scholarly journals Nuclear-dominated accretion flows in two dimensions – II. Ejecta dynamics and nucleosynthesis for CO and ONe white dwarfs

2019 ◽  
Vol 488 (1) ◽  
pp. 259-279 ◽  
Author(s):  
Rodrigo Fernández ◽  
Ben Margalit ◽  
Brian D Metzger
Keyword(s):  
White Dwarf ◽  
Rotation Axis ◽  
High Energy ◽  
Two Dimensions ◽  
Electromagnetic Transients ◽  
Fusion Reactions ◽  
Global Models ◽  
Accretion Flows ◽  
Nuclear Fusion Reactions ◽  
Self Gravity

ABSTRACT We study mass ejection from accretion discs formed in the merger of a white dwarf with a neutron star or black hole. These discs are mostly radiatively inefficient and support nuclear fusion reactions, with ensuing outflows and electromagnetic transients. Here we perform time-dependent, axisymmetric hydrodynamic simulations of these discs including a physical equation of state, viscous angular momentum transport, a coupled 19-isotope nuclear network, and self-gravity. We find no detonations in any of the configurations studied. Our global models extend from the central object to radii much larger than the disc. We evolve these global models for several orbits, as well as alternate versions with an excised inner boundary to much longer times. We obtain robust outflows, with a broad velocity distribution in the range 102–104 km s−1. The outflow composition is mostly that of the initial white dwarf, with burning products mixed in at the ${\lesssim } 10\rm {-}30{{\ \rm per\ cent}}$ level by mass, including up to ∼10−2 M⊙ of 56Ni. These heavier elements (plus 4He) are ejected within ≲ 40° of the rotation axis, and should have higher average velocities than the lighter elements that make up the white dwarf. These results are in broad agreement with previous one- and two-dimensional studies, and point to these systems as progenitors of rapidly rising (∼ few day) transients. If accretion on to the central BH/NS powers a relativistic jet, these events could be accompanied by high-energy transients with peak luminosities ∼1047–1050 erg s−1 and peak durations of up to several minutes, possibly accounting for events like CDF-S XT2.

scholarly journals Electromagnetic transients and gravitational waves from white dwarf disruptions by stellar black holes in triple systems

2020 ◽  
Vol 495 (1) ◽  
pp. 1061-1072
Author(s):  
Giacomo Fragione ◽  
Brian D Metzger ◽  
Rosalba Perna ◽  
Nathan W C Leigh ◽  
Bence Kocsis
Keyword(s):  
White Dwarf ◽  
Gamma Ray ◽  
High Energy ◽  
Stellar Mass ◽  
Compact Objects ◽  
Electromagnetic Transients ◽  
Tidal Disruption ◽  
Single Star ◽  
Triple Systems ◽  
Nearby Galaxies

ABSTRACT Mergers of binaries comprising compact objects can give rise to explosive transient events, heralding the birth of exotic objects that cannot be formed through single-star evolution. Using a large number of direct N-body simulations, we explore the possibility that a white dwarf (WD) is dynamically driven to tidal disruption by a stellar-mass black hole (BH) as a consequence of the joint effects of gravitational wave (GW) emission and Lidov–Kozai oscillations imposed by the tidal field of an outer tertiary companion orbiting the inner BH–WD binary. We explore the sensitivity of our results to the distributions of natal kick velocities imparted to the BH and WD upon formation, adiabatic mass loss, semimajor axes and eccentricities of the triples, and stellar-mass ratios. We find rates of WD–tidal disruption events (TDEs) in the range 1.2 × 10−3 − 1.4 Gpc−3 yr−1 for z ≤ 0.1, rarer than stellar TDEs in triples by a factor of ∼3–30. The uncertainty in the TDE rates may be greatly reduced in the future using GW observations of Galactic binaries and triples with LISA. WD–TDEs may give rise to high-energy X-ray or gamma-ray transients of duration similar to long gamma-ray bursts but lacking the signatures of a core-collapse supernova, while being accompanied by a supernova-like optical transient that lasts for only days. WD–BH and WD–NS binaries will also emit GWs in the LISA band before the TDE. The discovery and identification of triple-induced WD–TDE events by future time domain surveys and/or GWs could enable the study of the demographics of BHs in nearby galaxies.

scholarly journals Simulation of Spectra Code (SOS) for ITER Active Beam Spectroscopy

Atoms ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 30 ◽  
Author(s):  
Manfred von Hellermann ◽  
Maarten de Bock ◽  
Oleksandr Marchuk ◽  
Detlev Reiter ◽  
Stanislav Serov ◽  
...  
Keyword(s):  
Charge Exchange ◽  
Stark Effect ◽  
Fusion Reaction ◽  
Line Emission ◽  
High Energy ◽  
Fusion Reactions ◽  
General Applicability ◽  
Generic Structure ◽  
Nuclear Fusion Reactions ◽  
Simulation Of Spectra

The concept and structure of the Simulation of Spectra (SOS) code is described starting with an introduction to the physics background of the project and the development of a simulation tool enabling the modeling of charge-exchange recombination spectroscopy (CXRS) and associated passive background spectra observed in hot fusion plasmas. The generic structure of the code implies its general applicability to any fusion device, the development is indeed based on over two decades of spectroscopic observations and validation of derived plasma data. Four main types of active spectra are addressed in SOS. The first type represents thermal low-Z impurity ions and the associated spectral background. The second type of spectra represent slowing-down high energy ions created from either thermo-nuclear fusion reactions or ions from injected high energy neutral beams. Two other modules are dedicated to CXRS spectra representing bulk plasma ions (H+, D+, or T+) and beam emission spectroscopy (BES) or Motional Stark Effect (MSE) spectrum appearing in the same spectral range. The main part of the paper describes the physics background for the underlying emission processes: active and passive CXRS emission, continuum radiation, edge line emission, halo and plume effect, or finally the charge exchange (CX) cross-section effects on line shapes. The description is summarized by modeling the fast ions emissions, e.g., either of the α particles of the fusion reaction or of the beam ions itself.

scholarly journals Hot laser fusion or low temperature nuclear reactions? Analysis and current prospects of the first experiments on laser fusion

2021 ◽  
Vol 13 (1) ◽  
pp. 59-70
Author(s):  
Vladimir I. Vysotskii ◽  
◽  
Alla A. Kornilova ◽  
Mykhaylo V. Vysotskyy ◽  
◽  
...  
Keyword(s):  
Laser Plasma ◽  
Nuclear Reactions ◽  
Nuclear Fusion ◽  
High Energy ◽  
Laser Fusion ◽  
Neutron Generation ◽  
Fusion Reactions ◽  
Target Composition ◽  
High Energy Tail ◽  
Nuclear Fusion Reactions

The paper considers the features and quantitative characteristics of the first successful laser experiments on the formation of a thermonuclear plasma and registration of neutrons in nuclear fusion reactions under pulsed irradiation of a LiD crystal. Quantitative analysis shows that the production of neutrons recorded in these experiments is not associated with thermonuclear reactions in hot laser plasma. The most probable mechanism of neutron generation is associated with nuclear reactions at low energies and is due to the formation of coherent correlated states (CCS) of deuterons. In this experiment, such states can be formed in two different processes: due to the effect of a shock wave in the undisturbed part of the target lattice on the vibrational state of deuterium nuclei or when deuterium nuclei with energy of about 500 eV move in the lattice. This part of the deuterium nuclei corresponds to the high-energy "tail" of the Maxwellian distribution of the total flux of particles entering from the laser plasma into the interplanar channel. In this second case, the process of the formation of the CCS is associated with the longitudinal periodicity of the interplanar crystal channel, which is equivalent to a nonstationary oscillator in the own coordinate system of moving particle. The expediency of repeating these experiments is shown, in which, in addition to neutrons, one should expect a more efficient generation of other nuclear fusion products due to low-energy reactions involving lithium isotopes from the target composition.

scholarly journals Significantly super-Chandrasekhar mass-limit of white dwarfs in noncommutative geometry

2021 ◽  
Vol 30 (05) ◽  
pp. 2150034
Author(s):  
Surajit Kalita ◽  
Banibrata Mukhopadhyay ◽  
T. R. Govindarajan
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Compact Object ◽  
Type Ia Supernovae ◽  
Mass Limit ◽  
Fusion Reactions ◽  
Standard Candle ◽  
Type Ia ◽  
Nuclear Fusion Reactions ◽  
Ia Supernovae

Chandrasekhar made the startling discovery about nine decades back that the mass of compact object white dwarf has a limiting value once nuclear fusion reactions stop therein. This is the Chandrasekhar mass-limit, which is [Formula: see text] for a nonrotating non-magnetized white dwarf. On approaching this limiting mass, a white dwarf is believed to spark off with an explosion called type Ia supernova, which is considered to be a standard candle. However, observations of several over-luminous, peculiar type Ia supernovae indicate the Chandrasekhar mass-limit to be significantly larger. By considering noncommutativity among the components of position and momentum variables, hence uncertainty in their measurements, at the quantum scales, we show that the mass of white dwarfs could be significantly super-Chandrasekhar and thereby arrive at a new mass-limit [Formula: see text], explaining a possible origin of over-luminous peculiar type Ia supernovae. The idea of noncommutativity, apart from the Heisenberg’s uncertainty principle, is there for quite sometime, without any observational proof however. Our finding offers a plausible astrophysical evidence of noncommutativity, arguing for a possible second standard candle, which has many far-reaching implications.

New approach to elucidating the physical nature of the processes that occur in the friction zone of mates of machine parts

2020 ◽  
Vol 98 (4) ◽  
pp. 13-19
Author(s):  
V. Aulin ◽  
S. Lysenko ◽  
A. Hrinkiv ◽  
A. Chernai ◽  
I. Zhylova ◽  
...  
Keyword(s):  
Friction And Wear ◽  
Physical Nature ◽  
High Energy ◽  
Unstable State ◽  
Fusion Reactions ◽  
Surface Layers ◽  
Tribochemical Reactions ◽  
Subsequent Transformation ◽  
Nuclear Fusion Reactions ◽  
Mechanocaloric Effect

It has been found that during frictional contact in separate local areas of a thin surface layer of parts under significant loads and deformations and high contact temperatures, the material of the tribocontact zone of parts transforms into a special activating unstable state of magma-plasma or triboplasma. General issues in which the nature of the processes of friction and wear of mating parts is clarified are considered at a higher fundamental level with the involvement of nanotribology. A number of processes that accompany interactions of triboconjugations of parts are analyzed: mechanoemission, mechanochemical, gas-discharge, etc., tribochemical reactions, fluxes of high-energy particles: excited molecules, atoms, ions, fast electrons, phonons (sound quanta and quanta of electromagnetic radiation). Regularities of additivity of elastic and magnetic aftereffect in the volumetric parts and surface layers of tribo-interface parts made of ferromagnetic materials and alloys have been revealed. Also, the regularity of the additivity of the diffusion aftereffect in their surface layers has been established. A tribophysical model of self-organization is built on the basis of a carbon-nitrogen cycle of tribochemical reactions that have the content of thermonuclear fusion reactions and which can be considered at the nanoscale. In these reactions, the carbon atom plays the role of a catalyst for the process of fusion of protons with subsequent transformation into a radioactive isotope, which decays into ordinary carbon and helium. It has been established that the mechanism of nuclear fusion reactions in the surface layers of triboconjugation parts is due to the directional movement of dislocations in the crystal structures of materials with the implementation of the proton cycle and the conversion of hydrogen into helium. It has been shown that this makes it possible to change the idea of the mechanocaloric effect, the process of friction and wear, and to substantiate a number of effects and processes from the physical positions of nanotribology. This will allow the creation of competitive tribotechnologies in various industries.

Status of muon catalysis of nuclear fusion reactions

1990 ◽  
Vol 160 (8) ◽  
pp. 47-103 ◽  
Author(s):  
Leonid I. Men'shikov ◽  
L.N. Somov
Keyword(s):  
Nuclear Fusion ◽  
Fusion Reactions ◽  
Nuclear Fusion Reactions ◽  
Muon Catalysis

Proposed Solutions to Achieve Nuclear Fusion

Engevista ◽  
2017 ◽  
Vol 19 (5) ◽  
pp. 1496
Author(s):  
Relly Victoria Virgil Petrescu ◽  
Raffaella Aversa ◽  
Antonio Apicella ◽  
Florian Ion Petrescu
Keyword(s):  
Nuclear Reactor ◽  
Nuclear Reactions ◽  
Nuclear Fusion ◽  
Nuclear Fission ◽  
Light Nuclei ◽  
Fast Neutrons ◽  
Fusion Reactions ◽  
Nuclear Fusion Reactions ◽  
The Masses ◽  
Fusion Products

Despite research carried out around the world since the 1950s, no industrial application of fusion to energy production has yet succeeded, apart from nuclear weapons with the H-bomb, since this application does not aims at containing and controlling the reaction produced. There are, however, some other less mediated uses, such as neutron generators. The fusion of light nuclei releases enormous amounts of energy from the attraction between the nucleons due to the strong interaction (nuclear binding energy). Fusion it is with nuclear fission one of the two main types of nuclear reactions applied. The mass of the new atom obtained by the fusion is less than the sum of the masses of the two light atoms. In the process of fusion, part of the mass is transformed into energy in its simplest form: heat. This loss is explained by the Einstein known formula E=mc2. Unlike nuclear fission, the fusion products themselves (mainly helium 4) are not radioactive, but when the reaction is used to emit fast neutrons, they can transform the nuclei that capture them into isotopes that some of them can be radioactive. In order to be able to start and to be maintained with the success the nuclear fusion reactions, it is first necessary to know all this reactions very well. This means that it is necessary to know both the main reactions that may take place in a nuclear reactor and their sense and effects. The main aim is to choose and coupling the most convenient reactions, forcing by technical means for their production in the reactor. Taking into account that there are a multitude of possible variants, it is necessary to consider in advance the solutions that we consider them optimal. The paper takes into account both variants of nuclear fusion, and cold and hot. For each variant will be mentioned the minimum necessary specifications.

scholarly journals Understanding the origin of the positron annihilation line and the physics of supernova explosions

2021 ◽  
Author(s):  
F. Frontera ◽  
E. Virgilli ◽  
C. Guidorzi ◽  
P. Rosati ◽  
R. Diehl ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Large Scale ◽  
Gamma Ray ◽  
Nuclear Astrophysics ◽  
High Energy ◽  
Radioactive Isotopes ◽  
Fusion Reactions ◽  
Dark Matter Annihilation ◽  
Annihilation Line ◽  
Supernova Explosions

AbstractNuclear astrophysics, and particularly nuclear emission line diagnostics from a variety of cosmic sites, has remained one of the least developed fields in experimental astronomy, despite its central role in addressing a number of outstanding questions in modern astrophysics. Radioactive isotopes are co-produced with stable isotopes in the fusion reactions of nucleosynthesis in supernova explosions and other violent events, such as neutron star mergers. The origin of the 511 keV positron annihilation line observed in the direction of the Galactic Center is a 50-year-long mystery. In fact, we still do not understand whether its diffuse large-scale emission is entirely due to a population of discrete sources, which are unresolved with current poor angular resolution instruments at these energies, or whether dark matter annihilation could contribute to it. From the results obtained in the pioneering decades of this experimentally-challenging window, it has become clear that some of the most pressing issues in high-energy astrophysics and astro-particle physics would greatly benefit from significant progress in the observational capabilities in the keV-to-MeV energy band. Current instrumentation is in fact not sensitive enough to detect radioactive and annihilation lines from a wide variety of phenomena in our and nearby galaxies, let alone study the spatial distribution of their emission. In this White Paper (WP), we discuss how unprecedented studies in this field will become possible with a new low-energy gamma-ray space experiment, called ASTENA (Advanced Surveyor of Transient Events and Nuclear Astrophysics), which combines new imaging, spectroscopic and polarization capabilities. In a separate WP (Guidorzi et al. 39), we discuss how the same mission concept will enable new groundbreaking studies of the physics of Gamma–Ray Bursts and other high-energy transient phenomena over the next decades.

OBSERVATIONAL CONSTRAINTS ON STRONG GRAVITY

2011 ◽  
Vol 20 (14) ◽  
pp. 2755-2760
Author(s):  
CHRIS DONE
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Strong Field ◽  
Field Tests ◽  
High Energy ◽  
Observational Constraints ◽  
Tests Of General Relativity ◽  
Strong Gravity ◽  
Accretion Flows ◽  
Spacetime Curvature

Accretion onto a black hole transforms the darkest objects in the universe to the brightest. The high energy radiation emitted from the accretion flow before it disappears forever below the event horizon lights up the regions of strong spacetime curvature close to the black hole, enabling strong field tests of General Relativity. I review the observational constraints on strong gravity from such accretion flows, and show how the data strongly support the existence of such fundamental General Relativistic features of a last stable orbit and the event horizon. However, these successes also imply that gravity does not differ significantly from Einstein's predictions above the event horizon, so any new theory of quantum gravity will be very difficult to test.

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