Professor Steve Eales comments on the significance of the first SPIRE images

 

These images illustrate the power of Herschel for studying galaxies. The most obvious feature of the images is the bright spiral galaxies in their centres. This is the first time anyone has seen what galaxies look like at these wavelengths, and although these pictures may look like optical photographs of spirals, the big difference is in what is producing the radiation: in an optical photograph it is stars; in these images it’s dust, the tiny solid grains of matter between the stars. Dust grains may not sound terribly exciting, but they are the key to how stars form, and they also act like smoke, hiding half a galaxy’s optical light from traditional telescopes like Hubble. These images, the first of thousands of images that Herschel will obtain of nearby galaxies, therefore hold huge clues about the metabolic processes within galaxies.

Equally important, however, is something that is not quite as obvious to the eye. The image of M74, in particular, is surrounded by hundreds of ‘blobs’. Each of these blobs is a distant galaxy.  Because of the finite speed of light, distance equates to time, and a galaxy at a distance of one billion light years is being seen as it was one billion years in the past. Therefore, these galaxies are not only a long way away, they are a long time ago. By studying the properties of the hundreds of thousands of distant galaxies that will be detected by Herschel, of which these are a foretaste, we will be able to take a major step forward in our understanding of how galaxies were formed and how they have changed over time.