Introduction to the Universe

Learning Objectives Know some ages & distances Distinguish different types of large quantities Understand the consequences of light traveling over large distances

Astronomical numbers 1 light sec = distance light travels in … 1 million = 1,000,000. (aka. Mega or M) 1 million sec = 11.6 days 1 billion = 1,000,000,000 (aka. Giga or G). 1 giga-sec = 31.8 years. 1 light sec = distance light travels in … = 300,000 km = 186,000 miles. Almost to the Moon. 1 light year = distance light travels in one year TRIVIA: 1 light year = 6 trillion miles. Nearest star to Sun = 4.3 light-years away. The Sun, all 8 planets are about 4.6 Gyr old. How many years is that? Distance to Sun? 3 answers. __ Light __, ____ miles, __AU Universe & everything in it is 13.7 Gyr old (some things weren’t born at the beginning, so are younger)

Today, astronomers can detect a galaxy that is 10 billion light-years away. True False 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Can astronomers detect something 20 billion light years away, right now? Yes No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Will it ever be possible to see something 20 billion LY away? Yes No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Finding baby & senior citizen galaxies Talk to your neighbor for 1 minute and answer these: Where would astronomers need to look to take a picture of galaxies in their earliest stages of life (babies)? Hint given after 30 seconds. DV: the hint is Unogen. Where would we look to take pictures of galaxies in their later stages (senior citizens)?

Where would astronomers need to look to take a picture of galaxies in their earliest stages of life (babies)? Nearby Far away 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Light years and observations Like letter through post office: Letters from far away take longer to arrive We receive “ancient” letters Letters from Los Angeles arrive quickly We receive “today’s” letters FOR MORE HELP: See figure 1.5 on p. 9 Lecture Tutorial workbook “Looking at Distant Objects,” page 131.

Furthest things seen As of 11/5/2009, the furthest object ever seen by astronomers* is a Gamma Ray Burst (giant star explosion, “hypernova”) 13.035 billion light years away. The light arrived on Earth on April 23, 2009. Dist measured by its Doppler redshift = 8.2 (see chapter 5) GRB occurred only 630 million years after the Big Bang. Probably a 1st generation HUGE star death. Gigantic early generation stars make a GRB, which are probably a hypernova (big supernova with powerful jets at the north and poles) “Merely” large or newer stars “only” make a supernova We also see LIGHT leftover from the Big Bang, emitted only 380,000 yrs after the Big Bang. *One of my former roommates, Edo Berger, is one of the astronomers who made this discovery!

Learning Objectives What is the universe composed of? How do we know? Is the composition changing? Why or why not?

What the universe is made of & how we know. Part 1. Things in the universe: Stars Star leftovers such as _______________ Gas clouds (and other stuff) between stars Galaxies (HUGE collections of stars) Analyzing their light (chapter 5), we discover, all of these* are made of: Hydrogen (often gas) ~73% Helium (often inert gas) ~25% Everything else ~2% Oxygen, Carbon, Iron, Sulfur, Neon, Potassium, etc. Gold, silver, platinum are VERY rare. *except not inner 4 planets. But outer planets are.

What the universe is made of & how we know. Part 2a. Astronomers studied motions of stars, star clusters, and gas clouds inside galaxies Move too fast  must be extra gravity inside galaxies Don’t see anything causing gravity Extra gravity from invisible stuff “Dark matter” Existence hypothesized in 1933, Fritz Zwicky @ CIT Vera Rubin gathered first STRONG evidence described above in 1970s. She’s still doing astronomy today!

What the universe is made of & how we know. Part 2b. Then, studying gravity, found “dark matter” in MANY other places: Halos of galaxies Inside & around galaxy clusters especially in center of clusters Based on gravity: there is 10 times more dark matter than regular matter! H, He, etc (elements) are only 10% of stuff Dark matter is 90% of stuff We know dark matter is NOT elements We know some properties of dark matter based on gravity (how it clumps with elements, called “bias”)

What the universe is made of & how we know. Part 3. Measure how quickly universe expands. (more on this soon) In 1998-99, multiple researchers discovered far away galaxies are moving faster than predicted Discovered by seeing supernovas in distant galaxies Confirmed by studying Cosmic Background Radiation Universe expands faster today than in the past Don’t know why, “Dark energy” Dark energy accounts for 73% of the universe’s mass-energy. Matter/stuff (including “dark”) only is 27%.

Summary: Universe’s mass-energy composition

What grade do astronomers get for understanding the universe? B C D F 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Normal (NOT dark) matter Everything you know about is normal matter, (baryonic) made of a few elements Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Gold Periodic Table, page A-13 @ end of textbook. Most things are molecules: 2+ atoms Water (H2O), Carbon dioxide (CO2) Science tells us right after the Big Bang, the universe only had 2 elements: Hydrogen (75%), Helium (25%) TINY bit of 1-2 more. Where did everything else come from? Book calls it “recycling”. See pages 6-7. Only makes up 2% of matter today. But that’s enough to form planets like Earth, luckily.

Increasing Decreasing Staying the Same How is the amount of elements OTHER THAN hydrogen & helium in the universe changing? Increasing Decreasing Staying the Same 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Learning Objectives Know some ages & distances Put the ages and distances into perspective with other, more familiar things Understand motions on Earth, of Earth and of the Solar System

Ages of a few things When things formed: The Big Bang = 13.7 billion years ago The Sun & Earth = 4.6 billion years ago The Milky Way galaxy = 12-13 billion years ago See the calendar & discussion on page 14.

Sizes & Distances – See pages 9-14 Planet order & sizes with hands… In the “Voyage” scale model, 10 billion:1 Sun is the size of a large grapefruit Earth is the size of 1mm, located 50 ft from Sun. Real radius is ______________. Moon is ¼ Earth’s size, located 1.5 inches from Earth Jupiter is … Pluto is … Nearest star is named …, size & dist … Size of Milky Way is … Light travel times to these objects…

Are you moving right now? Yes No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Motions Daily motion – Earth’s rotation once per __ Speed varies: ___ for Santa, 1000 mph for Ecuador Yearly motion – Earth’s revolution once per __ Distance: 1AU = ____ Speed: average ~66,000 mph Direction “tilted” 23.5˚ relative to rotation. Sun orbits Milky Way center once per 200-230 Myr 28,000 ly radius, speed ~500,000 mph Studying this motion  dark matter discovered Galaxies moving relative to each other. Nearest galaxies get closer to us. Most move away.

Do all continents take 24 hours to make one circle around the Earth’s axis? Yes No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Galaxies outside the Local Group are moving: Towards us Away from us Randomly towards & away 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Learning Objectives Understand the nature of the “expanding universe” and how we know it’s expanding Hubble’s Law Interpret expansion of universe to determine a fundamental property “Car universe” Understand what we need to measure about the universe to determine its age

Expanding universe means “objects are getting _________”? Further apart Bigger Both further apart and bigger 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Expanding universe Expansion refers to empty space between galaxies Objects don’t grow because … Gravity and other forces hold THINGS together. Examples: Stars, galaxies, planets, people. We see galaxies moving away Draw a picture on chalkboard – space expands Speed away from us depends on distance Objects twice as far are moving twice as fast Objects 100x further are moving 100x faster This rule is now called “Hubble’s Law” Let’s see how Hubble’s law works with cars

Car “expanding universe” Make a chart like the one I put on the board Car 1 is 60 miles away and travels 30 mph Car 2 is 120 miles away. How fast is it moving if it follows Hubble’s Law? Car 3 is 240 miles away. How fast? How long since Car 1 left you? Car 2? Car 3? How old is the “car universe?” This is exactly what we see with galaxies, except the time is _________ years.

Composition Speed Distance Brightness Luminosity Number of stars Which of the properties below do astronomers need to measure about galaxies to determine the age of the universe? Select all that apply. DON’T VOTE UNTIL YOU’VE MADE YOUR FINAL DECISION. Composition Speed Distance Brightness Luminosity Number of stars 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Is the composition of the universe changing? Yes No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Born recently Born long ago (Question asked by a student) Stars that were made of the MOST Hydrogen and Helium are: Born recently Born long ago And the stars that have the LEAST? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Learning Objectives Know some ages & distances Distinguish different types of large quantities Put the ages and distances into perspective with other, more familiar things Understand the consequences of light traveling over large distances What is the universe composed of? How do we know? Is the composition changing? Why or why not? Understand motions on Earth, of Earth and of the Solar System Understand the nature of the “expanding universe” and how we know it’s expanding Hubble’s Law Interpret expansion of universe to determine a fundamental property “Car universe” Understand what we need to measure about the universe to determine its age

Summary – chapter 1 Astronomical numbers Light travel time Composition of universe Why the composition changes What causes the change? Sizes, distances, and ages Motions Expanding universe, how we measure age