ty. Next, a region of condensing matter will begin to heat up and star to glow, forming protostars. The temperature at this point is 5 million degrees centigrade. When this temperature is reached, hydrogen fuses and forms helium. A star then begins to release energy which causes it to contract and shine. After millions of years, the core of the star which is helium, contracts and a reaction begins to occur in a shell around the core. The core is at a high enough temperature for helium to form into carbon and the out layer of the star expands, cools and becomes less bright. The core then burns out and the outer layer leaves the core as a gaseous shell. The rest of the core cools and becomes a white dwarf and is less bright. When the white dwarf stops shining, it is called a black dwarf.Every now and then, a large star reaching the end of its life collapses in on itself, and then explodes very violently. The star explodes so violently that for a few weeks the star can out shine its parent galaxy. This type of explosion is known as a supernova. Neutron stars form during a supernova.What is a nebula?Nebula are clouds of gas and dust many light years across. They can be formed by dying stars as in supernova remnants or planetary nebula. They can be formed by young stars just emerging from their nurseries and beginning to illuminate the surrounding gas cloud. A nebula is comprised of interstellar gas, such as hydrogen, helium and other heavy elements. The crab nebula, for example, formed when a supernova exploded. Chinese astronomers saw this explosion and also saw a star six times brighter than Venus in the southern horn of the constellation Taurus. The star was then later named the crab because of its tentacle-like structure resembling the legs of a crustacean.M42 or the Orion Nebula is located in the Orion constellation. It is in the middle of the region known as the Sword of Orion. It is visible to humans through binoculars.GalaxyGalaxies...
