Image Credit: Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA/ESA
Hubble 5 (also designated ESO 455-42, PN G359.3-00.9 or Hen 2-286) is a “butterfly” or bipolar (two-lobed) planetary nebula located about 2,200 light-years away in the constellation of Sagittarius. This nebula – sometimes nicknamed the Hubble Double Bubble Planetary Nebula – is approaching us at approximately 24 kilometers per second.
Despite their name, planetary nebulae have nothing to do with planets. The name of planetary nebulae arose because of the visual similarity between some round planetary nebulae and the planets Uranus and Neptune when viewed through early telescopes.
When a star with a mass up to eight times that of the Sun runs out of fuel at the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly.
Over the next several thousand years, the nebula will gradually disperse into space, and then the white dwarf will cool and fade away for billions of years. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.
In the case of Hubble 5, the heat generated by fast winds from the dying central star (which might as well be a binary system) causes each of the lobes to expand into the surrounding interstellar medium. A supersonic shock-wave can form at the boundary, causing newly excited gas there to shine.
This image was taken on September 9, 1997 by the Wide Field and Planetary Camera 2 2 onboard the Hubble Space Telescope.