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Mapping the Milky Way

December 19, 2000

A new map of the centre of our own galaxy, The Milky Way, is the biggest, most detailed, and most sensitive yet made. The map shows giant streamers and huge clouds of interstellar gas where stars are being born 26,000 light years from Earth - shedding new light on the exotic structures in this unusual region of our own galaxy.

An international team of astronomers, led by groups from Cambridge University in the UK and the Joint Astronomy Centre [JAC] in Hawaii, has analysed the cold interstellar dust [particles similar to soot and very fine sand] in the centre of The Milky Way to map the clouds of molecular gas out of which new stars are formed.

Douglas Pierce-Price of Cambridge University said, ~This breathtaking survey is bigger and more sensitive than any previously made. It is the first detailed map to show essentially all the interstellar gas in the galactic centre.~

Cambridge Team Leader Dr John Richer added, ~These observations were the result of many months of careful planning. But luck also played its part - during the observations we experienced the driest, clearest weather that I have seen in more than ten years of observing at the telescopes in Hawaii.~

The unprecedented detail in the map reveals not only dense clouds of gas, but also a wide network of wispy filaments linking them. The region is also peppered with gas bubbles and shells. Although the origin of these structures is not fully understood, astronomers believe they must have been shaped by intense winds from stars, twisted magnetic field lines, and the explosions of supernovae.

The team used ~SCUBA~, a state of the art camera built by the UK Astronomy Technology Centre (Royal Observatory, Edinburgh), together with the 15-metre ~James Clerk Maxwell Telescope~ [JCMT] in Hawaii.

Wayne Holland, who led the group in Hawaii, said, ~SCUBA is a wonderful instrument, and the most sensitive camera of its type. Its unmatched mapping speed has revolutionised this field of astronomy.~ Holland added, ~Over a two year period we spent 15 nights at the telescope making these observations. SCUBA~s successor, SCUBA-2, could do the same job in less than half an hour, so mapping the entire galactic plane becomes a real possibility.~

The physical conditions in the central nucleus of our Galaxy are dramatically different from those nearer the Earth. The gas and dust clouds in what is known as the `Central Molecular Zone~ are much denser and more turbulent. At the very centre is a mysterious object called Sagittarius A*, thought to be a supermassive black hole, which has a mass about 2.6 million times that of our Sun.

If the nucleus of our own galaxy is so complex, then what of other much more active galaxies such as the ~starburst~ galaxy M82? Group member Jane Greaves said, ~In M82 we have already used SCUBA to detect giant regions of star formation surrounded by complex magnetic fields. We now need to fully unravel its mysteries using even more sensitive instruments.~

As other galaxies are much further away, they cannot yet be mapped with as much detail as this survey. However, the new Atacama Large Millimetre Array (ALMA) telescope consisting of 64, 12-meter radio telescopes to be built in the Atacama Desert, Chile, will enable UK astronomers to see at least 100 times more clearly to the nuclei of galaxies at the extremes of the Universe. ALMA will start construction in 2002.


The research will be published in the Astrophysical Journal Letters on the 20 December 2000.


Images:

Figure 1: The new map of gas and dust clouds in the Galactic centre, with the position of Sagittarius A* marked.
http://www.mrao.cam.ac.uk/~dpip100/galacticcentrepic.jpg
http://www.mrao.cam.ac.uk/~dpip100/galacticcentrepic.tif (higher quality)

Figure 2: Schematic diagram of our own galaxy, shown face on. The position of Sagittarius A* in the Galactic centre is marked. The green dot marks the position of the Earth and Sun, which are in the plane of the Galaxy, about two-thirds of the way out.
http://www.mrao.cam.ac.uk/~dpip100/schematic.jpg
http://www.mrao.cam.ac.uk/~dpip100/schematic.tif (higher quality)

Photo of ~James Clerk Maxwell Telescope~ in Hawaii:
http://www.mrao.cam.ac.uk/~jsr/wothers/jcmt_4.gif

Photo of Douglas Pierce-Price:
http://www.mrao.cam.ac.uk/people/d.pierceprice.jpg





Particle Physics and Astronomy Research Council (PPARC)