Life Cycle of a Star

Star Assignment1 Life Cycle of a Star (Science Worktext pages 391-392) Directions- Read and answer the following questions THE LIFE CYCLE OF A STAR Stars have life cycles just like all living things. They are “born” and live for millions or billions of years before they “die.” Stars die in different ways depending on their masses (remember that mass is a measure of the amount of matter in an object). But all stars-from white dwarfs to supergiants –form in the same way. NEBULAE AND PROTOSTARS Stars form inside clouds of gas and dust. A cloud of gas and dust is called a NEBULAE. Star-forming nebulae are cold, dark and dense. Gravity causes the densest parts to collapse, forming regions called PROTOSTARS. Protostars continue to contract, or become reduced in size, and pull in surrounding gas. Their cores become hot and dense and produce enormous amounts of heat energy. THE BIRTH OF A STAR Over thousands of years, the energy produced by protostars heats the gas and dust around the protostars. The gas and dust blow away over time and the protostars become visible as stars. Some of the left over material might become planets or objects that orbit the star. MAIN SEQUENCE STARS Stars spend most of their lives on the MAIN SEQUENCE. A star becomes a MAIN SEQUENCE star as soon as it begins to fuse (the process of combining two or more things into one) hydrogen into helium in the core. It remains on the main sequence for as long as this process continues. Average mass stars like our Sun remain on the main sequence for billions of years. High mass stars only stay on the main sequence for millions of years. High mass stars have more hydrogen but they process, or use it, at a faster rate. When a star’s hydrogen supply is almost gone, the star moves off the MAIN SEQUENCE. It begins the next phase of its life cycle (pictured on page 392 in your Science Worktext) We will read about how stars die in the next assignment. Lets see what you remember about the “Birth of a Star” QUESTIONS: 1. 2. 3. 4. Do all stars form in the same way? What is a Nebulae? How do protostars form? How does a star become a main sequence star?