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At least 973 records · Page 54
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DOE OSTI2019

Mass of dyonic black holes and entropy super-additivity

We study extremal static dyonic black holes in four-dimensional Einstein–Maxwell–Dilaton theory, for general values of the constant a in the exponential coupling e aΦ of the dilaton to the Maxwell kinetic term. Explicit solutions are known only for a = 0, a = 1 and a=$\sqrt3$, and for general a when the electric and magnetic charges Q and P are equal. We obtain solutions as power series expansions around Q = P, in terms of a small parameter c=a -1 log(Q/P). Using these, and also solutions constructed numerically, we test a relation between the mass and the charges that had been conjectured long ago by Rasheed. We find that although the conjecture is not exactly correct it is in fact quite accurate for a wide range of the black hole parameters. We investigate some improved conjectures for the mass relation. We also study the circumstances under which entropy super-additivity, which is related to Hawking's area theorem, is violated. This extends beyond previous examples exhibited in the literature for the particular case of a=$\sqrt3$ dyonic black holes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Melanopogenesis: dark matter of (almost) any mass and baryonic matter from the evaporation of primordial black holes weighing a ton (or less)

The evaporation of primordial black holes with a mass in the 1 gram≲ MPBH≲1000 kg range can lead to the production of dark matter particles of almost any mass in the range 0.1 MeV≲ m DM ≲ 10 18 GeV with the right relic density at very early times, τ≲ 10 -10 s. We calculate, as a function of the primordial black holes mass and initial abundance, the combination of dark matter particle masses and number of effective dark degrees of freedom leading to the right abundance of dark matter today, whether or not evaporation stops around the Planck scale. In addition, since black hole evaporation can also lead to the production of a baryon asymmetry, we calculate where dark matter production and baryogenesis can concurrently happen, under a variety of assumptions: baryogenesis via grand unification boson decay, via leptogenesis, or via asymmetric co-genesis of dark matter and ordinary matter. Finally, we comment on possible ways to test this scenario.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Stability of hairy black holes in shift-symmetric scalar-tensor theories via the effective field theory approach

Shift-symmetric Horndeski theories admit an interesting class of Schwarzschild-de Sitter black hole solutions exhibiting time-dependent scalar hair. The properties of these solutions may be studied via a bottom-up effective field theory (EFT) based on the background symmetries. This is in part possible by making use of a convenient coordinate choice — Lemaître-type coordinates — in which the profile of the Horndeski scalar field is linear in the relevant time coordinate. We construct this EFT, and use it to understand the stability of hairy black holes in shift-symmetric Horndeski theories, providing a set of constraints that the otherwise-free functions appearing in the Horndeski Lagrangian must satisfy in order to admit stable black hole solutions. The EFT is analyzed in the decoupling limit to understand potential sources of instability. Further, we also perform a complete analysis of the EFT with odd-parity linear perturbations around general spherically symmetric space-time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Neutrino and pair creation in reconnection-powered coronae of accreting black holes

A ubiquitous feature of accreting black hole systems is their hard X-ray emission which is thought to be produced through Comptonization of soft photons by electrons and positrons in the vicinity of the black hole, in a region with optical depth of order unity. The origin and composition of this Comptonizing region, known as the corona, is a matter open for debate. In this paper we investigate the role of relativistic protons accelerated in black-hole magnetospheric current sheets for the pair enrichment and neutrino emission of AGN coronae. Our model has two free parameters, namely the proton plasma magnetization σ p , which controls the peak energy of the neutrino spectrum, and the Eddington ratio λ X,Edd (defined as the ratio between X-ray luminosity L X and Eddington luminosity L Edd ), which controls the amount of energy transferred to secondary particles. For sources with λ X,Edd ≳ λ Edd,crit (where λ Edd,crit ∼ 10 -1 for σ p = 10 5 or ∼ 10 -2 for σ p = 10 7 ), proton-photon interactions and γγ annihilation produce enough secondary pairs to achieve Thomson optical depths τ T ∼ 0.1-10. In the opposite case of λ X,Edd ≲ λ Edd,crit , the coronal pairs cannot originate only from hadronic interactions. Additionally, we find that the neutrino luminosity scales as L 2 X /L Edd for λ X,Edd ≲ λ Edd,crit , while it is proportional to L X for higher λ X,Edd values. We apply our model to four Seyfert galaxies, including NGC 1068, and discuss our results in light of recent IceCube observations.

active galactic nuclei↗
DOE OSTI2022

Comptonization by reconnection plasmoids in black hole coronae II: Electron-ion plasma

ABSTRACT We perform 2D particle-in-cell simulations of magnetic reconnection in electron-ion plasmas subject to strong Compton cooling and calculate the X-ray spectra produced by this process. The simulations are performed for trans-relativistic reconnection with magnetization 1 ≤ σ ≤ 3 (defined as the ratio of magnetic tension to plasma rest-mass energy density), which is expected in the coronae of accretion discs around black holes. We find that magnetic dissipation proceeds with inefficient energy exchange between the heated ions and the Compton-cooled electrons. As a result, most electrons are kept at a low temperature in Compton equilibrium with radiation, and so thermal Comptonization cannot reach photon energies $\sim 100\,$ keV observed from accreting black holes. Nevertheless, magnetic reconnection efficiently generates $\sim 100\,$ keV photons because of mildly relativistic bulk motions of the plasmoid chain formed in the reconnection layer. Comptonization by the plasmoid motions dominates the radiative output and controls the peak of the radiation spectrum Epk. We find Epk ∼ 40 keV for σ = 1 and Epk ∼ 100 keV for σ = 3. In addition to the X-ray peak around 100 keV, the simulations show a non-thermal MeV tail emitted by a non-thermal electron population generated near X-points of the reconnection layer. The results are consistent with the typical hard state of accreting black holes. In particular, we find that the spectrum of Cygnus X-1 is well explained by electron-ion reconnection with σ ∼ 3.

Astronomy & Astrophysics↗
DOE OSTI2024

The invisible black widow PSR J1720−0534: implications for the electron density towards the North Polar Spur

Radio emission from pulsars can be used to map out their distances through dispersion measure (DM), which quantifies the amount of radio pulse dispersion. However, this method relies on accurately modelling the free electron density in the line of sight. Here, we present a detailed study of the multiwavelength emission from PSR J1720−0534, a black widow compact binary millisecond pulsar discovered in 2021, which the latest electron density model of the Galaxy places at only 191 pc. We obtained and analysed deep multiwavelength observations in the γ-ray ( Fermi -Large Area Telescope, 2008–2022), optical (Las Cumbres Observatory, 2.7 h), near-infrared (Nordic Optical Telescope, 3.5 h), and X-ray ( Swift -X-Ray Telescope, 10 ks) bands. We found no significant detection of γ-ray, optical, near-infrared, or X-ray counterparts around the radio-timing position of PSR J1720−0534, which we thus nickname ‘the invisible black widow’. Employing the most constraining near-infrared limit ( J > 23.4 mag), we established a lower limit on the source distance, d > 1.1 kpc, assuming conservative properties for the black widow companion star. This distance lower limit differs drastically (by a factor of more than 5) from the Yao et al. DM distance estimate. We attribute this difference to the inclusion in the Yao et al. model of a large and dense component towards the North Polar Spur. Considering our results and recent parallax distances to other pulsars in this direction, we argue that such a local and large component in the electron density model of the Galaxy is unnecessary.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Secularly powered outflows from AGNs: the dominance of non-merger driven supermassive black hole growth

ABSTRACT Recent observations and simulations have revealed the dominance of secular processes over mergers in driving the growth of both supermassive black holes (SMBHs) and galaxy evolution. Here, we obtain narrow-band imaging of AGN powered outflows in a sample of 12 galaxies with disc-dominated morphologies, whose history is assumed to be merger-free. We detect outflows in 10/12 sources in narrow-band imaging of the $\mathrm{[O\, \small {III}] }$ $5007~\mathring{\rm A}$ emission using filters on the Shane-3m telescope. We calculate a mean outflow rate for these AGNs of $0.95\pm 0.14~\rm {M}_{\odot }~\rm {yr}^{-1}$. This exceeds the mean accretion rate of their SMBHs ($0.054\pm 0.039~\rm {M}_{\odot }~\rm {yr}^{-1}$) by a factor of 18. Assuming that the galaxy must provide at least enough material to power both the AGN and outflow, this gives a lower limit on the average inflow rate of $1.01\pm 0.14~\rm {M}_{\odot }~\rm {yr}^{-1}$, a rate which simulations show can be achieved by bars, spiral arms, and cold accretion. We compare our disc-dominated sample to a sample of nearby AGNs with merger dominated histories and show that the black hole accretion rates in our sample are five times higher (4.2σ) and the outflow rates are five times lower (2.6σ). We suggest that this could be a result of the geometry of the smooth, planar inflow in a secular dominated system, which is both spinning up the black hole to increase accretion efficiency and less affected by feedback from the outflow, than in a merger-driven system with chaotic quasi-spherical inflows. This work provides further evidence that secular processes are sufficient to fuel SMBH growth.

Smethurst, R. J.↗
DOE OSTI2019

Magnetic ground state and magnetic excitations in black dioptase Cu 6 Si 6 O 18

The low-temperature magnetic properties and magnetic structure of fully dehydrated black dioptase Cu 6 Si 6 O 18 have been studied by single-crystal neutron diffraction and magnetization measurements in magnetic fields up to 30 T. Here, the intrachain J c and interchain J a b interactions as well as the anisotropy of the exchange coupling J c have been determined using inelastic neutron-scattering techniques. Zero-field antiferromagnetic order at T N = 6.7 K can be described by a commensurate propagation vector of k = ( 0 , 0 , 3 / 2 ) with respect to the hexagonal R 3 ¯ :H unit cell. The Cu magnetic moments are aligned antiferromagnetically along the c axis with about 12 ° tilt and are coupled ferromagnetically between the chains. The high-field magnetization measurements provide strong evidence for the presence of a spin-flop phase above 8 T. We found that J c in black dioptase is significantly increased, while J a b is much weaker compared to its counterpart, green dioptase Cu 6 [ Si 6 O 18 ] 6 H 2 O . We suggest that black dioptase behaves like a nearly ideal S = 1 / 2 antiferromagnetic Heisenberg spiral chain with enhanced quantum fluctuations and weak spinon confinement J a b / J c ~ 0.02 .

1-dimensional spin chains↗
DOE OSTI2021

Filling the black hole mass gap: Avoiding pair instability in massive stars through addition of nonnuclear energy

In standard stellar evolution, stars with masses ranging from approximately 150 to 240M ⊙ are expected to evolve to a pair instability supernova with no black hole (BH) remnant. This evolutionary behavior leads to a predicted gap in the black hole mass function from approximately 50 to 140M ⊙ . Yet the LIGO and Virgo Collaborations recently discovered black holes of masses 66M ⊙ and 85M ⊙ in the gravitational wave event GW190521. Here, we propose a new method to populate the BH mass gap. If an energy source is added throughout the star in addition to nuclear fusion, it is possible for the altered evolution to avoid the complete destruction of a pair instability supernova, and instead a BH remnant is left behind. An example of an extra energy source is dark matter annihilation within the star, but our results hold more generally. We show this phenomenon by exploring the effect of adding an energy source independent of temperature and density to a 180M ⊙ star, using the MESA one-dimensional stellar evolution software. If ~50% of the star’s energy is due to this new source, the star is capable of avoiding the pair instability entirely and evolving towards a core-collapse supernova and ultimately a BH remnant with mass ~ 120M ⊙ .

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Gravitational waves from a black hole orbiting in a wormhole geometry

Current ground-based gravitational wave detectors are tuned to observe compact object mergers from stellar mass black holes and neutron stars; ~50 such events have been published to date. More exotic compact objects may exist, collisions of which would also generate copious gravitational waves. In this work, we model a stellar mass black hole inspiral into a stable, nonspinning, traversable wormhole, and find a characteristic waveform—an antichirp and/or burst—as the black hole outspirals into our region of the Universe. This is a characteristic signature which can be useful in wormhole searches in gravitational wave data or used to constrain wormhole geometries.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Mode stability for massless scalars in five-dimensional black hole backgrounds

The mode stability of the Kerr black hole in four dimensions was demonstrated by Whiting in 1989, by separating the Teukolsky equation that describes gravitational perturbations and then transforming the radial and angular equations in such a way that the problem can be reformulated as a wave equation in an auxiliary spacetime in which the proof of stability is greatly simplified, owing to the absence of an ergoregion. As a preliminary step towards extending these ideas to higher-dimensional black holes, we study the mode stability of the massless scalar wave equation in the five-dimensional black hole solutions of Einstein gravity and supergravity. We show how the wave equation can again be mapped into one in an auxiliary spacetime in which there is no ergoregion, allowing us to give a proof of the mode stability of the solutions of the scalar wave equation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Numerical relativity higher order gravitational waveforms of eccentric, spinning, nonprecessing binary black hole mergers

We use the open source, community-driven, numerical relativity software, the EINSTEIN TOOLKIT to study the physics of eccentric, spinning, nonprecessing binary black hole mergers with mass-ratios q = {2; 4; 6}, individual dimensionless spin parameters chi 1z = +/- 0.6, chi 2z = +/- 0.3, that include higher order gravitational wave modes l <= 4, except for memory modes. Assuming stellar mass binary black hole mergers that may be detectable by the advanced LIGO detectors, we find that including modes up to l = 4 increases the signal-to-noise of compact binaries between 3.5% to 35%, compared to signals that only include the l = ImI = 2 mode. We use two waveform models, TEOBResumS and SEOBNRE, which incorporate spin and eccentricity corrections in the waveform dynamics, to quantify the orbital eccentricity of our numerical relativity catalog in a gauge-invariant manner through fitting factor calculations. Our findings indicate that the inclusion of higher order wave modes has a measurable effect in the recovery of moderately and highly eccentric black hole mergers, and thus it is essential to develop waveform models and signal processing tools that accurately describe the physics of these astrophysical sources.

Joshi, Abhishek V.↗
DOE OSTI2024

Primordial black hole versus inflaton

We compare the dark matter (DM) production processes and its parameters space in the background of reheating obtained from two chief systems in the early Universe: the inflaton ϕ and the primordial black holes (PBHs). We concentrated on the mechanism where DMs are universally produced only from the PBH decay and the generation of the standard model plasma from both inflaton and PBHs. Whereas the distribution of primordial black holes behaves like dust, the inflaton phenomenology depends strongly on its equation of state after the inflationary phase, which in turn is conditioned by the nature of the potential V ( ϕ ) . Depending upon the initial mass and population of PBHs, a large range of DM mass is shown to be viable if reheating is controlled by PBHs itself. Inflaton-dominated reheating is observed to further widen such possibilities depending on the initial population of black holes and its mass as well as the coupling of the inflaton to the standard model sector. Published by the American Physical Society 2024

Haque, Md Riajul (ORCID:0000000266184899)↗
DOE OSTI2024

Search for quantum black hole production in lepton + jet final states using proton-proton collisions at s = 13 TeV with the ATLAS detector

A search for quantum black holes in electron + jet and muon + jet invariant mass spectra is performed with 140 fb -1 of data collected by the ATLAS detector in proton-proton collisions at $\sqrt{s}$ =13 TeV at the Large Hadron Collider. The observed invariant mass spectrum of lepton + jet pairs is consistent with Standard Model expectations. Upper limits are set at 95% confidence level on the production cross section times branching fractions for quantum black holes decaying into a lepton and a quark in a search region with invariant mass above 2.0 TeV. The resulting quantum black hole lower mass threshold limit is 9.2 TeV in the Arkani-Hamed-Dimopoulos-Dvali model, and 6.8 TeV in the Randall-Sundrum model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Revisiting formation of primordial black holes in a supercooled first-order phase transition

We reexamine production of primordial black holes in a supercooled phase transition. While a mere overdensity associated with a surviving false-vacuum patch does not imply formation of a black hole, it is possible for such a patch to evolve and create a black hole, thanks to the gradient energy stored in the bubble wall. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Specific heats for quantum BTZ black holes in extended thermodynamics

It was shown recently that extended black hole thermodynamics, where the cosmological constant is a dynamical variable, giving rise to a pressure p and its conjugate volume V , can be given a natural setting in the context of braneworld models. We study the specific heat capacities C p ( T ) and C V ( T ) of the quantum version of the Bañados, Teitelboim, and Zanelli (BTZ) black hole that lives in the induced gravity theory on the brane. There are multiple branches of solutions, and we explore and characterize key features of the possible behavior. We identify and study a critical point in the space of solutions where both specific heats diverge. In the regime of weak backreaction where we are close to an ordinary theory of gravity, the black hole is “subentropic,” but as backreaction is increased we note that there are parts of parameter space that has regions where it is “superentropic.” While a study of the sign of the specific heats does not always show a corresponding instability (conjectured in the literature), the presence of strong backreaction makes interpretation unclear. Published by the American Physical Society 2024

Johnson, Clifford V. (ORCID:0000000189645830)↗
DOE OSTI2014

Disrupting entanglement of black holes

We study entanglement in thermofield double states of strongly coupled conformal field theories by analyzing two-sided Reissner-Nordström solutions in anti-de Sitter space. The central object of study is the mutual information between a pair of regions, one on each asymptotic boundary of the black hole. For large regions the mutual information is positive and for small ones it vanishes; we compute the critical length scale, which goes to infinity for extremal black holes, of the transition. We also generalize the butterfly effect of Shenker and Stanford [J. High Energy Phys. 03 (2014) 067] to a wide class of charged black holes, showing that mutual information is disrupted upon perturbing the system and waiting for a time of order logE/δE in units of the temperature. We conjecture that the parametric form of this time scale is universal.

Leichenauer, Stefan↗
DOE OSTI2018

Primordial black holes from inflaton fragmentation into oscillons

We demonstrate that fragmentation of the inflaton into long-lived spatially localized oscillon configurations can lead to copious production of black holes. In a single-field inflation model primordial black holes of sublunar mass can form, and they can account for all of the dark matter. Furthermore, we explore the possibility that solar-mass primordial black holes, particularly relevant for gravitational wave astronomy, are produced from the same mechanism.

79 ASTRONOMY AND ASTROPHYSICS↗