R-Process with Magnetized Nuclei at Dynamo-Explosive Supernovae and Neutron Star Mergers

Nucleosynthesis at latge magnetic induction levels relevant to core-collapse supernovae and neutron star mergers is considered. For respective magnetic fields of a strength up to ten teratesla, atomic nuclei exhibit a linear magnetic response due to the Zeeman effect. Such nuclear reactivity can be described in terms of magnetic susceptibility. Susceptibility maxima correspond to half-filled shells. The neutron component rises linearly with increasing shell angular momentum, while the contribution of protons grows quadratically due to considerable income from orbital magnetization. For a case j = l + 1/2, the proton contribution makes tens of nuclear magnetons and significantly exceeds the neutron values which give several units. In a case j = l − 1/2, the proton component is almost zero up to the g shell. A noticeable increase in the generation of corresponding explosive nucleosynthetic products with antimagic numbers is predicted for nuclei at charge freezing conditions. In the iron group region, new seeds are also created for the r-process. In particular, the magnetic enhancement of the volume of 44Ti isotopes is consistent with results from observations and indicates the substantial increase in the abundance of the main titanium isotope (48Ti) in the Galaxy’s chemical composition. Magnetic effects are proven to result in a shift of the r-process path towards smaller mass numbers, as well as an increase in the volume of low-mass nuclides in peaks of the r-process nuclei.

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Constraints on the Astrophysical Nature of r-Process Nucleosynthesis Sites from Inhomogeneous Chemical Evolution Models

Publications of the Astronomical Society of Australia ◽

10.1071/as04021 ◽

2004 ◽

Vol 21 (2) ◽

pp. 161-166 ◽

Cited By ~ 2

Author(s):

Dominik Argast ◽

Markus Samland

Keyword(s):

Neutron Star ◽

Chemical Evolution ◽

Core Collapse ◽

Lower Mass ◽

Evolution Study ◽

R Process ◽

First Time

AbstractWe present a detailed inhomogeneous chemical evolution study that considers for the first-time neutron star mergers as major r-process sources, and compare this scenario with the ones in which lower-mass (in the range 8–10 M⊙) or higher-mass core-collapse supernovae (with masses ≥20 M⊙) act as dominant r-process sites. We conclude that it is not possible at present to distinguish between the lower-mass and higher-mass supernovae scenarios within the framework of inhomogeneous chemical evolution. However, neutron-star mergers seem to be ruled out as the dominant r-process source, since their low rates of occurrence would lead to r-process enrichment that is not consistent with observations.

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Properties and Composition of Magnetized Nuclei

Particles ◽

10.3390/particles3020021 ◽

2020 ◽

Vol 3 (2) ◽

pp. 272-277

Author(s):

V.N. Kondratyev

Keyword(s):

Zeeman Effect ◽

Closed Shell ◽

Open Shell ◽

Heavy Ion ◽

Small Mass ◽

Binding Energies ◽

Ion Collisions ◽

Atomic Nuclei ◽

Supernova Explosions ◽

R Process

The properties and mass distribution of the ultramagnetized atomic nuclei which arise in heavy-ion collisions and magnetar crusts, during Type II supernova explosions and neutron star mergers are analyzed. For the magnetic field strength range of 0.1–10 teratesla, the Zeeman effect leads to a linear nuclear magnetic response that can be described in terms of magnetic susceptibility. Binding energies increase for open shell and decrease for closed shell nuclei. A noticeable enhancement in theyield of corresponding explosive nucleosynthesis products with antimagic numbers is predicted for iron group and r-process nuclei. Magnetic enrichment in a sampleof 44Ti corroborate theobservational results and imply a significant increase in the quantity of the main titanium isotope, 48Ti, in the chemical composition of galaxies. The enhancement of small mass number nuclides in the r-process peak may be due to magnetic effects.

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Neutron star mergers versus core-collapse supernovae as dominant r-process sites in the early Galaxy

Astronomy and Astrophysics ◽

10.1051/0004-6361:20034265 ◽

2004 ◽

Vol 416 (3) ◽

pp. 997-1011 ◽

Cited By ~ 231

Author(s):

D. Argast ◽

M. Samland ◽

F.-K. Thielemann ◽

Y.-Z. Qian

Keyword(s):

Neutron Star ◽

Core Collapse ◽

R Process ◽

Early Galaxy

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Neutron star mergers and rare core-collapse supernovae as sources of r-process enrichment in simulated galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa754 ◽

2020 ◽

Vol 494 (4) ◽

pp. 4867-4883 ◽

Cited By ~ 4

Author(s):

Freeke van de Voort ◽

Rüdiger Pakmor ◽

Robert J J Grand ◽

Volker Springel ◽

Facundo A Gómez ◽

...

Keyword(s):

Neutron Star ◽

Milky Way ◽

Small Variation ◽

Abundance Ratio ◽

Core Collapse ◽

Binary Neutron Star ◽

Low Metallicity ◽

Process Event ◽

R Process ◽

Process Elements

ABSTRACT We use cosmological, magnetohydrodynamical simulations of Milky Way-mass galaxies from the Auriga project to study their enrichment with rapid neutron capture (r-process) elements. We implement a variety of enrichment models from both binary neutron star mergers and rare core-collapse supernovae. We focus on the abundances of (extremely) metal-poor stars, most of which were formed during the first ∼Gyr of the Universe in external galaxies and later accreted on to the main galaxy. We find that the majority of metal-poor stars are r-process enriched in all our enrichment models. Neutron star merger models result in a median r-process abundance ratio, which increases with metallicity, whereas the median trend in rare core-collapse supernova models is approximately flat. The scatter in r-process abundance increases for models with longer delay times or lower rates of r-process-producing events. Our results are nearly perfectly converged, in part due to the mixing of gas between mesh cells in the simulations. Additionally, different Milky Way-mass galaxies show only small variation in their respective r-process abundance ratios. Current (sparse and potentially biased) observations of metal-poor stars in the Milky Way seem to prefer rare core-collapse supernovae over neutron star mergers as the dominant source of r-process elements at low metallicity, but we discuss possible caveats to our models. Dwarf galaxies that experience a single r-process event early in their history show highly enhanced r-process abundances at low metallicity, which is seen both in observations and in our simulations. We also find that the elements produced in a single event are mixed with ≈108 M⊙ of gas relatively quickly, distributing the r-process elements over a large region.

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R-Process Nucleosynthesis in Core-Collapse Supernova Explosions and Binary Neutron Star Mergers

Springer Proceedings in Physics - Nuclei in the Cosmos XV ◽

10.1007/978-3-030-13876-9_84 ◽

2019 ◽

pp. 437-440

Author(s):

Toshio Suzuki ◽

Shota Shibagaki ◽

Takashi Yoshida ◽

Toshitaka Kajino ◽

Takaharu Otsuka

Keyword(s):

Neutron Star ◽

Core Collapse ◽

Core Collapse Supernova ◽

Binary Neutron Star ◽

Supernova Explosions ◽

R Process

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Fission fragment distributions and their impact on the r -process nucleosynthesis in neutron star mergers

Physical Review C ◽

10.1103/physrevc.103.025806 ◽

2021 ◽

Vol 103 (2) ◽

Author(s):

J.-F. Lemaître ◽

S. Goriely ◽

A. Bauswein ◽

H.-T. Janka

Keyword(s):

Neutron Star ◽

Fission Fragment ◽

R Process

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A Superfluid Perspective on Neutron Star Dynamics

Universe ◽

10.3390/universe7010017 ◽

2021 ◽

Vol 7 (1) ◽

pp. 17

Author(s):

Nils Andersson

Keyword(s):

Neutron Star ◽

Degrees Of Freedom ◽

Temperature Scale ◽

Fluid System ◽

Fluid Core ◽

State Of Matter ◽

Entrainment Effect ◽

Neutron Component ◽

The Impact

As mature neutron stars are cold (on the relevant temperature scale), one has to carefully consider the state of matter in their interior. The outer kilometre or so is expected to freeze to form an elastic crust of increasingly neutron-rich nuclei, coexisting with a superfluid neutron component, while the star’s fluid core contains a mixed superfluid/superconductor. The dynamics of the star depend heavily on the parameters associated with the different phases. The presence of superfluidity brings new degrees of freedom—in essence we are dealing with a complex multi-fluid system—and additional features: bulk rotation is supported by a dense array of quantised vortices, which introduce dissipation via mutual friction, and the motion of the superfluid is affected by the so-called entrainment effect. This brief survey provides an introduction to—along with a commentary on our current understanding of—these dynamical aspects, paying particular attention to the role of entrainment, and outlines the impact of superfluidity on neutron-star seismology.

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The study of multipeaked type-I X-ray bursts in the neutron star low-mass X-ray binary 4U 1636 − 536 with RXTE

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3539 ◽

2020 ◽

Vol 501 (1) ◽

pp. 168-178

Author(s):

Chen Li ◽

Guobao Zhang ◽

Mariano Méndez ◽

Jiancheng Wang ◽

Ming Lyu

Keyword(s):

Neutron Star ◽

Flux Ratio ◽

Light Curves ◽

Type I ◽

X Ray ◽

Soft State ◽

Peak Flux ◽

Low Mass ◽

Two Peaks ◽

Second Peak

ABSTRACT We have found and analysed 16 multipeaked type-I bursts from the neutron-star low-mass X-ray binary 4U 1636 − 53 with the Rossi X-ray Timing Explorer (RXTE). One of the bursts is a rare quadruple-peaked burst that was not previously reported. All 16 bursts show a multipeaked structure not only in the X-ray light curves but also in the bolometric light curves. Most of the multipeaked bursts appear in observations during the transition from the hard to the soft state in the colour–colour diagram. We find an anticorrelation between the second peak flux and the separation time between two peaks. We also find that in the double-peaked bursts the peak-flux ratio and the temperature of the thermal component in the pre-burst spectra are correlated. This indicates that the double-peaked structure in the light curve of the bursts may be affected by enhanced accretion rate in the disc, or increased temperature of the neutron star.

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A Machine Learning Approach For Classifying Low-mass X-ray Binaries Based On Their Compact Object Nature

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3899 ◽

2020 ◽

Author(s):

R Pattnaik ◽

K Sharma ◽

K Alabarta ◽

D Altamirano ◽

M Chakraborty ◽

...

Keyword(s):

Machine Learning ◽

Black Hole ◽

Neutron Star ◽

Binary Systems ◽

Compact Object ◽

X Ray ◽

Average Accuracy ◽

Machine Learning Approach ◽

Low Mass ◽

X Ray Binaries

Abstract Low Mass X-ray binaries (LMXBs) are binary systems where one of the components is either a black hole or a neutron star and the other is a less massive star. It is challenging to unambiguously determine whether a LMXB hosts a black hole or a neutron star. In the last few decades, multiple observational works have tried, with different levels of success, to address this problem. In this paper, we explore the use of machine learning to tackle this observational challenge. We train a random forest classifier to identify the type of compact object using the energy spectrum in the energy range 5-25 keV obtained from the Rossi X-ray Timing Explorer archive. We report an average accuracy of 87±13% in classifying the spectra of LMXB sources. We further use the trained model for predicting the classes for LMXB systems with unknown or ambiguous classification. With the ever-increasing volume of astronomical data in the X-ray domain from present and upcoming missions (e.g., SWIFT, XMM-Newton, XARM, ATHENA, NICER), such methods can be extremely useful for faster and robust classification of X-ray sources and can also be deployed as part of the data reduction pipeline.

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