Chapter 16: Chapter 16: Other Other

GalaxiesGalaxies

WHAT DO YOU THINK?

Do all galaxies have spiral arms?Are galaxies isolated objects?Are all other galaxies moving away

from the Milky Way?

You will discover…You will discover…

How galaxies are categorized by their shapes.

That galaxies contain huge amounts of dark matter.

That galaxies are found in clusters.How some galaxies merge while others

devour their neighbors.That the universe is expanding.

Types of GalaxiesTypes of Galaxies

1.1. SpiralSpiral

2.2. Barred SpiralBarred Spiral

3.3. EllipticalElliptical

4.4. IrregularIrregular

Hubble’s Diagram of Galaxy TypesHubble’s Diagram of Galaxy Types

1. Spiral Galaxies1. Spiral Galaxies

Type Sa Type Sb Type Sc

Andromeda (M31)Andromeda (M31)

Spiral Galaxies Seen Edge-onSpiral Galaxies Seen Edge-on

M104: Sa galaxy NGC 891: Sb galaxy NGC 4631: Sc galaxy

Variety in Spiral ArmsVariety in Spiral Arms

M33: A Spiral Galaxy with Flocculent Spiral Arms – created by explosions.

M74: a Grand Design Spiral Galaxy – created by waves, like ripples in water.

2. Barred Spiral Galaxies2. Barred Spiral Galaxies

M58: SBa galaxy M83: SBb galaxy NGC 1365: SBc galaxy

3. Elliptical Galaxies3. Elliptical Galaxies

M105: E0 galaxy M49: E4 galaxy NGC 4526: E7 galaxy

4. Irregular Galaxies4. Irregular Galaxies

Large Magellanic Cloud, Irr 1 galaxy

NGC 4485 (Irr 2) and NGC 4490 (Sc) galaxies

Galaxies are Clumped in SpaceGalaxies are Clumped in Space

Galaxies occur in groups called Galaxies occur in groups called ClustersClusters. The . The galaxies in a Cluster are bound by gravity to galaxies in a Cluster are bound by gravity to each other, and can collide.each other, and can collide.

Our Galaxy belongs to a Cluster called “The Our Galaxy belongs to a Cluster called “The Local Group.”Local Group.”

Clusters of galaxies occur in bigger groups Clusters of galaxies occur in bigger groups called called SuperclustersSuperclusters. Most Superclusters are . Most Superclusters are not gravitationally bound units like Clusters are.not gravitationally bound units like Clusters are.

All the Clusters are moving away from each All the Clusters are moving away from each other as the Universe expandsother as the Universe expands..

A Cluster of GalaxiesA Cluster of Galaxies

The Fornax Cluster of Galaxies

The Local Group – Our ClusterThe Local Group – Our Cluster

Our Galaxy belongs to a poor, irregular (wimpy) cluster – consisting of about 40 galaxies (including M31 Andromeda) – called the Local Group.

Colliding GalaxiesColliding Galaxies

Galaxies that belong to the same Cluster Galaxies that belong to the same Cluster can collide.can collide.

Sometimes these galaxies pass through Sometimes these galaxies pass through each other, and sometimes they combine.each other, and sometimes they combine.

The The individual starsindividual stars in the colliding in the colliding galaxies galaxies do not hit each otherdo not hit each other, but the , but the huge clouds of gas and dust do collidehuge clouds of gas and dust do collide..

Colliding GalaxiesColliding Galaxies

Pairs of colliding galaxies often exhibit long “antennae” of stars ejected by the collision.

Colliding Galaxies “Mano a Mano”Colliding Galaxies “Mano a Mano”

NGC 2207 (right) and IC 2163 are orbiting and gravitationally distorting each other.

Our Local SuperclusterOur Local Superclusterand Other Superclustersand Other Superclusters

Our Local Group (cluster) is at the center of the diagram. Our Local Supercluster extends out to the Virgo Cluster.

Beyond Superclusters –Beyond Superclusters –Filamentary Structure in the UniverseFilamentary Structure in the Universe

2-Micron All Sky Survey (Infrared) – 1.6 million galaxies shown.

Beyond Superclusters –Beyond Superclusters –Filamentary Structure in the UniverseFilamentary Structure in the Universe

Distribution map of 62,559 galaxies in two wedges extending out in opposite directions from the Earth (done with galaxy redshifts).

The Universe is ExpandingThe Universe is Expanding

The Redshift of Superclusters shows us that The Redshift of Superclusters shows us that the Universe is expanding. This Redshift is the Universe is expanding. This Redshift is called the “called the “Cosmological RedshiftCosmological Redshift,” because ,” because it is it is caused by the expansion of spacecaused by the expansion of space..

The The farther awayfarther away a galaxy is from us, the a galaxy is from us, the faster it movesfaster it moves away from us: away from us: GALAXY SPEED = GALAXY DISTANCE x GALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (HHUBBLE’S CONSTANT (H00).).

This is called “Hubble’s Law,” after Edwin This is called “Hubble’s Law,” after Edwin Hubble, who discovered it.Hubble, who discovered it.

Hubble’s LawHubble’s Law

The The farther awayfarther away a galaxy is from us, the a galaxy is from us, the faster it movesfaster it moves away from us: away from us: GALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (HGALAXY SPEED = GALAXY DISTANCE x HUBBLE’S CONSTANT (H00).).

The Hubble Telescope looks back to when the The Hubble Telescope looks back to when the

Universe was very young.Universe was very young.

HST – Galaxies 12.5 Billion LY AwayHST – Galaxies 12.5 Billion LY Away

HST – Galaxies >13 Billion LY AwayHST – Galaxies >13 Billion LY Away

WHAT DID YOU THINK? Do all galaxies have spiral arms? No. Galaxies may be either spiral, barred spiral,

elliptical, or irregular. Only spirals and barred spirals have arms.

Are galaxies isolated objects? No. Galaxies are grouped in clusters, and

clusters are grouped in superclusters. Are all other galaxies moving away from the

Milky Way? All galaxies except those in our Local Group

(cluster) are receding from us. Some local galaxies are actually moving toward us.