The Hubble Space Telescope shows the youngest planetary nebula ever imagined. Only 20 years ago, the gas surrounding the dying central star was still not hot enough to shine. Known as the Stingray Nebula (Henize 1357), the incandescent gas sphere is about 18,000 light years away in the constellation Ara in the southern celestial hemisphere. The nebula is about 130 times larger than our Solar System, but it is only one tenth the size of other known planetary nebulae.
Hubble has been the first telescope to provide a close-up image of this small cloud of gas. Among the complex structure that includes a ring and gas bubbles, the image reveals that the central star is binary. Recently, astronomers have suggested that the presence of a companion is the key in creating the various forms of planetary nebulae.
While the surface expands and cools, a carbon core is produced in the center. When the Hydrogen and Helium are depleted, a compact carbon nucleus of the size of a planet like the Earth remains, but with a mass of the order of the Sun. Initially, this nucleus is at a very high temperature constituting a White Dwarf , but since new nuclear reactions no longer take place inside it, it is a thermally inert body that cools over time, passing from white dwarf to Brown Dwarf and finally to Black Dwarf.
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