Megan Argo talked about finding out different information by observing in different wavelengths, radio waves being the longest, X-rays very short. Colder objects are usually best seen in long wavelengths, hotter ones in shorter wavelengths. We see the cold dust between the stars at relatively long wavelengths, but very hot galactic centers give out X-rays.Â
Here are 5
images of our galactic neighbor Andromeda Galaxy. The Planck Mission explains:
At radio wavelengths we measure the gas in the outskirts of the galaxy, while at infrared wavelengths we measure the dust between the spiral arms. The stars making up the spiral arms and central bulge are seen at visible wavelengths, while in the ultraviolet we see just the brighter, hotter younger stars along the edges of the spiral arms. The X-ray image shows only the most energetic regions of the galaxy, particularly near the centre.
(Image credits: Radio:WSRT/R. Braun; Infrared:NASA/Spitzer/K. Gordon; Visible: Robert Gendler; Ultraviolet: NASA/GALEX; X-ray: ESA/XMM/W. Pietsch)