The Calabash Nebula from Hubble
Fast expanding gas clouds mark the end for a central star in the Calabash Nebula. The once-normal star has run out of nuclear fuel , causing the central regions to contract into a white dwarf . Some of the liberated energy causes the outer envelope of the star to expand. In this case, the result is a photogenic proto- planetary nebula . As the million-kilometer per hour gas rams into the surrounding interstellar gas , a supersonic shock front forms where ionized hydrogen and nitrogen glow blue. Thick gas and dust hide the dying central star. The Calabash Nebula , also known as the Rotten Egg Nebula and OH231.8+4.2, will likely develop into a full bipolar planetary nebula over the next 1000 years. The nebula, featured here , is about 1.4 light-years in extent and located about 5000 light-years away toward the constellation of Puppis .