相关论文: Retro-MACHOs: Pi in the sky?
From any location outside the event horizon of a black hole there are an infinite number of trajectories for light to an observer. Each of these paths differ in the number of orbits revolved around the black hole and in their proximity to…
There is abundant evidence that the mass of the Universe is dominated by dark matter of unknown form. The MACHO project is one of several teams searching for the dark matter around our Galaxy in the form of Massive Compact Halo Objects…
Black holes are a common feature of the Universe. They are observed as stellar mass black holes spread throughout galaxies and as supermassive objects in their centres. Observations of stars orbiting close to the centre of our Galaxy…
Simulated images of a black hole surrounded by optically thin emission typically display two main features: a central brightness depression and a narrow, bright "photon ring" consisting of strongly lensed images superposed on top of the…
Many black hole (BH) candidates exist, ranging from supermassive ($\sim10^{6}$--$10^{10}$ M$_{\odot}$) to stellar masses ($\sim 1$--$100$ M$_{\odot}$), all of them identified by indirect processes. Although there are no known candidate BHs…
When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the…
Compact objects with a light sphere such as black holes and wormholes can reflect light rays like a mirror. This gravitational lensing phenomenon is called retrolensing and it is an interesting tool to survey dark and compact objects with a…
Black holes are capable of reflection: there is a finite probability for any particle that approaches the event horizon to bounce back. The albedo of the black hole depends on its temperature and the energy of the incoming particle. The…
Advances in high angular resolution astronomy make it conceivable that black hole dark matter could be detected via angular deviation effects. Assuming the dark matter in the galaxy is made of solar mass black holes, there is a non-trivial…
It is known that magnetic fields exist near black holes and photons can go around black holes due to strong gravity. Utilizing these facts, we can probe hypothetical pseudoscalar particles, so-called axions. In fact, photons can be…
We calculate the effect of dark matter on the ringdown waveform and shadow of supermassive black holes at the core of galaxies. Our main focus is on the supermassive black hole at the core of M87, which is large enough to allow for viable…
Black holes are real astrophysical objects, but their interiors are hidden and can only be "observed" through mathematics. The structure of rotating black holes is typically illustrated with the help of special coordinates. But any such…
The first LIGO-Virgo detections have confirmed the existence of massive black holes (BHs), with mass $30-40$ M$_\odot$. Such BHs might originate from massive metal-poor stars ($Z<0.3$ Z$_\odot$) or from gravitational instabilities in the…
Photons emitted by light sources in the neighbourhood of a black hole can wind several times around it before fleeing towards the observer. For spherically symmetric black holes, two infinite sequences of images are created for any given…
The compact dark objects with very large masses residing at the centres of galaxies are believed to be black holes. Due to the gravitational lensing effect, they would cast a shadow larger than their horizon size over the background, whose…
Observations by the MACHO collaboration suggest that a significant proportion of the galactic halo dark matter is in the form of compact objects with typical masses $M\sim 0.5M_{\odot}$. One of the current mysteries is the nature and origin…
If the Dark Matter consists of primordial black holes (PBHs), we show that gravitational lensing of stars being monitored by NASA's Kepler search for extra-solar planets can cause significant numbers of detectable microlensing events. A…
We consider the possibility that the black-hole (BH) binary detected by LIGO may be a signature of dark matter. Interestingly enough, there remains a window for masses $20\,M_\odot \lesssim M_{\rm bh} \lesssim 100\, M_\odot$ where…
Dark matter could take the form of dark massive compact halo objects (dMACHOs); i.e., composite objects that are made up of dark-sector elementary particles, that could have a macroscopic mass from the Planck scale to above the solar mass…
The parameters of the original log-normal mass spectrum of primordial black holes (PBH) are approximately adjusted on the basis of existing observational data on supermassive black holes in the galactic centers and the mass distribution of…