As the material shrinks, massive stars form. Ultraviolet radiation emitted by these stars ionises the surrounding gas, making it visible to telescopes back on Earth.
Its name comes from Greek mythology. According to legend, the galaxy is milk spilt by Zeus’s wife Hera while suckling the infant Heracles.
In the foreground is St Michael’s tower, atop Glastonbury Tor, UK, a site famously associated with Arthurian legend.