Transcript 20HubblesLaw_RJx

Objectives
• What is a supercluster?
• How are galaxies distributed in the universe?
• Is the universe expanding, contracting or neither? How do we
know?
• What is Hubble’ Law? Can you apply it to stars? To galaxies
in the Local Group? To more distant galaxies?
• How do astronomers calculate distances to galaxies?
• What does Hubble’s Law tell us about the origin of the
universe? Explain how it suggests that.
• Is the red shift caused by galaxies moving through space or
by space-time expanding?
• Is the universe expanding? Is it cooling?
• Discuss the raisin bread model or balloon model to explain
why we do not have to be at the center of the universe.
Hubble’s Law
• Galaxies Collide
• Cluster of Galaxies
– The Local Group
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•
•
•
Superclusters
Hubble’s Law
Red Shift of galaxies
Big Bang model
Do galaxies collide?
• Galactic collision simulation
• http://www.youtube.com/watch?v=Lru7F
od1Evg&feature=related
•
NGC 2207 and IC 2163 colliding, 80 MLY away
http://apod.nasa.gov/apod/ap041121.html
Clusters of Galaxies
Galaxy cluster mass ~160 trillion times the mass of the sun
http://www.spacetelescope.org/news/heic1416/
The Local Group
• Group of galaxies including Milky Way
Virgo Cluster
• Cluster of Galaxy Clusters
– We are part of
the Virgo Cluster
http://heasarc.nasa.gov/docs/cosmic/local_supercluster_info.html
Neigboring Superclusters
within 1 billion light years
Every dot is a galaxy
http://www.atlasoftheuniverse.com/superc.html
Laniakea Supercluster
Superclusters
• How are galaxies distributed?
– In great strings and voids
• What does the distribution look like to you?
– Edges of soap bubbles
– Holes of Swiss cheese
Superclusters
• Laniakea: Our home supercluster
• Watch Video by Nature
https://www.youtube.com/watch?v=rENyyRwxpHo
Doppler Effect
• What does the red shift or blue shift tell you?
Doppler Effect
• Red shift / blue shift tells you…
Direction of motion and speed
• Bigger shift means …faster
• All cases like galaxies, stars, cars…
For galaxies only (not stars, cars)
Edwin Hubble
• Measured distance, D, to galaxies
• Recall: Type of star gave L, then Edwin Hubble
• B = kL/D2
1929
• Measured red shift of those galaxies to get
their speeds, v.
Speed, v
Distance, D
Edwin Hubble, 1929
Graphed v vs D
Hubble’s Law
Straight Line!!
V
speed
*
*
*
*
*
*
*
D
Distance
Hubble’s Law
Distant galaxies
move faster.
V
speed
*
*
*
*
*
*
*
D
Distance
Hubble’s Law
V
*
*
*
* *
*
v = HD
*
Distant galaxies move faster
D
Hubble’s Law
Implications?
V
For galaxies, the speed
gives you the distance!
v = HD
H = Hubble’s Constant
(slope)
*
*
* *
* *
*
D
Hubble’s Law
So, today, to measure
distance to galaxy …
V
Measure the Red Shift.
*
That gives the speed.
*
* *
* *
*
D
Then use Hubble’s Law ( v = HD ) to get distance.
(Don’t try this with stars or cars! Only for galaxies.)
Hubble’s Law
All galaxies
(outside the Local Group)
show a Red Shift.
Distant galaxies move faster
v = HD
V
*
*
* *
* *
*
D
Hubble’s Law
Implications?
All galaxies Red Shifted
All galaxies moving away
from us!
Universe is expanding!
This expansion is from the
expansion of space-time.
V
*
*
* *
* *
*
D
Hubble’s Law
But if universe is
expanding, what was it
like yesterday?
Smaller!
V
*
*
* *
* *
*
D
And billions of years ago??
Even smaller!
So at one point it must
have been very small.
V
Hence the name…
*
*
* *
* *
*
D
BIG BANG
BIG BANG
Bad Name (misnomer)
V
*
*
* *
* *
Was not BIG
*
D
Did not BANG
More descriptive name
Great Unfolding
Or
Big Stretch
Warning: The Astronomy General has
determined that this image may be
hazardous to your misconceptions.
Big Bang (old model)
Universe (space and time)
Springs into existence (tiny)
About 14 billion years ago
Expanding ever since
Rate of expansion??
1. Slowing down
2. Speeding up
3. Not changing
Big Bang (old model)
Universe (space and time)
Springs into existence (tiny)
About 14 billion years ago
Expanding, cooling ever since
Rate of expansion slowing
due to gravity
Big Bang
Universe (space and time)
Springs into existence (tiny)
About 14 billion years ago
Expanding, cooling ever since
Rate of expansion is speeding up
due to dark energy.
Expansion Rate is about 45 (miles/sec)/megaparsec
(1 megaparsec is about 3 million light years)
After accounting for the universe expansion:
Galaxies moving away from us are in red, those moving
toward us in blue (Nature Video, based on Tully et al 2014)
Why do distant galaxies move
faster?
Remember that space-time itself is
expanding!
Galaxies are NOT moving much
through space but space-time is
expanding, dragging galaxies with it.
Why do distant galaxies move faster?
Think of a rubber map and stretch it.
Why do distant galaxies move faster?
Think of a rubber map and stretch it.
• Example: Triple size (3X) in one hour.
• A city 10 miles away will then be 30 miles away
– moved at 20 mi/h
• A city 100 miles away will then be 300 miles away.
– moved 200 mi in 1 h or at 200 mi/h
• When the map stretches, more distant city moves
faster.
Similarly, as space-time expands, more distant
galaxies move faster.
Universe Expansion
⇒ Distant objects move faster
Doesn’t seeing a Red Shift of ALL galaxies
imply that we are at the center of the
universe? (all moving away?)
Raisin Bread
Model
Balloon Expanding
• Demo
• One piece of
balloon sees all
other pieces
moving away
• That piece does not
need to be at the
center
http://www.noaa.inel.gov/Capabilities/smartballoon/
Doesn’t seeing a Red Shift of ALL galaxies
imply that we are at the center of the
universe? (all moving away?)
Think of object/event (model) in everyday life
Expansion
You see all other parts moving away
You are not at center
Where is the center?
I see a galaxy 10
BLY away…
…as it was 10
Byrs ago…
…when the
universe was
smaller…
…so I’m looking
back toward the
center.
Yes and so are
we looking out
toward the
center.
…so I’m
looking out
toward the
center.
We’re all
looking out
toward the
center
Center is
here
Center is
here
Center is
here
Center is
here
Center is
here
Center is
here
Center is
here
Center is
here
Center is
here
An ant on the
balloon has no way
to know where the
center is.
z


Measure Red Shift (z) of a galaxy
z


= change in λ
λ
= shift in λ
λ
z


Measure Red Shift (z) of a galaxy
Large z means:

z
• Large red shift

• Large speed
• Large distance
• Large look back time
• Universe young when light left
Big Bang and Evolution of the
Universe
•
Homework
&
Updates
Lab Students: pickup notebooks today after lecture
(I’m in my office until 12pm)
– Check lab grades on website
– You must email me if you want to take the optional Test 2 (11/29 or 12/1)
• Test 3 on Dec. 6, Tuesday, in 2 weeks
– All multiple choice questions: about 60 questions
– Objectives listed on calendar
– Practice D2L Quizzes 9-11 (#12 next week)
• Observations
– Binoculars available for Moon Craters on your own. Fill out loan form.
• RETURN BINOCULARS BY RETURN DATE; View Moon before Sunrise
– Sunset Part 2. Work on this. Due Dec.1; view sunset about 4pm
– Planetarium Start: Sep. 6, Due: Dec. 8 (10 points)
– Star Gazing Start: Aug. 25, Due: Dec. 8 (25 points)
– Telescope Start: Aug. 25, Due: Dec. 8 (25 points)
– Moon Craters Start: Aug. 25, Due: Dec. 8 (10 points)
– Beautiful Planet Movie at Science Museum Due: Dec. 8 (10 pts) turn in ticket
• Reminder to register for spring classes
• No classes 11/24-25. Happy Thanksgiving!
Final (3 weeks) 12/13
MCTC Survey