|This mosaic of the Andromeda spiral galaxy highlights explosive stars in its interior, and cooler, dusty stars forming in its many rings. Image credit: ESA|
Herschel provides a detailed look at the cool clouds of star birth that line the galaxy's five concentric rings. Massive young stars are heating blankets of dust that surround them, causing them to glow in the longer-wavelength infrared light, known as far-infrared, that Herschel sees.
In contrast, XMM-Newton is capturing what happens at the end of the lives of massive stars. It shows the high-energy X-rays that come from, among other objects, supernova explosions and massive dead stars rotating around companions. These X-ray sources are clustered in the center of the galaxy, where the most massive stars tend to form.
Andromeda is our Milky Way galaxy's nearest large neighbor. It is located about 2.5 million light-years away and holds up to an estimated trillion stars. Our Milky Way is thought to contain about 200 billion to 400 billion stars.