The center of our Milky Way galaxy lies ~ 27 000 ly away in the direction of the constellation of Sagittarius. At its core is a black hole ~ 4 million solar masses in size. Around the black hole is a donut-shaped structure ~ 8 ly across that rings the inner volume of neutral gas and thousands of individual stars. Around that, stretching out to ~ 700 ly, is a dense zone of activity called the
Central Molecular Zone (
CMZ).
It contains almost 80% of all the dense gas in the galaxy - a reservoir of tens of millions of solar masses of material - and hosts giant molecular clouds and massive star forming clusters of luminous stars, among other regions many of which are poorly understood. For example, the CMZ contains many dense molecular clouds that would normally be expected to produce new stars, but which are instead eerily desolate.
It also contains gas moving at highly supersonic velocities - hundreds of km/s. Where did the CMZ come from? No place else in the Milky Way is remotely like it (although there may be analogues in other galaxies). How does it retain its structure as its molecular gas moves, and how do those rapid motions determine its evolution? One difficulty facing astronomers is that
there is so much obscuring dust between us and the CMZ that visible light is extinguished by factors of over a trillion. Infrared, radio, and some X-ray radiation can penetrate the veil, however, and they have allowed astronomers to develop the picture just outlined.
Dense gas is shown in red, and warm and cold dust in green and blue respectively.
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