MILKY WAY GLOBULAR CLUSTERS: CLOSE ENCOUNTER RATES WITH EACH OTHER AND WITH THE CENTRAL SUPERMASSIVE BLACK HOLE

We present a new investigation of the habitability of the Milky Way bulge, that expands previous studies on the Galactic Habitable Zone. We discuss existing knowledge on the abundance of planets in the bulge, metallicity and the possible frequency of rocky planets, orbital stability and encounters, and the possibility of planets around the central supermassive black hole. We focus on two aspects that can present substantial differences with respect to the environment in the disk: (i) the ionizing radiation environment, due to the presence of the central black hole and to the highest rate of supernovae explosions and (ii) the efficiency of putative lithopanspermia mechanism for the diffusion of life between stellar systems. We use analytical models of the star density in the bulge to provide estimates of the rate of catastrophic events and of the diffusion timescales for life over interstellar distances.

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Testing the No-Hair Theorem with Sgr A*

Advances in Astronomy ◽

10.1155/2012/486750 ◽

2012 ◽

Vol 2012 ◽

pp. 1-9 ◽

Cited By ~ 17

Author(s):

Tim Johannsen

Keyword(s):

Black Hole ◽

Free Parameter ◽

Milky Way ◽

Very Long Baseline Interferometry ◽

Angular Size ◽

High Brightness ◽

Supermassive Black Hole ◽

Long Baseline ◽

Nearby Stars ◽

Sgr A

The no-hair theorem characterizes the fundamental nature of black holes in general relativity. This theorem can be tested observationally by measuring the mass and spin of a black hole as well as its quadrupole moment, which may deviate from the expected Kerr value. Sgr A*, the supermassive black hole at the center of the Milky Way, is a prime candidate for such tests thanks to its large angular size, high brightness, and rich population of nearby stars. In this paper, I discuss a new theoretical framework for a test of the no-hair theorem that is ideal for imaging observations of Sgr A* with very long baseline interferometry (VLBI). The approach is formulated in terms of a Kerr-like spacetime that depends on a free parameter and is regular everywhere outside of the event horizon. Together with the results from astrometric and timing observations, VLBI imaging of Sgr A* may lead to a secure test of the no-hair theorem.

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Visible Shapes of Black Holes M87* and SgrA*

Universe ◽

10.3390/universe6090154 ◽

2020 ◽

Vol 6 (9) ◽

pp. 154

Author(s):

Vyacheslav I. Dokuchaev ◽

Natalia O. Nazarova

Keyword(s):

Black Hole ◽

Event Horizon ◽

Milky Way ◽

Dark Spot ◽

Disk Model ◽

Milky Way Galaxy ◽

Supermassive Black Hole ◽

The Galaxy ◽

Visible Images ◽

Inner Parts

We review the physical origins for possible visible images of the supermassive black hole M87* in the galaxy M87 and SgrA* in the Milky Way Galaxy. The classical dark black hole shadow of the maximal size is visible in the case of luminous background behind the black hole at the distance exceeding the so-called photon spheres. The notably smaller dark shadow (dark silhouette) of the black hole event horizon is visible if the black hole is highlighted by the inner parts of the luminous accreting matter inside the photon spheres. The first image of the supermassive black hole M87*, obtained by the Event Horizon Telescope collaboration, shows the lensed dark image of the southern hemisphere of the black hole event horizon globe, highlighted by accreting matter, while the classical black hole shadow is invisible at all. A size of the dark spot on the Event Horizon Telescope (EHT) image agrees with a corresponding size of the dark event horizon silhouette in a thin accretion disk model in the case of either the high or moderate value of the black hole spin, a≳0.75.

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The Supermassive Black Hole at the Center of the Milky Way

Beyond the Desert 2003 - Springer Proceedings in Physics ◽

10.1007/978-3-642-18534-2_40 ◽

2004 ◽

pp. 627-638

Author(s):

Andreas Eckart ◽

Christian Straubmeier

Keyword(s):

Black Hole ◽

Milky Way ◽

Supermassive Black Hole

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OUR MILKY WAY AND ITS SUPERMASSIVE BLACK HOLE

10.2307/j.ctv1htpf4h.8 ◽

2021 ◽

pp. 98-112

Author(s):

Michael A. Strauss

Keyword(s):

Black Hole ◽

Milky Way ◽

Supermassive Black Hole

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IS THERE A SUPERMASSIVE BLACK HOLE AT THE CENTER OF THE MILKY WAY?

International Journal of Modern Physics D ◽

10.1142/s0218271809014820 ◽

2009 ◽

Vol 18 (06) ◽

pp. 889-910 ◽

Cited By ~ 40

Author(s):

MARK J. REID

Keyword(s):

Black Hole ◽

Radio Source ◽

Milky Way ◽

Mass Density ◽

Apparent Size ◽

Central Mass ◽

Infrared Wavelength ◽

Supermassive Black Hole ◽

Focal Position ◽

Sgr A

This review outlines the observations that now provide an overwhelming scientific case that the center of the Milky Way harbors a supermassive black hole. Observations at infrared wavelength trace stars that orbit about a common focal position and require a central mass (M) of 4 × 106 M⊙ within a radius of 100 AU. Orbital speeds have been observed to exceed 5,000 km s-1. At the focal position there is an extremely compact radio source (Sgr A*), whose apparent size is near the Schwarzschild radius (2GM/c2). This radio source is motionless at the ~ 1 km s-1 level at the dynamical center of the Galaxy. The mass density required by these observations is now approaching the ultimate limit of a supermassive black hole within the last stable orbit for matter near the event horizon.

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