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

GalaxiesGalaxies

GalaxiesGalaxiesA galaxy is a huge region of space that A galaxy is a huge region of space that

contains hundreds of billions of stars, contains hundreds of billions of stars, planets, glowing nebulae, dust, empty planets, glowing nebulae, dust, empty space, and possibly black holes.space, and possibly black holes.

Galaxies began when large clouds of Galaxies began when large clouds of gas and dust started to shrink as a gas and dust started to shrink as a result of their gravity.result of their gravity.

GalaxiesGalaxies

Galaxies are held together by gravity. Galaxies are held together by gravity.

According to Hubble’s Law, galaxies According to Hubble’s Law, galaxies are moving away from one another.are moving away from one another.

100 billion or so exist in the universe100 billion or so exist in the universe..

Shapes of GalaxiesShapes of Galaxies

Hubble categorized these shapes or Hubble categorized these shapes or basic schemes of galaxies:basic schemes of galaxies:

1. Spiral1. Spiral

2. Elliptical (nearly circular)2. Elliptical (nearly circular)

3. Irregular3. Irregular

Spiral GalaxiesSpiral Galaxies

Arms tightly wound around galaxy, like a Arms tightly wound around galaxy, like a pinwheelpinwheel

A group of objects in center (stars and A group of objects in center (stars and possibly a black hole)possibly a black hole)

Surrounded by a halo and an invisible Surrounded by a halo and an invisible cloud of matter.cloud of matter.


Rotating – which forms armsRotating – which forms arms

May lose arms and become ellipticalMay lose arms and become elliptical

Examples: Milky Way and Andromeda Examples: Milky Way and Andromeda GalaxiesGalaxies


Elliptical GalaxiesElliptical Galaxies

Can be round, oval, flattened or sphericalCan be round, oval, flattened or spherical

Resembles the nucleus of a spiral galaxy Resembles the nucleus of a spiral galaxy without the armswithout the arms

Very little gas or dustVery little gas or dust


Mostly older starsMostly older stars

Collect into globular clustersCollect into globular clusters

Examples: Maffei 1, M32Examples: Maffei 1, M32


Irregular GalaxiesIrregular Galaxies

Neither spiral or ellipticalNeither spiral or elliptical

Disk, but no spiral armsDisk, but no spiral arms

Caused by the formation of new stars in Caused by the formation of new stars in the galaxy or by the pull of neighboring the galaxy or by the pull of neighboring gravitational fieldsgravitational fields


In some irregular galaxies one can see In some irregular galaxies one can see individual stars, nebulae, and clustersindividual stars, nebulae, and clusters

Mixture of old and new starsMixture of old and new stars

Large amounts of gas and dustLarge amounts of gas and dust

Examples: Large and Small Magellanic Examples: Large and Small Magellanic CloudsClouds


Barred Spiral GalaxiesBarred Spiral Galaxies

Spirals with bright bar Spirals with bright bar of gas down center.of gas down center.

Lenticular GalaxiesLenticular Galaxies

Consists of bulge and Consists of bulge and disk with little or no disk with little or no new star formation.new star formation.

Example: Spindle Example: Spindle GalaxyGalaxy

Parts of a GalaxyParts of a Galaxy

The galaxy is made up of two visible The galaxy is made up of two visible components:components:

1. Disk1. Disk

2. Bulge2. Bulge

Parts of a Galaxy – The DiskParts of a Galaxy – The Disk

Contains clouds of gas and dust called Contains clouds of gas and dust called nebulaenebulae

In a spiral galaxy, most stars are in the In a spiral galaxy, most stars are in the diskdisk

Open Cluster (Galactic Clusters) are Open Cluster (Galactic Clusters) are younger, asymmetric groups of stars. younger, asymmetric groups of stars.

Parts of a Galaxy – The DiskParts of a Galaxy – The Disk

An example of a An example of a galactic cluster is galactic cluster is Pleiades (M45)Pleiades (M45)

Parts of a Galaxy - BulgeParts of a Galaxy - Bulge

A large squashed sphere surrounding the A large squashed sphere surrounding the galaxy’s centergalaxy’s center

Contains older starsContains older stars

Not very much gas or dustNot very much gas or dust

One fifth of the total light comes from the One fifth of the total light comes from the bulgebulge


The bulge can be used to determine the The bulge can be used to determine the age of the galaxyage of the galaxy

Above and around the bulge are globular Above and around the bulge are globular clusters – hundreds of thousands of stars clusters – hundreds of thousands of stars bound in a tight spherical swarmbound in a tight spherical swarm


An example of a An example of a globular cluster is globular cluster is M13 (Hercules M13 (Hercules Globular Cluster)Globular Cluster)

The Milky Way GalaxyThe Milky Way Galaxy

Over 100 billion stars and possibly a black Over 100 billion stars and possibly a black hole in the center.hole in the center.

Has star clusters, planets, glowing Has star clusters, planets, glowing nebulae, dust and empty space.nebulae, dust and empty space.

Older stars and globular cluster near the Older stars and globular cluster near the centercenter


Younger stars and galactic clusters in diskYounger stars and galactic clusters in disk

One hundred thousand (100,000) light One hundred thousand (100,000) light years in diameter. Ten thousand (10,000) years in diameter. Ten thousand (10,000) light years thicklight years thick

Our solar system is located on the Orion Our solar system is located on the Orion Arm – 30,000 light years from the center.Arm – 30,000 light years from the center.


Part of the Local Group of galaxies with 30 Part of the Local Group of galaxies with 30 others. (Andromeda is also part of this others. (Andromeda is also part of this group)group)

Astronomers use radio and infrared Astronomers use radio and infrared telescopes to “see” the center of the galaxytelescopes to “see” the center of the galaxy

We can’t actually “see” the center of the We can’t actually “see” the center of the galaxy because of dust and gas!galaxy because of dust and gas!


The Milky Way is getting larger because it The Milky Way is getting larger because it is “eating” the Large Magellanic Cloud. Its is “eating” the Large Magellanic Cloud. Its stars are being added to the Milky Way.stars are being added to the Milky Way.

The Milky Way is falling toward the The Milky Way is falling toward the Andromeda Galaxy and both are feeling Andromeda Galaxy and both are feeling the tug of the great the tug of the great Virgo ClusterVirgo Cluster, which , which is 50 million light years away.is 50 million light years away.

Virgo ClusterVirgo Cluster


Andromeda Galaxy (M31)Andromeda Galaxy (M31) Can only be seen by astronomers in the Can only be seen by astronomers in the

Northern hemisphereNorthern hemisphere

2.2 million light years away2.2 million light years away

Can see without a telescope, appears as a faint Can see without a telescope, appears as a faint fuzzy patchfuzzy patch

About the same size as the Milky WayAbout the same size as the Milky Way

Two times more massive than the Milky WayTwo times more massive than the Milky Way

Andromeda GalaxyAndromeda Galaxy

Large and Small Magellanic CloudsLarge and Small Magellanic Clouds

Can only be seen by astronomers in the Can only be seen by astronomers in the Southern HemisphereSouthern Hemisphere

The two closest galaxies to the Milky Way The two closest galaxies to the Milky Way (Less than 200,000 light years away)(Less than 200,000 light years away)

Visible to the naked eyeVisible to the naked eye

Large and Small Magellanic CloudsLarge and Small Magellanic Clouds

Relatively small and irregular in shapeRelatively small and irregular in shape

Only five percent of the mass of the Milky Only five percent of the mass of the Milky WayWay

Large Magellanic is being “eaten” by the Large Magellanic is being “eaten” by the Milky WayMilky Way

Large Magellanic CloudsLarge Magellanic Clouds

Small Magellanic CloudsSmall Magellanic Clouds

Messier Catalog SystemMessier Catalog SystemCharles Messier was looking for comets.Charles Messier was looking for comets.

Made a list of star clusters, galaxies and Made a list of star clusters, galaxies and nebula so that he would not mistake them nebula so that he would not mistake them for comets.for comets.

Listed 110 objects, including 32 galaxies Listed 110 objects, including 32 galaxies by 1780.by 1780.

Andromeda – M31Andromeda – M31

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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