What are the characteristics of the ring nebula?

Ring nebula, that is, planetary nebula, so there is a high-temperature star in the center of the quasi-star cloud, surrounded by a circle of cloud-like material, just like a planet orbiting the sun, hence the name; Because it is shaped like a halo, it is also called a ring nebula.

Its cause is caused by a supernova explosion. When a star with a mass of 1.4 ~ 2 times the mass of the sun explodes, its external matter is thrown into space to form a circular nebula, and the core of the planet is compressed into a neutron star with extremely high density and temperature, which illuminates the thrown matter around it and is seen by people. This is a ring nebula, which is completely different from gas nebula and exonebula, and the number of such nebulae is much higher than others.

The ring nebula was created by the famous British astronomer William? Herschel found it. At that time, Herschel was a pianist in the British Royal Band, but he loved astronomy and often observed the stars with a telescope.

1one night in the summer of 779, when Herschel aimed his telescope at Lyra, among many stars, he found a small round celestial body with a slightly light green color and a clear edge. He vaguely saw that it should be a nebula. But Herschel didn't know what kind of nebula it was. Because the resolution of his telescope is too poor to see the details of the nebula clearly, but it looks like a big planet, so Herschel named this nebula a planetary nebula. In fact, planetary nebulae have nothing to do with planets, but this inappropriate name has been used all the time.

Anthony, a contemporary French astronomer of Herschel? Dalqueye also discovered this celestial body. He saw the comet when he was observing it. Messier, a French astronomer, put this celestial body in his catalog, ranking 57th, or M57 for short.

With the continuous improvement of observation ability, many planetary nebulae have been discovered one after another, and the total number currently exceeds 1000. Astronomers estimate that there are about 40,000 to 50,000 planetary nebulae in our galaxy, just because they are hidden in the depths of space, too small and too dark for us to find at present.