Star Life Cycles

1. Star Life Cycles

2. We Classify Stars by Their Characteristics All stars are huge balls of glowing gas that produce or have produced energy by fusion Stars differ in size, brightness, and temperature

3. We Classify Stars by Their Characteristics Stars look like small points of light because they are very faraway Light-year – the distance light travels in one year

4. Brightness and Distance The amount of light a star gives off and its distance from Earth determines how bright it appears to an observer Parallax – the apparent shift in the position of an object when viewed from different locations

5. Size Giant and supergiant stars range from ten to hundreds of times larger Because giant and supergiant stars have such huge surfaceareas to give off light, they are very bright

6. Size Stars called whitedwarfs are about 100 times smaller in diameter than the Sun, or roughly the size of Earth White dwarfs cannot be seen without a telescope

7. Color and Temperature If you observe stars closely, you may notice that they vary slightly in color The differences in color are due to differences in temperature

8. Color and Temperature The coolest stars are red - the hottest stars are blue-white The colors and lines in a spectrum reveal which gases are present in the star’s outer layers

9. Stars Have Life Cycles Although stars last for very long periods, they are not permanent The life cycle of a star varies, depending on the mass of the star Stars form inside a cloud of gas and dust called a nebula

10. Stars Have Life Cycles Gravity pulls gas and dust closer together in some regions of a nebula – as the matter contracts, it forms a hot, dense sphere – the sphere becomes a star if its center grows hot and dense enough for fusion to occur When a star dies, its matter may eventually become part of new stars

11. Stages in the Life Cycles of Stars Lower-Mass Stars • The stage in which stars produce energy through the fusion of hydrogen into helium is called the mainsequence • When a lower-mass star runs out of hydrogen, it expands into a giant star, in which helium fuses into carbon

12. Stages in the Life Cycles of Stars • Over time a giant star sheds it outer layers and becomes a white-dwarf – the dead core of a giant star • Although no fusion occurs in white dwarfs, they remain hot for billions of years

13. Stages in the Life Cycles of Stars High-Mass Stars • Stars more than eight times as massive as our Sun spend much less time in the main-sequence stage because they use their fuel rapidly • After millions of years, a higher-mass star expands to become a supergiant star – fusion produces heavier and heavier elements

14. Stages in the Life Cycles of Stars - When an iron core forms, fusion stops and gravity causes the core to collapse and the star erupts in an explosion called a supernova

15. Neutron Stars and Black Holes The collapsed core of a supergiant may form an extremely dense body called a neutron star Neutron stars emit little visible light Some neutron stars emit beams of radio waves as they spin – these stars are called pulsars because the seem to pulse as the beams rotate

16. Neutron Stars and Black Holes Sometimes a supernova leaves behind a core with a mass more than three times that of the Sun – it collapses forming an invisible object called a blackhole The gravity of a black hole is so strong that no form of radiation can escape from it

17. Stages in the Life Cycle of Stars

18. Star Systems A binary star system consists of two stars that orbit each other A multiple star system consists of more than two stars