A100 Exploring the Universe: Discovering Galaxies. Martin D. Weinberg UMass Astronomy

A100 Exploring the Universe: Discovering Martin D. Weinberg UMass Astronomy astron100-mdw@courses.umass.edu November 13, 2014 Read: Chaps 19, 20 11/13/14 slide 1

! and Elliptical Irregular : summary Exam #2 questions returned after class today Solutions posted on the website in the exams tab. See http://courses.umass.edu/astron100-mdw Begin by reviewing top 4 low-scoring exam questions Today: What are the three major types of galaxies? How are galaxies grouped together? How do we determine distances to galaxies? Read: Chaps 19, 20 11/13/14 slide 2

Discussion of exam questions: #39! and Elliptical Irregular : summary Degeneracy pressure is the source of the pressure that stops the crush of gravity in all of the following except (A) a brown dwarf. (B) a neutron star. (C) the central core of the Sun after hydrogen fusion ceases but before helium fusion begions. (D) a very massive main-sequence star. (E) a white dwarf. Read: Chaps 19, 20 11/13/14 slide 3

Discussion of exam questions: #24! and Elliptical Irregular : summary Which of the following characteristics of stars has the greatest range in values? (A) surface temperature (B) luminosity (C) mass (D) radius (E) core temperature Read: Chaps 19, 20 11/13/14 slide 4

Discussion of exam questions: #29! and Elliptical Irregular : summary Which cluster is 10 billion years old? Read: Chaps 19, 20 11/13/14 slide 5

Discussion of exam questions: #41! and Elliptical Irregular : summary What is the ultimate fate of an isolated white dwarf? (A) The electron degeneracy pressure will eventually overwhelm gravity and the white dwarf will slowly evaporate. (B) As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova. (C) It will cool down and become a cold black dwarf. (D) As gravity overwhelms the electron degeneracy pressure, it will explode as a nova. (E) As gravity overwhelms the electron degeneracy pressure, it will become a neutron star. Read: Chaps 19, 20 11/13/14 slide 6

!! and Elliptical Irregular : summary Read: Chaps 19, 20 11/13/14 slide 7

! Hubble Deep Field and Elliptical Irregular : summary Our deepest images of the universe show a great variety of galaxies, some of them billions of light-years away Read: Chaps 19, 20 11/13/14 slide 8

and A galaxys age, its distance, and the age of the universe are all closely related The study of galaxies is thus intimately connected with cosmology the study of the structure and evolution of the universe Read: Chaps 19, 20 11/13/14 slide 9

! and Elliptical Irregular : summary Hubble Ultra Deep Field Read: Chaps 19, 20 11/13/14 slide 10

! and Elliptical Irregular : summary Read: Chaps 19, 20 11/13/14 slide 11

! and Elliptical Irregular : summary Disk Component: stars of all ages, many gas clouds Spheroidal Component: bulge & halo, old stars, few gas clouds Read: Chaps 19, 20 11/13/14 slide 12

! and Elliptical Irregular : summary Disk Component: stars of all ages, many gas clouds Spheroidal Component: bulge & halo, old stars, few gas clouds Read: Chaps 19, 20 11/13/14 slide 13

! and Elliptical Irregular : summary Why does ongoing star formation lead to a blue-white appearance? (A) There aren t any red or yellow stars (B) Short-lived blue stars outshine others (C) Gas in the disk scatters blue light Read: Chaps 19, 20 11/13/14 slide 14

Other! and Elliptical Irregular : summary Barred Spiral Galaxy: Has a bar of stars across the bulge Read: Chaps 19, 20 11/13/14 slide 15

Other of! and Elliptical Irregular : summary Lenticular Galaxy: Has a disk like a spiral galaxy but much less dusty gas (intermediate between spiral and elliptical) Read: Chaps 19, 20 11/13/14 slide 16

Elliptical Elliptical Galaxy: All spheroidal component, virtually no disk component Read: Chaps 19, 20 11/13/14 slide 17

Elliptical Elliptical Galaxy: All spheroidal component, virtually no disk component Red-yellow color indicates older star population Read: Chaps 19, 20 11/13/14 slide 17

Irregular! and Elliptical Irregular : summary Large Magellanic Cloud Read: Chaps 19, 20 11/13/14 slide 18

Irregular Large Magellanic Cloud Blue-white color indicates ongoing star formation Read: Chaps 19, 20 11/13/14 slide 19

! and Elliptical Irregular : summary Spheroid dominates Disk Dominates Read: Chaps 19, 20 11/13/14 slide 20

How are galaxies grouped together?! and Elliptical Irregular : summary Read: Chaps 19, 20 11/13/14 slide 21

! and Elliptical Irregular : summary Spiral galaxies are often found in groups of galaxies (up to a few dozen galaxies) Read: Chaps 19, 20 11/13/14 slide 22

! and Elliptical Irregular : summary Elliptical galaxies are much more common in huge clusters of galaxies (hundreds to thousands of galaxies) Read: Chaps 19, 20 11/13/14 slide 23

: summary! and Elliptical Irregular : summary How are the lives of galaxies connected with the history of the universe? generally formed when the universe was young and have aged along with the universe What are the three major types of galaxies? Spiral galaxies, elliptical galaxies, and irregular galaxies Spirals have both disk and spheroidal components; ellipticals have no disk How are galaxies grouped together? Spiral galaxies tend to collect into groups of up to a few dozen galaxies Elliptical galaxies are more common in large clusters containing hundreds to thousands of galaxies Read: Chaps 19, 20 11/13/14 slide 24

to galaxies Read: Chaps 19, 20 11/13/14 slide 25

! and Elliptical Irregular : summary The Distance Ladder Step 1: Measure the Solar System by RADAR to determine the Astronomical Unit Read: Chaps 19, 20 11/13/14 slide 26

! and Elliptical Irregular : summary The Distance Ladder Step 2: Determine distances of stars out to a few hundred light-years using parallax Read: Chaps 19, 20 11/13/14 slide 27

! and Elliptical Irregular : summary The Distance Ladder Luminosity passing through each sphere is the same Area of sphere: 4π(radius) 2 Divide luminosity by area to get brightness Read: Chaps 19, 20 11/13/14 slide 28

! and Elliptical Irregular : summary The Distance Ladder The relationship between apparent brightness and luminosity depends on distance: Brightness = Luminosity 4π(distance) 2 We can determine a stars distance if we know its luminosity and can measure its apparent brightness: Luminosity distance = 4πBrightness A standard candle is an object whose luminosity we can determine without measuring its distance Read: Chaps 19, 20 11/13/14 slide 29

! and Elliptical Irregular : summary The Distance Ladder Step 3: Apparent brightness of star clusters main sequence tells us its distance Read: Chaps 19, 20 11/13/14 slide 30

! and Elliptical Irregular : summary The Distance Ladder Knowing a star clusters distance, we can determine the luminosity of each type of star within it Read: Chaps 19, 20 11/13/14 slide 31

! and Elliptical Irregular : summary Which kind of stars are best for measuring large distances? (A) High-luminosity stars (B) Low-luminosity stars Read: Chaps 19, 20 11/13/14 slide 32

! and Elliptical Irregular : summary Step 4 Cepheid variable stars are very luminous Because the period of a Cepheid variable star tells us its luminosity, we can use these stars as standard candles Read: Chaps 19, 20 11/13/14 slide 33

Cepheid Period-Luminosity relation! and Elliptical Irregular : summary Cepheid variable stars with longer periods have greater luminosities Read: Chaps 19, 20 11/13/14 slide 34

! and Elliptical Irregular : summary Type Ia Supernova White-dwarf supernovae can also be used as standard candles Read: Chaps 19, 20 11/13/14 slide 35

! and Elliptical Irregular : summary Type Ia Supernova Step 5 Apparent brightness of white-dwarf supernova tells us the distance to its galaxy (up to 10 billion lightyears) Read: Chaps 19, 20 11/13/14 slide 36

relation! and Elliptical Irregular : summary Entire galaxies can also be used as standard candles because galaxy luminosity is related to rotation speed Read: Chaps 19, 20 11/13/14 slide 37

:! and Elliptical Irregular : summary We measure galaxy distances using a chain of interdependent techniques Read: Chaps 19, 20 11/13/14 slide 38

:! and Elliptical Irregular : summary The distance-measurement chain begins with parallax measurements that build on radar ranging in our solar system Using parallax and the relationship between luminosity, distance, and brightness, we can calibrate a series of standard candles We can measure distances greater than 10 billion light years using white dwarf supernovae as standard candles Read: Chaps 19, 20 11/13/14 slide 39