arXiv subjects

Itzhak Goldman

Publications and source records attributed to Itzhak Goldman.

At least 19 recordsLinked to original sources

arXiv2026

Is the Radcliffe wave turbulent?

We use the observed vertical velocity field, of various young tracers of the gas kinematics, obtained by Li and Chen (2022), Konietzka et al. (2024) and Zhu et al. (2024), in order to test for the existence of turbulence. We do so by computing the power spectrum and the structure function of the vertical velocity field. The latter suggest the existence of compressible, Burgers, turbulence. The turbulence timescale on the largest spatial scale is about 500 Myr , implying that the turbulence has been generated 500 Myr ago. The turbulence region depth in a direction perpendicular to the Radcliffe wave direction is about 400 pc.

astro-ph.GA↗

arXiv2026

Small scale turbulence alongside with large scale turbulence in a z=1.87 star Forming Galaxy with outflowing wind, revealed by Multi-point structure functions

Recently, Goldman (2024) obtained evidence for a large scale compressible, Burgers turbulence in the ism of a gravitationally lensed, star-forming galaxy at $z = 1.87$, with an outflowing wind. The turbulent timescale on the largest spatial scale has been found to be ~500 Myr . This together with the large spatial scale of~ 6.4 kpc suggest a large scale generating mechanism (such as tidal interaction or merger) that lasted for ~500 Myr. On the other hand, the outflowing wind is much younger and is probably the result of the intense star formation. Therefore, could it be that the star formation drives also turbulence on small scales? In the present work we utilize multi-point second order structure functions to find whether there exists also a small scale turbulence in this galaxy, and if so, try to identify its drivers. We obtained evidence for small scale turbulence whose largest spatial scale ~240 pc for the nebular gas velocity field and ~ 290 pc$ for the outflowing wind velocity field. These values suggest that stellar sub clumps or giant star clusters with an high concentration of young massive stars could be responsible for both the outflow and for the small scale turbulence.

astro-ph.GA↗

arXiv2024

Evidence for large scale compressible turbulence in the ism of CSWA13, a star-Forming Lensed Galaxy at z = 1.87 with outflowing wind

Recently, Keerthi Vasan G. et al.(2024 presented spatially resolved observations of a wind outflow in CSWA13, a gravitationally lensed Star-Forming galaxy at z = 1.87. The gravitational lensing allowed for a substantially improved spatial and kinematic resolution of the wind and of the nebular gas. In this paper we take advantage of the resolved data to test for the existence of turbulence and to study its nature.We obtained the autocorrelation functions of the two velocity fields, and derived the spatial structure functions of the residual nebular and wind velocities along the major axis of the galaxy. The structure functions, of both velocity fields, reveal the existence of an underlying Burgers power spectrum scaling. This scaling suggests the existence of supersonic compressible turbulence. The autocorrelation functions exhibit correlations over scales comparable to the total extent of the velocity fields. Thus, the turbulence is a large scale one. The turbulent timescale corresponding to the largest scale is about 200 Myr, an order of magnitude larger than the estimated age of the wind and of the young stars. This implies that the turbulence in the ism formed well before the wind and the young stars. Given the large spatial scale of the turbulence, it is plausible that the source of the turbulence is a large scale one e.g. a merger or tidal event that triggered the formation of molecular clouds, in the cores of which, the young stars formed. A steepening of the structure functions on the smaller scales provides an estimate for the effective depth along the line of sight of the turbulent layer. The latter turns out to be about 2kpc

astro-ph.GA↗

arXiv2024

Effects of Neutron-Antineutron Transitions in Neutron Stars

We analyze effects of neutron-antineutron transitions in neutron stars, specifically on (i) cooling, (ii) rotation rate, and (iii) for binary pulsars, the increase in the orbital period. We show that these effects are negligibly small.

hep-ph↗

arXiv2024

Neutron Stars constraints on a late G transition

It has been suggested recently that the Hubble tension could be eliminated by a sharp, $\sim 10\%$ increase of the effective gravitational constant at $z \sim 0.01$. This would decrease the luminosities of type 1a supernovae in just the needed amount to explain the larger value of the Hubble parameter. In the present paper we call attention to a dramatic effect of such transition on neutron stars. A neutron star that existed at $z=0.01$ would contract, conserving the baryon mass but undergoing a mass reduction. We computed neutron star models, with a realistic equation of state, and obtained that this reduction is typically $ 0.04 M_{\odot}$. This amounts to an energy of $7 \times 10^{52}$ erg. The transition will affect {\it all} neutron stars that formed along the history of each galaxy prior to the transition. Given the large number of neutron stars per galaxy, the liberated energy is huge. An estimate of the expected fluxes of neutrinos and x-rays yields values exceeding observational upper limits, thus rendering the late G transition scenario non-viable.

astro-ph.CO↗

arXiv2022

Constraints on Neutron-Mirror-Neutron Oscillation from Neutron Star Cooling

We address a method of limiting neutron-mirror neutron mixing ($ε_{nn'}$) by analyzing its effect on neutron star (NS) heating. This method employs observational bounds on the surface temperature of NSs to constrain $ε_{nn'}$. It has been suggested that the bound obtained this way is so stringent that it would exclude any discovery of $n-n'$ oscillation in the currently planned terrestrial experiments at various laboratories. This conclusion motivated us to critically analyze this suggestion in more detail. In this note, we point out a very interesting new effect present in nearly exact mirror models, which can significantly affect this bound. The new element is that in nearly exact mirror models there is the mirror analog of $β$ decay, i.e. $n' \to p' + e' + \barν'_e$, which creates a cloud of mirror particles $n'$, $p'$, $e'$, $D'$ and He$'$ inside the NS. The resulting $e'$ can "rob" the energy generated by the $n \to n'$ transition from the NS, via $e-e'$ scattering enabled by the presence of a (minute) millicharge in mirror particles. Such a tiny millicharge on mirror particles is highly likely in these models. This results in energy being emitted as unobserved mirror photons via fast mirror bremsstrahlung, whose effect is to relax the stringent bounds on $ε_{nn'}$.

hep-ph↗

arXiv2022

Neutron-Mirror-Neutron Oscillation and Neutron Star Cooling

It was pointed out in a recent paper that the observed cooling rate of old, cold neutron stars (NS) can provide an upper limit on the transition rate of neutron to mirror neutron ($n-n'$). This limit is so stringent that it would preclude any discovery of $n \to n'$ oscillation in the current round of terrestrial searches for the process. Motivated by this crucially important conclusion, we critically analyze this suggestion and note an interesting new effect present in nearly exact mirror models for $n \to n'$ oscillation, which significantly affect this bound. The new element is the $β$ decay $n' \to p'+ e' +\barν'_{e}$, which creates a cloud of mirror particles $n'$, $p'$, $e'$ and $D'$ inside the NS core. The $e'$ can "rob" the energy generated by the $n \to n'$ transition via $e-e'$ scattering enabled by the presence of a (minute) milli-charge in mirror particles. This energy is emitted as unobserved mirror photons via fast mirror bremsstrahlung leading to a relaxation of this upper limit.

hep-ph↗

arXiv2022

Gas accretion onto galaxies and Kelvin-Helmholtz turbulence

Continued star formation over the lifetime of a galaxy suggests that low metalicity gas is steadily flowing in from the circumgalactic medium. Also, cosmological simulations of large-scale structure formation imply that gas is accreted onto galaxies from the halo inside which they formed. Direct observations are difficult, but in recent years observational indications of gas inflows from a circumgalactic medium were obtained. Here we suggest an indirect observational probe: looking for large-scale (exceeding few kpc) turbulence caused by the accretion. As a specific example we consider an accretion flow coplanar with the galaxy disk, and argue that Kelvin-Helmholtz turbulence will be generated. We employ a semi-analytic model of turbulence and derive the expected turbulence power spectrum. The latter turns out to be of a distinctive shape that can be compared with observational power spectra. As an illustrative example we use parameters of the Milky Way galaxy.

astro-ph.GA↗

arXiv2021

Analytic derivation of the inertial range of compressible turbulence

An analytic model for steady state turbulence is employed to obtain the inertial range power spectrum of compressible turbulence. We assume that for homogeneous turbulence, the timescales controlling the energy injected at a given wavenumber from all smaller wave-numbers, are equal for each spatial component. However, the longitudinal component energy is diverted into compression, so the rate controlling the energy that is transferred to all larger wave-numbers by the turbulent viscosity is reduced. The resulting inertial range is a power law with index -2. Indeed such power spectra were observed in various astrophysical settings and also in numerical simulations.

physics.flu-dyn↗

arXiv2021

The power spectrum and structure function of the Gamma Ray emission from the Large Magellanic Cloud

The Fermi-LAT observational data of the diffuse $γ$ ray emission from the Large Magellanic Cloud (LMC), were examined to test for the existence of underlying long range correlations. A statistical test applied to the data indicated that the probability that data are random is $\sim 10^{-99}$. Thus we proceeded and have used the counts-number data to compute 2D spatial autocorrelation, power spectrum, and structure function. The most important result of the present study is a clear indication for large scale spatial underlying correlations. This is evident in {\bf all} the functions mentioned above. The 2D power spectrum has a logarithmic slope of -3 on large spatial scales and a logarithmic slope of -4 on small spatial scales. The structure function has logarithmic slopes equaling 1 and 2 for the large and small scales respectively. The logarithmic slopes of the structure function and the power spectrum are consistent. A plausible interpretation of these results is the existence of a large scale {\it compressible turbulence} with a 3D logarithmic slope of -4 extending over the entire extent of the LMC. This may reflect the fact that the $γ$ Ray emission is in star forming regions, where jets and shocks are abundant. Both the power spectrum and structure function exhibit steeper logarithmic slopes for smaller spatial scales. This is interpreted as an indication that the turbulent region has an effective depth of about 1.5 kpc.

astro-ph.GA↗

arXiv2021

Revisiting the structure function of PSR B0950+08 scintillations

The observational structure function of the scintillations of the radio pulsar PSR B0950+08, was fitted, a decade ago, with a power law with index $1 \pm 0.01$. This was interpreted as an {\em appreciable deviation} from the, commonly observed index of $5/3$, expected for Kolmogorov turbulence. In this paper it is suggested that the observations are consistent with a Kolmogorov turbulence and that the {\em apparent} deviation is due to a turbulent region with an effective depth which is {\em comparable} to the observed lateral scales on the plane of the sky, spanned by the pulsar beam. Alternatively, the fitted index of $1$ is consistent with an underlying compressive turbulence and an even {\it smaller} depth. In the first interpretation the depth is $(5.5 \pm 1.8) \times 10^8 cm$. In the second one, the depth is $\lesssim 4\times 10^7 cm $. These estimates lend support for the existence of extremely thin, ionized scattering screens in the local interstellar cloud, that have been proposed a decade ago.

astro-ph.GA↗

arXiv2020

Astrophysical bounds on mirror dark matter derived from binary pulsars timing data

Mirror Dark Matter (MDM) has been considered as an elegant framework for a particle theory of Dark Matter (DM). It is supposed that there exists a dark sector which is mirror of the ordinary matter. Some MDM models allow particle interactions mirror and ordinary matter, in addition to the gravitational interaction. The possibility of neutron to mirror neutron transition has recently been discussed both from theoretical and experimental perspectives. This paper is based on a previous work in which we obtained stringent upper limits on the possibility of converting neutrons to mirror neutrons in the interiors of neutron stars, by using timing data of binary pulsars. Such a transition would imply mass loss in neutron stars leading to a significant change of orbital period of neutron star binary systems. The observational bounds on the period changes of such binaries, therefore put strong limits on the above transition rate and hence on the neutron -- mirror-neutron mixing parameter $ε'$. Our limits are much stronger than the values required to explain the neutron decay anomaly via $n-n'$ mixing.

astro-ph.HE↗

arXiv2020

Interpretation of the power spectrum of the quiet Sun photospheric turbulence

Observational power spectra of the photospheric magnetic field turbulence, of the quiet-sun, were presented in a recent paper by Abramenko and Yurchyshyn. Here I focus on the power spectrum derived from the observations of the Near InfraRed Imaging Spectrapolarimeter (NIRIS) operating at the Goode Solar Telescope. The latter exhibits a transition from a power law with index $-1.2$ to a steeper power law with index $-2.2$, for smaller spatial scales. The present paper presents an interpretation of this change. Furthermore, this interpretation provides an estimate for the effective width of the turbulent layer probed by the observations. The latter turns out to be practically equal to the depth of the photosphere.

astro-ph.SR↗

arXiv2019

Solar luminosity bounds on mirror matter

We present bounds on mirror dark matter scenario derived by using the effect of mirror matter on the luminosity of the Sun. In the perturbative regime where the mirror matter concentration is small relative to the ordinary matter we estimate the heat transfer from ordinary matter to the mirror sector by simple analytic consideration. That amount of heat transfer is radiated via mirror photons and increases the required energy production in order to maintain the observed luminosity. We then present more detailed numerical calculations of the total amount of this energy transfer.

astro-ph.HE↗

arXiv2019

Bounds on Neutron- Mirror Neutron Mixing from Pulsar Timings and Gravitational Wave Detections

The mass loss in putative neutron star to mixed neutron - mirror neutron star transition implies a significant change of orbital period. The precise constancy of the latter can restrict scenarios recently suggested where neutron to mirror neutron mixing occurring in neutron stars, transforms them into mixed stars helping explain the narrow mass distribution observed for pulsars in binary systems. The observation of a very old millisecond pulsar with a mass of 2 solar masses is an additional strong constraint on the above transition.We also note that the observed gravitational waves signals from neutron-neutron stars merger constrain the neutron to mirror neutron transitions inside neutron stars. These considerations exclude a large region in the $ε'$, $δm'$ plane of the neutron-mirror neutron mixing and mass

hep-ph↗

arXiv2011

Implications of Mirror Dark Matter on Neutron Stars

We study the implications of asymmetric dark matter on neutron stars. we construct a "mixed neutron star" model composed of ordinary baryons and of asymmetric dark matter baryons. We derive the general relativistic structure equations for each specie, the equation for the mass within a given radius, and the redshift as function of radius. We present one specific numerical model as an illustrative example. In this example, the mass of the dark neutron equals half that of the ordinary neutron. The main results are: a total mass of $3.74 M_{\odot}$, a total mass within the neutron-sphere equaling $1.56 M_{\odot}$, the neutrons mass is $1.34 M_{\odot}$, the star radius is 31.9 km, the neutron-sphere radius is 11.1 km, and the redshifts from the neutron-sphere and from the star surface are 0.72, 0.25, respectively. We comment briefly on possible astrophysical implications.

astro-ph.CO↗

arXiv2011

Shock-Generated Turbulence In the Innermost 50 pc of the Galaxy Center

The center of the Milky Way galaxy (MW) is an extreme environment which contains a massive black hole surrounded by a very dense star cluster, two other adjacent star clusters, and a giant molecular cloud which would serve as an incubator to a new generation of stars. The gas and dust in its vicinity are denser by 2-3 orders of magnitude than in other locations in the MW. This is also the case with the magnetic field. The kinematics of the gas is characterized by apparently random, supersonic flows. In this paper we provide observational evidence for the existence of a supersonic turbulence, most likely generated by the shock waves. Moreover, the mere existence of turbulence and its characteristics are shown to be instrumental in testing the validity and consistency of theoretical modeling of the spectra of the gas filaments.

astro-ph.GA↗

arXiv2010

The power spectrum of the residual rotation curve velocity as a probe of past mergers

According to the $ΛCDM$ cosmological framework, galaxies underwent multiple mergers in their history. In this paper we propose to use the power spectrum of the residual fluctuations of the rotation curve velocity as a probe of past mergers. The proposition relies on the assertion that mergers are expected to induce large scale flows and in case of major mergers shocks are induced as well. Instabilities of the large scale flows and shocks could generate a large scale turbulence whose size is comparable to the galactic disk dimensions. We develop expressions relating underlying turbulence spectral function to the observational power spectrum of the residual of the rotation curve velocity. This relation can be used to test whether turbulence exists in a given galaxy. The method is applied to the regular spiral galaxy NGC3198 with the conclusion that it underwent a minor merger about 7 Gyr ago.

astro-ph.GA↗