january 2 nd 2013 objective warm-up students will know how galaxies are classified in order to...
TRANSCRIPT
January 2nd 2013
Objective Warm-Up
Students will know how galaxies are classified in order to identify the various types
What is the name of the galaxy that contains the sun, the earth and the known planets?
What is bigger: the solar system or a galaxy?
What is the name of our galaxy?
What is a Galaxy? A dense group of
stars, dark matter, dust and gas held together by gravity.
Dark matter- matter that produces no detectable light or other form of energy, but can be detected through its gravitational pull on visible stars and gas.
Galaxies: Small galaxies
Contain only about a million stars Dust and gas
Milky Way galaxy Contains several hundred billion stars Dust and gas Dark Matter -90% of the total mass of the galaxy
Large galaxies Contain more than one trillion stars Dust and gas
At the center (heart) of most galaxies there is a supermassive black hole
Formation of Galaxies Theory 1:
Galaxies were formed when vast clouds of dust and gas collapsed under their own gravitational pull, allowing stars to form
Theory 2: The young universe
contained many small “lumps” of matter which clumped together to form galaxies.
Hubble space telescope has gathered images to support this theory
Most of the early galaxies were spirals but over time many spirals merged to form elliptical
Galaxy Mergers Larger galaxies consume
smaller galaxies. Most bright galaxies are formed from the merger of two or more smaller galaxies.
Galaxies are very massive which means they also have a strong gravitational pull. This force can cause
galaxies to attach themselves to one another and merge over time Few hundred million to a few
billion years to complete
Results of Galaxy Mergers When two or more
large spiral galaxies merge they form elliptical galaxies containing more than a trillion stars.
Trigger intense bursts of new star formation
Create gigantic black holes
Galaxy Collision
Types of Galaxies: Shape Classification Spiral Galaxy
Most beautiful type of galaxy Examples: Milky way,
Andromeda(M31) Flat disks of stars with
bright bulges at the center Spiral arms wrap around the
bulge Arms are a result of density
waves which influence matter as they pass.
Color of the spiral arms depend on the new born stars and their characteristics.
Dark spaces between the arms contain older stars, which are not as bright
Types of Galaxies: Shape Classification Spiral Barred
Galaxies Stars in the center
form a bar The arms of the spiral
shoot out from the end of the bar The Milky Way galaxy is
a spiral bar galaxy
Types of Galaxies: Shape Classification Elliptical
Look like fat, fuzzy footballs
Stars wrap completely around the galaxy’s heart in all directions
Largest galaxies in the universe are elliptical in shape Contain more than a
trillion stars Span more than one
million light years
Types of Galaxies: Shape Classification Irregular Galaxies
This category has a mixture of shapes- anything that is not a spiral or elliptical
No identifiable form Usually the smallest
galaxies are irregular in shape Contain about one
million stars Irregular galaxies are
hypothesized to be the building blocks that came together to form the first larger galaxies
Types of Galaxies: Energy Classification
Active Galaxies Observing these galaxies in the
X-ray, ultraviolet, infrared and radio wavelengths, they appear to be giving off enormous amounts of energy
4 Classifications of Active galaxies Seyfert galaxies
Have broad spectra indicating cores of hot, low-density ionized gas.
Radio galaxies Nuclei emit jets of high-velocity
gas above and below the galaxy -- the jets interact with magnetic fields and emit radio signals.
Quasars Most energetic objects in the
universe. Blazars
Jet emanating from the galaxy.
Types of Galaxies: Energy Classification
Normal Galaxies most of the light comes
from the stars in visible wavelengths and is evenly distributed throughout the galaxy
Closure What is the most common way for
classifying galaxies? Classify one of the galaxies from the
activity. Explain why it is classified that way.
Objective: You will use the different types of galaxies and their characteristics in order to explain the major systems within the universe and earth’s place in it. Warm-Up: Classify the following galaxies by shape
A
B
C
1 2 3 4
The Milky Way Galaxy The Milky Way galaxy
consists of a bulge of stars in the core, probably a thick bar of stars flanking the core, and bright spiral arms wrapping around the core.
The Milky Way Galaxy Size and structure of our
galaxy Spiral galaxy Thin flat disk
100,000 light-years in diameter 2,000 light years thick
Milky Way disk The disk is surrounded by a halo of
about 200 globular star clusters Objects near the center of the
galaxy move faster Contains between 200 billion
and 400 billion stars A black hole (~ 4 million times
more massive than our sun) at the center of the galaxy
Our solar system 27,000 light years from the
center
The Local Group The Milky Way Galaxy is part of
a larger cosmic neighborhood- a collection of more than 35 galaxies known as the local group. These galaxies move through space as a single unit, bound by mutual gravitational pull.
Largest and heaviest members of the Local Group Milky Way Galaxy
Large collection of satellite galaxies Largest and best known satellite
galaxies Large and small Magellanic Clouds
200,000 light years away
Andromeda Galaxy (M31) 2.5 million light years away
In about 4 billion years
Astronomers predict that in several billion years, the Milky way galaxy and Andromeda will merge to form a galactic giant
Hubble’s Law An observational effect of the expansion is that the farther a
galaxy is from you, the faster it appears to be receding (Red shift in spectral line). This creates a relationship between the recessional velocity and distance. This phenomenon is known as Hubble's Law
Recessional Velocity = Hubble's Constant X Distance
V = Ho D
V is the observed velocity of the galaxy away from us, usually in
km/sec Ho is Hubble's Constant, in km/sec/Mpc (Ho = 73 km/sec/Mpc). D is the distance to the galaxy in Mpc