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| The Owl Planetary Nebula, Messier 97. The COAST robotic telescope SHO filters, Mount Teide, Tenerife, Open University, telescope.org. Images processed by Kurt Thrust |
Planetary nebulae have nothing at all to do with planets. They are the glowing gas 'left overs' from stars, which having run out of hydrogen to fuse, consequently left the main sequence to end their existence as white dwarf stars surrounded by glowing ionised gas shed by the progenitor stars earlier in the process.
The Owl Nebula may be found in the constellation Ursa Major, the Great Bear, and is approximately 2000 light years distant. The progenitor star, some 8000 years ago, swelled to become a red giant and then over a period of time shed mass in three shells. The nebula contains hydrogen, helium, nitrogen, oxygen and sulphur and is currently approximately 2 light years in diameter. At its centre a white dwarf star is condensing, with an effective temperature of 123,000K. For comparison our sun has an effective temperature of just under 6000K. So white dwarf stars are very very hot even though nuclear fusion has long stopped. Over aeons, white dwarf stars will lose their residual heat, cool to absolute zero and become cold black dwarf stars.
The Owl Nebula cannot be seen with the naked eye or with the aid of 10x50 binoculars but on a good clear night from a dark rural site, it might be glimpsed through a small telescope. - Joel Cairo CEO the Jodrell Plank Observatory.
