ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars - - PowerPoint PPT Presentation

ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies

NNOUNCEMENTS NNOUNCEMENTS

• Alternate final date

Alternate final date: Monday, Dec 7, 5:30-8pm.

• Next observing night: Mon, Nov. 16, 7pm
• Homework #7 due on Tuesday 11/10, by 5pm

Mapping the Universe: We Mapping the Universe: We need Distances to Galaxies! need Distances to Galaxies!

Methods we are familiar with: Radar Radar and Stellar parallax Stellar parallax The problem:

• r

Only useful inside the Solar Only useful inside the Solar System System A few thousand A few thousand ly ly

REVIEW

Main-Sequence Fitting Main-Sequence Fitting

• Start with cluster

Start with cluster A A (upper) (upper) whose whose distance known via distance known via parallax parallax

• Compare with other

Compare with other cluster cluster B (lower) B (lower)

• Get

Get distance to B distance to B from brightness from brightness difference difference

DISTANCE DISTANCE ESTIMATE 1 ESTIMATE 1

A A B B

Distances up to Distances up to ~1 million ~1 million

light years

light years

REVIEW

Cepheid variable stars Cepheid variable stars

brighter brighter Cepheids Cepheids have longer periods have longer periods

Period - Period - Luminosity Luminosity relation relation

DISTANCE DISTANCE ESTIMATE 2 ESTIMATE 2

REVIEW

Tully-Fisher Relation Tully-Fisher Relation

• Fast rotation speeds in

Fast rotation speeds in spiral galaxies spiral galaxies

• more mass in galaxy

more mass in galaxy

• higher luminosity

higher luminosity Measure Measure rotation speeds rotation speeds to infer to infer luminosity luminosity Need bright Need bright “ “edge-on edge-on” ” spirals, estimate tilt spirals, estimate tilt DISTANCE DISTANCE ESTIMATE 3 ESTIMATE 3 Distances up to ~1 billion Distances up to ~1 billion ly ly

REVIEW

Even brighter:

Even brighter: White dwarf supernovae White dwarf supernovae

• Nearly the

Nearly the same same amount amount of energy

• f energy

released every released every time. time.

why? why?

• “

“Standard Standard explosion explosion” ” = = fusion of 1.4 solar fusion of 1.4 solar masses of masses of material material

DISTANCE DISTANCE ESTIMATE 4 ESTIMATE 4

REVIEW

Summary Summary “ “Distance Ladder Distance Ladder” ” to measure universe to measure universe

Different standard candles are useful Different standard candles are useful for different distances for different distances

REVIEW

Distance measurements Distance measurements allowed to allowed to make make a a MAJOR MAJOR discovery about our discovery about our Universe Universe

• Before 1924, “spiral

nebulae” were thought to be small and located inside the Milky Way

Andromeda found to be far Andromeda found to be far outside

• utside Milky Way!

Milky Way!

• Edwin Hubble

Edwin Hubble in 1924 in 1924 identified identified Cepheids Cepheids in in Andromeda (M33) Andromeda (M33)

• showed they were

showed they were far far

• utside
• utside of Milky Way!
• f Milky Way!

– – “ “Island Universes Island Universes” ”

• His first big discovery!

His first big discovery!

• But then he turned his

But then he turned his attention to attention to OTHER OTHER galaxies galaxies

Hubble using new Hubble using new 100 100” ” Hooker telescope Hooker telescope at Mt. Wilson (above LA) at Mt. Wilson (above LA)

Hubble Hubble’ ’s s

• bservations showed a
• bservations showed a

very very startling startling result about the result about the universe. universe.

• Vesto Slipher

Vesto Slipher (1912) reported that most (1912) reported that most galaxies showed Doppler galaxies showed Doppler redshifts redshifts

• Edwin Hubble

Edwin Hubble, using new 100 , using new 100” ” telescope, telescope, started busily measuring galaxy started busily measuring galaxy redshifts redshifts

• Hubble

Hubble (1929) announced that (1929) announced that redshifts redshifts of

• f

galaxies galaxies appear to appear to increase with distance increase with distance from us from us

• This was startling: Suggested an

This was startling: Suggested an EXPANDING UNIVERSE EXPANDING UNIVERSE ! !

v = Ho d

Velocity of Recession (Doppler Shift) Hubble’s Constant Distance (km/sec) (km/sec/Mpc) (Mpc)

“ “Hubble Hubble’ ’s Law s Law” ”

velocity velocity distance distance

Best current Best current values for values for expansion expansion

H Ho

• =

= 71 71+ +/- 4 /- 4 km/s/Mpc

km/s/Mpc

Hubble Space Telescope was Hubble Space Telescope was designed to designed to accurately measure accurately measure the Hubble constant the Hubble constant

• High resolution

images to find faint Cepheid variable stars in very distant galaxies

What is Hubble What is Hubble’ ’s Law? s Law?

A. A. An idea stating that more distant galaxies An idea stating that more distant galaxies move move away from us faster away from us faster than closer ones than closer ones B. B. An equation giving the maximum luminosity for a An equation giving the maximum luminosity for a white dwarf supernova white dwarf supernova C.

• C. The relationship between the period and

The relationship between the period and luminosity of a Cepheid luminosity of a Cepheid variable star. variable star. D.

• D. The

The law giving the maximum speed that a law giving the maximum speed that a galaxy can move at. galaxy can move at. E. E. The idea that there are more galaxies outside The idea that there are more galaxies outside

• ur own and that the universe contains immense
• ur own and that the universe contains immense

numbers of these numbers of these “ “island universes. island universes.” ”

Clicker Question Clicker Question

What is Hubble What is Hubble’ ’s Law? s Law?

A. A. An idea stating that more distant galaxies An idea stating that more distant galaxies move move away from us faster away from us faster than closer ones than closer ones B. B. An equation giving the maximum luminosity for a An equation giving the maximum luminosity for a white dwarf supernova white dwarf supernova C.

• C. The relationship between the period and

The relationship between the period and luminosity of a Cepheid luminosity of a Cepheid variable star. variable star. D.

• D. The

The law giving the maximum speed that a law giving the maximum speed that a galaxy can move at. galaxy can move at. E. E. The idea that there are more galaxies outside The idea that there are more galaxies outside

• ur own and that the universe contains immense
• ur own and that the universe contains immense

numbers of these numbers of these “ “island universes. island universes.” ”

Clicker Question Clicker Question

Balloon analogy for Balloon analogy for expanding universe expanding universe

• Each dot on the

Each dot on the balloon can be balloon can be thought of as a thought of as a galaxy. galaxy. As the balloon As the balloon expands, galaxies expands, galaxies move farther away move farther away from each other from each other

What are the velocities of B, C and D What are the velocities of B, C and D as measured by A? as measured by A?

A.

• A. B: 1 cm/s; C: 2 cm/s; D: 3

B: 1 cm/s; C: 2 cm/s; D: 3 cm/s cm/s B.

• B. B: 3 cm/s; C: 1cm/s; D:

B: 3 cm/s; C: 1cm/s; D: 2 2 cm/s cm/s C.

• C. B: 2 cm/s; C: 4 cm/s; D:

B: 2 cm/s; C: 4 cm/s; D: 6 6 cm/s cm/s D.

• D. B: 1cm/s; C: 3 cm/s; D:

B: 1cm/s; C: 3 cm/s; D: 6 6 cm/s cm/s

Clicker Question Clicker Question

What are the velocities of B, C and D What are the velocities of B, C and D as measured by A? as measured by A?

A.

• A. B: 1 cm/s; C: 2 cm/s; D: 3

B: 1 cm/s; C: 2 cm/s; D: 3 cm/s cm/s B.

• B. B: 3 cm/s; C: 1cm/s; D:

B: 3 cm/s; C: 1cm/s; D: 2 2 cm/s cm/s C.

• C. B: 2 cm/s; C: 4 cm/s; D:

B: 2 cm/s; C: 4 cm/s; D: 6 6 cm/s cm/s D.

• D. B: 1cm/s; C: 3 cm/s; D:

B: 1cm/s; C: 3 cm/s; D: 6 6 cm/s cm/s

Clicker Question Clicker Question

Balloon analogy for Balloon analogy for expanding universe expanding universe

• On an expanding

On an expanding balloon, no galaxy is balloon, no galaxy is at the at the “ “center center” ” of

• f

expansion; no edge expansion; no edge

• Expansion happens

Expansion happens into a higher into a higher dimension dimension (2-D (2-D surface into a 3-D surface into a 3-D space) space)

• Is our 3-D space

Is our 3-D space expanding through a expanding through a 4 4th

th dimension?

dimension?

A Better Way To Image the A Better Way To Image the Expanding Universe Expanding Universe

• NOT

NOT like an explosion of galaxies THROUGH THROUGH space from a center place

• The space BETWEEN

BETWEEN galaxies is expanding expanding, carrying the galaxies away from each other

– Why don’t galaxies themselves expand? Gravity!

No matter which direction we look, we see No matter which direction we look, we see galaxies moving away from us. Therefore, we galaxies moving away from us. Therefore, we must be at the center of the expansion. must be at the center of the expansion. A.

• A. True

True B.

• B. False

False Clicker Question Clicker Question

No matter which direction we look, we see No matter which direction we look, we see galaxies moving away from us. Therefore, we galaxies moving away from us. Therefore, we must be at the center of the expansion. must be at the center of the expansion. A.

• A. True

True B.

• B. False

False Clicker Question Clicker Question

The Cosmological Principle The Cosmological Principle

• Matter is

Matter is evenly distributed evenly distributed on very large

• n very large

scales in the universe scales in the universe

• No

No center center & no & no edges edges

• Not proven but consistent with all observations

Not proven but consistent with all observations to date to date The universe looks about the same no matter where you are within it

Since the universe Since the universe is expanding, light traveling is expanding, light traveling through the through the universe universe “ “feels feels” ” the stretch as it travels the stretch as it travels

Cosmological Cosmological Redshift Redshift

v = Ho d

Velocity of Recession (Doppler Shift) Hubble’s Constant Distance (km/sec) (km/sec/Mpc) (Mpc)

“ “Hubble Hubble’ ’s Law s Law” ”

velocity velocity distance distance

Implies the Expansion

• f the Universe!

What does the What does the “ “expansion of expansion of the universe the universe” ” most accurately most accurately mean? mean?

• A. Galaxies are moving apart through space
• B. Space itself is expanding
• C. Everything is expanding, including the earth,
• ur bodies, etc
• D. The Milky Way is at the center of the

universe and all other galaxies are expanding away from us.

Clicker Question Clicker Question

What does the What does the “ “expansion of expansion of the universe the universe” ” most accurately most accurately mean? mean?

• A. Galaxies are moving apart through space
• B. Space itself is expanding
• C. Everything is expanding, including the earth,
• ur bodies, etc
• D. The Milky Way is at the center of the

universe and all other galaxies are expanding away from us.

Clicker Question Clicker Question

Your friend leaves your house. She later calls you on her Your friend leaves your house. She later calls you on her cell phone, saying that she cell phone, saying that she’ ’s been driving at 60 mph s been driving at 60 mph (miles (miles per hour) directly away from you the whole time per hour) directly away from you the whole time and is now 60 miles away. Without looking at your and is now 60 miles away. Without looking at your watch, can you tell how long has she been gone? watch, can you tell how long has she been gone?

• A. Yes, 1 minute
• A. Yes, 1 minute
• B. Yes, 30 minutes
• B. Yes, 30 minutes
• C. Yes, 60 minutes
• C. Yes, 60 minutes

D.

• D. Yes, 120 minutes

Yes, 120 minutes E. E. No, not enough information to tell No, not enough information to tell

Clicker Question Clicker Question

Your friend leaves your house. She later calls you on her Your friend leaves your house. She later calls you on her cell phone, saying that she cell phone, saying that she’ ’s been driving at 60 mph s been driving at 60 mph (miles (miles per hour) directly away from you the whole time per hour) directly away from you the whole time and is now 60 miles away. Without looking at your and is now 60 miles away. Without looking at your watch, can you tell how long has she been gone? watch, can you tell how long has she been gone?

• A. Yes, 1 minute
• A. Yes, 1 minute
• B. Yes, 30 minutes
• B. Yes, 30 minutes

C.

• C. Yes, 60 minutes

Yes, 60 minutes D.

• D. Yes, 120 minutes

Yes, 120 minutes E. E. No, not enough information to tell No, not enough information to tell

Clicker Question Clicker Question

Expansion and the Age of the Expansion and the Age of the Universe Universe

IF the universe has been expanding at the same speed always: Distance = velocity time time = distance/velocity Hubble’s Law: v = Ho D Ho = velocity/distance

Time (Age) = 1 / H Time (Age) = 1 / Ho

• For 71 km/sec/Mpc: Age ~ 13.7 billion years

For larger Ho, shorter time For smaller Ho, longer time

Is this anywhere near correct? Is this anywhere near correct?

• Age of the solar system ~ 4.6 billion years

4.6 billion years

• Age of the oldest star clusters ~ 13 billion

13 billion years years

• General agreement

General agreement, but we’ll revisit the assumption of constant expansion soon..