Transcript The Milky Way powepoint

THE MILKY WAY
Intro Info
The Universe has about
100 billion to 1 trillion
galaxies, and each galaxy has on
the average
100 billion and 1 trillion numbers
of stars .
So how many stars are there
roughly???
• Minimum Average: 1011 x 1011
• Maximum Average: 1012 x 1012
• BETWEEN 1022 AND 1024 STARS!!!
• 10 sextillion and 1 septillion STARS!
Dwarf Galaxies
• About 10 million stars
Irregular Galaxies
• Can have up to 10 trillion stars
The Milky Way
• Barred spiral galaxy
• Over 200 billion stars
• One of tens of billions of galaxies in the
observable universe
The Milky Way is about 100 000
light-years across, about 10 000
light-years thick.
Our Solar System is located near
the edge of one of the arms. It is
located about 30 000 light-years
from the middle.
Size and Shape
• Clouds of interstellar medium (dust and gas) fill
the galactic disk and prevent our ability to see
through it.
– This long fooled astronomers to think we lived near
the centre of our galaxy
• In the 1920s, Harlow Shapley found that the
globular clusters orbit a point tens of thousands
of light years from our Sun.
– This point is the centre of our galaxy, not our Sun!!
– Also not the centre of our Universe!!!
Size and Shape
• Radio and infrared technologies allow us to
see through the interstellar dust.
• Our Sun lies about 28 000 light-years from
the centre of the Milky Way
Size and Shape
• Flat disk of stars with a
bright central bulge (bar)
• Spiral arms
• Dimmer round halo
surrounding everything
• A few hundred globular
clusters of stars orbit the
galaxy’s centre
• In 2005, the Spitzer Space
Telescope collected
evidence that the Milky
Way is a Barred Spiral
Terms
Gas Halo: also called galactic halo
A gas halo is a ring of gas and stars surrounding
a galaxy.
A globular cluster is a spherical collection of
stars that orbits a galaxy core as a satellite.
They are older stars.
The Milky Way
• Has satellite galaxies (it is very large)
The Local Group
• The Milky Way is part of the Local Group.
• The Milky Way and Andromeda are the
two most massive galaxies in this group
(both spiral galaxies).
• Composed of 30 galaxies with the
gravitational centre between the Milky
Way and Andromeda.
• 10 million light years in diameter.
Virgo Cluster
• The Milky Way is
part of the Local
Group which is part
of the Virgo Cluster.
• 1300 galaxies in this
group.
• Many members of
this galaxy are
visible with a
telescope.
• It is located in the
constellation Virgo.
Virgo Supercluster (Local Supercluster)
• An irregular supercluster of galaxies that
contains the Milky Way, Local Group and Virgo
Cluster.
• Contains 100 galaxy groups and clusters
• Diameter of 110 million light years
http://www.atlasoftheuniverse.com/vi
rgo.html
Comparison of Solar System to Virgo
Supercluster
http://upload.wikimedia.org/wikipedia/commons/a/a7/Universe_Reference_Map_
%28Location%29_001.jpeg
It appears that we are in the
middle of the Universe. That isn’t
true. We are only in the middle of
what we can
see.
We can see the same distance in all
directions.
The next closest galaxy to us is
Andromeda and is about
2 million light years away.
In 1842, Christian Doppler explained
why an object making a noise sounds
more shrill when it is coming towards
you, and sounds deeper when it is
going away from you. When an object
is coming towards you, the sound
vibrations in the air are travelling in
the same direction as the object.
When the object passes you and
moves away, the sound vibrations
are travelling in the opposite
direction from the moving object.
Every star sends out light waves. The
light appears bluer if the star is
coming towards us, and redder if it is
moving away.
In the 1930’s, astronomers found that
most galaxies show a red shift.
This means that they are moving
away from our galaxy. The
farthest galaxies are moving
away at thousands of kilometres
a minute!
In the 1950s, astronomers discovered
that some galaxies sent out radio
waves. Their light was very strange
because the light waves were
stretched out. These galaxies were
called
quasars
and they have the largest red shifts
known. They are the farthest from
us. Looking at quasars is like looking
into the past.
The farthest known quasar is about
12 billion light-years away.
When we look out into space, out beyond
the quasars, we are really looking back into
time.
Why are all galaxies moving away from us?
Why should the galaxies farthest away
from us move away the fastest? What’s so
special about us?
Quasars
• A very energetic and distant ACTIVE galaxy.
They are the most luminous objects in the
universe.
• QUASAR: quasi-stellar radio source
• Quasars were first identified as being high
redshift sources of electromagnetic energy,
including radio waves and visible light, that
were point-like, similar to stars, rather than
extended sources similar to galaxies.
Rotation of Galaxies – The Missing Mass Problem
•Doppler Effect used to
measure the speed of
material orbiting
around the center of a
galaxy.
•Photographs of
galaxies show that
luminous material
appears to be
concentrated towards
the center and drops off
with increasing
distance.
Observed
Expected
Distance from galaxy center
Rotation of Galaxies – The Missing Mass Problem
If matter were really
concentrated in this fashion,
we would see “rotation
curves” following the
“expected” path in the
diagram at right.
What is observed instead is
that rotation curves tend to
remain high as far out as they
can be measured. This means
the existence of massive
halos of dark matter in
galaxies. The nature of the
material comprising this dark
matter is completely unknown
at present, making this one of
the greatest problems of
contemporary astronomy.
Observed
Expected
Distance from galaxy center
Gravitational Lensing in Abell 2218 Cluster
As predicted by Einstein’s General Theory of Relativity, a compact intervening object is bending and
distorting light from individual members of this cluster so that we see a halo effect.
Hubble Space Telescope Image
A Lensed Quasar
An intervening galaxy
between us and this
distant quasar is causing
light from the quasar to
be bent along curved
paths that give rise to an
Einstein cross, a
phenomenon predicted by
Einstein’s General
Theory of Relativity.
National Optical Astronomy Observatories Image