Sulfur Administration in Fe–S Cluster Homeostasis

Mitochondria are the key organelles of Fe–S cluster synthesis. They contain the enzyme cysteine desulfurase, a scaffold protein, iron and electron donors, and specific chaperons all required for the formation of Fe–S clusters. The newly formed cluster can be utilized by mitochondrial Fe–S protein synthesis or undergo further transformation. Mitochondrial Fe–S cluster biogenesis components are required in the cytosolic iron–sulfur cluster assembly machinery for cytosolic and nuclear cluster supplies. Clusters that are the key components of Fe–S proteins are vulnerable and prone to degradation whenever exposed to oxidative stress. However, once degraded, the Fe–S cluster can be resynthesized or repaired. It has been proposed that sulfurtransferases, rhodanese, and 3-mercaptopyruvate sulfurtransferase, responsible for sulfur transfer from donor to nucleophilic acceptor, are involved in the Fe–S cluster formation, maturation, or reconstitution. In the present paper, we attempt to sum up our knowledge on the involvement of sulfurtransferases not only in sulfur administration but also in the Fe–S cluster formation in mammals and yeasts, and on reconstitution-damaged cluster or restoration of enzyme’s attenuated activity.

Probing nuclear cluster symmetries through the harmonic oscillator

The present contribution explores the symmetries of the deformed harmonic oscillator for both prolate and oblate deformations. It demonstrates the emergence of clustering from the degeneracies of the deformed harmonic oscillator and the appearance of the cluster structures in the associated densities. The universality of molecular structures is presented, demonstrating that molecular-like exchange of protons and neutrons is encoded into the mean-field. The nature of oblate-like structures is also explored.

Resolving the hyper-triton yield description puzzle in high energy nuclear collisions

The recently developed hadron resonance gas model with multicomponent hard-core repulsion is used to address and resolve the long standing problem to describe the light nuclear cluster multiplicities including the hyper-triton measured by the STAR Collaboration, known as the hyper-triton chemical freeze-out puzzle. An improved description for the hadronic and light nuclear cluster data measured by STAR at the collision energy $$\sqrt{s_{NN}} =200$$ s NN = 200 GeV and by ALICE at $$\sqrt{s_{NN}} =2.76$$ s NN = 2.76 TeV is obtained. This is achieved by applying a new strategy of analyzing the light nuclear cluster data and by using the value for the hard-core radius of the (anti-)$$\varLambda $$ Λ hyperons found in earlier work. One of the most striking results of the present work is that for the most probable scenario of chemical freeze-out for the STAR energy the obtained parameters allow to simultaneously reproduce the values of the experimental ratios $$S_3$$ S 3 and $${\overline{S}}_3$$ S ¯ 3 which were not included in the fit.

Use of Microscopic Theoretical Methods for The Construction of The Nuclear Wavefunction of 7Li

Microscopic theoretical studies of scattering and reaction problems for light nuclei have been extensively carried out using resonating group method. In this paper we have used the nuclear cluster model, the resonating group method, the generator coordinate method and complex generator coordinate technique for the construction of microscopic antisymmetrized nuclear wavefunction of 7Li nucleus. This wavefunction can be further used to calculate the structural properties of the nucleus. The 7Li nucleus in ground state is considered as a nuclear system consisting of three clusters namely an alpha cluster, a deuteron cluster and a neutron cluster. We have chosen spatial, spin and isospin function of cluster internal functions. The arguments of internal wavefunction include the parameter coordinates. These parameters can be adjusted to some extent to obtain predictions close to experimental results. The wavefunction is written using shell model with definite parity and angular momentum. The complex generator coordinate technique allows this wavefunction to write it as an antisymmetrized product of seven single particle functions after inclusion of the wavefunction for the center- of -mass motion

Proximity effect of pair correlation in the inner crust of neutron stars

We study proximity effect of pair correlation in the inner crust of neutron stars by means of the Skyrme-Hartree-Fock-Bogoliubov theory formulated in the coordinate space. We describe a system composed of a nuclear cluster immersed in neutron superuid, which is confined in a spherical box. Using a density-dependent effective pairing interaction which reproduces both the pair gap of neutron matter obtained in ab initio calculations and that of finite nuclei, we analyze how the pair condensate in neutron superuid is affected by the presence of the nuclear cluster. It is found that the proximity effect is characterized by the coherence length of neutron superuid measured from the edge position of the nuclear cluster. The calculation predicts that the proximity effect has a strong density dependence. In the middle layers of the inner crust with baryon density 5 × 10-4 fm-3 ≲ ρb ≲ 2 × 10-2 fm-3, the proximity effect is well limited in the vicinity of the nuclear cluster, i.e. in a sufficiently smaller area than the Wigner-Seitz cell. On the contrary, the proximity effect is predicted to extend to the whole volume of the Wigner-Seitz cell in shallow layers of the inner crust with ρb ≲ 2 × 10-4 fm-3, and in deep layers with ρb ≲ 5 × 10-2 fm-3.

Aligning nuclear cluster orbits with an active galactic nucleus accretion disc

ABSTRACT Active galactic nuclei (AGN) are powered by the accretion of discs of gas on to supermassive black holes (SMBHs). Stars and stellar remnants orbiting the SMBH in the nuclear star cluster (NSC) will interact with the AGN disc. Orbiters plunging through the disc experience a drag force and, through repeated passage, can have their orbits captured by the disc. A population of embedded objects in AGN discs may be a significant source of binary black hole mergers, supernovae, tidal disruption events, and embedded gamma-ray bursts. For two representative AGN disc models, we use geometric drag and Bondi–Hoyle–Littleton drag to determine the time to capture for stars and stellar remnants. We assume a range of initial inclination angles and semimajor axes for circular Keplerian prograde orbiters. Capture time strongly depends on the density and aspect ratio of the chosen disc model, the relative velocity of the stellar object with respect to the disc, and the AGN lifetime. We expect that for an AGN disc density $\rho \gtrsim 10^{-11}{\rm g\, cm^{-3}}$ and disc lifetime ≥1 Myr, there is a significant population of embedded stellar objects, which can fuel mergers detectable in gravitational waves with LIGO-Virgo and LISA.

The Milky Way’s nuclear star cluster: Old, metal-rich, and cuspy

Context. The environment of Sagittarius A* (Sgr A*), the central black hole of the Milky Way, is the only place in the Universe where we can currently study the interaction between a nuclear star cluster and a massive black hole and infer the properties of a nuclear cluster from observations of individual stars. Aims. This work aims to explore the star formation history of the nuclear cluster and the structure of the innermost stellar cusp around Sgr A*. Methods. We combined and analysed multi epoch high quality AO observations. For the region close to Sgr A* we apply the speckle holography technique to the AO data and obtain images that are ≥50% complete down to Ks ≈ 19 within a projected radius of 5″ around Sgr A*. We used H-band images to derive extinction maps. Results. We provide Ks photometry for roughly 39 000 stars and H-band photometry for ∼11 000 stars within a field of about 40″ × 40″, centred on Sgr A*. In addition, we provide Ks photometry of ∼3000 stars in a very deep central field of 10″ × 10″, centred on Sgr A*. We find that the Ks luminosity function (KLF) is rather homogeneous within the studied field and does not show any significant changes as a function of distance from the central black hole on scales of a few 0.1 pc. By fitting theoretical luminosity functions to the KLF, we derive the star formation history of the nuclear star cluster. We find that about 80% of the original star formation took place 10 Gyr ago or longer, followed by a largely quiescent phase that lasted for more than 5 Gyr. We clearly detect the presence of intermediate-age stars of about 3 Gyr in age. This event makes up about 15% of the originally formed stellar mass of the cluster. A few percent of the stellar mass formed in the past few 100 Myr. Our results appear to be inconsistent with a quasi-continuous star formation history. The mean metallicity of the stars is consistent with being slightly super solar. The stellar density increases exponentially towards Sgr A* at all magnitudes between Ks = 15−19. We also show that the precise properties of the stellar cusp around Sgr A* are hard to determine because the star formation history suggests that the star counts can be significantly contaminated, at all magnitudes, by stars that are too young to be dynamically relaxed. We find that the probability of observing any young (non-millisecond) pulsar in a tight orbit around Sgr A* and beamed towards Earth is very low. We argue that typical globular clusters, such as they are observed in and around the Milky Way today, have probably not contributed to the nuclear cluster’s mass in any significant way. The nuclear cluster may have formed following major merger events in the early history of the Milky Way.