic coupling exists between UAVs and manipulators. In addition, UAMs meet external disturbances such as gusts of wind during movements. Also, the control performance metrics, such as tracking accuracy and control stability, are seriously affected. Therefore, a cooperative control method is developed for a UAM system with a UAV and a 2-degree-of-freedom manipulator. First, the Euler–Lagrange formulation is employed to study the UAM dynamics like inertial forces and coupling effects. Then, an integral sliding mode control (ISMC) method with an integral term is developed to enhance robustness and eliminate steady-state errors. Finally, the proposed ISMC method is validated through numerical simulations in Matlab R2024a, introducing comparative analyses with the Proportional–Integral–Derivative (PID) and SMC controllers. The simulation results and the comparative analyses validate the effectiveness of ISMC, showing its superiority over the PID and SMC controllers in handling dynamic coupling and external disturbances, where the overshoot of ISMC is reduced by an average of more than 90%. The ISMC method provides a high-performance control strategy to promote the practical application of UAMs in various aerial manipulation tasks and lays the foundation for further optimizing control methods for more complex UAM systems.

Rahul K. Kushwaha, Murthy S. Gudipati, Bryana L. Henderson

Amorphous ice is understood to be the predominant phase of water in cometary nuclei. A significant number of other volatiles can be trapped in amorphous H _2 O ice and released during the amorphous-to-crystalline phase transition (ACPT). This phase transition is an exothermic and is considered a potential cause of cometary outbursts, such as those observed in Comet 1P/Halley and Comet Hale–Bopp. However, only a single experimental study reported in the literature suggests that the presence of impurities (>2%) in amorphous H _2 O ice suppresses the exothermic effect and results in an endothermic phase transition, which contradicts the hypothesis of exothermic-phase-transition-driven comet outbursts. To further explore this phenomenon, we conducted experiments on pure H _2 O, CO:H _2 O, and CO _2 :H _2 O ice mixtures with varying fractions (11%, 50%, and 80% CO, and 11%, 25%, and 50% CO _2 , both relative to H _2 O (100%)). Our experimental setup is a highly sensitive cryogenic differential scanning calorimeter with a μ K noise floor and fifth-decimal resolution in temperature ratio of reference and ice. Our calorimetric data have been internally calibrated to ice sublimation endotherm to derive quantitative calorimetric data. We find that ACPT is exothermic in all CO:H _2 O mixtures and CO _2 :H _2 O mixtures with lower CO _2 fractions. In mixtures with the highest CO _2 content (50% relative to H _2 O (100%)) examined, the ACPT exotherm is weakened. Our results demonstrate that ACPT exothermicity persists throughout the CO and CO _2 mixing ratios observed in a majority of comets, and it should play an important role in comet outbursts when CO and CO _2 are the major volatiles trapped in amorphous H _2 O ice.

R. Siebenmorgen, Frank Heymann, R. Chini

The distance to the stars is a fundamental parameter, which is determined via two primary methods—parallax and luminosity. While the parallax is a direct trigonometric method, the luminosity distance is usually influenced by interstellar extinction. As long as the optical properties of dust grains are wavelength-dependent this contamination can be corrected. However, as the grain size increases, the extinction properties become gray, meaning these particles contribute by a constant at wavelengths $\lesssim $ 1 μ m, making them undetectable by photometry in the optical. In this study, we compare the parallactic and luminosity distances of a pristine sample of 33 well-known early-type stars with nonpeculiar reddening curves and find that the luminosity distance overestimates the parallactic distance in 80% of the cases. This discrepancy can be removed when incorporating a population of large, submicrometer-sized dust grains in a dust model that provides gray extinction, which diminishes the luminosity distance accordingly.

Madhusudhan Raman, Aditi Shahani

Abstract We compute trace relations governing chiral ring elements of fully Ω-deformed N $$ \mathcal{N} $$ = 2⋆ gauge theories with SU(N) gauge groups by demanding the regularity of the fundamental qq-character.

Xue Wang, Xu Cao, Aiqiang Guo et al.

Abstract We investigate the exclusive $$J/\psi $$ J / ψ production at the future Electron-ion collider in China by utilizing the eSTARlight event generator. We model the cross-section and kinematics by fitting to the world data of $$J/\psi $$ J / ψ photoproduction. Projected statistical uncertainties on $$J/\psi $$ J / ψ production are based on the design of a central detector, which consists of a tracker and vertex subsystem. The precision of the pseudo-data allows us to probe the near-threshold mechanism, e.g. the re-scattering effect. The significance of the forward amplitudes is discussed as well. The design and optimization of the detector enhance the potential for exploring the near-threshold region and the realm of high four-momentum transfer squared, which is of particular interest on several physics topics.

Shenglan Sun, Ke Wang, Xunchuan Liu et al.

Long and skinny molecular filaments running along Galactic spiral arms are known as “bones,” since they make up the skeleton of the Milky Way. However, their origin is still an open question. Here, we compare spectral images of HI taken by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) with archival CO and Herschel dust emission to investigate the conversion from HI to H _2 in two typical Galactic bones, CFG028.68-0.28 and CFG047.06+0.26. Sensitive FAST HI images and an improved methodology enabled us to extract HI narrow self-absorption (HINSA) features associated with CO line emission on and off the filaments, revealing the ubiquity of HINSA toward distant clouds for the first time. The derived cold HI abundances, [HI]/[H _2 ], of the two bones range from ∼(0.5 to 44.7) × 10 ^−3 , which reveal different degrees of HI–H _2 conversion, and are similar to those of nearby, low-mass star-forming clouds, Planck Galactic cold clumps, and a nearby active high-mass star-forming region G176.51+00.20. The HI–H _2 conversion has been ongoing for 2.2–13.2 Myr in the bones, a timescale comparable to that of massive star formation therein. Therefore, we are witnessing young giant molecular clouds (GMCs) with rapid massive star formation. Our study paves the way of using HINSA to study cloud formation in Galactic bones and, more generally, in distant GMCs in the FAST era.

Alex Gough, Cora Uhlemann

Ultralight candidates for dark matter can present wavelike features on astrophysical scales. Full wave based simulations of such candidates are currently limited to box sizes of 1--10 Mpc/$h$ on a side, limiting our understanding of the impact of wave dynamics on the scale of the cosmic web. We present a statistical analysis of density fields produced by perturbative forward models in boxes of 128 Mpc/$h$ side length. Our wave-based perturbation theory maintains interference on all scales, and is compared to fluid dynamics of Lagrangian perturbation theory. The impact of suppressed power in the initial conditions and interference effects caused by wave dynamics can then be disentangled. We find that changing the initial conditions captures most of the change in one-point statistics such as the skewness of the density field. However, different environments of the cosmic web, quantified by critical points of the smoothed density, appear to be more sensitive to interference effects sourced by the quantum potential. This suggests that certain large-scale summary statistics may need additional care when studying cosmologies with wavelike dark matter.

Trey V. Wenger

$\texttt{bayes_spec}$ is a Bayesian spectral line modeling framework for astrophysics. Given a user-defined model and a spectral line dataset, $\texttt{bayes_spec}$ enables inference of the model parameters through different numerical techniques, such as Monte Carlo Markov Chain (MCMC) methods, implemented in the PyMC probabilistic programming library. The API for $\texttt{bayes_spec}$ is designed to support astrophysical researchers who wish to ``fit'' arbitrary, user-defined models, such as simple spectral line profile models or complicated physical models that include a full physical treatment of radiative transfer. These models are ``cloud-based'', meaning that the spectral line data are decomposed into a series of discrete clouds with parameters defined by the user's model. Importantly, $\texttt{bayes_spec}$ provides algorithms to determine the optimal number of clouds for a given model and dataset.

Yan Li, Rong-Feng Shen, Bin-Bin Zhang

Short-duration gamma-ray bursts (sGRBs) are commonly attributed to the mergers of double neutron stars (NSs) or the mergers of a neutron star with a black hole (BH). While the former scenario was confirmed by the event GW170817, the latter remains elusive. Here, we consider the latter scenario in which an NS is tidally disrupted by a fast-spinning low-mass BH and the accretion onto the BH launches a relativistic jet and hence produces an sGRB. The merging binary’s orbit is likely misaligned with the BH’s spin. Hence, the Lense–Thirring precession around the BH may cause a hyperaccreting thick disk to precess in a solid-body manner. We propose that a jet, initially aligned with the BH spin, is deflected and collimated by the wind from the disk, therefore being forced to precess along with the disk. This would result in a quasiperiodic oscillation or modulation in the gamma-ray light curve of the sGRB, with a quasi-period of ∼0.01–0.1 s. The appearance of the modulation may be delayed respective to the triggering of the light curve. This feature, unique to the BH–NS merger, may have already revealed itself in a few observed sGRBs (such as GRB 130310A), and it carries the spin–orbit orientation information of the merging system. Identification of this feature would be a new approach to reveal spin–orbit misaligned merging BH–NS systems, which are likely missed by the current gravitational-wave searching strategy that is principally targeting aligned systems.

Amy Secunda, Jenny E. Greene, Yan-Fei Jiang et al.

The variability of quasar light curves can be used to study the structure of quasar accretion disks. For example, continuum reverberation mapping uses delays between variability in short and long wavelength bands ( short lags) to measure the radial extent and temperature profile of the disk. Recently, a potential reverse lag, where variations in shorter wavelength bands lag the longer wavelength bands at the much longer viscous timescale, was detected for Fairall 9. Inspired by this detection, we derive a timescale for these long negative lags from fluctuation propagation models and recent simulations. We use this timescale to forecast our ability to detect long lags using the Vera Rubin Legacy Survey of Space and Time (LSST). After exploring several methods, including the interpolated cross-correlation function, a Von-Neumann estimator, javelin , and a maximum-likelihood Fourier method, we find that our two main methods, javelin and the maximum-likelihood method, can together detect long lags of up to several hundred days in mock LSST light curves. Our methods work best on proposed LSST cadences with long season lengths, but can also work for the current baseline LSST cadence, especially if we add observations from other optical telescopes during seasonal gaps. We find that LSST has the potential to detect dozens to hundreds of additional long lags. Detecting these long lags can teach us about the vertical structure of quasar disks and how it scales with different quasar properties.

D. John Hillier

Photoionization and its inverse, electron-ion recombination, are key processes that influence many astrophysical plasmas (and gasses), and the diagnostics that we use to analyse the plasmas. In this review we provide a brief overview of the importance of photoionization and recombination in astrophysics. We highlight how the data needed for spectral analyses, and the required accuracy, varies considerably in different astrophysical environments. We then discuss photoionization processes, highlighting resonances in their cross-sections. Next we discuss radiative recombination, and low and high temperature dielectronic recombination. The possible suppression of low temperature dielectronic recombination (LTDR) and high temperature dielectronic recombination (HTDR) due to the radiation field and high densities is discussed. Finally we discuss a few astrophysical examples to highlight photoionization and recombination processes.