Related papers: Black Hole Event Horizons and X-ray Nova Luminosit…
We present the results of our recent Hubble Space Telescope imaging study, in which we have successfully deconvolved host and nuclear flux for the some of the most luminous quasars in the Universe. Host morphologies have been recovered for…
In this work, we consider two recently introduced novel regular black hole solutions and investigate the circular null geodesics to find the connection between the photon sphere, the horizon and the black hole shadow radii. We also study…
The visual distortion effects visible to an observer traveling around and descending to the surface of an extremely compact star are described. Specifically, trips to a ``normal" neutron star, a black hole, and an ultracompact neutron star…
We present evidence that the power law part of the quiescent x-ray emissions of neutron stars in low mass x-ray binaries is magnetospheric in origin. It can be very accurately calculated from known rates of spin and magnetic moments…
I discuss some of what is known and unknown about the behavior of black hole binary systems in the quiescent accretion state. Quiescence is important for several reasons: 1) the dominance of the companion star in the optical and IR…
The nature of black holes (BHs) and their potential deviations from classical General Relativity (GR) remain central questions in modern astrophysics. Nonlinear electrodynamics (NED) offers a promising mechanism to construct regular BHs…
This paper investigates the optical appearance of a Schwarzschild-like black hole (BH) surrounded by a Dehnen-(1, 4, 5/2) type dark matter (DM) halo, with a focus on how the DM halo's density $\rho_{s}$ and radius $r_{s}$ influence the BH's…
Four XMM-Newton X-ray observations of the central region of the Andromeda Galaxy (M31) have revealed an X-ray source that varies in luminosity over \~1--3, 10^{38} erg s^{-1} between observations and also displays significant variability…
In the second half of the last century the "frozen star" or "collapsed star" models of black hole formation were largely abandoned. The result is that later models appear to either assume that black hole event horizons already exist (such…
Here we provide shadow images of a Kerr-like black hole (BH) in cold dark matter (CDM) halo illuminated with a celestial light source and a thin accretion disk. The impact of spin parameter, critical density and the scale radius on the…
Several recently found properties of the event horizon of black holes are discussed. One of them is the reflection of the incoming particles on the horizon. A particle approaching the black hole can bounce on the horizon back, into the…
We report on our analysis of 300 ks of Chandra observations of the neutron star soft X-ray transient 1H1905+000 in quiescence. We do not detect the source down to a 95% confidence unabsorbed flux upper limit of 2E-16 erg cm-2 s-1 in the…
Studies of nearby galaxies reveal that roughly half of their low mass X-ray binary (LMXB) populations are associated with globular clusters (GCs). We have established that the LMXB hosting frequency is correlated to various GC properties…
We calculate the neutrino luminosity in an astrophysical scenario where dark matter is captured by a neutron star which eventually implodes to form a low mass black hole. The Trojan horse scenario involves the collapse of a neutron star…
Event horizons are a defining feature of black holes. Consequently, there have been many efforts to probe their existence in astrophysical black hole candidates, spanning ten orders of magnitude in mass. Nevertheless, horizons remain an…
We present coordinated multiwavelength observations of the high Galactic latitude (b=+50 deg) black hole X-ray binary (XRB) J1357.2-0933 in quiescence. Our broadband spectrum includes strictly simultaneous radio and X-ray observations, and…
Swift J164449.3+573451 is an exciting transient event, likely powered by the tidal disruption of a star by a massive black hole. The distance to the source, its transient nature, and high internal column density serve to complicate several…
A large number of Ultra-Luminous X-ray Sources in external galaxies is now known, but the discussion about their nature is still unsettled: intermediate-mass black holes or stellar-mass black holes accreting above the Eddington limit? A…
Observations of the black hole and neutron star X-ray binaries show that the luminosity of the hard-to-soft state transition is usually higher than that of the soft-to-hard state transition, indicating additional parameters other than the…
The images of supermassive black holes surrounded by optically-thin, radiatively-inefficient accretion flows, like those observed with the Event Horizon Telescope, are characterized by a bright ring of emission surrounding the black-hole…