ABSTRACT
In this population synthesis work, we study a variety of possible origin channels of supernovae type Ia (SNe Ia). Among them mergers of carbon–oxygen (CO) and oxygen–neon (ONe) white dwarfs ...(WDs) under the influence of gravitational waves are considered as the primary channel of SNe Ia formation. We estimated frequencies of mergers of WDs with different chemical compositions and distributions of masses of merging WDs. We computed the dependence of the ratio of merger frequencies of ONe and CO WDs as primaries in corresponding binaries on time. The scatter of masses of considered sources (up to the factor 1.5–2) of SNe Ia is important and should be carefully studied with other sophisticated methods from theoretical point of view. Our ‘game of parameters’ potentially explains the increased dimming of SNe Ia in the redshift range z ≈ 0.5–1 by the changes in the ratio of ONe and CO WDs, i.e. to describe the observed accelerated expansion of the Universe in terms of the evolution of properties of SNe Ia instead of cosmological explanations. This example shows the extreme importance of theoretical studies of problems concerning SNe Ia, because evolutionary scenario and parameter games in nature potentially lead to confusions in their empirical standardization and, therefore, they can influence on cosmological conclusions.
The diversity of close binary stars (CBSs) and the rich manifestation of their activity as a result of the interaction of stellar components have turned their observed family into a very developed ...and effective tool for studying the evolution of stars. This review presents the main features of modern ideas about the evolution of CBSs from their origin to the formation of finite compact remnants of components: degenerate dwarfs, neutron stars and stellar black holes. The main phenomena related to their interaction with each other and accompanying the process of fusion of compact components of the CBS are also listed, considering the effect of common envelopes, radiation of gravitational waves in cataclysmic and X-ray binaries, supernovae (SN Ia, SN Ib), gamma-bursters and other systems. The paper is based on a report presented at the astrophysical memorial seminar “Novelties in Understanding the Evolution of Binary Stars,” dedicated to the 90th anniversary of Professor M.A. Svechnikov.
ABSTRACT
The neutron star low-mass X-ray binary (LMXB) AX J1745.6−2901 was detected with an anomalously fast decrease of its orbital period. The decreasing rate of the orbital period exceeds the ...contribution of all processes extracting angular momentum from the binary star in the standard model. Using the scenario machine code, we conducted a population synthesis study of X-ray novae with neutron stars to investigate a possible formation and evolution of such binaries. Such close LMXBs should experience a preceding common envelope stage, in which the magnetic fields of the low-mass main-sequence donor stars can be dramatically amplified. Our calculations show that the magnetic stellar wind of the optical companion can efficiently extract angular momentum from the binary systems, and produce the observed orbital-period derivatives of AX J1745.6−2901 and black hole LMXBs. The estimated values of the required magnetic field induction are the following: Bd ≈ 400 G (AX J1745.6−2901), Bd ≈ 1500 G (KV UMa), Bd ≈ 400 G (A0620−00) and Bd ≈ 1800 G (Nova Muscae). We successfully reproduced the current observational abundance of such anomalous neutron star X-ray novae, and computed the appropriate value of the parameter of magnetic braking λMSW (0.8−0.6 for Roche lobe filling stars and 0.4−0.15 for binaries with partial Roche lobe filling).
Abstract
Relativistic velocity is a kinematic feature of micro-objects (elementary particles). Their application to macro objects (stars, planets, asteroids, neutron stars, and stellar-mass black ...holes) is currently under scientific discussion. This potential was recognized after Warren Brown discovered hypervelocity stars (HVSs) at the beginning of the 21st century. Jack Hills predicted these stars in 1988 due to the dynamical capture of a binary star by the central supermassive black hole (SMBH). The acceleration mechanism due to momentum exchange in the classical three-body problem provides the kinetic resource for HVS formation by the gravitational capture of the remaining component. The present threshold of the anomalous stellar kinematics exceeds ∼1700 km s
−1
and can be reproduced by some mechanisms as alternatives to Hills’s scenario. HVSs can arise due to the collisional evolution of stellar clusters, supernova explosions in close binary stars, the orbital instability of triple stars, stellar captures from other galaxies, etc. Scenarios with the participation of black holes with masses ranging from stellar values to several billion solar masses are the most promising for the generation of anomalously high stellar velocities. Hills’s scenario has a special place in HVS studies, because, being based on the accidental capture of a binary star by the SMBH, it does not relate to the problem of the Galactic Center population. This scenario predicts self-consistent statistics of HVSs and captured stars which may be identified with S-stars. The discovery of S-stars played an essential role in studies of the Galactic Center; their dynamics have independently provided incontestable proof of the SMBH’s existence. This review briefly discusses the history of the discovery and investigation of HVSs and S-stars, provides an account of their observational statistics, and describes their modeling methods in the classical three-body and
N
body problems. We study the limits of the effective acceleration of stars in the classical Hills scenario and the modified mechanism that allows a change of one of the binary components to another SMBH. The acceleration acquired by the star in a mutual field of two SMBHs can produce stars with relativistic velocities (1/2
c
−2/3
c
). Using a self-consistent probabilistic model combining the classical and modified Hills scenarios, we predict the formation probability of HVSs in the Galaxy and of extragalactic stars with relativistic velocities. We discuss the prospects of searches for stars and asteroids with relativistic velocities by future space missions and using new knowledge about the Universe.
We propose a new code named AstroPhi for simulation of the dynamics of astrophysical objects on hybrid supercomputers equipped with Intel Xenon Phi computation accelerators. The details of parallel ...implementation are described, as well as changes to the computational algorithm that facilitate efficient parallel implementation. A single Xeon Phi accelerator yielded 27-fold acceleration. The use of 32 Xeon Phi accelerators resulted in 94% parallel efficiency. Several collapse problems are simulated using the AstroPhi code.
Program title: AstroPhi
Catalogue identifier: AEUM_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEUM_v1_0.html
Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland
Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html
No. of lines in distributed program, including test data, etc.: 99604
No. of bytes in distributed program, including test data, etc.: 305433
Distribution format: tar.gz
Programming language: C++.
Computer: MVS-10P - RSC Tornado, Xeon E5-2690 8C 2.900 GHz, Infiniband FDR, Intel Xeon Phi SE10X.
Operating system: Linux.
Has the code been vectorized or parallelized?: Parallelized on MPI + OpenMP for Intel MIC architecture, 32 Intel Xeon Phi (60 cores per 1 Intel Xeon Phi = 1920 cores of Intel Xeon Phi).
RAM: 137438953472 bytes (128 GB) bytes
Classification: 1.9.
External routines: MPI, OpenMP for Intel Xeon Phi, FFTW 2.1.5
Nature of problem:
Complex numerical simulation of dynamics of astrophysical objects plays an important role due to significant growth of observational astronomic data. The new astrophysical models and codes need to be developed for detailed simulation of different physical effects in astrophysics with the use of modern supercomputers with hybrid architecture.
Solution method:
AstroPhi code consisting of particle-in-cell and Godunov methods combination adapted for hybrid supercomputer architecture.
Restrictions:
For this version maximum grid size is restricted to 10243.
Running time:
Typical running on MVS-10P is 24 h. The test provided only takes a few minutes.
The possible evolution of a bright low-mass X-ray binary system Sco X-1 is numerically investigated within the framework of a model assuming that the donor-star of the system (a satellite of a ...neutron star) fills its Roche lobe. The calculations consider a strong induced stellar wind (ISW) of the donor, which occurs due to irradiation by hard radiation of an accreting relativistic star. At the same time, using the example of Sco X-1, three hypotheses are investigated, within the framework of which a high rate of mass exchange can be obtained for semi-detached X-ray binaries. The first hypothesis is the presence of a strong ISW of the donor with standard magnetic braking. Calculations have shown that in this case it is possible to obtain a high rate of mass exchange, but at the same time the donor cannot fill the Roche lobe—it “goes under it.” The second hypothesis is an increase of magnetic braking, that is, an increase of the loss of angular momentum from the system due to the magnetic stellar wind of the donor (MSW). Such an amplification may be associated with the intense ISW of the donor in the presence of a strong magnetic field. Numerical modeling shows that with an increase of MSW by
times, a high rate of mass exchange is possible when the donor fills its Roche lobe. The third hypothesis suggests the possibility of canceling the direct exchange of angular momentum between the orbital moment of the system and the moment of accreted matter passing from a low-mass donor to a more massive accretor. With such cancellation, the main process, increasing the semi-axis of the orbit, disappears. Calculations show that in this case it is possible to obtain a sufficiently high rate of mass exchange. However, the most likely reason for the increase of the rate of mass exchange in low-mass X-ray binary systems is probably the increase of magnetic braking.
We review modern concepts in the physics and evolution of close binary stars. The review is based, on the one hand, on numerical simulations of the evolution of their components and the processes ...that accompany that evolution and, on the other hand, on the entire set of observational information in all ranges of electromagnetic and gravitation-wave radiation. These concepts underlie modern astrophysics, the most extensive laboratory wherein the properties of matter in the Universe and the Universe itself are explored. We present the modern picture of the evolution of close binary stars, constructing which has been driving progress in the physics and evolution of astronomical objects for the last 50 years.
Abstract
We present an investigation of NGC 2158 using Gaia DR2 data. We identified 800 most likely cluster members with membership probability higher than 90%. The mean proper motions of this object ...are determined as (
μ
x
= −0.203 ± 0.003,
μ
y
= −1.99 ± 0.004) mas yr
−1
. The limiting radius, log(age), and distance of the cluster are obtained as 23.5 arcmin, 9.38 ± 0.04 Gyr, and 4.69 ± 0.22 kpc, respectively. The overall mass function slope (0.93 ± 0.14) is flatter than the Salpeter value (1.35) within the mass range of 1.17–1.44
M
⊙
. This cluster also shows the mass-segregation effect and our study demonstrates that NGC 2158 is a dynamically relaxed open cluster. Using the apex diagram (AD), the apex coordinates of the cluster are obtained in different ways and are examined using the (
μ
U
,
μ
T
) diagram. The best value of the apex coordinates is determined as
A
= 8724 ± 160,
D
= −3661 ± 530. We also determined the orbit of the cluster and found that NGC 2158 moves almost in the solar antapex direction. The resulting spatial velocity of NGC 2158 is 51 km s
−1
. A significant oscillation along the
Z
-coordinate up to 529 pc is detected. Various scenarios regarding the origin of this cluster are also discussed.
This paper continues the search for mechanisms for the formation of free planets and considers the problem of the dynamic capture of a planetary system by the vicinity of a supermassive black hole ...(SMBH) with a mass of one million solar masses. A simplified model of a planetary system is used, which includes a solar-mass parent star, a giant planet with the mass of Jupiter, and
small bodies such as asteroids, comets, and dwarf planets (ACP objects) co-orbital with the giant planet. Statement of numerical simulation is reduced to the problem of four bodies, duplicated
times. The spectra of scattering velocities of the ACP objects are studied depending on the collision parameters: pericentric distance and angle of approach of the planetary system to the SMBH. The effectiveness of the gravitational scattering of the planetary system on the SMBH is noted: up to 50% of all small planetary bodies receive the status of free objects, including ~1% of hypervelocity ACPs with velocities up to a thousand and more kilometers per second. The share of ACP objects destroyed or swallowed by SMBHs is analyzed. We present the estimate for the frequency of collisions of planetary systems with SMBHs, based on which the existence of a well-populated component of free planets, asteroids and comets in dense galactic nuclei is assumed.
Within the framework of the induced stellar wind (ISW) model, the possible evolution of the X-ray binary system Sco X-1 after the formation of a neutron star in it is simulated and theoretically ...reproduced. We showed that, within the allowable limits of the ISW model parameter interval, it is possible to reproduce the system characteristics obtained earlier in the model of incomplete filling of the Roche lobe with a donor—an optical star (with a filling factor of 0.38) by modeling the optical orbital light curves of Sco X-1. The high rate of mass loss by the donor is due to its irradiation with hard radiation arising from accretion onto a neutron star. In the tracks that seem to be the most suitable for the evolution of Sco X-1, we obtained the same filling factor of the Roche lobe by the donor (0.38). According to the results of our calculations, the most probable value of the initial mass of the donor at the time of formation of a neutron star in the system does not greatly exceed its current mass
and can be close to (0.5–0.7)
. The ratio of the donor stellar wind velocity to the parabolic velocity on its surface α
ISW
in our calculations turns out to be close to 0.5–0.6. The main meaning of this parameter in our model is to determine the fraction of the donor matter captured by the accretor. With such
, this fraction is quite large, which is necessary for the appearance of an intense ISW. However, in a real system, there may be processes that increase this fraction even at high wind speeds. Thus, its real rate can be higher than the rate corresponding to values of
obtained by us.
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