Astrophysical Problems Research Articles

Analytical solution to the conformable fractional Lane-Emden type equations arising in astrophysics

Lane-Emden equations have many applications in physical science and so make great attention to researchers. In most cases there is are no exact solutions to these equations and only approximate solutions could be performed. This paper introduces analytical solutions to Lane-Emden type equations using the fractional Adomian decomposition method. We solve six examples related to astrophysical and physical problems. The approximate solutions are derived in the form of a divergent series. In the case of the fractional parameter equal one, the integer order, we obtained the same results as obtained by the method of Adomian decomposition.

Spectra of Protons and Alpha Particles and Their Comparison in the NUCLEON Experiment Data

The aim of the NUCLEON space experiment was to measure spectra of high-energy cosmic rays. Direct measurements of energy spectra of protons and nuclei of cosmic rays which allow separating particles in charge are required to solve important astrophysical problems. The satellite was launched on December 26, 2014, and operated for three years. Measured spectra of protons and alpha particles in the energy range of 2–500 TeV per particle have been presented. The results have been analyzed and compared to other experimental data for lower energies. The ratio of fluxes of protons and alpha particles is nearly constant in a wide range of magnetic rigidities (3–100 TV). Thus, the behavior of the ratio of the spectra is significantly different from a similar dependence in the region of lower magnetic rigidities measured in other experiments. One of the possible explanation of this effect can be given within a model with one close source.

CALCULATION OF CROSS SECTIONS AND ASTROPHYSICAL S-FACTORS AT 0-5 MeV ENERGY RANGE FOR 8Li (α, n)11B REACTION

Explaining the origin and evolution of elements is one of the most important problems in astrophysics. The r-process in the current nucleosynthesis scenario; roughly responsible for the production of half of the nuclei heavier than iron. 8Li(α,n)11B reaction plays an important role in the r-process of this scenario because of being a cosmic radiation induced reaction. In particular, it is important to know the change with energy in the low energy zone for testing the accuracy of the model calculations. In this study, the astrophysical S-factors of the 8Li(α,n)11B reaction and the probability of reaction at low energies were calculated in the 0-5 MeV energy range. TALYS 1.8 code was used for the theoretical calculations. The obtained theoretical values were compared with experimental data obtained from the EXFOR database.

Technologies for supporting high-order geodesic mesh frameworks for computational astrophysics and space sciences

Many important problems in astrophysics, space physics, and geophysics involve flows of (possibly ionized) gases in the vicinity of a spherical object, such as a star or planet. The geometry of such a system naturally favors numerical schemes based on a spherical mesh. Despite its orthogonality property, the polar (latitude-longitude) mesh is ill suited for computation because of the singularity on the polar axis, leading to a highly non-uniform distribution of zone sizes. The consequences are (a) loss of accuracy due to large variations in zone aspect ratios, and (b) poor computational efficiency from a severe limitations on the time stepping. Geodesic meshes, based on a central projection using a Platonic solid as a template, solve the anisotropy problem, but increase the complexity of the resulting computer code. We describe a new finite volume implementation of Euler and MHD systems of equations on a triangular geodesic mesh (TGM) that is accurate up to fourth order in space and time and conserves the divergence of magnetic field to machine precision. The paper discusses in detail the generation of a TGM, the domain decomposition techniques, three-dimensional conservative reconstruction, and time stepping.

A variational approach to relativistic superfluid vortex elasticity

It is well known that a superfluid rotates by forming an array of quantized vortices. A relativistic formulation for superfluid vortex dynamics is required for a range of problems in astrophysics and cosmology, from neutron star interiors and radio pulsar glitches to possible dark matter condensates on galactic scales. This paper develops a formalism for such systems, extending the well-established variational approach to relativistic fluids to account for the presence of a collection of quantized vortices. The model is firmly anchored in the geometry of the problem (drawing on aspects from basic string dynamics) and accounts for elastic aspects associated with a vortex array, providing a precise foundation for applications which have so far been based on somewhat ad hoc phenomenology.

Image Simulations for Strong and Weak Gravitational Lensing

Gravitational lensing has been identified as a powerful tool to address fundamental problems in astrophysics at different scales, ranging from exoplanet identification to dark energy and dark matter characterization in cosmology. Image simulations have played a fundamental role in the realization of the full potential of gravitational lensing by providing a means to address needs such as systematic error characterization, pipeline testing, calibration analyses, code validation, and model development. We present a general overview of the generation and applications of image simulations in strong and weak gravitational lensing.

On some integral‐consistent methods for calculating magnetohydrodynamic phenomena in problems of computational astrophysics

When constructing difference schemes for calculating complex problems of computational astrophysics considering magnetohydrodynamic and gravitational phenomena, the processes of matter overcompression (with a change in density by several orders of magnitude) should be taken into account, and it is important at a discrete level to take into account the corresponding energy transformations of magnetohydrodynamic, gravitational, kinetic, and internal energy during the evolution of a star. This problem is solved by constructing completely conservative difference schemes in a view of these magnetohydrodynamic processes and self‐gravitating phenomena. In this work, to study and apply the difference methods for solving problems of magnetic gas dynamics, a discrete representation of symmetrized spatial deformations of the medium was obtained. The representation is consistent with changes in the magnetic, kinetic, and internal energies and does not lead to their distortions when the matter is overcompressed.

The Lyman Alpha Reference Sample. X. Predicting Lyα Output from Star-forming Galaxies Using Multivariate Regression*

Abstract Understanding the production and escape of Lyα radiation from star-forming galaxies is a long-standing problem in astrophysics. The ability to predict the Lyα luminosity of galaxies would open up new ways of exploring the epoch of reionization (EOR) and estimating Lyα emission from galaxies in cosmological simulations where radiative transfer calculations cannot be done. We apply multivariate regression methods to the Lyman Alpha Reference Sample data set to obtain a relation between the galaxy properties and the emitted Lyα. The derived relation predicts the Lyα luminosity of our galaxy sample to good accuracy, regardless of whether we consider only direct observables (rms dispersion around the relation of ∼0.19 dex) or derived physical quantities (rms ∼ 0.27 dex). We confirm the predictive ability on a separate sample of compact star-forming galaxies and find that the prediction works well, but that aperture effects on measured Lyα luminosity may be important, depending on the redshift of the galaxy. We apply statistical feature selection techniques to determine an order of importance of the variables in our data set, enabling future observations to be optimized for predictive ability. When using physical variables, we are able to determine that the most important predictive parameters are, in order, star formation rate, dust extinction, compactness, and the gas covering fraction. We discuss the application of our results in terms of studying the EOR and intensity mapping experiments.

A new proxy to estimate the cosmic ray ionization rate in dense cores

ABSTRACT Cosmic rays are a global source of ionization, and the ionization fraction represents a fundamental parameter in the interstellar medium. Ions couple to magnetic fields, and affect the chemistry and the dynamics of star-forming regions as well as planetary atmospheres. However, the cosmic ray ionization rate represents one of the bottlenecks for astrochemical models, and its determination is one of the most puzzling problems in astrophysics. While for diffuse clouds reasonable values have been provided from ${\mathrm{ H}_3}^+$ observations, for dense clouds, due to the lack of rotational transitions, this is not possible, and estimates are strongly biased by the employed model. We present here an analytical expression, obtained from first principles, to estimate the cosmic ray ionization rate from observational quantities. The theoretical predictions are validated with high-resolution 3D numerical simulations and applied to the well-known core L1544; we obtained an estimate of ζ2 ∼ 2–3 × 10−17 s−1. Our results and the analytical formulae provided represent the first model-independent robust tool to probe the cosmic ray ionization rate in the densest part of star-forming regions (on spatial scales of R ≤ 0.05 pc). An error analysis is presented to give statistical relevance to our study.

DIAPHANE: A portable radiation transport library for astrophysical applications

diaphane is a portable, scalable, and extensible library for modelling the transport of energy by radiation or relativistic particles (in particular neutrinos). Energy transport modelling is crucial for the hydrodynamic modelling of a wide range of astrophysical phenomena such as planet and galaxy formation, supernova explosions, and cosmic structure evolution. The diaphane library provides a computational framework and functionality to incorporate energy transport modelling into hydrodynamical astrophysics simulations. The transport routines are called from, and operate independently of, the underlying hydrodynamic code of choice. It is designed to be utilized by hydrodynamic astrophysical simulations through a simplified interface layer, allowing it to operate independently of the underlying hydrodynamic code. We provide a sample interface layer to three widely-used astrophysics-focussed smoothed-particle hydrodynamic codes, gadget2, gasoline and sphynx. The initial release comprises a particle-based implementation of Flux Limited Diffusion and Starrad, a ray casting method that we have developed. diaphane development has been supported the Platform for Advanced Scientific Computing. Program summaryProgram Title: DiaphaneProgram Files doi:http://dx.doi.org/10.17632/rwyd5k5rjh.1Code Ocean capsule:https://doi.org/10.24433/CO.5068717.v1Licensing provisions: MITProgramming language: C/C++Nature of problem: The ability to model and hence understand many important astrophysical processes has often been limited by the approximations and incompleteness in the treatment of radiation and relativistic particles, even though many algorithms exist for modelling the transport of energy by radiation and relativistic particles. For many problems, multiple algorithms must be used because each algorithm is best-suited in terms of speed and accuracy only in some particular physical regime. A comprehensive library that contains multiple radiation/relativistic transport techniques is needed in order to model astrophysical problems and their wide range in physical regimes. This library framework must be able to be easily and efficiently utilized by a hydrodynamic simulation code.Solution method: We provide a framework for solving radiation and neutrino transport in a portable, scalable, and extensible library. We provide a sample interface for multiple simulation codes, at this time gadget2 [2,3], gasoline [4] and sphynx [5,6]. Community development to develop new algorithms and support new hydrodynamic codes is welcome. The library framework allows multiple energy transport methods to be used simultaneously.Additional comments: This work has been supported by the Swiss Platform for Advanced Scientific Computing (PASC, http://www.pasc-ch.org/) project DIAPHANE (DR and RC) and by the European Research Council (FP7) under ERC Advanced Grant Agreement No. 321263-FISH (RC).A more detailed description of the library and framework are described in [1].Declaration of Competing InterestThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.[1] D. S. Reed, T. Dykes, R. Cabezón, C. Gheller, L. Mayer, Computer Physics Communications 226 (2018) 1–9.[2] V. Springel, N. Yoshida, S. D. M. White, New Astronomy6 (2) (2001) 79–117.[3] V. Springel, Mon. Not. R. Astron. Soc. 364 (4) (2005) 1105–1134.[4] J. W. Wadsley, B. W. Keller, T. R. Quinn, Mon. Not. R. Astron. Soc. 471 (2) (2017) 2357–2369.[5] R. M. Cabezon, D. Garcia-Senz, (Sep 2017).[6] R. M. Cabezón, D. García-Senz, J. Figueira, Astronomy & Astrophysics 606 (2017) A78.

Purification of the NaI(Tl) crystal for dark matter search project PICOLON

Direct search for dark matter is one of the most important problems in astrophysics. Significant signal for dark matter will be a hint to clarify the origin of the universe. Only DAMA/LIBRA experiment with NaI(Tl) detector has ever suggested the presence of dark matter signal. Verifying the DAMA/LIBRA result by a NaI(Tl) detector is urgent and important task. We have tried to purify NaI(Tl) crystal to search for dark matter. In this presentation, the present status of purification will be discussed. The concentration of potassium is successfully reduced to desired sensitivity. The 210Pb, which is difficult to reduce, has been reduced effectively. Present status of low background measurement in Kamioka observatory will be shown.

Distinguishing Brans\u2013Dicke\u2013Kerr type naked singularities and black holes with their thin disk electromagnetic radiation properties

The possible existence of naked singularities, hypothetical astrophysical objects, characterized by a gravitational singularity without an event horizon is still an open problem in present day astrophysics. From an observational point of view distinguishing between astrophysical black holes and naked singularities also represents a major challenge. One possible way of differentiating naked singularities from black holes is through the comparative study of thin accretion disks properties around these different types of compact objects. In the present paper we continue the comparative investigation of accretion disk properties around axially-symmetric rotating geometries in Brans–Dicke theory in the presence of a massless scalar field. The solution of the field equations contains the Kerr metric as a particular case, and, depending on the numerical values of the model parameter gamma , has also solutions corresponding to non-trivial black holes and naked singularities, respectively. Due to the differences in the exterior geometries between black holes and Brans–Dicke–Kerr naked singularities, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution and equilibrium radiation spectrum) are different for these two classes of compact objects, consequently giving clear observational signatures that could discriminate between black holes and naked singularities.

First In Situ Measurements of Electron Density and Temperature from Quasi-thermal Noise Spectroscopy with Parker Solar Probe/FIELDS

Abstract Heat transport in the solar corona and wind is still a major unsolved astrophysical problem. Because of the key role played by electrons, the electron density and temperature(s) are important prerequisites for understanding these plasmas. We present such in situ measurements along the two first solar encounters of the Parker Solar Probe, between 0.5 and 0.17 au from the Sun, revealing different states of the emerging solar wind near the solar activity minimum. These preliminary results are obtained from a simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by the Radio Frequency Spectrometer (FIELDS). The local electron density is deduced from the tracking of the plasma line, which enables accurate measurements, independent of calibrations and spacecraft perturbations, whereas the temperatures of the thermal and suprathermal components of the velocity distribution, as well as the average kinetic temperature, are deduced from the shape of the plasma line. The temperature of the weakly collisional thermal population, similar for both encounters, decreases with the distance as R −0.74, which is much slower than adiabatic. In contrast, the temperature of the nearly collisionless suprathermal population exhibits a virtually flat radial variation. The 7 s resolution of the density measurements enables us to deduce the low-frequency spectrum of compressive fluctuations around perihelion, varying as f −1.4. This is the first time that QTN spectroscopy is implemented with an electric antenna length not exceeding the plasma Debye length. As PSP will approach the Sun, the decrease in the Debye length is expected to considerably improve the accuracy of the temperature measurements.

Nuclear mass measurements

Mass is a fundamental property of atomic nuclei. Nuclear masses are widely used in nuclear physics and astrophysics researches as well as nuclear technique applications. Currently it is the mass spectrometry that dominates the research field of nuclear mass measurement. Thanks to the developments of radioactive nuclear beam facilities and novel mass spectrometers, the experimental knowledge of atomic masses is rapidly expanding along two main directions, namely measurements aimed at high-precision mass values and at the most exotic nuclei far from the stability. In this article, we will review briefly the history of nuclear mass measurements and present the current status. By evaluating all available experimental data from nuclear reactions, radioactive decays and direct mass measurements, the AME (Atomic Mass Evaluation) serves the research community with the most reliable source for comprehensive information related to the nuclear masses. The latest AME was published in March, 2017 as AME2016, which will also be introduced in this article. In recent years, based on the large-scale research facility HIRFL-CSR, we have carried out precision mass measurements for short-lived nuclides by using the isochronous mass spectrometry at Institute of Modern Physics, Chinese Academy of Sciences. We achieved the highest precision of mass measurements using the Isochronous Mass Spectrometry (IMS) method and set the world record of the shortest half-life of a nuclear state whose mass has ever been measured directly. The IMS with double-time-of-flight has been established for the first time, with which the IMS experiments will be carried out in future. Masses of more than 50 short-lived nuclides have been determined with relative mass uncertainties of 10−6–10−7. The newly obtained mass values have been used to study the relevant nuclear physics and nuclear astrophysics problems. We will discuss the impact of the mass results on investigations concerning isospin symmetry in nuclides and rp nucleosynthesis process as examples.

Solution of fractional kinetic equations involving class of functions and Sumudu transform

Fractional kinetic equations (FKEs) including a wide variety of special functions have been widely and successfully applied in describing and solving many important problems of physics and astrophysics. In this paper, we derive the solutions for FKEs including the class of functions with the help of Sumudu transforms. Many important special cases are then revealed and analyzed. The use of the class of functions to obtain the solution of FKEs is fairly general and can be efficiently used to construct several well-known and novel FKEs.

ERROR ESTIMATION FOR ILL-POSED PROBLEMS WITH PRIORI INFORMATION

The theory of solving linear and nonlinear ill-posed problems is advanced greatly today (see, e.g., [1, 2]). A general scheme for constructing regularizing algorithms using Tikhonov’s variational approach is considered in [2]. It is very well known that ill-posed problems have unpleasant properties even in the cases when stable methods (regularizing algorithms) of their solution exist. E.g., it is impossible to estimate an error of an approximate solution of an illposed problem without very strong assumptions concerning the unknown solution. The following assumptions are under consideration: 1) the unknown solution is an element of the given compact set; 2) the unknown solution is sourcewise represented with a compact operator. For these cases the theory of error estimation or a posteriori error estimation was developed and applied for solving operator equations including integral equations and some inverse problems for differential equations. Numerical methods for solving ill-posed problems and their error estimation are based on convex programming. The results above were used for the solution of practical problems in astrophysics, acoustics, physical chemistry, electron microscopy, nuclear physics, etc.

Linking gravitational waves and X-ray phenomena with joint LISA and Athena observations

The evolution of cosmic structures, the formation and growth of the first black holes and the connection to their baryonic environment are key unsolved problems in astrophysics. The X-ray Athena mission and the gravitational-wave Laser Interferometer Space Antenna (LISA) offer independent and complementary angles on these problems. We show that up to about 10 black hole binaries in the mass range of approximately 105 to 108 solar masses discovered by LISA at redshift below about 3.5 could be detected by Athena in an exposure time up to 100 ks, if prompt X-ray emission of 1–10% of the Eddington luminosity is present. Likewise, if any LISA-detected extreme-mass-ratio inspirals occur in accretion disks, Athena can detect associated electromagnetic emission out to a redshift of about 1. Finally, warned by LISA, Athena can point in advance and stare at stellar-mass binary black hole mergers at redshift less than about 0.1. These science opportunities emphasize the vast discovery space of simultaneous observations from the two observatories, which would be missed if they were operated in different epochs. This Perspective highlights the science opportunities and the vast discovery space of simultaneous observations from the LISA and Athena observatories, which would be missed if they were operated in different epochs .

Hypersphere World-Universe Model: Basic Ideas

Hypersphere World-Universe Model (WUM) envisions Matter carried from the Universe into the World from the fourth spatial dimension by Dark Matter Particles (DMPs). Luminous Matter is a byproduct of Dark Matter (DM) self-annihilation. WUM introduces Dark Epoch (spanning from the Beginning of the World for 0.45 billion years) and Luminous Epoch (ever since for 13.77 billion years). Big Bang discussed in Standard Cosmology (SC) is, in our view, transition from Dark Epoch to Luminous Epoch due to Rotational Fission of Overspinning DM Supercluster’s Cores and self-annihilation of DMPs. WUM solves a number of physical problems in SC and Astrophysics through DMPs and their interactions: Angular Momentum problem in birth and subsequent evolution of Galaxies and Extrasolar systems; Fermi Bubbles—two large structures in gamma-rays and X-rays above and below Galactic center; Coronal Heating problem in solar physics—temperature of Sun’s corona exceeding that of photosphere by millions of degrees; Cores of Sun and Earth rotating faster than their surfaces; Diversity of Gravitationally-Rounded objects in Solar system and their Internal Heating. Model makes predictions pertaining to Rest Energies of DMPs, proposes New Type of their Interactions. WUM reveals Inter-Connectivity of Primary Cosmological Parameters and calculates their values, which are in good agreement with the latest results of their measurements.

STUDY OF THE INTERACTION OF PARTICLES OF SPACE RADIATION BY THE HYBRID IONIZATION CALORIMETER METHOD

At present, in cosmic rays at energies above 1015 eV, a certain number of phenomena are observed mainly in the trunk (center) region of a wide air shower (EAS) that do not fit into the traditional concepts of the nuclear cascade process in the atmosphere. If we consider that the trunk region with a radius of up to 10 meters at a distance of 20–30 km from the point of the first interaction of a particle that produced an EAS, belongs to the pseudo-fastness region that is inaccessible on accelerators, then the study of the central part of EAS is a good addition to accelerator experiments. It is also possible that unusual particles can be present in the cosmic-ray flux at energies above 1015 eV, which are the primary cause of the observed anomalous phenomena in experiments with cosmic radiation and which, due to their properties, are not observed in accelerator experiments. The complex installation “ADRON-55” is located at an altitude of 3340 meters above sea level and is part of the unified system of registration of particles of cosmic radiation at the Tian-Shan high-altitude scientific station. The “ADRON-55” facility is aimed at solving a number of astrophysical and nuclear physics problems: the study of interactions of high-energy hadrons in the central part of EAS trunks, the search for sources of high-energy cosmic rays.

An improved particle shifting algorithm for multiphase flows in SPH method

Multiphase flows, such as underwater explosions, rising bubbles, flooding of damaged cabins, etc., are widespread in nature and engineering. When conventional Eulerian mesh-based methods are adopted in the simulation of multiphase flows, some challenges are always encountered, including the large deformation and fragmentation of fluid, the capture of the multiphase interface, and so on. Therefore, many scholars turned their attention to meshless particle methods. As an important member of meshfree methods, smoothed particle hydrodynamics (SPH) was invented to solve astrophysical problems, and then it was applied to the simulation of hydrodynamics. In the SPH method, the computational domain is represented by a collection of particles whose properties, including density, velocity, internal energy, etc, are updated by the interaction between particles. Since the SPH method is free from the restriction of the mesh, it is good at handling large deformations of fluid. More importantly, the free-surface or multiphase interface does not need to be detected because the interface of the particles of different phases is also the interface of fluid. For these reasons, the SPH method has been widely used in the simulation of multiphase flows. Due to the natural Lagrangian characteristic of the SPH method, particles move strictly along streamlines, which may lead to uneven particle distributions and thus reducing the numerical accuracy in some cases. To solve this problem, some particle regularization schemes have been developed in the SPH method, in which the particle shifting algorithm is the most widely used one. The core idea of the shifting algorithm is to artificially move particles from a region with a high concentration of particles to a region with a low concentration of particles in each time step, thereby obtaining uniform particle distributions throughout simulations. In the published literature, there have been several multiphase models in the SPH method, and some of them adopt the particle shifting algorithm to make the discontinuous multiphase interface more stable and accurate. At present, the most commonly used shifting algorithm for multiphase flows is proposed by Mokos et al. When it is adopted, the moving material interface should be firstly detected. Then particles belonging to different phases are shifted by applying different treatments, aiming to avoid mutual mixing of different phase materials. These treatments are generally complicated and time-consuming, and sometimes they may result in unphysical gaps near the multiphase interface, reducing the numerical accuracy and stability. To tackle the problems mentioned above, a simpler and more accurate shifting algorithm is proposed in this paper. In this algorithm, the treatments applied to different fluids are consistent. Meanwhile, to ensure the clarity of the multiphase interface, the shifting magnitude of the particles near the interface is slightly increased. Compared with the shifting algorithm proposed by Mokos et al., the improved shifting algorithm is simpler and more efficient. More importantly, through the simulations of several classical multiphase problems in the SPH method, the proposed improved shifting algorithm is proved to be able to maintain perfectly uniform particle distributions near the interface even for long-term simulations, and thus the numerical accuracy and energy conservation are enhanced.