Why does the Ring Nebula look like a donut?

On August 3, 2023, NASA released the latest photos sent back by the Webb Space Telescope, giving an image of the M57 Ring Nebula with unprecedented clarity. At a distance of 1.5 million kilometers from the Earth, the Webb Telescope cleverly captured the detailed structural image of M57, which is about 2,600 light-years away from the Earth. In addition to being extremely spectacular, more importantly, scientists can observe this kind of photo in depth and explore the last moments of the life of stars. In another 5 billion years, the sun that gave birth to life on Earth will also face the same fate. Now, regarding the M57 Ring Nebula, I will give you three popular science questions.

Figure 1 Ring Nebula M57

Question 1 : Who discovered the doughnut-like M57 Ring Nebula? In January 1779, French astronomer Antoine Darquier de Pellepoix discovered a ring nebula. Coincidentally, a few weeks later, another French astronomer, Charles Messier, listed this "ring nebula" as "Messier 57" in his deep sky object catalog. At the time, Messier didn't know what this object was, but he concluded that it was a group of dim stars. It was not until the late 19th century that British astronomer William Huggins pointed out that it was not composed of stars at all, but of luminous gas. In the late 20th century, the Hubble Space Telescope revealed the true nature of the beauty of the Ring Nebula.

Question 2: How was the "Ring Nebula" formed? Scientists speculate that the event that produced the "Ring Nebula" occurred about 4,000 years ago. It was formed by a small star shedding its mass at the end of its life cycle, and the core of this star still exists in the form of a white dwarf, which ionized the surrounding gas. These gases continue to diffuse around this white dwarf, and under the high-energy radiation of the white dwarf, they produce impressively different colors of light. Therefore, these different colors of light are the various ionized gases surrounding this white dwarf.

Scientists have also speculated about its future: the original star that formed the Ring Nebula should be several times larger than the sun, but not large enough to explode into a supernova. The Ring Nebula is about 1 light-year in diameter and is expanding at a speed of 1.5 million kilometers per day. In the next few thousand years, the diameter of the Ring Nebula will increase by 50%, and then begin to fade and disperse.

**Question 3,** M57 is also called the Ring Nebula. So why is it called the "Ring Nebula"? Astronomers explain that it is named because its "Ring Nebula" image presents a slender structure shape. In addition, when the French astronomer Perepres discovered the Ring Nebula, he described the object as "... as big as Jupiter, like a fading planet." This also led to the term "planetary nebula". However, when people later observed M57 through a small telescope, they also found that it did have a "planetary" appearance. Therefore, the "Ring Nebula" is also classified as a "planetary" nebula, but it has nothing to do with planets.

(November 23, 1718 - January 18, 1802) French astronomer Charles Messier, credited with discovering the Ring Nebula in 1779, but in fact he discovered it independently after reading Charles Messier's report on his observations of Comet Bode.

(June 26, 1730 - April 12, 1817) French astronomer Charles Messier. Messier discovered 40 nebulae and 13 comets. He compiled a list of nebulous objects in the northern hemisphere called the "Messier Catalogue".

(7 February 1824 – 12 May 1910) Sir William Huggins, in full Sir William Huggins, was a British astronomer who revolutionized observational astronomy by applying spectroscopic methods to determine the chemical composition of stars and other celestial bodies.