Images made using the Hubble Space Telescope in 1995, by Jeff Hester and Paul Scowen, greatly improved scientific understanding of processes inside the nebula. One of these, a famous photograph known as the "Pillars of Creation", depicts a large region of star formation. Its small, dark areas are believed to be protostars. The pillar structure of the region resembles that of a much larger star formation region, imaged with the Spitzer Space Telescope in 2005, in Cassiopeia, which is designated W5 and has been dubbed the "Pillars of Creation". These columns––which resemble stalagmites protruding from the floor of a cavern––are composed of interstellar hydrogen gas and dust, which act as incubators for new stars. Inside and on their surface astronomers have found knots or globules of denser gas, called EGGs ("Evaporating Gaseous Globules"). Stars are being formed inside a portion of these EGGs. Combinations of X-ray images from the Chandra observatory with Hubble's "Pillars" image have shown that X-ray sources (from young stars) do not coincide with the pillars, but instead randomly dot the area. This suggests that star formation may have peaked approximately one million years ago in the Eagle Nebula and any protostars in the pillar's EGGs are not yet hot enough to emit X-rays. The longest of the 'Pillars' is seven light years long, and because of their massive density interior gasses contract gravitationally to form stars. At each 'pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. Due to the huge distance between us, the Pillars of Creation may already be gone, and instead a stellar star nursery could have taken its place. In early 2007, scientists using the Spitzer discovered evidence that potentially indicates that the Pillars were destroyed by a nearby supernova explosion about 6,000 years ago, but the light showing the new shape of the nebula will not reach Earth for another millennium. herical shells ejected by the central star in the distant past. The exact mechanism of those ejections, however, is unclear.