The term Planetary Nebula are Nebula's, they are large clouds of dust and dust that have been created in the aftermath of the death of a star. They despite their name are nothing to do with planets. They do get their name from the mistaken belief that they are planets. They have been referred to as Planetary Nebulas by Charles Messier and Sir William Herschel in the eighteen century. Herschel had recently discovered Uranus and that the colours were similar. Space
A star will only end its life as a Planetary Nebula when it is less than eight times the mass of the Sun. If the star has more than eight times then it will end its life as a planetary nebula.
At the end of a stars life, when the star has grown old, it will move into the red supergiant phase as the outward pressure overrides the inward pressure of gravity. Our Sun will do this in billions of years time, all life on Earth will have disappeared long before then. As the Sun expands, it will consume the inner planets including Earth. The planets at the edge of such as Uranus, Neptune and Pluto (dwarf planet) will most likely survive. Hopefully mankind would have found a way to move off the planet by then to continue survival.
During the later phases of its red supergiant phase, the excess gas will been ejected as a planetary nebula leaving behind a white dwarf. Large stars will explode in a supernova, leaving a Supernova Remnant behind, a similarly looking phenomena. The difference being a Remnant and a Planetary Nebula is that a Remnant will contain a neutron star or a pulsar at the heart. Stack-Exchange
A planetary nebula may only exist for 20,000 years or thereabouts as the nebula breaks down and dissipates amongst the stars leaving the white dwarf on its own. Those white dwarfs out there would therefore have been a planetary nebula at one time. In a galaxy of over 250 billion, there are only about 1,500 known planetary nebulae. Harvard. It is believed though there are about 20,000 objects to exist in the milky way Galaxy. Britannica
The enriched gas from the planetary nebula will spread out into space and be used by future generations of stars. Once a star dies, its matter is recycled and from the death comes life. Our Sun has been classed as a third generation star. When a star dies, it creates heavy elements. A star can only create elements up to Iron on the periodic table, to get higher, it has to explode. Some of the heavier elements in the Sun would therefore have been created from the death of a star.
The White Dwarf at the centre of the planetary nebula will be extremely hot, over 100,000°C. Over time, the white dwarf star will begin to fade and turn into a black dwarf and then that will eventually break apart and dissipate. The length of time to turn into a black dwarf is longer than the age of the Universe which is why no black dwarves have ever been spotted. White dwarves will have the mass of the Sun but only be as large as the Earth. Schools Observatory
The first planetary nebula to be discovered was the Dumbbell Nebula, located in the southern hemisphere constellation of Vulpecula. It was discovered by Charles Messier who added it to his Messier catalogue as entry 27.
The picture was taken using a ground based telescope by the European Southern Observatory in Chile. At the centre of the Dumbbell is a white dwarf star. The scientists who took the photo tried to show it in nebula's true colours.
The apparent magnitude of the Dumbbell Nebula is 8 which means it is too dim to be able to see with the naked eye. You would need a pair of 12x50 binocular or high magnification to be able to see the object.
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