Exploring Beyond Our Solar System

1. Beyond Our Solar System – The Universe in a Nutshell! Chapter 25

2. Star Temperature • Color is a clue to a star’s temperature • Very hot (30,000 K) stars emit their light in the blue spectrum, red stars are much cooler, stars with temperatures between 5000 and 6000 K appear yellow

3. Binary Stars • Binary Stars – pairs of stars, pulled together by gravity, that orbit each other • Binary stars are used to determine the star property most difficult to calculate – its mass

4. Parallax • The nearest stars have large parallax angles, while those of distant stars are too small to calculate • Light-Year – unit used to express stellar distance, the distance light travels in one year (~9.5 trillion kilometers) • Our closest star (besides the sun), Proxima Centauri, is about 4.5 light-years away from the sun

5. Stellar Brightness • Apparent Magnitude – a star’s brightness as it appears to Earth • Absolute Magnitude – how bright a star actually is

6. A Hertzsprung-Russell diagram shows the relationship between the absolute magnitude and temperature of stars

7. Nebulae – clouds of dust and gases in space Reflection Nebula in Orion Dark Nebula – Horsehead Nebula Emission Nebula – N11

8. The Birth of a Star • The birthplaces are dark, cool interstellar clouds (nebulae) • The initial contraction of the nebula can be triggered by the shock wave from an explosion of a nearby star The Orion Nebula in normal color and infrared

9. Protostar – a developing star not yet hot enough to engage in nuclear fusion • When the core of a protostar has reached about 10 million K, pressure within is so great that nuclear fusion of hydrogen begins, and a star is born Protostars in the Horsehead Nebula are circled

10. Main-Sequence Stage – From the moment of birth until the star’s death • The more massive a main-sequence star, the shorter its life span • A yellow star, like our sun, can remain in the main-sequence for approximately 10 billion years

11. Red-Giant Stage • The Sun will spend less than 1 billion years as a Red-Giant Globular Star Cluster, some of the oldest stars in the universe

12. White Dwarf – remains of low and medium mass stars, extremely small stars with densities greater than anything on Earth

13. Life Cycle of a Sun-like Star

14. Neutron Stars – remnants of supernova events, stars that are smaller and more massive than white dwarfs

15. Black Hole – A massive star that has collapsed to such a small volume that its gravity prevents the escape of everything, including light

17. Stellar Evolution

18. The Milky Way Galaxy • Galaxies – groups of stars, dust, and gases held together by gravity • The Milky Way is a large spiral galaxy whose disk is about 100,000 light-years wide and about 10,000 light-years thick at the nucleus • It has at least three distinct spiral arms, the sun lies about 2/3 of the way from the center on one of these arms and orbits the nucleus about every 200 million years • There may be more than 100 billion stars in our galaxy alone

19. Structure of the Milky Way

20. Spiral Galaxies – like our galaxy, these galaxies have multiple arms that sweep out from a central nucleus

21. Elliptical Galaxies – do not have spiral arms, makes up ~60% of known galaxies, can range from round to oval

22. Irregular Galaxies – consist mostly of younger stars, appear as clouds of stars

23. Galaxy Cluster – a system of galaxies containing from several to thousands of member galaxies

24. The Expanding Universe • Hubble’s Law – galaxies are retracting from us at a speed that is proportional to their distance • The red shifts from distant galaxies indicate that the universe is expanding

25. Big Bang Theory – The universe began as a violent explosion from which the universe continues to expand, evolve, and cool • The big bang theory states that at one time, the entire universe was confined to a dense, hot, supermassive ball. Then, about 13.7 billion years ago, a violent explosion occurred, hurling this material in all directions