Phys 214. Planets and Life

Transcription

1 Phys 214. Planets and Life Dr. Cristina Buzea Department of Physics Room (Please use PHYS214 in subject) Lecture 6. The Structure and Scale of the Universe + Movie (Page 52-61, ) January 18

2 The structure and scale of the Universe Next Monday, January 21st: Quiz! Textbook Page 52-61, Structure and scale of the Universe The scale of Solar System Distances to the stars (+movie 8 min) Parallax and star luminosity The scale of a galaxy The content of the Universe (+ 8 min movies) The Big Bang Movie: Hubble 15 years of discovery (6 min) Ch. 8. Birth and death of the Universe

3 Structure and Scale of the Universe

4 Structure of the Universe Solar System, Milky Way Galaxy, Local Group, Local Supercluster The Milky Way galaxy has about 100 billion stars. The Local Group has about 40 galaxies

5 The Scale of the Solar System Understanding the scale of the Universe is crucial for the study of life in the Universe, because it tells us of great challenges that confront us as we search for life on other worlds. Jupiter radius 69,910 km; Earth 6,371 km; Sun 695,500 km

6 The Scale of the Solar System Distances from Sun to: Earth = 1 AU = 150,000,000,000 m = 1.5 x m = = 150 million km Jupiter = 5.2 AU Neptune =30 AU Eris (Xena) = 97 AU Sedna = 525 AU Oort cloud = 50,000 AU!

7 Distances to the Stars The scale of our Solar system is astronomical, however is small compared to the distances that separate the stars. If the Solar System size would be 0.6 miles, the distance to the nearest star would be as far as Washington DC to California. The distances between stars are measured in light-years. One light year is the distance that light travels in one year. Light speed = 300,000 km/sec Distance = Speed x Time 1 light year = (speed of light ) x (1yr) = 9.46 trillion km = 60,000 AU!

8 Distances to the Nearest Stars The nearest star system to our own is Alpha Centauri, located at about 4.4 light years away. It takes light 4.4 years to reach us, this means that we see Alpha Centauri what it looked 4.4 years ago, and not how it looks today. Implications for detecting Life on near stars If we send a radio message to the nearest star Alpha Centauri, it will take 4.4 years to reach it, a reply another 4.4 years Most of the extrasolar planets are indirectly detected. Voyager 2 launched in 1977, passed Jupiter in 1979, Saturn in 1981, Uranus in 1986, Neptune in It is bounded for the stars at a speed of 50,000 km/hr (100 times faster than a bullet). It would take Voyager 100,000 years to reach Alpha Centauri at its speed of 50,000 km/hour (if headed in that direction..).

9 Distances to the stars We see Orion Nebula how it looked 1,500 years ago, about the time of the fall of the Roman Empire. If we send now a message to Orion Nebula and receive a message in return, the reply would come after at least 3,000 years!!! And the Orion Nebula is quite near compared to the scale of Milky Way! Orion Nebula located 1,500 light years away.

10 Distances to the stars Movie (8 min) Hubble DVD 15 Years of Discovery, Chapter 5, COSMIC COLLISIONS 0px/hst15_chapter05.html

11 Parallax- method to measure large distances NOT IN THE TEXTBOOK! Will be required for the exams How dual-eye vision system perceives depth in the world Hold a pencil close to your face and alternately blink one eye The pencil appears to move against more distant background objects! We photograph the sky when earth is at one point in its orbit and 6 month later when Earth rotated 180 degrees around the Sun. We superimpose the two images; the stars shifted the most are the closest

12 Parallax- method to measure large distances NOT IN THE TEXTBOOK! It may appear in the exams If the parallax angle angle is small, the distance to the star is approximated as D = 1AU 1AU=150 million km, and angle should be in radians. " 360 degrees = 2! radians,!= The sky spans half a complete circle 180 degrees, each degrees has 60 min, each minute of arc has 60 seconds. There are 3,600 arcseconds per degree and 1.3 million arcseconds in 360 deg circle Roughly 1 second of arc =1/200,000 of a radian 1 parsec = distance from a star that has a parallax of 1 arc second D =1.5 "10 8 km " 200,000 = 3"10 13 km = 3.26 light years

13 Parallax- method to measure large distances NOT IN THE TEXTBOOK! Will be required for the exam Distant objects have small parallax Close objects have large parallax Size of moon = 31 minutes of arc (half degree) Alpha centauri C (nearest star) 1.5 seconds of arc

14 Stars luminosity and apparent brightness NOT IN THE TEXTBOOK! The total amount of energy that a star radiates out into space is referred to as its luminosity, L (Joules/sec = Watts). Flux or apparent brightness (W/m 2 ) at a distance R spreads over a sphere of radius R F = Flux decreases as 1/R 2 L 4"R 2 The luminosity of a star is determined by its apparent brightness and distance. Star brightness is measured using a Magnitude system Brightness is related to surface temperature (Hertzsprung-Russell diagram)

15 Star luminosity and surface temperature

16 Star luminosity and surface temperature A star s brightness depends on Its distance Intrinsic luminosity Dimming effect of interstellar dust Stars have also different colors - from blue to red, reflecting temperatures of outer gas layers; A star spectral type indicates a star s surface temperature The hottest (most blue) stars are more luminous than cooler stars. The stars are not scattered at random in the luminosity-temperature diagram (Hertzsprung-Russell), but fall in 3 main groups - main sequence (stable stars burning hydrogen in their cores, majority, sun is in the middle - average star) - the giants and supergiants (mostly cool and red, but very luminous, at the end stages of their lives, having exhausted their hydrogen) - White dwarfs (hot but dim, collapsed remains of stars like the sun, corpses) - More on this diagram in Chapter 11

17 The Scale of the Milky Way Galaxy Milky Way has more than 100 billion stars. It will take to count them more than 3,000 yr if you count one star per/sec. How long will it take to study each star?

18 The Scale of the Milky Way Galaxy Milky Way is 100,000 light-yrs diameter The Solar System is 28,000 light-yrs from the galactic centre, located in the disk Imagine: light travels very fast by earth standards. Circling Earth at the speed of light = 8 circuits in 1 sec We would need more than thousands of years to study the stars in Milky Way galaxy, to search for their planets, and signs of life!

19 The Solar neighbourhood within 12.5 Light Years Number of stars within 12.5 light years = 33

20 Milky Way Galaxy Number of stars within light years = 200 billion The Sun is located in the disk of Milky Way.

21 The satellite Galaxies Number of large galaxies within light years = 1 * Number of dwarf galaxies within light years = 12 * Number of stars within light years = 225 billion

22 Local group of galaxies Number of large galaxies within 5 million light years = 3 * Number of dwarf galaxies within 5 million light years = 46 * Number of stars within 5 million light years = 700 billion

23 The Virgo Supercluster Number of galaxy groups within 100 million light years = 200 * Number of large galaxies within 100 million light years = 2500 * Number of dwarf galaxies within 100 million light years = * Number of stars within 100 million light years = 200 trillion

24 The Neighbouring Superclusters Number of superclusters within 1 billion light years = 100 * Number of galaxy groups within 1 billion light years = * Number of large galaxies within 1 billion light years = 3 million * Number of dwarf galaxies within 1 billion light years = 60 million * Number of stars within 1 billion light years = trillion

25 The Visible Universe Number of superclusters in the visible universe = 10 million * Number of galaxy groups in the visible universe = 25 billion * Number of large galaxies in the visible universe = 350 billion * Number of dwarf galaxies in the visible universe = 7 trillion * Number of stars in the visible universe = 30 billion trillion (3x10 )

26 The Search for Extraterrestrial Intelligence SETI Due to impossibility of traveling to the stars (immense distances) we are confined to observing and listening to the Universe. SETI, which listens for signals from alien civilizations, is a search for civilizations that used radio technology some decades, centuries, or millennia in the past.

27 The Content of the Universe The Universe is the sum total of all matter and energy. Until recently, it was assumed that the matter was found mainly in stars and galaxies, and the energy was in the form of light. However, it seems that the visible matter and energy is just the tip of the iceberg. The Universe is composed of visible matter, light, and a mysterious dark matter and dark energy! The Universe is made mostly of a mixture of dark matter and dark energy.

28 The Content of the Universe By studying stellar orbits, astronomers have mapped out the matter in Milky Way. Most of the mass of Milky Way lies unseen in the form of dark matter in a larger spherical halo that surrounds the flat disk. Most galaxies are surrounded by some "dark" form of matter that cannot be observed by radio, infrared, optical, ultraviolet, X-ray, or gamma-ray telescopes.

29 The invisible dark matter Dark Matter Movie 1 Hubble (5 min) This Hubble Space Telescope composite image shows a ghostly "ring" of dark matter in the galaxy cluster ZwCl

30 The Invisible Dark Matter 3D map of large-scale distribution of dark matter. Loose network of dark matter filaments, gradually collapsing under the relentless pull of gravity, and growing clumpier over time. The dark matter filaments began to form first and provided an underlying scaffolding for the subsequent construction of stars and galaxies from ordinary matter. Without dark matter, there would have been insufficient mass in the Universe for structures to collapse and galaxies to form. Movie 2 NASA (3 min). NASA & Caltech

31 Dark Matter and Dark Energy In addition to Dark Matter, the Universe seems to contain a mysterious form of energy called Dark Energy. Dark Energy is pushing galaxies apart, while the gravity of visible and dark matter tries to keep them together. NASA/ESA NASA & Caltech

32 Dark Matter and Dark Energy The ordinary matter that makes up stars and planets and life represents only a few percents of all the matter and the energy in the Universe. Dark matter and dark energy are the main ingredients of the Universe. Dark matter and dark energy don t seem to affect our study of life in the Universe, however they should remind us that we do not yet understand Nature.

33 Our cosmic origin

34 The Universe At the beginning of the last century, most astronomers assumed that the universe is unchanging. Images from telescopes proved this assumption to be wrong. Edwin Hubble observed that the distances between galaxies are increasing with time. 1) Every galaxy in the Universe (except the Local Group) is moving away from us. 2) The more distant the galaxy, the faster it appears to be racing away. The Universe is expanding! Edwin Hubble ( )

35 The expanding Universe Hubble and Humason showed that v=h 0 d where v = velocity of expansion, d = distance, H 0 - Hubble s constant. Galaxies are moving at speeds of hundreds of kilometers per second away from us! Doppler shift: "# # = v c V = radial velocity (positive if object moving away from us) "# = wavelength shift, # = wavelength for stationary source, c - speed of light (Useful formulas Page A-4 textbook)

36 The expanding Universe There is no center of expansion, or every point is the center. Movie 3. Hubble - 15 years of discovery Ch. 8. Birth and death of the Universe (6 min)

37 Next lecture Next Monday, January 21st: Quiz! Stellar lives and galactic recycling The scale of time How big is the Universe And Hubble movie