An infrared and multi-wavelength image of the Central Molecular Zone in the Milky Way. Dense gas is shown in red, and warm and cold dust in green and blue respectively. Several key objects in the region are labeled, along with a set of embedded young stellar clusters seen at 24 microns. Credit: C. Battersby
The center of our Milky Way galaxy lies ~27,000 light-years 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 about 8 light-years across that rings the inner volume of neutral gas and thousands of individual stars. Around that, stretching out to ~700 light-years, is a dense zone of activity called the Central Molecular Zone (CMZ). It contains ~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.
Eg, 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 – 100s 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.
CfA astronomers used the Australian Mopra radio telescope to study the HNCO, N2H+, and HNC in the CMZ. These particular molecules were selected because they do a good job of tracing the wide range of conditions thought to be present in the CMZ, from shocked gas to quiescent material, and also because they suffer only minimally from cluttering and extinction effects that complicate more abundant species like carbon monoxide. The scientists developed a new computer code to analyze efficiently the large amounts of data they had.
They found, consistent with previous results, CMZ is not centered on the black hole, but is offset; they also confirm that the gas motions throughout are supersonic. They identify 2 large-scale flows across the region, and suggest they represent one coherent (or at most two independent) streams of material, perhaps even spiral-like arms. They also analyze the gas in several previously identified zones of the CMZ, finding that one shell-like region thought to be the result of supernova explosions may instead be several regions that are physically unrelated, and that a giant cloud thought to be independent is actually an extension of the large-scale flows. This work is a first step in unraveling an intrinsically complex galactic environment, and that pending research will trace the gas motions to larger distances and try to model the CMZ gas motions with computer simulations. https://www.cfa.harvard.edu/news/su201609
http://phys.org/news/2016-02-milky-central-molecular-zone.htmljCp
Recent Comments