Dark Dust Research Articles

Novel conservative methods for adaptive force softening in collisionless and multispecies N-body simulations

ABSTRACT Modelling self-gravity of collisionless fluids (e.g. ensembles of dark matter, stars, black holes, dust, and planetary bodies) in simulations is challenging and requires some force softening. It is often desirable to allow softenings to evolve adaptively, in any high-dynamic range simulation, but this poses unique challenges of consistency, conservation, and accuracy, especially in multiphysics simulations where species with different ‘softening laws’ may interact. We therefore derive a generalized form of the energy-and-momentum conserving gravitational equations of motion, applicable to arbitrary rules used to determine the force softening, together with consistent associated time-step criteria, interaction terms between species with different softening laws, and arbitrary maximum/minimum softenings. We also derive new methods to maintain better accuracy and conservation when symmetrizing forces between particles. We review and extend previously discussed adaptive softening schemes based on the local neighbour particle density, and present several new schemes for scaling the softening with properties of the gravitational field, i.e. the potential or acceleration or tidal tensor. We show that the ‘tidal softening’ scheme not only represents a physically motivated, translation and Galilean invariant and equivalence-principle respecting (and therefore conservative) method but also imposes negligible time-step or other computational penalties, ensuring that pairwise two-body scattering is small compared to smooth background forces and can resolve outstanding challenges in properly capturing tidal disruption of substructures (minimizing artificial destruction) while also avoiding excessive N-body heating. We make all of this public in the GIZMO code.

Dark dust

The nature of dust in the diffuse interstellar medium can be best investigated by means of reddening curves where only a single interstellar cloud lies between the observer and the background source. Published reddening curves often suffer from various systematic uncertainties. We merged a sample of 820 reddening curves of stars for which both FORS2 polarization spectra and UVES highresolution spectra are available. The resulting 111 sightlines towards OB-type stars have 175 reddening curves. For these stars, we derived their spectral-type from the UVES high-resolution spectroscopy. To obtain high-quality reddening curves, we excluded stars with composite spectra in the IUE/FUSE data due to multiple stellar systems. Likewise, we omitted stars that have uncertain spectral-type designations or stars with photometric variability. We neglected stars that show inconsistent parallaxes when comparing data releases two and three from Gaia. Finally, we identified stars that show differences in the space- and ground-based-derived reddening curves between 0.28 µm and the U band or in RV. In total, we find 53 stars with one or more reddening curves passing the rejection criteria. This provides the highest-quality Milky Way reddening curve sample available today. Averaging the curves from our high-quality sample, we find RV = 3.1 ± 0.4, confirming previous estimates. A future paper in this series will use the current sample of precise reddening curves and combine them with polarization data to study the properties of dark dust.

Novel theorems for a Bochner flat Lorentzian K[formula omitted]hler space-time manifold with [formula omitted]-Ricci-Yamabe solitons

In the current work, we examine η-Ricci-Yamabe solitons in a Bochner flat Lorentzian Ka¨hler space-time manifolds. We have addressed various circumstances for Ricci-Yamabe solitons to be steady, shrinking or expanding in terms of isotropic pressure, the cosmological constant, energy density and gravitational constant in different perfect fluids such as dark fluid, Stiff matter, dust fluid and radiation fluid.

Dark dust

Distance estimates derived from spectroscopy or parallax have been unified by considering extinction by large grains. The addition of such a population of what is called dark dust to models of the diffuse interstellar medium is tested against a contemporary set of observational constraints. By respecting representative solid-phase element abundances, the dark dust model simultaneously explains the typical wavelength-dependent reddening, extinction, and emission of polarised and unpolarised light by interstellar dust particles between far-UV and millimeter wavelengths. The physical properties of dark dust were derived. Dark dust consists of micrometer-sized particles. These particles have recently been detected in situ. Dark dust provides significant wavelength-independent reddening from the far-UV to the near-infrared. Light absorbed by dark dust is re-emitted in the submillimeter region by grains at dust temperatures of 8–12 K. This very cold dust has frequently been observed in external galaxies. Dark dust contributes to the polarisation at ≳1 mm to ~35% and marginally at shorter wavelengths. Optical constants for silicate dust analogous were investigated. By mixing 3% in mass of Mg0.8Fe0.22+ SiO3 to MgO−0.5 SiO2, a good fit to the data was derived that can still accommodate up to 5–10% of mass in dark dust. The additional diming of light by dark dust is unexplored when supernova Ia light curves are discussed and in other research. Previous models that ignored dark dust do not account for the unification of the distance scales.

IDENTIFICATION OF YOUNG STAR OBJECTS NEAR DUST BUBBLE N10

Over the past decade, the most important observations of the interstellar medium have been made in the infrared and radio regions of electromagnetic radiation. Of particular interest were GLIMPSE (Galactic Legacy Infrared Midplane Survey Extraordinaire), MIPSGAL and WISE (Wide-field Infrared Survey Explorer) surveys of several areas of star formation. Distinctive features of the infrared view of the Galactic disk at wavelengths from 3.4 μm to 22 μm include regions of ionized hydrogen HII, infrared bubbles, young stellar objects, massive star formation, infrared dark clouds, diffuse dust, include hydrocarbons and radiation from millions of stars. Based on current literature, infrared signatures in hot regions around young massive stars have been identified as dust bubbles, so in this paper, the regions around bubble N10, one of the northern infrared bubbles included in Churchwell's catalog, were investigated. Using archival data from the WISE and 2MASS catalogs, we searched for candidates for young stellar objects around the N10 dust bubble and found 117 emission objects. Koenig et al. (2014) plotted diagrams of their color indices and energy distribution in the spectrum for each studied object under different classification conditions. According to the results of studies around the infrared dust bubble N10, objects at an early stage of evolution were discovered: 13 objects are young class I stars and 13 objects are young class II stars, 3 objects are classified as transitional disks.

Imprints of decaying dark matter on cosmic voids

The Standard Cosmological Model assumes that more than 85\% of matter is in the form of collisionless and pressureless dark matter. Unstable decaying dark matter has been proposed in the literature as an extension to the standard cold dark matter model. In this paper we investigate a scenario when dark matter decays and the resultant particle moves with respect to the dark matter. A covariant hydrodynamical model is developed in which the decay is modeled by the transfer of energy-momentum between two dark dust fluid components. We parameterise the model in terms of the decay rate $\Gamma$ and injection velocity $v_i$ of the resultant dark matter particles. We apply the framework to study the evolution of cosmic voids which are environments with low content of baryonic matter. Thus, unlike baryon-rich environments, voids provide an opportunity to measure dark matter signals that are less contaminated by complex baryonic processes. We find that the growth of S-type voids is modified by the dark matter decay, leading to imprints at the present day. This paper serves as a proof-of-concept that cosmic voids can be used to study dark mater physics. We argue that future cosmological observations of voids should focus on signs of reported features to either confirm or rule out the decaying dark matter scenario. Lack of presence of reported features could put constraints of the decay of dark matter in terms of $\Gamma > H_0^{-1}$ and $v_i<10$ km/s.

The Coma Dust of Comet C/2013 US10 (Catalina): A Window into Carbon in the Solar System

Abstract Comet C/2013 US10 (Catalina) was a dynamically new Oort cloud comet whose apparition presented a favorable geometry for observations near close-Earth approach (≃0.93 au) at heliocentric distances ≲2 au when insolation and sublimation of volatiles drive maximum activity. Here we present mid-infrared 6.0 ≲ λ(μm) ≲ 40 spectrophotometric observations at two temporal epochs from NASA’s Stratospheric Observatory for Infrared Astronomy and the NASA Infrared Telescope Facility that yield an inventory of the refractory materials and their physical characteristics through thermal modeling analysis. The grain composition is dominated by dark dust grains (modeled as amorphous carbon) with a silicate-to-carbon ratio ≲0.9, little crystalline stoichiometry (no distinct 11.2 μm feature attributed to Mg-rich crystalline olivine), and the submicron grain-size distribution peaking at ≃0.6 μm. The 10 μm silicate feature was weak, ≈12.8% ± 0.1% above the local continuum, and the bolometric grain albedo was low (≲14%). Comet C/2013 US10 (Catalina) is a carbon-rich object. This material, which is well represented by the optical constants of amorphous carbon, is similar to the material that darkens and reddens the surface of comet 67P/Churyumov–Gerasimenko. We argue this material is endemic to the nuclei of comets, synthesizing results from the study of Stardust samples, interplanetary dust particle investigations, and micrometeoritic analyses. The atomic carbon-to-silicate ratio of comet C/2013 US10 (Catalina) and other comets joins a growing body of evidence suggesting the existence of a C/Si gradient in the primitive solar system, providing new insight into planetesimal formation and the distribution of isotopic and compositional gradients extant today.

Cosmological exact solution of Petrov type D of a mixture of fluids of dark energy and dust and a non disrupted primordial magnetic field

Cosmological exact solution of Petrov type D of a mixture of fluids of dark energy and dust and a non disrupted primordial magnetic field

Dark dust and single-cloud sightlines in the ISM

The precise characteristics of clouds and the nature of dust in the diffuse interstellar medium can only be extracted by inspecting the rare cases of single-cloud sightlines. In our nomenclature such objects are identified by interstellar lines, such as K I, that show at a resolving power of λ∕Δλ ~ 75 000 one dominating Doppler component that accounts for more than half of the observed column density. We searched for such sightlines using high-resolution spectroscopy towards reddened OB stars for which far-UV extinction curves are known. We compiled a sample of 186 spectra, 100 of which were obtained specifically for this project with UVES. In our sample we identified 65 single-cloud sightlines, about half of which were previously unknown. We used the CH/CH+ line ratio of our targets to establish whether the sightlines are dominated by warm or cold clouds. We found that CN is detected in all cold (CH/CH+ &gt; 1) clouds, but is frequently absent in warm clouds. We inspected the WISE (3−22 μm) observed emission morphology around our sightlines and excluded a circumstellar nature for the observed dust extinction. We found that most sightlines are dominated by cold clouds that are located far away from the heating source. For 132 stars, we derived the spectral type and the associated spectral type-luminosity distance. We also applied the interstellar Ca II distance scale, and compared these two distance estimates with Gaia parallaxes. These distance estimates scatter by ~40%. By comparing spectral type-luminosity distances with those of Gaia, we detected a hidden dust component that amounts to a few mag of extinction for eight sightlines. This dark dust is populated by ≳ 1 μm large grains and predominately appears in the field of the cold interstellar medium.

Shadow Images of a Rotating Dyonic Black Hole with a Global Monopole Surrounded by Perfect Fluid

In this paper, we revisit the rotating global monopole metric and extend the metric to a rotating dyonic global monopole in the presence of a perfect fluid. We then show that the surface topology at the event horizon, related to the metric computed, is a 2-sphere using the Gauss-Bonnet theorem. By choosing ω = − 1 / 3 , 0 , 1 / 3 we investigate the effect of dark matter, dust and radiation on the silhouette of a black hole. The presence of the global monopole parameter γ and the perfect fluid parameters υ also deform the shape of a black hole’s shadow, which has been depicted through graphical illustrations. Finally, we analyse the energy emission rate of a rotating dyonic global monopole surrounded by perfect fluid with respect to parameters.

Improvement of the shadow tracking setup as a method to measure the velocities values of dark dust in order to reduce the risks of radioactive releases or explosions

The mobilisation of dust is a key security issue in nuclear and industrial plants because it can provoke both explosions (in particular temperature and pressure conditions) and dangerous radioactive releases. This work is focused on the tungsten dust resuspension inside small tank for aerosol removal and DUST (STARDUST)-Upgrade, an experimental facility used to reproduce different conditions typical of the loss of vacuum accidents. In this paper, the authors present the facility and the materials used to mount the experimental setup together with the methods and algorithms implemented to track the dust velocity vectors. Tungsten dust is also analyzed through scanning electron microscopy and X-ray diffraction to find some correlation between the variation of the dust morphology, due to the different experimental conditions, with the dust mobilisation paths. The materials and methods together with the experimental results are analyzed and discussed to demonstrate the implementation with the shadow tracking setup presented in the previous facility STARDUST.

History of globulettes in the Milky Way

Globulettes are small (radii {<} 10 kAU) dark dust clouds, seen against the background of bright nebulae. A majority of the objects have planetary mass. These objects may be a source of brown dwarfs and free floating planetary mass objects in the galaxy. In this paper we investigate how many globulettes could have formed in the Milky Way and how they could contribute to the total population of free floating planets. In order to do that we examine H-alpha images of 27 H II regions. In these images, we find 778 globulettes.We find that a conservative value of the number of globulettes formed is 5.7times 10^{10}. If 10% of the globulettes form free floating planets then they have contributed with 5.7times 10^{9} free floating planets in the Milky Way. A less conservative number of globulettes would mean that the globulettes could contribute 2.0times 10^{10} free floating planets. Thus the globulettes could represent a non-negligible source of free floating planets in the Milky Way.

Concurrent Occurrence of Lower Respiratory Aspergillosis and Pneumoconiosis in a Turkey Flock

AbstractThis study describes a concurrent occurrence of lower respiratory aspergillosis and pneumoconiosis in a turkey flock. From one flock of 1000 turkeys, 4 clinically affected turkeys were examined pathologically and microbiologically. Clinically affected turkeys showed anorexia, lethargy, drooping of the wing, vomiting, dyspnea and open-beak breathing, or sudden dead. Gross lesions were observed in the air sacs and lungs which presented white to yellowish granulomas of varying size. Microscopic there was multifocal granulomatous airsacculitis and pneumonia. At the center of the granulomas, fungal hyphae were clearly highlighted in the lungs and air sacs by Gomori methenamie silver (GMS) staining. In the microbiological cultivation of the affected lungs and air sacs, Aspergillus fumigatus was isolated on Sabouraud dextrose agar. Furthermore, dark black dust accumulations were present in the cytoplasm of macrophages or interstitial tissue in the lungs and air sacs. There were also fibrosis and lymphohistiocytic cell infiltrations around the particles. Overall, this study could implicated that pneumoconiosis might be a predisposing factor in the development of respiratory aspergillosis in turkeys.

Independent recruitment of a novel seed dispersal system by camel crickets in achlorophyllous plants.

The seeds of most heterotrophic plants, commonly referred to as dust seeds, are typically dispersed in the air like dust particles. Therefore, little attention has been paid to how seeds of heterotrophic plants are dispersed, owing to the notion that wind dispersal is the dominant strategy. However, inconspicuous but fleshy, indehiscent fruit can be observed in distantly related plants that have independently evolved full heterotrophy. Here I investigated the seed dispersal system in three unrelated fully heterotrophic plants with fleshy, indehiscent fruits (Yoania amagiensis, Monotropastrum humile and Phacellanthus tubiflorus) by direct observation, a differential exclusion experiment of fruit feeders and investigation on seed viability through the digestive tract. The present study revealed that camel crickets are the major seed disperser in three achlorophyllous plants in the study population. This represents the first evidence of seed dispersal by camel crickets in any angiosperm species. These heterotrophic plants grow in the understorey of densely vegetated forests where wind is probably an ineffective seed dispersal agent. Life-history traits of the achlorophyllous plants associated with heterotrophic lifestyles, such as colonization of dark understorey habitats and dust seeds, could facilitate independent recruitment of the novel endozoochorous seed dispersal system by camel crickets.

Darkness without dark matter and energy – generalized unimodular gravity

We suggest a Lorentz non-invariant generalization of the unimodular gravity theory, which is classically equivalent to general relativity with a locally inert (devoid of local degrees of freedom) perfect fluid having an equation of state with a constant parameter w. For the range of w near −1 this dark fluid can play the role of dark energy, while for w=0 this dark dust admits spatial inhomogeneities and can be interpreted as dark matter. We discuss possible implications of this model in the cosmological initial conditions problem. In particular, this is the extension of known microcanonical density matrix predictions for the initial quantum state of the closed cosmology to the case of spatially open Universe, based on the imitation of the spatial curvature by the dark fluid density. We also briefly discuss quantization of this model necessarily involving the method of gauge systems with reducible constraints and the effect of this method on the treatment of recently! suggested mechanism of vacuum energy sequestering.

First detection of equatorial dark dust lane in a protostellar disk at submillimeter wavelength.

In the earliest (so-called "Class 0") phase of Sun-like (low-mass) star formation, circumstellar disks are expected to form, feeding the protostars. However, these disks are difficult to resolve spatially because of their small sizes. Moreover, there are theoretical difficulties in producing these disks in the earliest phase because of the retarding effects of magnetic fields on the rotating, collapsing material (so-called "magnetic braking"). With the Atacama Large Millimeter/submillimeter Array (ALMA), it becomes possible to uncover these disks and study them in detail. HH 212 is a very young protostellar system. With ALMA, we not only detect but also spatially resolve its disk in dust emission at submillimeter wavelength. The disk is nearly edge-on and has a radius of ~60 astronomical unit. It shows a prominent equatorial dark lane sandwiched between two brighter features due to relatively low temperature and high optical depth near the disk midplane. For the first time, this dark lane is seen at submillimeter wavelength, producing a "hamburger"-shaped appearance that is reminiscent of the scattered-light image of an edge-on disk in optical and near infrared light. Our observations open up an exciting possibility of directly detecting and characterizing small disks around the youngest protostars through high-resolution imaging with ALMA, which provides strong constraints on theories of disk formation.

The dusty silhouette jet HH 1019 in the Carina Nebula

We report the discovery in Hubble Space Telescope (HST) images of the new Herbig-Haro jet, HH 1019, located near the Tr 14 cluster in the Carina Nebula. Like other HH jets in the region, this bipolar collimated flow emerges from the head of a dark dust pillar. However, HH 1019 is unique because -- unlike all other HH jets known to date -- it is identified by a linear chain of dark, dusty knots that are seen primarily in silhouette against the background screen of the H II region. Proper motions confirm that these dark condensations move along the jet axis at high speed. [S II] emission traces a highly collimated jet that is spatially coincident with these dust knots. The high extinction in the body of the jet suggests that this outflow has lifted a large amount of dust directly from the disk, although it is possible that it has entrained dust from its surrounding protostellar envelope before exiting the dust pillar. If dust in HH 1019 originates from the circumstellar disk, this provides further evidence for a jet launched from a range of radii in the disk, including those outside the dust sublimation radius. HH 1019 may be the prototype for a new subclass of dusty HH objects seen primarily in extinction against the background screen of a bright H II region. Such jets may be common, but difficult to observe because they require the special condition of a very bright background in order to be seen in silhouette.

Cosmological aspects of a unified dark energy and dust dark matter model

Recently, a model of modified gravity plus single scalar field was proposed, in which the scalar couples both to the standard Riemannian volume form given by the square root of the determinant of the Riemannian metric, as well as to another non-Riemannian volume form given in terms of an auxiliary maximal rank antisymmetric tensor gauge field. This model provides an exact unified description of both dark energy (via dynamically generated cosmological constant) and dark matter (as a “dust” fluid due to a hidden nonlinear Noether symmetry). In this paper, we test the model against Supernovae type Ia experimental data and investigate the future Universe evolution which follows from it. Our results show that this model has very interesting features allowing various scenarios of Universe evolution and in the same time perfectly fits contemporary observational data. It can describe exponentially expanding or finite expanding Universe and moreover, a Universe with phase transition of first kind. The phase transition occurs to a new, emerging at some time ground state with lower energy density, which affects significantly the Universe evolution.

Gaia-ESO Survey: Gas dynamics in the Carina nebula through optical emission lines

We present observations from the Gaia-ESO Survey in the lines of H$\alpha$, [N II], [S II] and He I of nebular emission in the central part of the Carina Nebula. We investigate the properties of the two already known kinematic components (approaching and receding, respectively), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV $>$50 km/s) gas emission. We show that gas giving rise to H$\alpha$ and He I emission is dynamically well correlated, but not identical, to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arises from several distinct shell-like expanding regions, the most evident found around $\eta$ Car, the Trumpler 14 core, and the star WR25. Such "shells" are non-spherical, and show distortions probably caused by collisions with other shells or colder, higher-density gas. Part of them is also obscured by foreground dust lanes, while only very little dust is found in their interior. Preferential directions, parallel to the dark dust lanes, are found in the shell geometries and physical properties, probably related to strong density gradients in the studied region. We also find evidence that the ionizing flux emerging from $\eta$ Car and the surrounding Homunculus nebula varies with polar angle. The high-velocity components in the wings of H$\alpha$ are found to arise from expanding dust reflecting the $\eta$ Car spectrum.

Unified dark energy and dust dark matter dual to quadratic purely kinetic K-essence

We consider a modified gravity plus single scalar-field model, where the scalar Lagrangian couples symmetrically both to the standard Riemannian volume-form (spacetime integration measure density) given by the square root of the determinant of the Riemannian metric, as well as to another non-Riemannian volume-form in terms of an auxiliary maximal-rank antisymmetric tensor gauge field. As shown in a previous paper, the pertinent scalar-field dynamics provides an exact unified description of both dark energy via dynamical generation of a cosmological constant, and dark matter as a “dust” fluid with geodesic flow as a result of a hidden Noether symmetry. Here we extend the discussion by considering a non-trivial modification of the purely gravitational action in the form of $$f(R) = R - \alpha R^2$$ generalized gravity. Upon deriving the corresponding “Einstein-frame” effective action of the latter modified gravity-scalar-field theory we find explicit duality (in the sense of weak versus strong coupling) between the original model of unified dynamical dark energy and dust fluid dark matter, on one hand, and a specific quadratic purely kinetic “k-essence” gravity–matter model with special dependence of its coupling constants on only two independent parameters, on the other hand. The canonical Hamiltonian treatment and Wheeler–DeWitt quantization of the dual purely kinetic “k-essence” gravity–matter model is also briefly discussed.