Nuclear Star Research Articles

Evidence of Large Recoil Velocity from a Black Hole Merger Signal.

The final black hole left behind after a binary black hole merger can attain a recoil velocity, or a "kick," reaching values up to 5000 km/s. This phenomenon has important implications for gravitational wave astronomy, black hole formation scenarios, testing general relativity, and galaxy evolution. We consider the gravitational wave signal from the binary black hole merger GW200129_065458 (henceforth referred to as GW200129), which has been shown to exhibit strong evidence of orbital precession. Using numerical relativity surrogate models, we constrain the kick velocity of GW200129 to v_{f}∼1542_{-1098}^{+747} km/s or v_{f}≳698 km/s (one-sided limit), at 90% credibility. This marks the first identification of a large kick velocity for an individual gravitational wave event. Given the kick velocity of GW200129, we estimate that there is a less than 0.48% (7.7%) probability that the remnant black hole after the merger would be retained by globular (nuclear star) clusters. Finally, we show that kick effects are not expected to cause biases in ringdown tests of general relativity for this event, although this may change in the future with improved detectors.

The changing-look AGN NGC 1566 in quiescence with XMM-Newton: a nuclear starburst and an AGN competing in power?

ABSTRACT Star formation accretion on to the super massive black holes (SMBHs) and feedback processes link the evolution of galaxies with their SMBHs. X-ray observations in the imaging and spectral regime have revealed to be an important tool to study the connection between nuclear activity and circumnuclear star formation in nearby active galactic nuclei (AGN). X-ray spectral diagnostics can lead to disentangle, which is the ionization mechanism in the central kiloparsecs of nearby AGN. In this paper, we investigate, by means of XMM-Newton observations, the nuclear X-ray emission of the changing-look AGN NGC 1566 during its quiescent state. European Photon Imaging Camera (EPIC) soft X-ray images show an extended arm-like morphology. A detailed analysis of the high-resolution Reflection Grating Spectrometer (RGS) and medium resolution EPIC spectra shows that the material concentrated in the central kiloparsecs region is not in the photoionization-dominated regime while the presence of collisionally ionized plasma is needed to explain the observed spectral features. In the inner region (∼1.5 kpc), the brightness of the collisionally ionized gas is comparable to the brightness of the photoionized gas: the inner region hosts a luminous starburst whose ionized gas shows up bright in the X-rays when the AGN is in quiescence.

Asymmetric nuclear matter and neutron star properties within the extended Brueckner theory

Microscopically, the equation of state (EOS) and other properties of asymmetric nuclear matter at zero temperature have been investigated extensively by adopting the non-relativistic Brueckner-Hartree-Fock (BHF) and the extended BHF approaches by using the self-consistent Green’s function approach or by including a phenomenological three-body force. Once three-body forces are introduced, the phenomenological saturation point is reproduced and the theory is applied to the study of neutron star properties. We can calculate the total mass and radius for neutron stars using various equations of state at high densities in $ \beta$ -equilibrium without hyperons. A comparison with other microscopic predictions based on non-relativistic and density-dependent relativistic mean-field calculations has been done. It is found that relativistic EOS yields however larger mass and radius for neutron star than predictions based on non-relativistic approaches. Also the three-body force plays a crucial role to deduce the theoretical value of the maximum mass of neutron stars in agreement with recent measurements of the neutron star mass.

Nuclear Energy Density Functionals and Neutron Star Properties

Recently, a method based on relativistic nuclear energy density functional (EDF) has been employed to study relations between collective excitations in finite nuclei with the nuclear matter symmetry energy, and the phase transition density nt and pressure Pt at the inner edge separating the liquid core and the solid crust of a neutron star. By using the thermodynamic method, relativistic EDF and experimental data on the properties of charge-exchange dipole transitions, isovector giant dipole and quadrupole resonances and pygmy dipole transitions, the neutron star liquid-to-solid phase transition density and pressure are constrained. The analysis shows that accurate measurements are necessary to further constrain the symmetry energy parameters and the structure of neutron star crust.

Recent Results from the SAFIR Project

The "Seyfert and star formation Activity in the Far-Infrared" (SAFIR) project is aimed at studying the physical nature of the nuclear IR emission and star formation properties of a small sample of nearby Seyfert galaxies observed with the PACS and SPIRE instruments on board the Herschel space observatory. In this paper, we review the achieved results, that reveal the importance of the far-IR range to improve the quality and reliability of the estimates of basic AGN torus parameters, and describe some preliminary outcome from the on-going work on the dust properties of resolved AGN host galaxies.

Temperature and density dependence of asymmetric nuclear matter and protoneutron star properties within an extended relativistic mean field model

The effect of temperature and density dependence of the asymmetric nuclear matter properties is studied within the extended relativistic mean field (ERMF) model, which includes the contribution from the self and mixed interaction terms by using different parametrizations obtained by varying the neutron skin thickness $\Delta$r and $\omega$-meson self-coupling ($\zeta$). We observed that the symmetry energy and its slope and incompressibility coefficients decrease with increasing temperatures up to saturation densities. The ERMF parametrizations were employed to obtain a new set of equations of state (EOS) of the protoneutron star (PNS) with and without inclusion of hyperons. In our calculations, in comparison with cold compact stars, we obtained that the gravitational mass of the protoneutron star with and without hyperons increased by $\sim 0.4M_{\odot}$ and its radius increased by $\sim 3$km. Whereas in case of the rotating PNS, the mass shedding limit decreased with increasing temperature, and this suggested that the keplerian frequency of the PNS, at T = 10 MeV should be smaller by $14-20%$ for the EOS with hyperon, as compared to the keplerian frequency of a cold compact star.

Erratum: Correlation energy of nuclear matter and neutron star masses [Phys. Rev. C81, 048801 (2010)

Erratum: Correlation energy of nuclear matter and neutron star masses [Phys. Rev. C<b>81</b>, 048801 (2010)

Obscured Star Formation in the Central Region of the Dwarf Galaxy NGC 5253

We present Hubble Space Telescope (HST) NICMOS observations (1.1-2.2 μm) and 1.9-4.1 μm spectroscopy of the central region of the dwarf galaxy NGC 5253. The HST NICMOS observations reveal the presence of a nuclear double star cluster separated by 03-04, or 6-8 pc (for a distance d = 4.1 Mpc). The double star cluster, also a bright double source of Paα emission, appears to be coincident with the double radio nebula detected at 1.3 cm. The eastern near-infrared star cluster (C1) is identified with the youngest optical cluster, whereas the western star cluster (C2), although it is almost completely obscured in the optical, becomes the brightest star cluster in the central region of NGC 5253 at wavelengths longer than 2 μm. Both clusters are extremely young, with ages of approximately 3.5 Myr. C2 is more massive than C1 by a factor of 6-20 (MC2 = 7.7 × 105-2.6 × 106 M☉, for a Salpeter initial mass function [IMF] in the mass range 0.1-100 M☉). Analysis of the circumnuclear spectrum excluding C1 and C2, as well as of a number of other near-infrared-selected clusters with a range of (young) ages, suggests that the star formation was triggered across the central regions of the galaxy. We have also modeled the nuclear UV to mid-infrared spectral energy distribution (SED) of NGC 5253 and found that the infrared part is well modeled by a highly obscured (AV = 17 mag) young starburst with a stellar mass consistent with our photometric estimates for C1 and C2. The SED model predicts a moderately bright polycyclic aromatic hydrocarbon (PAH) feature at 3.3 μm that is not detected in our nuclear L-band spectrum. NGC 5253's low metallicity and a top-heavy IMF likely combine to suppress the 3.3 μm PAH emission that is commonly seen in more massive starburst systems.

NEUTRON STARS WITH PARAMETRIZED MESON COUPLINGS

We investigate static properties of nuclear and neutron star matter by using a relativistic mean field theory with parametrized couplings. With a suitable choice of mathematical parameters, the couplings allow one to reproduce results of current quantum hadrodynamics models. For other parametrizations, a better description of bulk properties of nuclear matter is obtained. The formalism is extended to include hyperon and lepton degrees of freedom, and an analysis on the effects of the phenomenological couplings in the fermion populations and mass of neutron stars is performed. The results show a strong similarity between the predictions of ZM-like models and those with exponential couplings. We have observed in particular an extreme sensibility of the predictions of these theories on the specific choice of the values of the binding energy of nuclear matter and saturation density. Additionally, the role of the very intense scalar meson mean field found in the interior of neutron stars in the screening of the nucleon mass is discussed.

Kaon condensation in “nuclear star” matter

The critical density for kaon condensation in “nuclear star” matter is computed up to two-loop order in medium (corresponding to next-to-next-to-leading order in chiral perturbation theory in free space) with a heavy-baryon effective chiral Lagrangian whose parameters are determined from KN scattering and kaonic atom data. To the order considered, the kaon self-energy has highly non-linear density dependence in dense matter. We find that the four-Fermi interaction terms in the chiral Lagrangian play an important role in triggering condensation, predicting for “natural” values of the four-Fermi interactions a rather low critical density, ϱ c < 4 ϱ 0.

Kaon-nucleon scattering from chiral Lagrangians

The s-wave K ± N scattering amplitude is computed up to one-loop order corresponding to next-to-next-to-leading order (or N 2LO in short) in chiral perturbation with a heavy-baryon effective chiral Lagrangian. Constraining the low-energy constants by on-shell scattering lengths, we predict the off-shell s-wave K − N scattering amplitudes relevant to kaonic atoms and K − condensation in “nuclear star” matter. The crossing-even one-loop corrections are found to play an important role in determining the higher-order chiral corrections.

Nuclear space mishaps and Star Wars

Despite the Reagan Administrations public assertions, nuclear technology is increasingly important to the Star Wars program, and its eventual deployment in space will pose serious threats to public health.

Discussion

In the period following the papers on instability among the hot stars of low luminosity, Dr L. Gratton presented a brief account of work in progress on η Carinae by Dr Platseck, Miss Ringuelet, and himself at Córdoba and La Plata. The bright line spectrum of η Carinae is being studied in detail; one interesting observation is that the emission lines of Ti 11 are quite weak as compared to their intensities in novae of comparable excitation. The Balmer lines are also faint. The hydrogen emission lines consist of fairly wide structures upon which are superimposed narrow emission cores, as well as absorption features. The La Plata workers find that the narrow emission lines originate in the nuclear star, while the bright lines that arise from the nebulosity in the immediate vicinity are very wide, their breadths corresponding to a velocity range of 500 to 1000 km./sec. The radial velocities vary greatly from one part of the nebula to another. Gratton and his colleagues believe that η Carinae is actually a member of the Carina O-association upon which it is seen superimposed. The corrected distance modulus of this complex is 12.3 magnitudes, with an uncertainty of less than half a magnitude. It follows that η Carinae at its maximum in 1843 had an absolute magnitude almost certainly exceeding −13, and even now is a fairly luminous object of M = −5 or −6. The La Plata astronomers believe it to be improbable, therefore, that η Carinae is a nova-like variable or a super-nova, but think rather that the object is to be regarded as similar to S Doradus or Hubble's variables in extragalactic nebulae. They comment on the probable membership of both S Doradus and η Carinae in O-associations, and suspect that this connexion may be of great evolutionary significance.

The Spectrum of R Aquarii, 1936-1949.

view Abstract Citations (49) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Spectrum of R Aquarii, 1936-1949. Merrill, Paul W. Abstract Fifty spectrograms of R Aquar , including fifteen with dispersion 10 A/mm, have been obtained from 1936 to 1949. During this interval the red variable has continued to exhibit the striking periodic changes characteristic of Me variables. The "companion" or nuclear star seems to have made little direct contribution to the photographed spectrum. The nebular lines were weak in 1936, increased in intensity toward 1940, and have since remained strong. The radial velocities from various groups of lines were studied in some detail. The displacement of the absorption lines, -22 km/sec, probably represents the actual velocity of the red variable. Emission lines definitely associated with the variable yield a velocity of - 33 km/sec. The nebular lines exhibit variable velocities, those arising in regions of lowest density yielding the largest changes. The curve for X 4363 [0 iii] resembles that of a spectroscopic binary of period 26.7 years, e = 0.5. The orbital interpretation is dubious. R Aquarii might be characterized as a "simmering nova." Publication: The Astrophysical Journal Pub Date: November 1950 DOI: 10.1086/145364 Bibcode: 1950ApJ...112..514M full text sources ADS | data products SIMBAD (1)

Physical Processes in Gaseous Nebulae. XVII. Fluorescence in High-Excitation Planetaries.

view Abstract Citations (6) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Physical Processes in Gaseous Nebulae. XVII. Fluorescence in High-Excitation Planetaries. Menzel, Donald H. ; Aller, Lawrence H. Abstract Some years ago Bowen attributed the appearance of "fractional multiplets" of 0 iii in the spectra of high-excitation planetaries to absorption by 0 m atoms in the 2p2 3~2 level of the X 303.80 "Lyman alpha" radiation of helium. The subsequent cascading of these atoms from 2p3d 3D2 of 0 m back to the ground level via the 2p3p and 2~3S configurations are supposed to produce the observed lines. We have attempted to put this theory on a quantitative basis by setting up the appropriate equations of sta- tistical equilibrium for the excited levels and predicting the relative intensities of the observed ultraviolet lines. A comparison of observed relative intensities with predicted relative intensities yields a con- sistency check on the theory. The populations of the excited levels are found to be 10 4~IoI6 atoms cm3. The intensity of the radiation in the 0 m 303.80 line is from ~ to ~ times greater than that radiated by the nuclear star, which illustrates why permitted lines of 0 rn other than those originating by cascade from 3d~P2, are not observed. The excess is attributed to the concentration of radiation in these lines, by cyclic processes resulting from ionization of He+. We have also shown that theoretically the images of the Bowen lines shoiild be about 5 per cent larger than those of the He ii lines, which is in rough agreement with the observational data. The paper contains tables of the relevant f's and A's computed from approximate wave functions based on Slater's rules Publication: The Astrophysical Journal Pub Date: November 1941 DOI: 10.1086/144350 Bibcode: 1941ApJ....94..436M full text sources ADS | data products SIMBAD (2) Related Materials (17) Part 1: 1937ApJ....85..330M Part 2: 1937ApJ....86...70M Part 3: 1938ApJ....88...52B Part 4: 1938ApJ....88..313M Part 5: 1938ApJ....88..422B Part 6: 1939ApJ....89..587A Part 7: 1939ApJ....90..271B Part 8: 1939ApJ....90..601A Part 9: 1940ApJ....91..307S Part 10: 1940ApJ....92..408H Part 11: 1941ApJ....93..178S Part 12: 1941ApJ....93..195M Part 13: 1941ApJ....93..230M Part 14: 1941ApJ....93..236A Part 15: 1941ApJ....93..244G Part 16: 1941ApJ....94...30M Part 18: 1945ApJ...102..239A