Download Galaxies

Galaxies
Galaxies
A
galaxy is a huge region of space
that contains hundreds of billions of
stars, planets, glowing nebulae, dust,
empty space, and possibly black
holes.
 Galaxies
began when large clouds of
gas and dust started to shrink as a
result of their gravity.
Galaxies
 Galaxies
are held together by gravity.
 According
to Hubble’s Law, galaxies
are moving away from one another.
 100
billion or so exist in the universe.
Shapes of Galaxies
 Hubble
categorized these shapes or
basic schemes of galaxies:
1. Spiral
2. Elliptical (nearly circular)
3. Irregular
Spiral Galaxies

Arms tightly wound around galaxy, like a
pinwheel

A group of objects in center (stars and
possibly a black hole)

Surrounded by a halo and an invisible
cloud of matter.
Spiral Galaxies

Rotating – which forms arms

May lose arms and become elliptical

Examples: Milky Way and Andromeda
Galaxies
Spiral Galaxies
Elliptical Galaxies

Can be round, oval, flattened or spherical

Resembles the nucleus of a spiral galaxy
without the arms

Very little gas or dust
Elliptical Galaxies

Mostly older stars

Collect into globular clusters

Examples: Maffei 1, M32
Elliptical Galaxies
Irregular Galaxies

Neither spiral or elliptical

Disk, but no spiral arms

Caused by the formation of new stars in
the galaxy or by the pull of neighboring
gravitational fields
Irregular Galaxies

In some irregular galaxies one can see
individual stars, nebulae, and clusters

Mixture of old and new stars

Large amounts of gas and dust

Examples: Large and Small Magellanic
Clouds
Irregular Galaxies
Barred Spiral Galaxies

Spirals with bright bar
of gas down center.
Lenticular Galaxies


Consists of bulge and
disk with little or no
new star formation.
Example: Spindle
Galaxy
Parts of a Galaxy

The galaxy is made up of two visible
components:
1. Disk
2. Bulge
Parts of a Galaxy – The Disk

Contains clouds of gas and dust called
nebulae

In a spiral galaxy, most stars are in the
disk

Open Cluster (Galactic Clusters) are
younger, asymmetric groups of stars.
Parts of a Galaxy – The Disk

An example of a
galactic cluster is
Pleiades (M45)
Parts of a Galaxy - Bulge

A large squashed sphere surrounding the
galaxy’s center

Contains older stars

Not very much gas or dust

One fifth of the total light comes from the
bulge
Parts of a Galaxy - Bulge

The bulge can be used to determine the
age of the galaxy

Above and around the bulge are globular
clusters – hundreds of thousands of stars
bound in a tight spherical swarm
Parts of a Galaxy - Bulge

An example of a
globular cluster is
M13 (Hercules
Globular Cluster)
The Milky Way Galaxy

Over 100 billion stars and possibly a black
hole in the center.

Has star clusters, planets, glowing
nebulae, dust and empty space.

Older stars and globular cluster near the
center
The Milky Way Galaxy

Younger stars and galactic clusters in disk

One hundred thousand (100,000) light
years in diameter. Ten thousand (10,000)
light years thick

Our solar system is located on the Orion
Arm – 30,000 light years from the center.
The Milky Way Galaxy

Part of the Local Group of super clusters
(Andromeda is also part of this group)

Astronomers use radio and infrared
telescopes to “see” the center of the
galaxy

We can’t actually “see” the center of the
galaxy because of dust and gas!
The Milky Way Galaxy

The Milky Way is getting larger because it
is “eating” the Large Magellanic Cloud. Its
stars are being added to the Milky Way.

The Milky Way is falling toward the
Andromeda Galaxy and both are feeling
the tug of the great Virgo Cluster, which
is 50 million light years away.
Virgo Cluster
The Milky Way Galaxy
Andromeda Galaxy (M31)

Can only be seen by astronomers in the
Northern hemisphere

2.2 million light years away

Can see without a telescope, appears as a faint
fuzzy patch

About the same size as the Milky Way

Two times more massive than the Milky Way
Andromeda Galaxy
Large and Small Magellanic Clouds

Can only be seen by astronomers in the
Southern Hemisphere

The two closest galaxies to the Milky Way
(Less than 200,000 light years away)

Visible to the naked eye
Large and Small Magellanic Clouds

Relatively small and irregular in shape

Only five percent of the mass of the Milky
Way

Large Magellanic is being “eaten” by the
Milky Way
Large Magellanic Clouds
Small Magellanic Clouds
Messier Catalog System

Charles Messier was looking for comets.

Made a list of star clusters, galaxies and
nebula so that he would not mistake them
for comets.

Listed 110 objects, including 32 galaxies
by 1780.

Andromeda – M31