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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Smooth Horizonless Geometries Deep Inside the Black-Hole Regime

Here we construct the first family of horizonless supergravity solutions that have the same mass, charges, and angular momenta as general supersymmetric rotating D1 − D5 − P black holes in five dimensions. This family includes solutions with arbitrarily small angular momenta, deep within the regime of quantum numbers and couplings for which a large classical black hole exists. These geometries are well approximated by the black-hole solution, and in particular exhibit the same near-horizon throat. Deep in this throat, the black-hole singularity is resolved into a smooth cap. We also identify the holographically dual states in the $\mathscr{N}$ = (4, 4) D1 − D5 orbifold conformal field theory (CFT). Our solutions are among the states counted by the CFT elliptic genus, and provide examples of smooth microstate geometries within the ensemble of supersymmetric black-hole microstates.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Black-Starting Microgrids Using Inverter-Based Distributed Energy Resources

Recent trends in power systems show increasing deployment of inverter-based distributed energy resources (DERs) at the distribution level. Efforts have also been made to use inverter-based DERs for system restoration of critical sections of distribution feeders. In the past few years, there has been active consideration of using local grid-forming (GFM) DERs, which can form their own voltage and frequency, to black-start microgrids instead of waiting for the bulk system for supply restoration. However, using current-limited inverter-based DERs for black-start operations with high inrush currents can pose some technical challenges. This paper presents detailed electromagnetic transient studies on a digital real-time simulator to assess the operational feasibility of using local inverter-based GFM DERs for microgrid black-start operations as a bottom-up approach instead of a top-down approach where the substation is used to restore critical sections of the feeder. The paper presents key modeling details for distribution system components for studying GFM DER-based microgrid black-start operations. The paper presents simulation results comparing different black-start approaches using GFM DERs for two test systems: i) a simple test microgrid and ii) a real-world utility microgrid currently being designed and deployed by Holy Cross Energy in Colorado.

black start↗
DOE OSTI2012

Gauss-bonnet black holes and possibilities for their experimental search

Corollaries of gravity models with second-order curvature corrections in the form of a Gauss-Bonnet term and possibilities (or impossibilities) for their experimental search or observations are discussed. The full version of the four-dimensional Schwarzschild-Gauss-Bonnet black hole solution and the constraint on the possible minimal black hole mass following from this model are considered. Using our solution as a model for the final stages of Hawking evaporation of black holes with a low initial mass (up to 10{sup 15} g) whose lifetime is comparable to that of our Universe, we have revealed differences in the patterns of evaporation: we have obtained high values of the emitted energy and showed the impossibility of an experimental search for primordial black holes by their evaporation products. Scenarios for the evaporation of Gauss-Bonnet black holes in multidimensional gravity models and possibilities for their experimental search are also discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Model predictions of the results of interferometric observations for stars under conditions of strong gravitational scattering by black holes and wormholes

The characteristic and distinctive features of the visibility amplitude of interferometric observations for compact objects like stars in the immediate vicinity of the central black hole in our Galaxy are considered. These features are associated with the specifics of strong gravitational scattering of point sources by black holes, wormholes, or black-white holes. The revealed features will help to determine the most important topological characteristics of the central object in our Galaxy: whether this object possesses the properties of only a black hole or also has characteristics unique to wormholes or black-white holes. These studies can be used to interpret the results of optical, infrared, and radio interferometric observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Gravitational collapse of dark energy field configurations and supermassive black hole formation

Dark energy is the dominant component of the total energy density of our Universe. The primary interaction of dark energy with the rest of the Universe is gravitational. It is therefore important to understand the gravitational dynamics of dark energy. Since dark energy is a low-energy phenomenon from the perspective of particle physics and field theory, a fundamental approach based on fields in curved space should be sufficient to understand the current dynamics of dark energy. Here, we take a field theory approach to dark energy. We discuss the evolution equations for a generic dark energy field in curved space-time and then discuss the gravitational collapse for dark energy field configurations. We describe the 3 + 1 BSSN formalism to study the gravitational collapse of fields for any general potential for the fields and apply this formalism to models of dark energy motivated by particle physics considerations. We solve the resulting equations for the time evolution of field configurations and the dynamics of space-time. Our results show that gravitational collapse of dark energy field configurations occurs and must be considered in any complete picture of our Universe. We also demonstrate the black hole formation as a result of the gravitational collapse of the dark energy field configurations. The black holes produced by the collapse of dark energy fields are in the supermassive black hole category with the masses of these black holes being comparable to the masses of black holes at the centers of galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Spin and mass of the supermassive black hole in the Galactic Center

A new method for exact determination of the masses and spins of black holes from the observations of quasi-periodic oscillations is discussed. The detected signal from the hot clumps in the accretion plasma must contain modulations with two characteristic frequencies: the frequency of rotation of the black hole event horizon and the frequency of the latitudinal precession of the clump’s orbit. Application of the method of two characteristic frequencies for interpretation of the observed quasi-periodic oscillations from the supermassive black hole in the Galactic center in the X-rays and in the near IR region yields the most exact, for the present, values of the mass and the spin (Kerr parameter) of the Sgr A* black hole: M = (4.2 ± 0.2) × 10{sup 6}M{sub ⊙} and a = 0.65 ± 0.05. The observed quasi-periodic oscillations with a period of about 11.5 min are identified as the black hole event horizon rotation period and those with a period of about 19 min are identified as the latitudinal oscillation period of the hot spot orbits in the accretion disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A microscopic description of black hole evaporation via holography

Here, we propose a description of how a large, cold black hole (black zero-brane) in type IIA superstring theory evaporates into freely propagating D0-branes, by solving the dual gauge theory quantitatively. The energy spectrum of emitted D0-branes is parametrically close to thermal when the black hole is large. The black hole, while initially cold, gradually becomes an extremely hot and stringy object as it evaporates. As it emits D0-branes, its emission rate speeds up and it evaporates completely without leaving any remnant. Hence this system provides us with a concrete holographic description of black hole evaporation without information loss.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

A review of the shear rheology of carbon black suspensions

The microstructural link to the rheology of carbon black suspensions has recently become clear as a result of advances in computational and experimental methods. This understanding reveals the important role of the restructuring, build-up, and break-up of carbon black agglomerates in simple shear, rationalized by a dimensionless balance of the hydrodynamic forces acting to break the agglomerates apart against the cohesive forces holding them together (i.e., the Mason number). The Mason number not only can predict the origin of reversible thixotropy seen in carbon black suspensions observed at higher shear intensities, but can also be used to rationalize the evolution of microstructure at lower shear intensities. This review focuses on carbon black suspension behavior, but the insights derived from carbon black suspensions are broadly applicable to a diverse class of soft matter including colloidal gels relevant to a variety of applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

ADIABATIC BLACK HOLE GROWTH IN SÉRSIC MODELS OF ELLIPTICAL GALAXIES

We have examined the effect of slow growth of a central black hole on spherical galaxies that obey Sérsic or R{sup 1/m} surface-brightness profiles. During such growth the actions of each stellar orbit are conserved, which allows us to compute the final distribution function (DF) if we assume that the initial DF is isotropic. We find that black hole growth leads to a central cusp or “excess light,” in which the surface brightness varies with radius as R{sup −1.3} (with a weak dependence on Sérsic index m), the line-of-sight velocity dispersion varies as R{sup −1/2}, and the velocity anisotropy is β≃−0.24 to −0.28 depending on m. The excess stellar mass in the cusp scales approximately linearly with the black hole mass, and is typically 0.5–0.85 times the black hole mass. This process may strongly influence the structure of nuclear star clusters in spheroidal galaxies if they contain black holes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Upper limit of the viscosity parameter in accretion flows around a black hole with shock waves

Black hole accretion is necessarily transonic; thus, flows must become supersonic and, therefore, sub-Keplerian before they enter into the black hole. The viscous timescale is much longer than the infall timescale close to a black hole. Hence, the angular momentum remains almost constant and the centrifugal force ∼l{sup 2}/r{sup 3} becomes increasingly dominant over the gravitational force ∼1/r{sup 2}. The slowed down matter piles creating an accretion shock. The flow between shock and inner sonic point is puffed up and behaves like a boundary layer. This so-called Comptonizing cloud/corona produces hard X-rays and jets/outflows and, therefore, is an important component of black hole astrophysics. In this paper, we study steady state viscous, axisymmetric, transonic accretion flows around a Schwarzschild black hole. We adopt a viscosity parameter α and compute the highest possible value of α (namely, α{sub cr}) for each pair of two inner boundary parameters (namely, specific angular momentum carried to horizon, l{sub in} and specific energy at inner sonic point, E(x{sub in})) which is still capable of producing a standing or oscillating shock. We find that while such possibilities exist for α as high as α{sub cr}=0.3 in very small regions of the flow parameter space, typical α{sub cr} appears to be about ∼0.05–0.1. Coincidentally, this also happens to be the typical viscosity parameter achieved by simulations of magnetorotational instabilities in accretion flows. We therefore believe that all realistic accretion flows are likely to have centrifugal pressure supported shocks unless the viscosity parameter everywhere is higher than α{sub cr}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Does the intermediate-mass black hole in LEDA 87300 (RGG 118) follow the near-quadratic M{sub bh}–M{sub spheroid} relation?

The mass scaling relation between supermassive black holes and their host spheroids has previously been described by a quadratic or steeper relation at low masses (10{sup 5} < M{sub bh}/M{sub ⊙} ≲ 10{sup 7}). How this extends into the realm of intermediate-mass black holes (10{sup 2} < M{sub bh}/M{sub ⊙} < 10{sup 5}) is not yet clear, although for the barred Sm galaxy LEDA 87300, Baldassare et al. recently reported a nominal virial mass of M{sub bh} = 5 × 10{sup 4} M{sub ⊙} residing in a “spheroid” of stellar mass equal to 6.3 × 10{sup 8} M{sub ⊙}. We point out, for the first time, that LEDA 87300 therefore appears to reside on the near-quadratic M{sub bh}–M{sub sph,*} relation. However, Baldassare et al. modeled the bulge and bar as the single spheroidal component of this galaxy. Here we perform a 3-component bulge+bar+disk decomposition and find a bulge luminosity which is 7.7 times fainter than the published “bulge” luminosity. After correcting for dust, we find that M{sub bulge} = 0.9 × 10{sup 8} M{sub ⊙} and M{sub bulge}/M{sub disk} = 0.04—which is now in accord with ratios typically found in Scd–Sm galaxies. We go on to discuss slight revisions to the stellar velocity dispersion (40 ± 11 km s{sup −1}) and black hole mass (M{sub bh}=2.9{sub −2.3}{sup +6.7}×10{sup 4} f{sub 2.3} M{sub ⊙}) and show that LEDA 87300 remains consistent with the M{sub bh}–σ relation, and also the near-quadratic M{sub bh}–M{sub sph,*} relation when using the reduced bulge mass. LEDA 87300 therefore offers the first support for the rapid but regulated (near-quadratic) growth of black holes, relative to their host bulge/spheroid, extending into the domain of intermediate-mass black holes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Magnetohydrodynamic numerical simulation of wind production from hot accretion flows around black holes at very large radii

Numerical simulations of hot accretion flows around black holes have shown the existence of strong wind. Those works focused only on the region close to the black hole and thus it is unknown whether or where the wind production stops at large radii. To address this question, we have recently performed hydrodynamic (HD) simulations by taking into account the gravitational potential of both the black hole and the nuclear star cluster. The latter is assumed to be proportional to σ{sup 2}ln(r), with σ being the velocity dispersion of stars and r the distance from the center of the galaxy. It was found that when the gravity is dominated by nuclear stars, i.e., outside a radius R{sub A}≡GM{sub BH}/σ{sup 2}, winds can no longer be produced. That work, however, neglects the magnetic field, which is believed to play a crucial dynamical role in the accretion and thus must be taken into account. In this paper, we revisit this problem by performing magnetohydrodynamic (MHD) simulations. We confirm the result of our previous paper, namely that wind cannot be produced in the region R>R{sub A}. Our result, combined with recent results of Yuan et al., indicates that the formula describing the mass flux of wind, M-dot {sub wind}= M-dot {sub BH}(r/20r{sub s}), can only be applied to the region where the black hole potential is dominant. Here M-dot {sub BH} is the mass accretion rate at the black hole horizon and the value of R {sub A} is similar to the Bondi radius.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The role of the Kozai-Lidov mechanism in black hole binary mergers in galactic centers

In order to understand the rate of merger of stellar mass black hole binaries (BHBs) by gravitational wave (GW) emission it is important to determine the major pathways to merger. We use numerical simulations to explore the evolution of BHBs inside the radius of influence of supermassive black holes (SMBHs) in galactic centers. In this region, the evolution of binaries is dominated by perturbations from the central SMBH. In particular, as first pointed out by Antonini and Perets, the Kozai–Lidov mechanism trades relative inclination of the BHB to the SMBH for eccentricity of the BHB, and for some orientations can bring the BHB to an eccentricity near unity. At very high eccentricities, GW emission from the BHB can become efficient, causing the members of the BHB to coalesce. We use a novel combination of two N-body codes to follow this evolution. We are required to simulate small systems to follow the behavior accurately. We have completed 400 simulations that range from ∼300 stars around a 10{sup 3} M{sub ⊙} black hole to ∼4500 stars around a 10{sup 4} M{sub ⊙} black hole. These simulations are the first to follow the internal orbit of a binary near an SMBH while also following the changes to its external orbit self-consistently. We find that this mechanism could produce mergers at a maximum rate per volume of ∼100 Gpc{sup −3} yr{sup −1} or considerably less if the inclination oscillations of the binary remain constant as the BHB inclination to the SMBH changes, or if the binary black hole fraction is small.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Lidov–Kozai Cycles with Gravitational Radiation: Merging Black Holes in Isolated Triple Systems

We show that a black-hole binary with an external companion can undergo Lidov–Kozai cycles that cause a close pericenter passage, leading to a rapid merger due to gravitational-wave emission. This scenario occurs most often for systems in which the companion has a mass comparable to the reduced mass of the binary and the companion orbit has a semimajor axis within a factor of ∼10 of the binary semimajor axis. Using a simple population-synthesis model and three-body simulations, we estimate the rate of mergers in triple black-hole systems in the field to be about six per Gpc{sup 3} per year in the absence of natal kicks during black-hole formation. This value is within the low end of the 90% credible interval for the total black hole–black hole merger rate inferred from the current LIGO results. There are many uncertainties in these calculations, the largest of which is the unknown distribution of natal kicks. Even modest natal kicks of 40 km s{sup −1} will reduce the merger rate by a factor of 40. A few percent of these systems will have eccentricity greater than 0.999 when they first enter the frequency band detectable by aLIGO (above 10 Hz).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

How to Detect Inclined Water Maser Disks (and Possibly Measure Black Hole Masses)

We describe a method for identifying inclined water maser disks orbiting massive black holes and for potentially using them to measure black hole masses. Owing to the geometry of maser amplification pathways, the minority of water maser disks are observable: only those viewed nearly edge-on have been identified, suggesting that an order of magnitude additional maser disks exist. We suggest that inward-propagating masers are gravitationally deflected by the central black hole, thereby scattering water maser emission out of the disk plane and enabling detection. The signature of an inclined water maser disk would be narrow masers near the systemic velocity that appear to emit from the black hole position, as identified by the radio continuum core. To explore this possibility, we present high-resolution (0.″07–0.″17) Very Large Array line and continuum observations of 13 galaxies with narrow water maser emission and show that three are good inclined-disk candidates (five remain ambiguous). For the best case, CGCG 120−039, we show that the maser and continuum emission are coincident to within 3.5 ± 1.4 pc (6.7 ± 2.7 mas). Subsequent very long baseline interferometric maps can confirm candidate inclined disks and have the potential to show maser rings or arcs that provide a direct measurement of black hole mass, although the mass precision will rely on knowledge of the size of the maser disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Minidisk Accretion onto Spinning Black Hole Binaries: Quasi-periodicities and Outflows

We perform a full 3D general relativistic magnetohydrodynamical (GRMHD) simulation of an equal-mass, spinning, binary black hole approaching merger, surrounded by a circumbinary disk and with a minidisk around each black hole. For this purpose, we evolve the ideal GRMHD equations on top of an approximated spacetime for the binary that is valid in every position of space, including the black hole horizons, during the inspiral regime. We use relaxed initial data for the circumbinary disk from a previous long-term simulation, where the accretion is dominated by a m = 1 overdensity called the lump. We compare our new spinning simulation with a previous non-spinning run, studying how spin influences the minidisk properties. We analyze the accretion from the inner edge of the lump to the black hole, focusing on the angular momentum budget of the fluid around the minidisks. We find that minidisks in the spinning case have more mass over a cycle than the non-spinning case. However, in both cases we find that most of the mass received by the black holes is delivered by the direct plunging of material from the lump. We also analyze the morphology and variability of the electromagnetic fluxes, and we find they share the same periodicities of the accretion rate. In the spinning case, we find that the outflows are stronger than the non-spinning case. Our results will be useful to understand and produce realistic synthetic light curves and spectra, which can be used in future observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

BASS. XXXVI. Constraining the Local Supermassive Black Hole–Halo Connection with BASS DR2 AGNs

We investigate the connection between supermassive black holes (SMBHs) and their host dark matter halos in the local universe using the clustering statistics and luminosity function of active galactic nuclei (AGNs) from the Swift/BAT AGN Spectroscopic Survey (BASS DR2). By forward-modeling AGN activity into snapshot halo catalogs from N -body simulations, we test a scenario in which SMBH mass correlates with dark matter (sub)halo mass for fixed stellar mass. We compare this to a model absent of this correlation, where stellar mass alone determines the SMBH mass. We find that while both simple models are able to largely reproduce the abundance and overall clustering of AGNs, the model in which black hole mass is tightly correlated with halo mass is preferred by the data by 1.8 σ . When including an independent measurement on the black hole mass–halo mass correlation, this model is preferred by 4.6 σ . We show that the clustering trends with black hole mass can further break the degeneracies between the two scenarios and that our preferred model reproduces the measured clustering differences on one-halo scales between large and small black hole masses. These results indicate that the halo binding energy is fundamentally connected to the growth of SMBHs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Accretion onto a Supermassive Black Hole Binary before Merger

While supermassive binary black holes (SMBBHs) inspiral toward merger they may also accrete matter from a surrounding disk. To study the dynamics of this system requires simultaneously describing the evolving spacetime and the magnetized plasma. We present the first relativistic calculation simulating two equal-mass, nonspinning black holes as they inspiral from a 20 M (G = c = 1) initial separation almost to merger. Our results imply important observational consequences: for instance, the accretion rate $\dot{M}$ onto the black holes first decreases and then plateaus, dropping by only a factor of ~3 despite the rapid inspiral. An estimated bolometric light curve follows the same profile, suggesting some merging SMBBHs may be significantly luminous past the predicted circumbinary disk decoupling. The minidisks are nonstandard: Reynolds, not Maxwell, stresses dominate, and they oscillate between two states. In one part of the cycle, "sloshing" streams transfer mass between minidisks, carrying kinetic energy at a rate sometimes as high as the peak minidisk bolometric luminosity. We also discover that episodic accretion drives time-varying minidisk tilts. These complex dynamics all contribute to unique cyclical behavior in the light curves of late-time inspiraling SMBBHs. The poloidal magnetic flux on the black holes is roughly constant at a dimensionless level $\phi$ ~ 2–3, but doubles just before merger; for significant black hole spin, this flux predicts powerful jets with variability driven by binary dynamics, another potentially unique electromagnetic signature. This simulation is the first to employ our multipatch infrastructure PATCHWORK MHD, decreasing the computational expense to ~3% of conventional single-grid methods' cost.

79 ASTRONOMY AND ASTROPHYSICS↗