Behind The Curtain
In about 5 billion years, when it starts running out of nuclear fuel, the Sun will morph into a red giant, expanding beyond the orbit of Venus. It will eventually collapse, ejecting its outer layers, and creating a beautiful shell of diffuse gas in the process, known as the planetary nebula. These short-lived objects, usually having a blue-green tint, last a few tens of thousands of years before dissolving into space. It is estimated that about 10,000 of these nebulas exist in the Milky Way, even though only about 1,500 of them have been detected, while the rest is shrouded in a thick curtain of interstellar dust. The term “planetary nebula” is a misnomer, invented by the astronomer William Herschel, who was compiling an astronomical catalog at the time. He had just discovered Uranus, which has a blue-green tint, and he assumed that these new objecta resembled the newly discovered planet.
When it comes to stars that are up to 8 times the mass of our Sun, the entire process will be duplicated, seeing as massive stars, at the end of their existence, explode into supernovas. Those exploding shells of gas form another type of nebula, called a supernova remnant. There are several other types of nebulae, such as emission nebulae, which are essentially clouds of ionized gas able to emit light which can vary in color, dark nebulae, which are also clouds of gas, but they are so dense, that they don’t allow for any of the background light to pass through, and protoplanetary nebulae, which are created when a star begins to shed its outer layers shortly before becoming a planetary nebula.
The Dumbbell Nebula M27 was the first one discovered, by Charles Messier in 1764, who went on to find four additional nebulae. In 1790, William Herschel also found NGC 1514, a planetary nebula hosting a bright star in its center. He was able to determine that these object consisted of gas or dust, as opposed to being clusters as thought at the time. Although he identified 79 objects as planetary nebulae, only 20 of them have been classified as such, while 13 others he categorized differently were actually nebulae. The development of technology has allowed the scientists to capture a number of fantastically detailed images which provide an in-depth look at these occurrences. This allowed them to observe the complexities which might happen at the of the life of our Sun.
Some of the more notable nebulae, aside from the already mentioned Dumbbell Nebula M27 and NGC 1514 are:
Ring Nebula (M57): The almost-perfect ring-like shape made naming M57 a no-brainer. The diffuse shell of gas and dust spread almost evenly after they were shucked off of their parent star.
Saturn Nebula NGC 7009: Located in the constellation Aquarius, the Saturn Nebula, or NGC 7009, has a bright central star surrounded by a football shaped array of gas and dust.
Stingray Nebula (Hen-1357): The youngest known planetary nebula, Hen-1357 is as large as 130 solar systems.
SuWt2: A close binary star system creates a ring-like structure of dust and gas inside of this planetary nebula.
NGC 2818: This beautiful spreading planetary nebula is located 10,400 light-years away in the southern constellation of Pyxis, the Compass.