What is star?
Stars are balls of gas that release energy produced by nuclear reactions within coerce. Most stars are similar to sun, our nearest star, but because they are so far away they appear to us as mere points of light. Throughout the Galaxy, stars are forming evolving, and being destroyed. By studying a range of stars, astronomers have been able to build a picture of how stars change over time and hence understand more about the past and probable future of the sun.
Stars from in huge clouds of gas and dust in space called nebulae, in a process that is continuing till today. The nebula shrinks under the inward pull of its own gravity, forming an embryonic star know as a protester. Eventually, the density and temperature of the gas at the protester’s center become high enough for nuclear reaction to begin. The object “switches on” to become a true star, generating its own heat and light. The star is then said to be on the main sequence. How long it stays like this and what happens next depend on the star’s mass
A main-sequence star with a mass of more than about 10 sun experience a spectacular end. It swells into a red supergiant with cooling, expanding outer layers. Eventually its core collapses. Casing a huge explosion know as a supernovas. For a few weeks, the supernova shines as brightly as an entire galaxy. While the outer layers of the star are scattered in space, the fate of the core again depend on its mass. A core of relatively low mass will be crushed into a tiny, superdense neutron star. If the core has a mass of more than about two suns, its own gravity will squash it further, into a black hole.
A star of similar mass to the sun undergoes a quieter end than a massive star. It swells into a red giant, eventually losing its outer layers, which form a gas shell know as a planetary nebula[ because of its resemblance to the disk of a distant planet] The core is exposed as a hot white dwarf that cools and fades over billions of years. On ceasing to emit light, it will become a black dwarf. The least massive stars, red dwarfs with only about one-tenth the sun’s mass, can last for 100 billion years or more, whereas the most massive stars burn out after only about a million years. The sun, which formed about halfway through its life cycle.