The Milky Way
The Milky Way system
is a spiral galaxy consisting of over 400 billion stars , plus gas and
dust arranged into three main areas: The halo - a roughly spherical distribution
which contains the oldest stars in the Galaxy, The nuclear bulge and Galactic
Center and
The disk, which contains the majority of the stars, including the sun,
and virtually all of the gas and dust
The Halo consists of the oldest stars known, including about 146 Globular
Clusters, believed to have been formed during the early formation of the
Galaxy with ages of 10-15 billion years . The halo is also filled with
a very diffuse, hot, highly-ionized gas. Neither the full extent nor the
mass of the halo is well known. Investigations of the gaseous halos of
other spiral galaxies show that the gas in the halo extends much further
than previously thought, out to hundreds of thousands of light years.
Studies of the rotation of the Milky Way show that the halo dominates
the mass of the galaxy, but the material is not visible, now called dark
matter.
The disk of the Galaxy is a flattened, rotating system which contains
the Sun and other intermediate-to-young stars. The sun sits about 2/3
of the way from the center to the edge of the disk (about 25,000l.y.).
The sun revolves around the center of the galaxy about once every 250
million years.
Radio observations have detailed the structure of the gas in the spiral arms, but it is still not known if our galaxy is a normal spiral like our neighbor Andromeda, or a barred spiral. The bulge of the galaxy is slightly elongated in the direction of the Sun.
The Milky Way Centre - best viewed during the Winter
Although there is no lack of fascinating questions about the Galactic Center, recent interest has been focused on the question of the possibility that a massive black hole exists at the center of the central star cluster. The presence of very high velocities in the stars and gas near the center of the galaxy has suggested to astronomers for a long time that a massive black hole might be present, providing a strong enough gravitational pull to keep the stars and gas in orbit.
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