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Issue 4.07

The Astrophysics Spectator

May 16, 2007

The latest addition to the web site is a page describing the larger features of the Galactic center. The center of our Galaxy is the most violent region of the Milky Way. We see this violence in the radio waves, infrared light, x-rays, and gamma-rays that manage to travel to us through the dust of the Galactic plane. The primary object of interest at the center is a massive black hole candidate called Sagittarius A* (Sgr A*). This object of 3.6×106 times the mass of the Sun is not only the object around which all other stars in the Galaxy orbit, it is also the most massive black hole candidate that we observe. Similar black holes are believed to live at the center of other galaxies, in particular the galaxies that are strong emitters of radio wave, x-rays, and gamma-rays.

Around Sgr A* orbits a dense cluster of stars. Within a radius of about 2 parsecs from Sgr A*, the mass of the stars in this cluster equals the mass of the central black hole. Within a radius of about 10 parsecs from the black hole, the stars have a total mass of 3×107 solar masses. Although the density of stars continues to fall as one moves away from the black hole, the density of stars remains high out to nearly a kiloparsec from the black hole. Over the larger volume of this star cluster lies a disk of gas, numerous supernova remnants, and threads of magnetic field and hot electrons. This disk lies in the plane of the Galaxy, extending several hundred parsecs in diameter, but with a thickness of order 50 parsecs.

The most compelling reason for astronomers to study the Galactic center, beyond the interesting physics involving clusters of stars, supernovae, energetic plasmas, and a black hole, is that our Galactic center may resemble the galactic centers of the very young distant active galaxies.

Next Issue: The next issue of The Astrophysics Spectator is scheduled for May 30.

Jim Brainerd


The Galactic Center. The center is the most violent region of the Milky Way Galaxy. Peering through the intervening dust with radio and infrared telescopes, we see a region of densely-clustered stars, supernova remnants, and hot gases in extended magnetic fields. At the very center of the Galaxy is Sagittarius A, a brilliant, extended radio emitter that contains the massive black hole candidate Sgr A* (continue)

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