We studied how the neutron star's spin changes with the mass accretion rate in the X-ray binary pulsar A 0535+262. Using the long-term light curve obtained with the MAXI/GSC and the time variation of the pulse period from the Fermi/GBM, we found a clear anti-correlation between the bolometric luminosity and the period derivative. We applied the accretion torque model proposed by Ghosh and Lamb...
Compact objects are an interdisciplinary research subject in high-energy physics, and studying compact objects has become one of the significant concerns in modified gravity theory. Modifications of gravitational theory predict the modified TOV equation, and observations of compact objects allow us to test the theory in a strong and non-perturbative gravitational field. This talk will discuss...
Although the relativistic Bose-Einstein condensates (BEC) of pion and kaon may emerge and impact the equation of state, the behavior of mesons in neutron stars is not well understood. The functional renormalization group (FRG) seems a promising tool to study the BEC formed through a second-order phase transition, where quantum fluctuations should be taken into account. Even in the local...
Since the advent of multi-messenger astronomy, nuclear physics constrains equation of state (EoS) for nuclear matter, particularly within neutron stars. Most studies attempting to impose such constraints have traditionally relied on spherical hydrostatic conditions described by the Tolman-Oppenheimer-Volkoff (TOV) equation. However, observational evidence shows that neutron stars are rotating,...
There emerges strong spatial correlation in dilute neutron matters, which is called "dineutron", and its formation also occurs on the surface of nuclei. For example, 8He can be regarded as $\alpha+^2\mathrm{n}+^2\mathrm{n}$ 3-cluster system and recently, its enhancement was observed in $0_2^+$ state. In this talk, we focus on dineutron-dineutron correlation in $^8\mathrm{He}(0_2^+)$.
We will...
Isospin-equilibrating weak processes, called “Urca" processes, are of fundamental importance in astrophysical environments like (proto-)neutron stars, neutron star mergers, and supernovae. In these environments, matter can reach high temperatures of tens of MeVs and be subject to large magnetic fields. We thus investigate Urca rates at different temperatures and field strengths by performing...
In the gravitational wave event GW170817, observed in 2017, electromagnetic counterparts were identified in a wide range of wavelengths from radio to gamma rays for the first time. A kilonova (AT2017gfo) was detected in visible and infrared bands and powered by the radioactive-decay heat of neutron-rich nuclei synthesized via the rapid neutron-capture process (r-process). Furthermore, heavy...
The neutrino reactions play a pivotal role in determining the dynamics of core-collapse supernovae such as the contraction of the proto-neutron star and the shock wave revival. However, most simulations have not considered the detailed neutrino reactions with light elements, which are found to be abundant in supernovae at subsaturation density [1]. Previous studies have shown the weak...
Supernovae emit their energy mostly as neutrinos. If a galactic supernova occurs, some of thousands of neutrinos are likely to be detected in Super-Kamiokande (SK) for more than a minute. Supernovae have high temperature environments so that beyond standard model particles such as axions are likely to be produced. In this study, we implemented a supernova simulator with the effects of...
There is a limit to the production of neutron-rich nuclei by traditional fusion reactions. Therefore, in recent years, multi-nucleon transfer (MNT) reactions have attracted attention as a method of producing neutron-rich nuclei [1]. However, the reaction mechanism is not yet well understood due to its novelty and complexity. In the future, it will be necessary to estimate the physical quantity...
Nucleosynthesis heavier than iron is critically driven by the rapid neutron capture process (r-process), where atomic nuclei capture neutrons faster than they undergo beta decay. The r-process requires a neutron-rich environment and involves the formation of neutron-rich nuclei. This study investigates the physical properties of neutron-rich nuclei, focusing on octupole deformation and the...
In recent years, the synthesis of new superheavy element (SHE) has been paid attention around the world. When synthesizing SHEs, hot fusion using 48Ca as projectile and actinides as targets is successful for many SHEs up to Og (Z=118) [1,2]. In synthesizing SHEs after Z=119 by hot fusion, if 48Ca is used as projectile, it is necessary to use nuclides after Es (Z=99) as targets. However,...
Prompt follow-up observation of the X-ray transient MAXI J1752−457 with the CubeSat X-ray observatory NinjaSat.
Neutron stars in low-mass X-ray binaries, accreting hydrogen- or helium-rich material from a companion star, frequently exhibit thermonuclear runaways on their surfaces known as Type-I X- ray bursts (XRBs). These bursts are powered by nuclear processes, such as the triple-α process, the αp process, and rapid proton capture process, which play a critical role in model-observation comparisons....
Massive stars ($> 10 M_\odot$) undergo core-collapse supernova explosions at the end of their evolution. These explosions release elements ranging from helium to the iron peak, which are (produced during the stellar evolution) to iron peak elements (synthesized in explosive nucleosynthesis near the supernova core region). Although the explosion mechanism of core-collapse supernovae is not...
The triple-alpha reaction plays a significant role in nucleosynthesis heavier than 12C and concomitant stellar evolution [1]. The reaction rates of this reaction at the helium-burning temperatures, T_9 > 0.1, are dominated by the sequential process via two narrow resonances: alpha+alpha -> 8Be(0+_1: g.s.), 8Be+alpha -> 12C(0+_2: E=0.379 MeV) [2,3], and they have been understood relatively well...
The Urca cooling strength of $^{63}$Fe-$^{63}$Mn exhibits a large range of variation due to the the uncertainty in the spin-parity of ground state of $^{63}$Fe, which is approaching the Island of Inversion at $N=40$, characterized by large nuclear deformation. To investigate the cooling effect on the thermal evolution of neutron star crust, we preformed simulations by using models for...
