Unit 6
Galaxies
*Basic Galaxy Info.
*Types of Galaxies
-Characteristics of The Milky Way (Spiral Galaxies)
*Red Shift & Hubble’s Law
Basic Galaxy Info.
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Vocab Words for “Basic Galaxy Info.”
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Galaxy
Gravitational Lens
Active Galaxy
Galactic Cannibalism
Pulsating/Variable Star
Basic Galaxy Info.
A Galaxy is a group of stars, gas, dust and
other interstellar matter all gravitationally
bound together
 Can be bound together in different
patterns
 We live in the Milky Way Galaxy!
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Basic Galaxy Info.
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Galaxies behave as a Gravitational Lens
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A Gravitational Lens is a body that refracts
passing by light
Our galaxy is currently an Active Galaxy
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An Active Galaxy a galaxy that is alive and has young
and forming stars as a part of it.
An active galaxy may be growing or decreasing in number
of stars.
An active galaxy may be performing Galactic
Cannibalism.
An active galaxy may contain Pulsating or Variable Stars.
Basic Galaxy Info.
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Galaxies (including the Milky Way)
sometimes perform Galactic
Cannibalism.
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Galactic Cannibalism is when larger galaxies
consume smaller galaxies to become larger!
Galaxies also contain a special type of
star, a Pulsating or Variable Star.
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A Pulsating or Variable Star is a rotating neutron
stars with beams of radiation coming out of its poles
Types of Galaxies
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Vocab. words for “Types of Galaxies”
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Spiral Galaxy
Barred Spiral Galaxy
Elliptical Galaxy
Irregular Galaxy
Types of Galaxies
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Spiral Galaxy –
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In a Spiral
Galaxy, the
gas, dust &
interstellar
matter is all
gravitationally
bound
together in a
spiral pattern
Types of Galaxies
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Special Type of Spiral Galaxy….
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In a Barred Spiral Galaxy gas, dust & interstellar
matter is all gravitationally bound together in a spiral
pattern with a barred, instead of circular center
Types of Galaxies
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Elliptical Galaxy –
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In an Elliptical
Galaxy, gas, dust &
interstellar matter is all
gravitationally bound
together in an elliptical
pattern
Types of Galaxies
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Irregular Galaxy
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In an Irregular
Galaxy, gas,
dust &
interstellar
matter is all
gravitationally
bound together
with no rhyme or
reason its shape
Types of Galaxies
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Characteristics of the Milky Way (Spiral Galaxies)
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Vocab Words for “Characteristics of the Milky Way (Spiral
Galaxies)
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Spiral Arm
Galactic Bulge
Galactic Disk
Globular Cluster
Galactic Halo
Local Group
Types of Galaxies
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Characteristics of the Milky Way (Spiral Galaxies)
The Milky Way is a spiral galaxy, so we
know a lot about spiral galaxies.
 We know they contain…
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A Galactic Bulge
 A Galacitc Halo
 A Galactic Disk
 Globular Clusters
 Spiral Arms
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Types of Galaxies
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Characteristics of the Milky Way (Spiral Galaxies)
Types of Galaxies
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Characteristics of the Milky Way (Spiral Galaxies)
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The Galactic Bulge is the group of stars surrounding the
immediate center of a spiral galaxy
The Galactic Disk is the portion of a spiral galaxy that
contains most of the interstellar matter, the nucleus and
the spiral arms are a part of it
The Spiral Arm is the winding offshoot from the center of
a spiral galaxy
The Globular Cluster is the group of thousands of stars
tightly packed together lying outside the galactic disk, but
within the galactic halo
The Galactic Halo is the imaginary sphere surrounding a
spiral galaxy that contains ALL of the interstellar matter of
that galaxy
Types of Galaxies
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Characteristics of the Milky Way (Spiral Galaxies)
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The Milky Way galaxy is part of a cluster of
galaxies called the Local Group
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The Local Group is the cluster of the Milky Way and
more than 30 other nearby galaxies
Two of these nearby galaxies are:
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Andromeda
Triangulum
Red Shift & Hubble’s Law
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Vocab Words for “Red Shift & Hubble’s
Law”
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Red Shift
Hubble’s Law
Dark Matter
Red Shift & Hubble’s Law
 All
the galaxies put together makes
up our Universe!
Red Shift is the idea that the universe is
expanding outward.
 The idea is that the galaxies are getting
further and further away from each other.
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Red Shift & Hubble’s Law
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Red Shift does NOT mean everything is
turning red!
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It means that the Doppler Effect is occurring with
light waves and radiation is shifting towards the
red end of the visible light spectrum.
Red Shift & Hubble’s Law
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This demonstrates what Red Shift means and how it
implies, objects (galaxies) are moving away!
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Remember - - there are wavelengths assigned to each of these colors!
Red Shift & Hubble’s Law
 Hubble’s
Law takes this idea of Red
Shift a step further
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Hubble’s Law states that the universe is expanding
outward and accelerating as it expands
It can be demonstrated by an equation of…
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V = H0D, where V is velocity, H0 is Hubble’s constant
and D is Distance.
 For our purposes, we will use Hubble’s constant as 60.
Red Shift & Hubble’s Law
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This is a graph of the
relationship between a
Galaixy’s distance
from us and the
Velocity of that Galaxy.
Red Shift & Hubble’s Law
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What is causing the galaxies to
accelerate as they move outward?
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Astronomer’s believe Dark Matter is causing these
galaxies to accelerate.
We don’t really know what dark matter is. We call
dark matter, matter that emits and reflects minimal to
no light. We know its there, because it does have a
gravitational influence that is causing the galaxies to
accelerate.
Red Shift & Hubble’s Law
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Picture of a Black Hole!
Red Shift & Hubble’s Law
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There is a picture of “Dark Matter” on the left and
a picture of “Not Dark Matter” on the right!