Transcript Ch. 26.5 - (www.ramsey.k12.nj.us).

Ch. 26.4 -5: Galaxies & the
Expanding Universe
•How do astronomers know the universe is
expanding?
•What is the big bang theory & what evidence
supports it?
•How can dark matter be detected?
Galaxies = Groups of millions - trillions stars
that are held together by gravity.
Milky Way Stats
100 000 LY across
2 000 LY thick
5 Spiral Arms
Our sun is 2/3 the way out
on the Orion spiral arm.
Moves around center at a
speed of 500,000 mi/hr (It
takes 200 million yrs to complete one
rotation)
Try this simulation:
http://www.telescope.org/btl/data/01904.gif
http://amazingspace.stsci.edu/resources/explorations/g
alaxies-galore/build/index.html
Galaxies: Classified by Shape
Spiral
Black holes &
old stars in
center; young
stars in arms
Elliptical
Old stars;
little nebula
Irregular
Young stars;
lots of nebula
Star
Spectrums
• Spectroscopes collect
visible light wavelength
from stars.
• Each element has a
unique pattern of lines
when viewed.
• Spectrums tell us about a
star’s COMPOSITION
Star
Spectrums
• Also used to determine
the DIRECTION and
SPEED of galaxies.
• Expect to see lines for
hydrogen …. But they
aren’t in the right place?!
• Why?
Doppler
Effect
Listen to the Doppler Effect
http://www.youtube.com/watch?v=a3RfULw7aAY
http://www.youtube.com/watch?v=imoxDcn2Sgo
A
RED SHIFT – a shift in
absorption lines of star
spectrum to the red
wavelengths
Objects moving away
have longer wavelengths
(red)
B
Which spectrum is from a
star/galaxy that is moving away
from us?
BLUE SHIFT
Objects moving towards
us have shorter
wavelengths (Blue)
Hubble’s Law = The farther a galaxy
is away from us, the faster it is
moving away from us
The Universe is EXPANDING!
Evidence: The Doppler Effect (Wavelengths
appear to change based on the motion of
objects)
If waves approach you … the waves bunch up on
top of one another … or shorten (Blue Shift)
If waves move away from you … the waves stretch
out or get longer (Red Shift)
What does this spectrum tell you about the motion of the
supercluster of galaxies?
Red Shifts
What is going on here?
•
Red Shift Explained
http://www.youtube.com/watch?v=FhfnqboacV0&NR=1
www.usask.ca/.../109_122_A/Age_Universe.htm
Red Shifted Spectrums
1
2
3
Which galaxy is farthest from us?
Which galaxy is moving away from us faster?
Hubble’s Law
More distant galaxies have
GREATER RED SHIFTS –
They are moving away from
Earth with faster velocity
than closer galaxies.
The UNIVERSE IS
EXPANDING!
Big Bang Theory
The universe came into being at a single
moment, in an event called BIG BANG.
All matter & energy of universe were
concentrated into an incredibly hot, small,
mass.
An enormous explosion sent matter and
energy out into space.
When: 13.7 billion yrs ago
http://www.youtube.com/watch?v=hVApTLE7Csc
Support for Big Bang
1. Red Shifts tell us Galaxies are
ACCELERATING AWAY from a center
(Expanding)
2. COSMIC Microwave BACKGROUND
RADIATION
Detected in 1965
Faint radiation coming from all directions
Believed to be energy from Big Bang
Background Cosmic Microwave Radiation
The Horn antenna in the Bell Telephone Laboratory discovered the universal
microwave background radiation.
What?
• Microwaves
coming at us
from
everywhere,
but no where
specific.
• It’s lingering
energy (echo)
from Big BANG
explosion!
Fate of Universe
A. Expand forever / Galaxies drift apart?
OR
B. “Big Crunch” – Galaxies collapse into a
center?
Depends on how much mass there is in the
universe … which is in dispute.
Dark Matter
Dark Matter = Does not give off radiation
& cannot be detected
Exerts gravitational force on visible matter
Universe may be 90% + dark matter
Why do we think Dark Matter exists?
Galaxies are accelerating faster than they should be
(based on the observable matter in the Universe). The
acceleration due to gravity does not match up with the
amount of matter that we can see. This tells us that
there must be more mass … we’re just not seeing it.
Ch 26.5 Questions
1.
What theory states that the universe began as an explosion of an incredibly dense
point of matter?
2.
According to the theory of Big Bang, how old is our universe?
3.
Our universe is currently …
a. Contracting b. Expanding c. Staying the same
4.
What does Hubble’s Law say about the motion of galaxies?
5.
When scientists look at the spectrum for Andromeda, our neighboring galaxy, they
notice that the lines are moved over to the blue end of the spectrum. Andromeda is
…
a.
b.
c.
d.
Moving towards us.
Moving away from us.
A constant distance from us.
Not moving.
6.
Quasars, are very distant galaxies. When scientists look at quasars with
a spectroscope they would see the lines on their spectrum shifted to the
(RED / BLUE) end of the spectrum.
7.
How does the red – shift of far away galaxies support the big bang
theory?
8.
What kind of wavelength on the electromagnetic spectrum is lingering
around like an echo from the Big Bang?
9.
What are two possible scenarios for the future of the universe?
10.
What is dark matter and how much of the universe do scientists think may
be dark matter?