Infrared images of M51 by the ISO satellite -

ISO’s first light image: Unprocessed 7 micron ISOCAM image of M51, as seen on

November 28, 1995.

ESA’s ISO telescope observes star formation in the Whirlpool Galaxy

The spiral arms of the Whirlpool Galaxy M51 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 thread for ISO’s

observing program.

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