Chapter 30. Galaxies and the Universe. Chapter 30:

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1 Chapter 30 Galaxies and the Universe Chapter 30: Galaxies and the Universe Chapter 30.1: Stars with varying light output allowed astronomers to map the Milky Way, which has a halo, spiral arm, and a massive galactic black hole at its center. 1

2 Chapter 30: Galaxies and the Universe Chapter 30.2: Finding galaxies with different shapes reveals the past, present, and future of the universe. Chapter 30: Galaxies and the Universe Chapter 30.3: The Big Bang Theory was formulated by comparing evidence and models to describe the beginning of the universe. 2

3 Section 30.1: The Milky Way Galaxy Objectives: Determine the size and shape of our galaxy. Distinguish the different kinds of variable stars. Identify different kinds of stars in a galaxy and their locations. The Milky Way Galaxy Galaxy: any of the very large groups of stars and associated matter found throughout the universe. 3

4 The Milky Way Galaxy Direct observation of the Milky Way galaxy is difficult because not only are we too close, but we are also inside the galaxy. The Milky Way Galaxy When we observe the band of stars stretching across the sky, we are seeing the edge of a disk from the inside of the disk. 4

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6 Variable Stars Variable star: A star in the giant branch of the H-R Diagram that pulsates in brightness due to its outer layers expanding and contracting. 6

7 Variable Stars 7

8 Variable Stars Astronomers can estimate the distance of globular clusters of stars within the Milky Way by identifying variable stars. Variable Stars RR Lyrae Variables: Stars that have periods of pulsation between 1.5 hours to and 1 day. 8

9 Variable Stars Cepheid Variables: Stars that have periods of pulsation between 1 and 100 days. (luminosity as much as doubles) Variable Stars By measuring the star s period of pulsation, astronomers can calculate how far away the star must be to appear this dim or this bright. 9

10 The Shape of the Milky Way Halo: spherical region where globular clusters are located; surrounds the Milky Way s nuclear bulge and disk. 10

11 Spiral Arms Astronomers have identified four major spiral arms and numerous minor arms of the Milky Way using hydrogen emissions. 11

12 Spiral Arms Orbital Period The orbital period of our sun around the galactic center is about 240 million years. In its 5 billion-year life, the Sun has orbited the galaxy approximately 20 times. 12

13 Orbital Speed The Sun s orbital speed is roughly 220km/s 792,000 km/h ~ 500,000 miles per hour Mass of the Milky Way The mass of the Milky Way is about 100 billion times the mass of our Sun. From this number, astronomers have concluded there are about 100 billion stars within the Milky Way. 13

14 A Galactic Black Hole Supermassive black holes occupy the center of most galaxies. These black holes are anywhere from a few million to a few billion times the mass of our Sun. (Much larger than stellar black holes) 14

15 Illustration: Supermassive Black Hole Stellar Populations in the Milky Way The differences among stars include differences in location, motion, and age. Stars are categorized based on their location: Disk: Population I Nuclear Bulge/Halo: Population II 15

16 Population II Population II Population I 16

17 Stellar Populations in the Milky Way Population I Stars: Found in Disk Arms 98% H and He <10 billion years old Young sequence stars Stellar Populations in the Milky Way Population II Stars: Found in Bulge and Halo 99.9% H and He >10 billion years old Old main sequence stars. 17

18 Evolution of the Milky Way The fact that the halo and nuclear bulge are made exclusively of old stars suggests that these parts of the galaxy formed first. Evolution of the Milky Way Our galaxy began as a spherical cloud in space. The first stars formed while this cloud was round. (PII) The young stars in the disk formed after the cloud collapsed by its own gravity. 18

19 Spiral Arms Most of the main features of the galaxy are understood by astronomers, except for the way in which the spiral arms are retained. 19

20 Spiral Arms One hypothesis is that a kind of wave called a spiral density wave is responsible. A second hypothesis is that the spiral arms are not permanent but are continually forming. 20

21 Section 30.2: Other Galaxies in the Universe Objectives: ohow astronomers classify galaxies ohow galaxies organized into clusters and superclusters othe universe is expanding Section 30.2: Other Galaxies in the Universe Vocabulary: odark matter osupercluster ohubble constant oradio galaxy oactive galactic nucleus oquasar 21

22 Discovering Other Galaxies In 1924, Edwin Hubble found evidence to suggest there were other galaxies in the universe. The first galaxy he discovered is now called the Andromeda galaxy. Properties of Galaxies Masses of galaxies have a wide range from 1 million to 1 trillion times the mass of our Sun. Dwarf ellipticals = 1 million x Sun s mass Large spirals = 100 billion x Sun s mass Giant ellipticals = 1 trillion x Sun s mass 22

23 Properties of Galaxies Luminosities of galaxies also vary over a wide range. Dwarf spheroidals = not much brighter than a globular cluster of stars Supergiant ellipticals = more than 100 times more luminous than our Milky Way galaxy. Classification of Galaxies Hubble went on to study galaxies and categorize them according to their shape. The Hubble Space Telescope was named after Edwin Hubble for his contributions to astronomy. 23

24 Disklike Galaxies Hubble classified disklike galaxies with spiral arms as spiral galaxies. Spiral galaxies are subdivided into normal spirals and barred spirals. 24

25 Disklike Galaxies A normal spiral galaxy is denoted by the letter S A barred spiral galaxy is denoted by the letters SB The letter a represents tightly wound arms, while the letter c represents loosely wound arms. 25

26 Sb SBb 26

27 Disklike Galaxies Disklike galaxies that do not have spiral arms are denoted as S0 or SB0 These types of galaxies are also called lenticular galaxies. 27

28 NCG 4866 Lenticular S0 28

29 Elliptical Galaxies Galaxies that are not flattened into a disk and do not have spiral arms are called elliptical galaxies. Round ellipticals are denoted E0 Elongated ellipticals are denoted E7 29

30 E0 30

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33 Irregular Galaxies Some galaxies do not have distinct shapes. These irregular galaxies are denote Irr The Large and Small Magellanic Clouds are examples of irregular galaxies. 33

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35 Bell Ringer Categorize the following galaxies using the classification system of galaxies

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37 Groups and Clusters of Galaxies The Milky Way belongs to a small cluster of galaxies called the Local Group. Diameter = 2 million ly There are about 40 known galaxies in the Local Group. 37

38 Local Galactic Group The largest galaxies in the Local Group are the Milky Way and the Andromeda Galaxy The closest Galaxies to us are the Small and Large Megellanic Clouds. Large Clusters Galaxy clusters larger than the Local Group may have hundreds or thousands of members with diameters up to 30 million ly across. Galaxies close together often collide to form strangely shaped galaxies or galaxies with more than one nucleus (Andromeda) 38

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40 Superclusters Clusters of galaxies are organized into even larger groups called superclusters. These gigantic formations can be hundreds of millions of light-years in size. 40

41 Earth s Address Earth 41

42 Solar System 42

43 Milky Way Galaxy Milky Way Galaxy 43

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45 The Expanding Universe In 1929, Edwin Hubble made another dramatic discovery. He found that all galaxies have redshifts. The redshift depends on its distance from Earth. In other words, the universe is expanding. 45

46 The Expanding Universe We can make an inference that if the Universe is expanding now, it must have been smaller and denser in the past. If we put this expansion in rewind, we can go back to a single point in the history of the Universe; The Big Bang. The Expanding Universe Hubble determined that the universe was expanding by making a chart of distance over time. The speed at which the Universe is expanding is called Hubble s constant. 46

47 Active Galaxies Active galaxies are galaxies that emit large amounts of energy from their core; the active galactic nucleus. Around 10% of all known galaxies are active. Active Galaxies There are two main forms of active galaxies: Radio Galaxies: elliptical galaxies that emit massive amounts of radio energy. Quasars: Small active galaxies around the size of our solar system that can emit thousands of times more energy than our entire galaxy. 47

48 Cosmology The study of the universe its nature, origin, and evolution is called cosmology. The mathematical basis for studying cosmology is general relativity (Einstein s theory of general relativity) Cosmology The fact that the universe is expanding implies that it had a beginning. The theory that the universe began as a single point and has been expanding since is called the Big Bang theory. 48

49 Cosmology Based on the best value for the expansion rate (Hubble s constant, H), the age of the universe can be pinpointed to 13.7 billion years. There are three possible outcomes for the Universe based on the Big Bang thoery. Cosmology Open Universe: The expansion of the universe will never stop Closed Universe: Expansion stops and turns into contraction caused by gravity. Flat Universe: Expansion slows down to a point which seems to stop. 49

50 Cosmology In 1965, scientists discovered a persistent background noise in their radio antennae caused by weak radiation. This noise is referred to as cosmic background radiation The radiation is interpreted to be from the beginning of the big bang. 50

51 Cosmology According to every standard model, the expansion of the Universe should be slowing down due to gravity Discoveries show that the universe is actually accelerating. The acceleration is caused by dark energy (an unknown force). 51