Hole In Ho Research Articles

Geodesically complete black holes in Lorentz-violating gravity

We present a systematic study of the geometric structure of non-singular spacetimes describing black holes in Lorentz-violating gravity. We start with a review of the definition of trapping horizons, and the associated notions of trapped and marginally trapped surfaces, and then study their significance in frameworks with modified dispersion relations. This leads us to introduce the notion of universally marginally trapped surfaces, as the direct generalization of marginally trapped surfaces for frameworks with infinite signal velocities (Hořava-like frameworks), which then allows us to define universal trapping horizons. We find that trapped surfaces cannot be generalized in the same way, and discuss in detail why this does not prevent using universal trapping horizons to define black holes in Hořava-like frameworks. We then explore the interplay between the kinematical part of Penrose’s singularity theorem, which implies the existence of incomplete null geodesics in the presence of a focusing point, and the existence of multiple different metrics. This allows us to present a complete classification of all possible geometries that neither display incomplete physical trajectories nor curvature singularities. Our main result is that not all classes that exist in frameworks in which all signal velocities are realized in Hořava-like frameworks. However, the taxonomy of geodesically complete black holes in Hořava-like frameworks includes diverse scenarios such as evaporating regular black holes, regular black holes bouncing into regular white holes, and hidden wormholes.

Phantom energy accretion onto a black hole in Hořava-Lifshitz gravity

In this Letter, we examine the phantom energy accretion onto a Kehagias-Sfetsos black hole in Ho$\check{r}$ava Lifshitz gravity. To discuss the accretion process onto the black hole, the equations of phantom flow near the black hole have been derived. It is found that mass of the black hole decreases because of phantom accretion. We discuss the conditions for critical accretion. Graphically, it has been found that the critical accretion phenomena is possible for different values of parameters. The results for the Schwarzschild black hole can be recovered in the limiting case.

A unified phase transition picture of the charged topological black hole in Hořava-Lifshitz gravity

Aiming at a unified phase transition picture of the charged topological black hole in Ho\v{r}ava-Lifshitz gravity, we investigate this issue not only in canonical ensemble with the fixed charge case but also in grand-canonical ensemble with the fixed potential case. We firstly perform the standard analysis of the specific heat, the free energy and the Gibbs potential, and then study its geometrothermodynamics. It is shown that the local phase transition points not only witness the divergence of the specific heat, but also witness the minimum temperature and the maximum free energy or Gibbs potential. They also witness the divergence of the corresponding thermodynamic scalar curvature. No matter which ensemble is chosen, the metric constructed can successfully produce the behavior of the thermodynamic interaction and phase transition structure while other metrics failed to predict the phase transition point of the charged topological black hole in former literature. In grand-canonical ensemble, we have discovered the phase transition which has not been reported before. It is similar to the canonical ensemble in which the phase transition only takes place when $k=-1$. But it also has its unique characteristics that the location of the phase transition point depends on the value of potential, which is different from the canonical ensemble where the phase transition point is independent of the parameters. After an analytical check of Ehrenfest scheme, we find that the new phase transition is a second order one. It is also found that the thermodynamics of the black hole in Horava-Lifshitz gravity is quite different from that in Einstein gravity.

Area spectrum and thermodynamics of KS black holes in Hořava gravity

We investigate the area spectrum of Kehagias-Sfetsos black hole in Ho\v{r}ava-Lifshitz gravity via modified adiabatic invariant $I=\oint p_i d q_i$ and Bohr-Sommerfeld quantization rule. We find that the area spectrum is equally spaced with a spacing of $ \Delta A=4 \pi l_p ^2$. We have also studied the thermodynamic behavior of KS black hole by deriving different thermodynamic quantities.

Particle motion around black hole in Hořava-Lifshitz gravity

Analytical solutions of Maxwell equations around black hole immersed in external uniform magnetic field in the background of the Kehagias-Sfetsos (KS) asymptotically flat black hole solution of Ho\v{r}ava-Lifshitz gravity have been found. Influence of magnetic field on effective potential of the radial motion of charged test particle around black hole immersed in external magnetic field in Ho\v{r}ava-Lifshitz gravity has been investigated by using Hamilton-Jacobi method. Exact analytical solution for dependence of the minimal radius of the circular orbits $r_{\rm mc}$ from KS parameter $\omega$ for motion of test particle around spherical symmetric black hole in Ho\v{r}ava-Lifshitz gravity has been derived. The critical values of the particle's angular momentum for captured particles by black hole in Ho\v{r}ava-Lifshitz gravity have been obtained numerically. The comparison of the obtained numerical results with the astrophysical observational data on radii of the innermost stable circular orbits gives us the estimation of the parameter as $\omega \simeq 3.6 \cdot 10^{-24} {\rm cm}^{-2}$.

Lifshitz scalar, brick wall method, and generalized uncertainty principle in Hořava-Lifshitz gravity

Using the brick-wall method, we study statistical entropy for spherically symmetric black holes in Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity. In particular, a Lifshitz scalar field is considered in order to incorporate foliation-preserving diffeomorphism, which eventually gives a modified dispersion relation. Finally, we obtain the area law without the UV cutoff for $z>3$ and discuss some of the consequences in connection with the generalized uncertainty principle.

Cardy-Verlinde Formula of Kehagias-Sfetsos Black Hole

In this paper, we have shown that the entropy of the Kehagias-Sfetsos black hole in Ho$\check{\textbf{r}}$ava-Lifshitz (HL) gravity can be expressed by the Cardy-Verlinde formula. The later is supposed to be an entropy formula of conformal field theory in any dimension.

Holographic superconductors with Hořava-Lifshitz black holes

We discuss the phase transition of planar black holes in Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity by introducing a Maxwell field and a complex scalar field. We calculate the condensate of the charged operators in the dual conformal field theories when the mass square of the complex scalar field is ${m}^{2}=\ensuremath{-}2/{L}^{2}$ and ${m}^{2}=0$, respectively. We compute the electrical conductivity of the Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz superconductor in the probe approximation. In particular, it is found that there exists a spike in the conductivity for the case of the operator with scaling dimension one. These results are quite similar to those in the case of Schwarzschild-AdS black holes, which demonstrates that the holographic superconductivity is a robust phenomenon associated with asymptotic AdS black holes.

DOES STELLAR FEEDBACK CREATE H I HOLES? AHUBBLE SPACE TELESCOPE/VERY LARGE ARRAY STUDY OF HOLMBERG II

We use deep Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) F555W and F814W photometry of resolved stars in the M81 Group dwarf irregular galaxy Ho II to study the hypothesis that the holes identified in the neutral interstellar medium (H i) are created by stellar feedback. From the deep photometry, we construct color–magnitude diagrams (CMDs) and measure the star formation histories (SFHs) for stars contained in H i holes from two independent holes catalogs, as well as select control fields, i.e., similar sized regions that span a range of H i column densities. The CMDs reveal young (< 200 Myr) stellar populations inside all H i holes, which contain very few bright OB stars with ages less than 10 Myr, indicating they are not reliable tracers of H i hole locations while the recent SFHs confirm multiple episodes of star formation within most holes. Converting the recent SFHs into stellar feedback energies, we find that enough energy has been generated to have created all holes. However, the required energy is not always produced over a timescale that is less than the estimated kinematic age of the hole. A similar analysis of stars in the control fields finds that the stellar populations of the control fields and H i holes are statistically indistinguishable. However, because we are only sensitive to holes ∼100 pc in diameter, we cannot tell if there are smaller holes inside the control fields. The combination of the CMDs, recent SFHs, and locations of young stars shows that the stellar populations inside H i holes are not coherent, single-aged, stellar clusters, as previously suggested, but rather multi-age populations distributed across each hole. From a comparison of the modeled and observed integrated magnitudes, and the locations and energetics of stars inside of H i holes, we propose a potential new model: a viable mechanism for creating the observed H i holes in Ho ii is stellar feedback from multiple generations of SF spread out over tens or hundreds of Myr, and thus, the concept of an age for an H i hole is intrinsically ambiguous. For H i holes in the outer parts of Ho ii, located beyond the HST/ACS coverage, we use Monte Carlo simulations of expected stellar populations to show that low level SF could provide the energy necessary to form these holes. Applying the same method to the SMC, we find that the holes that appear to be void of stars could have formed via stellar feedback from low level SF. We further find that Hα and 24 μm emission, tracers of the most recent star formation, do not correlate well with the positions of the H i holes. However, UV emission, which traces star formation over roughly the last 100 Myr, shows a much better correlation with the locations of the H i holes.

Topological black holes in Hořava-Lifshitz gravity

We find topological (charged) black holes whose horizon has an arbitrary constant scalar curvature $2k$ in Ho\v{r}ava-Lifshitz theory. Without loss of generality, one may take $k=1,0$ and -1. The black hole solution is asymptotically AdS with a nonstandard asymptotic behavior. Using the Hamiltonian approach, we define a finite mass associated with the solution. We discuss the thermodynamics of the topological black holes and find that the black hole entropy has a logarithmic term in addition to an area term. We find a duality in Hawking temperature between topological black holes in Ho\v{r}ava-Lifshitz theory and Einstein's general relativity: the temperature behaviors of black holes with $k=1, 0$ and -1 in Ho\v{r}ava-Lifshitz theory are respectively dual to those of topological black holes with $k=-1, 0$ and 1 in Einstein's general relativity. The topological black holes in Ho\v{r}ava-Lifshitz theory are thermodynamically stable.

A Test of the Standard Hypothesis for the Origin of the H [CSC]i[/CSC] Holes in Holmberg II

The nearby irregular galaxy Holmberg II (Ho II, DDO 50) has been extensively mapped in H I using the Very Large Array, revealing intricate structure in its interstellar gas component, as reported by Puche et al. in 1992. An analysis of these structures shows the neutral gas to contain a number of expanding H I holes. The formation of the H I holes has been attributed to multiple supernova (SN) events occurring within wind-blown shells around young, massive star clusters, with as many as 10–200 SNe required to produce many of the holes. From the sizes and expansion velocities of the holes, Puche et al. assigned ages of ~107 to 108 years. If the SN scenario for the formation of the H I holes is correct, it implies the existence of star clusters with a substantial population of late B, A, and F main-sequence stars at the centers of the holes. Many of these clusters should be detectable in deep ground-based CCD images of the galaxy. To test the SN hypothesis for the formation of the H I holes, we have obtained and analyzed deep broadband BVR and narrowband Hα images of Ho II. We compare the optical and H I data and search for evidence of the expected star clusters in and around the H I holes. We also use the H I data to constrain models of the expected remnant stellar population. Assuming that the H I holes are created by multiple SNe, that the number of SNe required can be determined from the observed energetics of the holes, and that the SNe represent the high-mass population of a cluster with a normal initial mass function, we show that in several of the holes the observed upper limits for the remnant cluster brightness are strongly inconsistent with the SN hypothesis described by Puche et al. Moreover, many of the H I holes are located in regions of very low optical surface brightness that show no indication of recent star formation. Here we present our findings, discuss their implications, and explore possible alternative explanations for the existence of the H I holes in Ho II, including the recent suggestion that some of the holes could be produced by gamma-ray burst events.