Download 25.4 Galaxies and the Universe

25.4 Galaxies and the Universe
 Objectives:
 Describe the different types of galaxy
 Describe the solar system’s position in
our galaxy
 Describe the universe and its origin
25.4 Galaxies and the Universe
 A galaxy is a group of stars, dust, and
gases held together by gravity.
Galaxy Messier 101 (also known
as NGC 5457 and nicknamed the
Pinwheel Galaxy) lies in the
northern circumpolar
constellation, Ursa Major (The
Great Bear), at a distance of 25
million light-years from Earth.
25.4 Galaxies
Types of Galaxies
 Spiral Galaxies
Spiral arms of stars and nebulae that wind out from
center
Can be barred – have a central bar of stars with
spiral arms extending out
Arms are the location of much star formation
More than half of the observed galaxies are spiral
galaxies.
Have large diameters of 10 000 to 300 000 lightyears and contain both young and old stars.
Spiral Galaxies
• This image is of NGC
1300, a spiral galaxy
with arms extending
from the ends of a
spectacularly
prominent central
bar. It is considered
a prototypical
example of barred
spiral galaxies and
lies at a distance of
about 65 million
light-years, in the
constellation of
Eridanus (the River).
Spiral Galaxies
• The bright galaxy NGC 3810 image
from Hubble.
25.4 Galaxies
Types of Galaxies
 Elliptical Galaxies
Shaped like large 3D elipses
About 10 percent of observed galaxies are
classified as elliptical galaxies.
Elliptical galaxies range in shape from round to
oval.
Contain little gas/dust
May contain mostly old (orange-red) stars
Elliptical Galaxies
• This image from NASA's
Hubble Space Telescope
shows the diverse
collection of galaxies in
the cluster Abell S0740
that is over 450 million
light-years away in the
direction of the
constellation
Centaurus.The giant
elliptical ESO 325-G004
looms large at the
cluster's center. The
galaxy is as massive as
100 billion of our suns.
25.4 Galaxies
Types of Galaxies
 Irregular Galaxies
• About 3 percent of the observed galaxies have
irregular shapes and are classified as irregular
galaxies.
• In addition to shape and size, one of the major
differences among different types of galaxies is the
age of their stars. Irregular galaxies may contain
mostly young stars.
Irregular Galaxy
• The irregular
galaxy
NGC 1427A
25.4 Galaxies
 Galaxy Clusters
• A galaxy cluster is a system of galaxies containing
few to thousands of member galaxies.
Contain a great deal of gas and dark matter
The Local Group is an example, containing Milky Way,
Andromeda and over 40 other galaxies
Galaxy Cluster
• The Fornax
Galaxy Cluster is
beyond our own
Local Group of
galaxies.
• It is at a
distance of
approximately
62 million light
years.
25.4 Milky Way
 Size of the Milky Way
The Milky Way is a large barred spiral galaxy
whose disk is about 100 000 light-years wide and
about 10 000 light-years thick at the nucleus.
The sun is about 26 000 light years from the center,
on an arm.
 Structure of the Milky Way
• Radio telescopes reveal that the Milky Way has
at least two large distinct spiral arms, with some
splintering.
The Milky Way
The Milky Way
• Image of the night sky
above Paranal on 21 July
2007, taken by
astronomer Yuri Beletsky
of the European Southern
Observatory (ESO). At the
center of the image, two
bright objects are visible:
the brightest is the planet,
Jupiter, while the other is
the star, Antares. Three of
the four 8.2-m telescopes
forming ESO's Very Large
Telescope (VLT) are seen,
with a laser beaming out
from Yepun, Unit
Telescope number 4. The
laser points directly at the
Galactic Center.
The Milky Way
• The Milky Way arch emerging from the Cerro Paranal, Chile,
on the left, and sinking into the Antofagasta's night lights. The
bright object in the center, above the Milky Way is Jupiter,
somehow elongated due to the panoramic projection. The
Magellanic Clouds are visible on the left side, and a plane
has left a visible trace on the right, along the Vista enclosure.
25.4 The Universe
The Expanding Universe
 Red Shifts
• Red shift, a Doppler shift toward the red end of
the spectrum, occurs because the light waves
are stretched, which shows that the receiver and
the source are moving away from each other.
 Hubble’s Law--1929
• Hubble’s law is a law that states that galaxies
are retreating from the Local Group at a speed
that is proportional to their distance.
• The red shifts of distant galaxies indicate that
the universe is expanding.
Raisin Bread Dough Analogy
25.4 The Universe
The Big Bang
 The big bang theory developed to
explain/understand the expanding universe
 States that at one time, the entire universe
was confined to a dense, hot, supermassive
ball
 About 13.75 billion years ago, a violent
expansion occurred, hurling this material in
all directions
25.4 The Universe
The Big Bang
 Supporting Evidence
Red shift of galaxies supports the big bang and the
expanding universe theories.
Cosmic microwave background radiation
Scientists think that this radiation was produced
during the big bang.
Distribution of galaxies
25.4 The Universe
 The Big Crunch or the Big Freeze?
• The future of the universe may follow two
possible paths:
1. The universe will expand forever and cool.
2. The outward expansion will stop and
gravitational contraction will follow.
• The view currently favored by most scientists is
an expanding universe with no ending point.
• It should be noted, however, that the methods
used to determine the ultimate fate of the
universe have substantial uncertainties.