August 1, 2002: Hold the pickles; hold the lettuce. Space is serving up giant hamburgers. NASA's Hubble Space Telescope has snapped a photograph of a strange object that bears an uncanny resemblance to a hamburger. The object, nicknamed Gomez's Hamburger, is a sun-like star nearing the end of its life. It already has expelled large amounts of gas and dust and is on its way to becoming a colorful, glowing planetary nebula. The ingredients for the giant celestial hamburger are dust and light. The hamburger buns are light reflecting off dust and the patty is the dark band of dust in the middle.
Stars with masses similar to our Sun's end their lives as planetary nebulae. This final stage occurs after a star expels its outer layers into space, exposing the hot core. Ultraviolet radiation from the core streams out into the surrounding ejected gas, causing it to glow. The colorful, glowing gas is called a planetary nebula.
Gomez's Hamburger is on its way to becoming a planetary nebula. In fact, it is called a "proto-planetary nebula," a planetary nebula in the making. In this stage, the core is still relatively cool. Consequently, the star emits ordinary visible light, not ultraviolet radiation. Therefore, the surrounding gas does not glow. The ejected material, however, contains vast numbers of microscopic dust particles, which can reflect the starlight and make the material visible. This same effect produces halos around streetlights on a foggy night.
The lifetime of a proto-planetary nebula is very brief. In less than a thousand years, astronomers expect that the star in Gomez's Hamburger will become hot enough to make the dust particles evaporate, thus exposing the star to view. At that time the surrounding gas will glow.