Related papers: New Approach to Sgr A* Problem
Sgr A* is probably the supermassive black hole being investigated most extensively due to its proximity. Several theoretical models for its steady state emission have been proposed in the past two decades. Both the radiative-inefficient…
Sgr A* exhibits flares in the near-infrared and X-ray bands, with the luminosity in these bands increasing by factors of $10-100$ for $\approx 60$ minutes. One of the models proposed to explain these flares is synchrotron emission of…
The nearby radio galaxy Centaurus A belongs to a class of Active Galaxies that are very luminous at radio wavelengths. The majority of these galaxies show collimated relativistic outflows known as jets, that extend over hundreds of…
We investigate radiatively inefficient accretion flow models for Sgr A*, the supermassive black hole in our Galactic Center, in light of new observational constraints. Confirmation of linear polarization in the submm emission argues for…
Recent measurements of stellar orbits provide compelling evidence that the compact radio source Sagittarius A* at the Galactic Centre is a 3.6-million-solar-mass black hole. Sgr A* is remarkably faint in all wavebands other than the radio…
Spectral and kinematic studies suggest that the nonthermal radio source Sgr A*, located at the center of the Milky Way, is a supermassive compact object with a mass 2-3 million solar masses. Winds from nearby stars, located approximately…
In the last several years, a number of observing campaigns of the massive black hole Sgr A* has been carried out in order to address two important issues: one concerns the underluminous nature of Sgr A* with its bolometric luminosity being…
The center of our Galaxy hosts the best constrained supermassive black hole in the universe, Sagittarius A* (Sgr A*). Its mass and distance have been accurately determined from stellar orbits and proper motion studies, respectively, and its…
The X-ray and near-IR emission from Sgr A* is dominated by flaring, while a quiescent component dominates the emission at radio and sub-mm wavelengths. The spectral energy distribution of the quiescent emission from Sgr A* peaks at sub-mm…
Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars…
To understand why supercritical accretion is feasible onto a neutron star, we carefully examine the accretion flow dynamics by 2.5-dimensional general relativistic (GR) radiation magnetohydrodynamic (RMHD) simulations, comparing the cases…
Sagittarius A* (Sgr A*) is the variable radio, near-infrared (NIR), and X-ray source associated with accretion onto the Galactic center black hole. We have analyzed a comprehensive submillimeter (including new observations simultaneous with…
We summarize recent observations and modeling of the brightest Sgr A* flare to be observed simultaneously in (near)-infrared and X-rays to date. Trying to explain the spectral characteristics of this flare through inverse Compton mechanisms…
In Sgr A* at the Galactic center, by far the closest and easiest supermassive black hole we can study, the observational evidence is increasingly pointing to the presence of a compact, hot, magnetized disk feeding the accretor. In such…
Recent infrared (IR) observations of the center of our Galaxy indicate that the supermassive black hole source Sgr A* is strongly variable in the IR. The timescale for the variability, $\sim 30$ min, is comparable to that of the X-ray…
The recent detection of significant linear polarization at mm and sub-mm wavelengths in the spectrum of Sgr A* (if confirmed) will be a useful probe of the conditions within several Schwarzschild radii ($r_S$) of the event horizon at the…
The basic mechanism responsible for radio emission in radio-loud active galactic nuclei (AGNs) is assumed to be synchrotron radiation. We suggest here that radio emission in radio-quiet objects is also due to synchrotron radiation of…
The radio source Sgr A* at the center of our Galaxy is believed to be a 2.6 x 10^6 solar mass black hole which accretes gas from the winds of nearby stars. We show that limits on the X-ray and infrared emission from the Galactic Center…
We review our current understanding to the accretion and ejection processes in Sgr A*. Roughly speaking, they correspond to the quiescent and flare states of the source respectively. The high-resolution {\it Chandra} observations to the gas…
This paper reviews our current understanding of low-luminosity AGNs (LLAGNs) in the context of the advection-dominated accretion flow. The best investigated source, the supermassive black hole in our galactic center, Sgr A*, is emphasized…