Transcript Galaxies and the Universe Chap. 31 The Milky Way 31.1

Galaxies and the
Universe
Chap. 31
The Milky Way 31.1
Other Galaxies in the Universe 31.2
Cosmology 31.3
The Milky Way
Objectives
• determine the size
and shape of the
Milky Way, as well
as Earth’s location
within it.
• describe how the
Milky Way formed.
I. Discovering the Milky Way
A. Distances to clusters determined
using variable stars.
I. Discovering the Milky Way
A. Distances to clusters determined
using variable stars.
Variable Stars
Stars in the ‘giant’ branch of
HR diagram that pulsate in
brightness
I. Discovering the Milky Way
A. Distances to clusters determined
using variable stars.
1. RR Lyrae variables
Brightness pulsates between 1.5 hours and 1 day
I. Discovering the Milky Way
A. Distances to clusters determined
using variable stars.
1. RR Lyrae variables
2. Cepheid variables
Brightness pulsates between 1 and 100 days
(graph this)
I. Discovering the Milky Way
A. Distances to clusters determined
using variable stars.
1. RR Lyrae variables
2. Cepheid variables
3. These stars make good standard
candles
The larger the period (time) of pulsation the
greater the luminosity.
(graph this)
Calculating distance
If a star is really bright
(__________ magnitude) but it
appears to be dim (_________
magnitude), you know it’s far.
The dimmer it looks the farther
it is.
II. Locating the Center of the
Galaxy
II. Locating the Center of the
Galaxy
A. Globular clusters are centered
around a point about 28,000 ly away
II. Locating the Center of the
Galaxy
A. Globular clusters are centered
around a point about 28,000 ly away
B. Center has high density of stars
II. Locating the Center of the
Galaxy
A. Globular clusters are centered
around a point about 28,000 ly away
B. Center has high density of stars
C. Center is toward Sagittarius
constellation
http://www.esa.int
III. Shape of Milky Way
A. The MW is a flattened disk shape
III. Shape of Milky Way
A. The MW is a flattened disk shape
B. Galactic center (nucleus) surrounded
by nuclear bulge
III. Shape of Milky Way
A. The MW is a flattened disk shape
B. Galactic center (nucleus) surrounded
by nuclear bulge
C. A spherical-shaped halo containing
older stars surrounds the disk.
III. Shape of Milky Way
D. Four major spiral arms (and
several minor spiral arms) have
been identified
IV. Mass of the Milky Way
IV. Mass of the Milky Way
A. Might be found by measuring
luminosity
Remember that luminosity is related to mass.
Stars that are bigger are also _________.
IV. Mass of the Milky Way
A. Might be found by measuring
luminosity
B. Mass is usually found by using our
orbital speed
Calculating Mass
(M1 + M2)P2 = a3 Kepler’s 3rd law
M1 is sun’s mass (measured in “sun masses”)
M2 is universe’s mass (measured in “sun masses”)
P is orbital period (years) = 240 million y
a is distance (in AU)
1 ly = 63,200 AU
IV. Mass of the Milky Way
A. Might be found by measuring
luminosity
B. Mass is usually found by using our
orbital speed
C. Since the MW is about 100 billion
times the mass of the Sun, an average
sized star, the MW must contain
about
stars.
IV. Mass of the Milky Way
A. Might be found by measuring
luminosity
B. Mass is usually found by using our
orbital speed
C. Since the MW is about 100 billion
times the mass of the Sun, an average
sized star, the MW must contain
about 100 billion stars.
V. Mass of the Center of the
Milky Way
A. Stars near the center orbit
center very fast – this indicates
a very
center
V. Mass of the Center of the
Milky Way
A. Stars near the center orbit
center very fast – this indicates
a very massive center
V. Mass of the Center of the
Milky Way
A. Stars near the center orbit
center very fast – this indicates
a very massive center
B. It is thought that there is a
super black hole at the center of
our galaxy
This center is about 2.6 million times the
Sun’s mass
VI. Age of Stars in Milky Way
VI. Age of Stars in Milky Way
A. Young stars form in the arms of
the MW
VI. Age of Stars in Milky Way
A. Young stars form in the arms of
the MW
B. Old stars are found in the
halo/nuclear bulge.
VII. Formation of Milky Way
VII. Formation of Milky Way
A. MW was originally round.
Notice the arrangement of the oldest stars.
VII. Formation of Milky Way
A. MW was originally round.
B. The MW cloud collapsed and
flattened into a disk shape.
The End
Other Galaxies – 30.2
Objectives
• Describe how
astronomers classify
galaxies
• Identify how galaxies
are organized into
clusters and
superclusters
• Describe the expansion
of the universe
I. Identifying
I. Identifying
A. Astronomers saw other galaxies
before they knew what they were.
I. Identifying
A. Astronomers saw other galaxies
before they knew what they were.
B. Edwin Hubble measured their
distances to confirm they were
not in MW.
He used variable stars to do it.
II. Classifying
II. Classifying
A. Spiral
M74 in pisces
“Cosmic Frisbee”
II. Classifying
A. Spiral
1. Normal spirals (S)
II. Classifying
A. Spiral
1. Normal spirals (S)
2. Barred spirals (SB)
NGC 1300 – in Eridanus
II. Classifying
A. Spiral
1. Normal spirals (S)
2. Barred spirals (SB)
3. These are further divided by how
tightly wound arms are (a, b, c)
Type a represents tightly wound arm with bright
nucleus.
II. Classifying
A. Spiral
B. Ellipticals
“Cosmic Football”
II. Classifying
A. Spiral
B. Ellipticals
1. Divided from E0 to E7.
II. Classifying
A. Spiral
B. Ellipticals
1. Divided from E0 to E7.
2. E7 has a large ratio of major
axis/minor axis, E0 is circular.
II. Classifying
A. Spiral
B. Ellipticals
C. Irregular Galaxies (Irr)
http://www.nasa.gov
II. Classifying
D. Masses
II. Classifying
D. Masses
1. Dwarf ellipticals have few stars
(about 1 million).
II. Classifying
D. Masses
1. Dwarf ellipticals have few stars
(about 1 million).
2. Large spirals, like MW, have
about 100 million stars.
II. Classifying
D. Masses
1. Dwarf ellipticals have few stars
(about 1 million).
2. Large spirals, like MW, have
about 100 million stars.
3. Giant ellipticals have mass of 100
trillion x the sun.
III. Groups & Clusters
III. Groups & Clusters
A. Local group
M33 member of the local group
III. Groups & Clusters
A. Local group
1. Includes Milky Way
http://www.spacetoday.org
III. Groups & Clusters
A. Local group
1. Includes Milky Way
2. About 35 known members
including Andromeda and
several dwarf galaxies.
http://www.via.ee
III. Groups & Clusters
A. Local group
1. Includes Milky Way
2. About 35 known members
including Andromeda and
several dwarf galaxies.
3. It’s about 2 million ly across
III. Groups & Clusters
A. Local group
B. There are clusters much bigger
than local group (ex. Virgo)
http://www.randybrewer.net
III. Groups & Clusters
A. Local group
B. There are clusters much bigger
than local group (ex. Virgo)
C. Mass of clusters are bigger than
the sum of the parts.
This is evidence for existence of dark matter
IV. The Expanding Universe
IV. The Expanding Universe
A. Discovered by Hubble in 1929
IV. The Expanding Universe
A. Discovered by Hubble in 1929
B. “Red shift”
Light waves are stretched out due to relative motion
of source and observer away from each other.
Red Shift
IV. The Expanding Universe
A. Discovered by Hubble in 1929
B. “Red shift”
1. Indicates galaxy is moving away
from us
IV. The Expanding Universe
A. Discovered by Hubble in 1929
B. “Red shift”
1. Indicates galaxy is moving away
from us
2. Hubble determined the degree of
red shift depends on the distance
away
IV. The Expanding Universe
A. Discovered by Hubble in 1929
B. “Red shift”
1. Indicates galaxy is moving away
from us
2. Hubble determined the degree of
red shift depends on the distance
away
3. All galaxies are moving away
from all other galaxies (not just
Earth)
IV. The Expanding Universe
A. Discovered by Hubble in 1929
B. “Red shift”
C. Hubble’s law
v = Hd
IV. The Expanding Universe
A. Discovered by Hubble in 1929
B. “Red shift”
C. Hubble’s law
v = Hd
velocity (km/s)
Distance (Mpc)
Hubble’s constant
V. Active Galaxies
V. Active Galaxies
A. Radio Galaxies
V. Active Galaxies
A. Radio Galaxies
1. Two lobes connected by jets of
hot gas.
NGC 5128 Radio galaxy
V. Active Galaxies
A. Radio Galaxies
1. Two lobes connected by jets of
hot gas.
2. Observed by radio telescopes
because they emit more radio
waves than visible light.
Radio telescope
V. Active Galaxies
B. Active Galactic Nuclei (AGN)
V. Active Galaxies
B. Active Galactic Nuclei (AGN)
1. Highly energetic galactic cores
V. Active Galaxies
B. Active Galactic Nuclei (AGN)
1. Highly energetic galactic cores
2. Output of energy varies
VI. Quasars
VI. Quasars
A. Like other galaxies, but these are
strong radio emitters.
VI. Quasars
A. Like other galaxies, but these are
strong radio emitters.
B. Create emission lines, instead of
absorption lines.
Absorption spectrum
Emission spectrum
VI. Quasars
A. Like other galaxies, but these are
strong radio emitters.
B. Create emission lines, instead of
absorption lines.
C. These objects have a very large
red shift (so they are very far
away).
VII. Looking back in time
VII. Looking back in time
A. We study stars/galaxies as they
were.
VII. Looking back in time
A. We study stars/galaxies as they
were.
B. Seeing quasars that are very far
(old) suggests a possible ‘quasar
stage’ during universe history.
The End
Cosmology – 31.3
Objectives
• Explain the different
theories about the
formation of the
universe
• Describe the possible
outcomes of
universal expansion
I. Models
I. Models
A. Steady State Theory
I. Models
A. Steady State Theory
1. The Universe does not change
with time.
I. Models
A. Steady State Theory
1. The Universe does not change
with time.
2. The Universe had no beginning
I. Models
A. Steady State Theory
1. The Universe does not change
with time.
2. The Universe had no beginning
3. The Density stays constant
I. Models
A. Steady State Theory
1. The Universe does not change
with time.
2. The Universe had no beginning
3. The Density stays constant
4. As Universe expands, new
material is created and added
I. Models
B. Big Bang Theory
I. Models
B. Big Bang Theory
1. All matter began at a point initially
I. Models
B. Big Bang Theory
1. All matter began at a point initially
2. The matter and space of our Universe
has been expanding ever since
II. Cosmic Background
Radiation (CBR)
II. Cosmic Background
Radiation (CBR)
A. Low-level microwave radiation
II. Cosmic Background
Radiation (CBR)
A. Low-level microwave radiation
B. This radiation comes from all
directions
II. Cosmic Background
Radiation (CBR)
A. Low-level microwave radiation
B. This radiation comes from all
directions
C. CBR is associated with cool
temperature (2.735 K)
II. Cosmic Background
Radiation (CBR)
A. Low-level microwave radiation
B. This radiation comes from all
directions
C. CBR is associated with cool
temperature (2.735 K)
D. The steady state theory does not
explain CBR
II. Cosmic Background
Radiation (CBR)
E. This has been mapped by
satellites.
III. Big Bang Model
III. Big Bang Model
A. Momentum carries material
outward while
pulls inward
III. Big Bang Model
A. Momentum carries material
outward while gravity pulls inward
III. Big Bang Model
A. Momentum carries material
outward while gravity pulls inward
B. The rate of expansion is slowing
III. Big Bang Model
A. Momentum carries material
outward while gravity pulls inward
B. The rate of expansion is slowing
C. Possible Outcomes
III. Big Bang Model
A. Momentum carries material
outward while gravity pulls inward
B. The rate of expansion is slowing
C. Possible Outcomes
1. Open Universe –
Expansion of Universe never stops
III. Big Bang Model
A. Momentum carries material
outward while gravity pulls inward
B. The rate of expansion is slowing
C. Possible Outcomes
1. Open Universe –
2. Closed Universe –
Expansion stops and becomes a contraction
III. Big Bang Model
A. Momentum carries material
outward while gravity pulls inward
B. The rate of expansion is slowing
C. Possible Outcomes
1. Open Universe –
2. Closed Universe –
3. Flat Universe –
Expansion slows to halt in infinite amt. of time
III. Big Bang Model
D. Critical Density
1. The outcome of the Universe
depends on the amount (density) of
material in it.
III. Big Bang Model
D. Critical Density
1. The outcome of the Universe
depends on the amount (density) of
material in it.
a) Less than critical density (10-26
kg/m3) results in open Universe.
III. Big Bang Model
D. Critical Density
1. The outcome of the Universe
depends on the amount (density) of
material in it.
a) Less than critical density (10-26
kg/m3) results in open Universe.
b) More than critical density
means closed Universe
III. Big Bang Model
D. Critical Density
1. The outcome of the Universe
depends on the amount (density) of
material in it.
a) Less than critical density (10-26
kg/m3) results in open Universe.
b) More than critical density
means closed Universe
c) Equal to Critical density means
flat Universe
III. Big Bang Model
D. Critical Density
1. The outcome of the Universe
depends on the amount (density) of
material in it.
d) Observations show less than
critical density, (but there is
dark matter)
IV. Decrease of Rate of
Expansion
IV. Decrease of Rate of
Expansion
A. This could be used to tell the
outcome of the Universe
IV. Decrease of Rate of
Expansion
A. This could be used to tell the
outcome of the Universe
B. Universe’s expansion should be
getting slower
IV. Decrease of Rate of
Expansion
A. This could be used to tell the
outcome of the Universe
B. Universe’s expansion should be
getting slower
C. We observed it’s actually
expanding faster
IV. Inflationary Universe
Universe began with a fluctuation in expansion.
For a brief instant its rate of expansion increased
Calculating Age
Calculate the number of years since
expansion of the Universe using
Hubble’s constant:
1/H = time
H = 50 km/s / Mpc
or
H = 100 km/s / Mpc
1 pc = 3.1 x 1013 km
‘mega’ (M) = 1 000 000 units
The End