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Found in the Vela constellation of the southern hemisphere, the Southern Ring Nebula is about 2000 light years from Earth. This nebula is one of many caused by the end stages of stars very much like our Sun. These stars exhaust their supply of hydrogen and helium as they fuse those into heavier elements. The radiant energy of the reactions pushes their outer boundary resulting in a large red giant stage. Our sun will grow to envelope the Earth as a red giant in about 4 billion years.
Gradually the star shrinks under the pull of gravity as the supply of hydrogen and helium runs out in the core. The outer layers of gases surround the star core. Eventually the core collapses triggering an explosion of energy. The outer layers of gases are scattered around the core. The core collapses to about the size of Earth with a mass of about a sun. It is a very small, hot, dense object radiating energetic ultraviolet light at temperatures exceeding 100,000˚C. It causes the surrounding gases to glow in various colors seen in images.
In the center of this nebula are two stars very close together. Click for detail. The very small one is the remaining hot dense core that caused this nebula display. The larger star of the two is younger and will eventually make a nebula.
This is another of the many examples of galaxies that appear to be in collision. But, the near one is tens of millions of light years closer to us than the far one. The alignment makes it appear they are interacting. They are not and won’t in the future.
The letters of the Greek alphabet are used to designate the stars of a constellation or grouping. Alpha, beta, gamma, etc. are the names from brightest to dimmest. I introduce you to Eta Carinae, the seventh brightest in Carina of the southern skies. It is about 100 times the mass of our Sun. It became extremely bright 150 years ago. It was almost as a supernova. But it survived and settled down. Surrounding the star are now two huge lobes of dust in a nebula shaped like a homunculus. It is likely to erupt any time into another spectacular display. Astronomers are watching closely.