Milky Way & Hubble Law

Transcription

1 Milky Way & Hubble Law Astronomy 1 Elementary Astronomy LA Mission College Spring F2015

2 Quotes & Cartoon of the Day Happy Thanksgiving!

3 Announcements 3rd midterm 12/3 I will drop the lowest midterm grade Final 12/15 at 10 AM! No Class Thursday!

4 Last Class Stellar Evolution wrapup. Black holes Binaries & Clusters Galaxies What s a Galaxy? Galaxy types LT Galaxy Classification Our Galaxy, the Milky Way

5 This Class Galaxies LT Galaxy Classification Our Galaxy, the Milky Way Hubble s Law

6 WARM-UP QUESTION

7 A galaxy that appears to be populated by mostly red stars, likely. A. never had blue stars in the galaxy. B. had blue stars that are not present anymore but were at one time long ago. C. has been around long enough for blue stars to all evolve into the red main sequence stars we see. D. never contained enough gas to have blue stars develop. E. as blue stars that are being blocked by dust.

8 LT GALAXY CLASSIFICATION

9 A galaxy that appears to be populated by mostly red stars, likely. A. never had blue stars in the galaxy. B. had blue stars that are not present anymore but were at one time long ago. C. has been around long enough for blue stars to all evolve into the red main sequence stars we see. D. never contained enough gas to have blue stars develop. E. as blue stars that are being blocked by dust.

10 Let s Practice

11 How would you classify the Milky Way? A. SBbc NASA/JPL-Caltech/R. Hurt B. Sb C. S0

12 The centers of most spiral galaxies appear redder than the arms. The most likely explanation for this is. A. young blue stars are primarily in the arms and old red stars in the bulge B. nuclear reactions in the center are creating heat C. the black hole in the center is glowing red

13 Elliptical galaxies contain mostly red stars. What can you conclude about the rate of star formation in elliptical galaxies? A. Few to no new stars are forming. B. Many new stars are forming. C. There is not enough information to conclude anything.

14 We live in a Galaxy: The Milky Way Astronomy 1 Elementary Astronomy LA Mission College Spring F2015

15 INTRO TO THE MILKY WAY

16 The Milky Way Our home galaxy A barred spiral galaxy From our solar system, we see this...

17 Milky Way over the VLT Image Credit: ESO (Yuri Beletsky) Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015

18 Structure of the Milky Way Looking through the disk from inside and combining the 2-D data with distance information allows us to construct a model of what the Milky Way looks like from outside...

19 Edge-on Model

20 Face-on Model Image Credit NASA/JPL-Caltech/R. Hurt Astronomy 1 - Elementary Astronomy Image Credit LA Mission NASA/JPL-Caltech/R. College Hurt Levine F2015

21 Structure of the Milky Way Bulge: spherioidal about 6000 ly diameter Densely packed old red stars Bar Disk: flat about 90,000 ly x 900 ly Stars and interstellar gas and dust, including young stars Sun about 24,000 ly from center Halo: Spheroidal about 300,000 ly diameter Image Credit: R.J. Hall old stars, globular clusters, dark matter, hot gas

22 3D Model

23 WHAT S IN THE MW?

24 Milky Way Recipe 300 ± 100 billion stars at least 1983 planets Interstellar Medium (ISM) ~ M Supermassive Black Hole ~ x 10 6 M Dark Matter to account for a total mass of x M

25 Where is the Interstellar Medium? Milky Way Galaxy Interstellar Medium = ISM Everywhere between stars not uniformly distributed, denser in bar and arms Image Credit NASA/JPL-Caltech/R. Hurt

26 THE GALACTIC CENTER

27 The Galactic Center Images about 8 across. GC in upper left Entirely obscured in visible light First explored using radio astronomy later further explored with IR astronomy

28 The Galactic Center The GC is very wierd place WAAAY down inside the bulge This image about 3 (1400 ly) across Sgr A* location of black hole

29 Supermassive BH in MW

30 The Galactic Center stellar orbits in the central 3 ly evidence for a supermassive black hole, with mass 4 million times the mass of the Sun.

31 DARK MATTER

32 The data (blue curve) indicate the stars in the outer Galaxy have higher orbital speeds than can be explained by the known mass. Dark matter that extends to great distances from the galactic center provides the gravitational force needed to give the outer stars these higher speeds. Predicted Keplerian orbit based on cataloged content Actual rotation of Milky Way Astronomy Elementary Astronomy LA Mission College Levine F2015

33 What is Dark Matter? Rotation curve provides evidence mass But we don t see it as stars, dust, gas We call it dark matter because we haven t directly detected it through observing light We don t really know what it is made out of, we just know where it is and how much of it there is! In the Milky Way, most is in the halo, and possibly an extended disk 6 x10 11 to 3 x M

34 Cosmology the origin fate and history of the universe in no time at all Astronomy 1 Elementary Astronomy LA Mission College Spring F2015

35 HUBBLE S LAW

36 Hubble s Observations Hubble obtained distances and velocities for galaxies beyond our local group Velocity from Doppler shift Distance from standard candles Cephied variables

37 Doppler Effect

38 Detecting Doppler Shift In astronomy, we detect red (and blue) shift using spectral lines

39 THE HUBBLE LAW

40 Hubble s Law

41 Hubble s Law A straight line! The galaxies are all receding and the speed with which they are doing so increases as the distance increases v=h 0d H 0 is the Hubble Constant

42 WHAT IS COSMOLOGY?

43 What is Cosmology Cosmology is the scientific study of the large scale properties of the universe as a whole. It endeavors to use the scientific method to understand the origin, evolution and ultimate fate of the entire Universe. WMAP Science Team, "Cosmology: The Study of the Universe," NASA's Wilkinson Microwave Anisotropy Probe,last modified June 6, 2011, or

44 THE EXPANDING UNIVERSE

45 Hubble s Law Hubble s Law: galaxies are redshifted & the further away they are, the more they are redshifted not traveling THROUGH space space itself is getting bigger cosmological redshift due to the expansion of space

46 The Raisin Bread Analogy every raisin travels away from every other raisin obeys Hubble s Law

47 The Raisin Bread Analogy raisins the stuff in the universe dough space (space-time) dough is expanding, not raisins Space is expanding, not the stuff in it

48 THE OBSERVABLE UNIVERSE

49 Telescopes are Time Machines object We see they as they were ago What they would see looking at earth Proxima Centauri 4.3 years August 2009 Sirius ~ 28 years Apartheid dismantled HD156668b (a 2 earth-mass planet) ~80 years Hitler s rise to power Rigel Center of MW ~860 years ~24, 000 years Henry II marries Eleanor of Aquitane The traces of the very last Neanderthals Andromeda Galaxy 2.5 million years Homo erectus learns to use tools Center of Virgo Cluster 65 million years Extinction of the Dinosaurs Galaxy Cluster MCS J billion years Formation of the Solar System Light takes time to travel We see things as they were

50 The Observable Universe we can only see the portion of the Universe which is within the distance light could travel in the time since the beginning of the universe. Even though the Universe is infinite, we see only a portion of it. That portion is called the observable universe.

51 The Cosmological Principle We only see part of the infinite universe. Theorists want to apply theory to the whole universe the Cosmological Principle (an assumption) Universe is homogeneous and isotropic when averaged over very large scales. i.e. our location in the Universe is not special, it s the same everywhere

52 IT ALL STARTED WITH

53 Expanding Universe + General Relativity + The Cosmological Principle implies...

54 It all started with a Big Bang

55 Editorial Note The Bearnaked Ladies got a lot right except for making all the elements... But very smart people had the same wrong idea for a long time Only H and He (a little Li) are made by Big Bang nucelosynthesis.

56 WRAP-UP

57 Topic for Next Class The Big Bang & the fate of the universe

58 Reading Assignment Astro: 11 Astropedia:17

59 Homework None at this time