Transcript Chapter 31 Galaxies & the Universe

Chapter 31
Galaxies & the Universe
Review
& Recap
The Hubble Space
Telescope
measures black
holes that cannot
be seen.
It does this by
precisely measuring
the speed of gas and
stars around a black
hole.
This provides clues for
the existence of a
black hole.
Astronomers measure
the motion of stars
swirling around the
black hole to determine
the mass.
A Black Hole
A black hole is an object with a gravitational pull so
intense that not even light can escape. It pulls in
other stars and gas with its gravitational force.
31.1 The Milky Way Galaxy
Objectives:
Determine the size and shape of the Milky
Way, as well as Earth’s Location within it.
Describe how the Milky Way was formed.
Variable Stars
By measuring a star's period of pulsation,
astronomers can determine its luminosity
and calculate how far away a variable star
must be to appear as dim or as bright as it
does.
Variable stars comparing and contrasting
Both are variable stars that have a relationship between its luminosity
and its pulsation period.
RR Lyrae variables
• have periods of
pulsations between 1.5
hours and 1 day and, on
average, have the same
luminosity
Cepheid variables
• have pulsation periods
between 1 day and more
than 100 days.
• the longer the pulsation
period the greater the
luminosity
The Shape of the Milky Way
Astronomers have determined the shape of the Milky Way by
using radio waves because they penetrate the interstellar gas
and dust without being scattered or absorbed.
Discovering Other
Galaxies
Other galaxies were first
believed to be nebulae or
star clusters within the
Milky Way.
Discovering Other
Galaxies – cont.
Edwin Hubble's discovery of
Cepheid variable stars in the
Great Nebula in the
Andromeda constellation
proved the existence of
galaxies outside the Milky
Way.
Mass of the Milky Way
Studies provide evidence that there is a great amount of
unseen matter called dark matter composed of dim stellar
remnants that have mass.
Estimates vary from 200 billion x , up to 1,000 billion x the Mass of our Sun.
Dark Matter
The strongest evidence that the universe contains a larger
amount of dark matter than visible matter is that by analyzing
the motion of member galaxies, the mass of galaxy clusters
can be determined. This mass of whole galaxy clusters is
always much larger than the sum of only the visible masses
of the galaxies.
Formation and Evolution of the Milky Way
The halo and bulge of the Milky Way are made of old stars
which suggests that the halo and bulge formed first.
Quiz – 31.1 The Shape of the Milky Way
31.2 Other Galaxies in the Universe
Objectives:
Describe how astronomers classify galaxies.
Identify how galaxies are organized into
clusters and super clusters.
Describe the expansion of the universe.
Superclusters
Gigantic formation of clusters of galaxies
hundreds of millions of light-years in size are
called superclusters.
Active Galaxies
Core of a galaxy in which highly energetic
objects or activities are located. (also known
as AGNs!)
Quasars
The redshift in many quasars is very large, which
means that those quasars are far away.
The Expanding Universe – Hubble’s Law
The farther away from Earth a galaxy is, the
faster it is moving.
Hubble Constant - A value of approximately 70
kilometers per second per megaparsec
Elliptical Galaxy
Please copy illustration
This is an elliptical
galaxy. Galaxies that
are not flattened into
disks and do not have
spiral arms. Their
shapes range from
round ellipticals to
very elongated
ellipticals. Possible
example: Virgo A
Elliptical Galaxy – cont.
Elliptical
galaxies are
divided into
subclasses based
on the ratio of
their major and
minor axes.
Spiral Galaxy
Please copy illustration
This is a spiral
galaxy. Disklike
galaxy with spiral
arms consisting of
interstellar matter
and young star
clusters. A bulge
consists of an old
stellar population.
There are normal and
barred spirals.
Possible example:
Milky Way.
Irregular Galaxy
Please copy illustration
This is an irregular
galaxy. These galaxies
do not fit the
elliptical or spiral
classification. They
typically have no
distinct shape.
Possible example:
Large and Small
Magellanic Clouds.
Galaxy Cluster
Please copy illustration
This is a galaxy cluster.
These groups of galaxies
may have from a few to
hundreds of member galaxies
and may range in sizes up
to 30 million ly. In a
cluster, most of the inner
region galaxies are
ellipticals. Galaxies in
the outer portions are a
mix of ellipticals and
spirals. The galaxies often
merge to form strangely
shaped galaxies with more
than one nucleus. Possible
example: Local Group.
Galaxy Clusters
– cont.
Most galaxies
in the inner
region of a
large cluster
are
ellipticals.
Galaxy Shapes
M74 Spiral Galaxy
An Sc galaxy is a
normal spiral with
loosely wound arms
and a small, dim
nucleus.
Galaxy shapes
Galaxy Shapes – Cont.
a
Tightly wound arm and
large, bright nucleus
c
Loosely wound arms and
a small, dim nucleus
E7
Very elongated
elliptical
EO
Round elliptical
Irr
Irregular galaxy
S
Normal spiral
SB
Barred spiral
SO
Flat disks that do not
have spiral arms
Quiz – 31.2 Other Galaxies in the Universe (10pts)
31.3 Cosmology
Objectives:
Explain the different theories about the
formation of the universe.
Describe the possible outcomes of universal
expansion.
Models of the Universe
Steady-state theory - Proposes
that the universe looks the same
on large scales to all observers
and that it has always looked that
way
Cosmic background radiation
Has a wavelength of approximately
1 mm, which makes it microwave
radiation.
Cosmic background radiation
Provides information about conditions very
early in the expansion of the universe.
The Hubble Constant
Recent observations show that the rate of
expansion of the universe is speeding up.
Models of the Universe – cont.
Big Bang Theory States that the
universe began as
a point and has
been expanding
ever since
The Big Bang – cont.
The theory does not suggest an
explosion into space, but instead
that there is an expansion of space
with matter going along for the ride.
Models of the Universe – cont.
Inflationary Universe Theory - Model says the universe began
as a fluctuation in a vacuum and expanded very rapidly for a
fraction of a second before settling into a more orderly
expansion
Inflationary Universe Theory – cont.
A flat universe was first predicted in the 1980’s by the
inflationary universe model.
The Critical Density
Average density and Critical Density are factors in the
expansion of the universe.
The Critical Density – cont.
The average density is the total matter of the universe.
The Critical Density – cont.
Critical density is the dividing point between a closed or an
open universe.
The Critical Density – cont.
If the average density is higher than the critical density, the
universe is closed.
The Critical Density – cont.
If the average density is lower than the critical density, the
universe is open.
The Critical Density – cont.
If the average density equals the critical density, the universe
is flat.
Quiz – 31.2 Other Galaxies in the Universe (10pts)
Quiz – 31.3 Cosmology (10pts)