Sgr A* as Source of the Positrons Observed in the Galactic Center Region

AbstractWe explore the possibility that a substantial fraction of the positrons observed to annihilate in the central region of our Galaxy come from the supermassive black hole Sgr A* that lies at the center. This idea was proposed by several authors, but the propagation of the emitted positrons into the bulge and beyond remained a serious problem for models of the origin of GC positrons.We assume models of positron production with different energies. The propagation of positrons from their production site is followed in detail with Monte-Carlo simulations, taking into account the physical conditions of the propagation regions as well as various physical interactions. Using the known physics of positron annihilation in astrophysical environments, we calculate the properties of the annihilation emission (time evolution and spatial distribution) for the different models under consideration.We present the results of these simulations and the conclusions/constraints that can be inferred from them.

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A new MIR bow shock source in the Galactic center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000428 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 150-152 ◽

Cited By ~ 1

Author(s):

N. Sabha ◽

M. Zamaninasab ◽

A. Eckart ◽

L. Moser

Keyword(s):

Black Hole ◽

Symmetry Axis ◽

Galactic Center ◽

Bow Shock ◽

Shock Source ◽

Stellar Cluster ◽

Supermassive Black Hole ◽

Sgr A ◽

Central Parsec

AbstractWe find a convex-like feature at a distance of 0.68 pc (17″) from the position of the supermassive black hole, Sgr A*, at the center of the nuclear stellar cluster. This feature resembles a stellar bow shock with a symmetry axis pointing to the center. We discuss the possible nature of the feature and the implications of its alignment with other dusty comet-like objects inside the central parsec.

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Mini-spiral as source of material for Sgr A* in bright state

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312019606 ◽

2012 ◽

Vol 8 (S290) ◽

pp. 199-200 ◽

Cited By ~ 1

Author(s):

Bozena Czerny ◽

Vladimír Karas ◽

Devaky Kunneriath ◽

Tapas K. Das

Keyword(s):

Black Hole ◽

Angular Momentum ◽

Molecular Clouds ◽

Galactic Center ◽

Supermassive Black Hole ◽

The Past ◽

Accretion Process ◽

Ring Mode ◽

Sgr A ◽

Bright Phase

AbstractThe question of the origin of the gas supplying the accretion process is pertinent especially in the context of enhanced activity of Galactic Center during the past few hundred years, seen now as echo from the surrounding molecular clouds, and the currently observed new cloud approaching Sgr A*. We discuss the so-called Galactic Center mini-spiral as a possible source of material feeding the supermassive black hole on a 0.1 parsec scale. The collisions between individual clumps reduce their angular momentum. and set some of the clumps on a plunging trajectory.We conclude that the amount of material contained in the mini-spiral is sufficient to sustain the luminosity of Sgr A* at the required level. The accretion episodes of relatively dense gas from the mini-spiral passing through a transient ring mode at ~ 104 Rg provide a viable scenario for the bright phase of Galactic Center.

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The missing X-rays in SGR A*: Evidence for a supermassive black hole in the galactic center

Lecture Notes in Physics - Jets from Stars and Galactic Nuclei ◽

10.1007/bfb0102618 ◽

1996 ◽

pp. 271-274

Author(s):

Heino Falcke ◽

Peter L. Biermann

Keyword(s):

Black Hole ◽

Galactic Center ◽

X Rays ◽

Supermassive Black Hole ◽

Sgr A

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Conversion of gas into stars in the Galactic center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000386 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 132-138

Author(s):

S. N. Longmore

Keyword(s):

Black Hole ◽

Star Formation ◽

Galactic Center ◽

High Redshift ◽

Formation Rate ◽

Extreme Environment ◽

Time Interval ◽

Supermassive Black Hole ◽

Mass Assembly ◽

Sgr A

AbstractThe star formation rate in the central 500 pc of the Milky Way is lower by a factor of > 10 than expected for the substantial amount of dense gas it contains, which challenges current star formation theories. I discuss which physical mechanisms could be causing this observation and put forward a self-consistent cycle of star formation in the Galactic center, in which the plausible star formation inhibitors are combined. Their ubiquity suggests that the perception of a lowered central SFR should be a common phenomenon in other galaxies with direct implications for galactic star formation and also potentially supermassive black hole growth. I then describe a scenario to explain the presence of super star clusters in the Galactic center environment, in which their formation is triggered by gas streams passing close to the minimum of the global Galactic gravitational potential at the location of the central supermassive black hole, Sgr A*. If this triggering mechanism can be verified, we can use the known time interval since closest approach to Sgr A* to study the physics of stellar mass assembly in an extreme environment as a function of absolute time. I outline the first results from detailed numerical simulations testing this scenario. Finally, I describe a study showing that in terms of the baryonic composition, kinematics, and densities, the gas in the Galactic center is indistinguishable from high-redshift clouds and galaxies. As such, the Galactic center clouds may be used as a template to understand the evolution (and possibly the life cycle) of high-redshift clouds and galaxies.

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Masers and Galactic structure: Micro-arcsecond astrometry with the VLBA

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307013361 ◽

2007 ◽

Vol 3 (S242) ◽

pp. 348-355 ◽

Cited By ~ 1

Author(s):

M. J. Reid ◽

A. Brunthaler ◽

K. M. Menten ◽

Xu Ye ◽

Zheng Xing-Wu ◽

...

Keyword(s):

Black Hole ◽

Galactic Center ◽

Galactic Plane ◽

Infrared Images ◽

Star Forming ◽

Supermassive Black Hole ◽

Star Forming Regions ◽

The Galaxy ◽

Trigonometric Parallaxes ◽

Sgr A

AbstractAstrometric observations with the VLBA with accuracies approaching ~ 10 μas are being conducted in order to better understand the Galaxy. The location of Sgr A* on infrared images can be determined with an accuracy of a few mas, using stars with SiO maser emission as a calibration grid for infrared images. The apparent proper motion of Sgr A*, which is dominated by the effects of the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0R0 and offers a dynamical definition of the Galactic plane with Sgr A* at its origin. The intrinsic motion of Sgr A* is very small and comparable to that expected for a supermassive black hole. When combined with infrared results, this provides overwhelming evidence that Sgr A* is a supermassive black hole. Finally, we are engaged in a large project to map the spiral structure and kinematics of the Galaxy. Preliminary trigonometric parallaxes, obtained with the VLBA, to eight massive star forming regions are presented.

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Observations of NIR polarized light from Sagittarius A*

Proceedings of the International Astronomical Union ◽

10.1017/s174392131400074x ◽

2013 ◽

Vol 9 (S303) ◽

pp. 283-287

Author(s):

B. Shahzamanian ◽

A. Eckart ◽

M. Zamaninasab ◽

G. Witzel ◽

N. Sabha

Keyword(s):

Black Hole ◽

Adaptive Optics ◽

Near Infrared ◽

Polarized Light ◽

Time Interval ◽

Physical Conditions ◽

Supermassive Black Hole ◽

Sagittarius A ◽

Linearly Polarized ◽

Sgr A

AbstractWe present a brief overview of results obtained from near-infrared polarized observations of Sgr A*, which is associated with the supermassive black hole at the center of the Milky Way. The observations have been carried out using the NACO adaptive optics instrument at the VLT UT4 in the infrared Ks-band from 2004 to 2012. Several polarized flares have been observed in this time interval which allow us to determine the statistical properties of NIR linearly polarized light from Sgr A*. Linear polarization at 2.2 μm and its variations can help us to constrain the physical conditions of the accretion process around this supermassive black hole.

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The 3 Ms Chandra campaign on Sgr A*: a census of X-ray flaring activity from the Galactic center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314000945 ◽

2013 ◽

Vol 9 (S303) ◽

pp. 374-378

Author(s):

J. Neilsen ◽

M. A. Nowak ◽

C. Gammie ◽

J. Dexter ◽

S. Markoff ◽

...

Keyword(s):

Black Hole ◽

Spectral Resolution ◽

Galactic Center ◽

Progress Report ◽

Deep Sleep ◽

X Ray ◽

Supermassive Black Hole ◽

Black Hole Accretion ◽

Sgr A ◽

Hole Accretion

AbstractOver the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief flares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole accretion. To study the accretion processes in the Galactic center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of the closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including the brightest flare ever seen from Sgr A*. Focusing on the statistics of the flares and the quiescent emission, we discuss the physical implications of X-ray variability in the Galactic center.

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On the Origin of the Galactic Center S Stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310006605 ◽

2009 ◽

Vol 5 (S267) ◽

pp. 330-330

Author(s):

Evgeny Griv

Keyword(s):

Black Hole ◽

Galactic Center ◽

Galactic Rotation ◽

Concentrated Mass ◽

Stellar Orbits ◽

Supermassive Black Hole ◽

Disk Rotation ◽

Single Disk ◽

Sgr A ◽

Central Parsec

Most, if not all, galaxies with a significant bulge component harbor a central supermassive black hole. In our own Milky Way Galaxy, a disk of stars at a distance r ~ 0.05–1 pc orbits the radio source Sgr A* at the center. Stellar orbits show that the gravitational potential on a scale of ~ 0.5 pc is dominated by a concentrated mass of MBH ≈ 3.6 × 106M⊙, which is associated with a supermassive black hole. In addition to the black hole, the models require the presence of an extended mass of (0.5–1.5) × 106M⊙ in the central parsec, which can be explained well by the mass of the stars that make up the cluster. Thus, the Galactic center star cluster is composed of a central supermassive black hole and a self-gravitating disk that is several Gyrs old and comprised of late-type CO absorption stars. Significant disk rotation in the sense of the general Galactic rotation has been detected. This system is probably a strongly warped, thin single disk; the mean eccentricity of the observed stellar orbits in the disk is e ≈ 0.36 ± 0.06.

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Null Geodesics and Strong Field Gravitational Lensing in a String Cloud Background

Advances in High Energy Physics ◽

10.1155/2015/635625 ◽

2015 ◽

Vol 2015 ◽

pp. 1-9 ◽

Cited By ~ 2

Author(s):

M. Sharif ◽

Sehrish Iftikhar

Keyword(s):

Black Hole ◽

Gravitational Lensing ◽

Galactic Center ◽

Deflection Angle ◽

Orbital Motion ◽

Strong Field ◽

Schwarzschild Black Hole ◽

Field Limit ◽

Null Geodesics ◽

Supermassive Black Hole

This paper is devoted to studying two interesting issues of a black hole with string cloud background. Firstly, we investigate null geodesics and find unstable orbital motion of particles. Secondly, we calculate deflection angle in strong field limit. We then find positions, magnifications, and observables of relativistic images for supermassive black hole at the galactic center. We conclude that string parameter highly affects the lensing process and results turn out to be quite different from the Schwarzschild black hole.

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