Whirlpool Galaxy: M51, NGC 5194/5
Credit: ESA/ISO, CEA Saclay and ISOCAM Consortium
STARMAKING REGIONS IN THE WHIRLPOOL GALAXY
The spiral arms of a galaxy 20 million light-years away in space are highlighted by clouds of dust and gas, opaque in visible light. Here the European Space Agency's new Infrared Space Observatory, ISO, sees star formation in progress. This image was obtained with the Camera in ISO (also called ISOCAM) at a wavelength of 15 microns. At this wavelength the Earth's atmosphere makes cosmic observations very difficult -- hence the need for Europe's space telescope dedicated to infrared astronomy.
The Whirlpool Galaxy, catalogued as M51 or NGC 5194, is a relatively near neighbour of our own Galaxy, the Milky Way Galaxy. Historically, it was the first "spiral nebula" identified by astronomers. In the infrared image the galaxy broadly resembles the whirlpool-like object seen by visible light.
Bright spots in the spiral arms correspond with warm dust clouds where star formation is proceeding on a large scale. These are linked by regions of cooler dust along the spiral arms and in the spaces between the arms, where previous generations of stars have left their debris. In the infrared image the spiral arms can be traced right into the heart of the galaxy, where there are hotspots of star formation on either side of a bright central nucleus.
A companion galaxy (NGC 5195) at the top of the image looks much smaller than it does by visible light. This is because starmaking is concentrated near its nucleus.
Star formation in the Milky Way and other galaxies is a major theme for ISO's observing programme.
Note about wavelengths:
A micron is a millionth of a metre. Visible light has wavelengths 0.4 to 0.7 microns. ISO's four instruments span the infrared range from 2.4 microns up to 240 microns, or about a quarter of a millimetre.
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Paris, 14 February 1996
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