Galaxy classification
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Galaxy Classification. Edwin Hubble was the first person to establish the distances to other galaxies. Because he studied so many galaxies, he began to classify them into different types. The shape and color of a galaxy tell us a lot about the events that have happened within that galaxy.

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Galaxy Classification

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Galaxy classification

Galaxy Classification


Galaxy classification

  • Edwin Hubble was the first person to establish the distances to other galaxies.

  • Because he studied so many galaxies, he began to classify them into different types.

  • The shape and color of a galaxy tell us a lot about the events that have happened within that galaxy.


4 general types of galaxies

4 General Types of Galaxies

  • Elliptical – spherical to football-shaped

  • Spiral – like a propeller

  • Barred Spiral – similar to a spiral, but with a straight bar through the nucleus

  • Irregular – no well-defined shape


Elliptical galaxies

Elliptical Galaxies

  • Look like enormous globular clusters.

  • Elliptical galaxies are often bigger than spiral galaxies.

  • Stars are yellow & red, with very little free dust & gas.

  • These galaxies are old & no longer forming new stars.


Elliptical galaxies1

Elliptical Galaxies

  • Elliptical galaxies may form from the collision of 2 or more spiral galaxies.

  • Spherical elliptical galaxies are E0’s. Very elongated ellipticals (football shaped) are E7’s.

  • All ellipticals fall in the E0 to E7 range.


Galaxy classification

M87 galaxy in Virgo – an E0 type


Galaxy classification

M32 in Andromeda, an E2 type


Galaxy classification

M110 in Andromeda, a dwarf elliptical

galaxy of E6 type.


Spiral galaxies

Spiral Galaxies

  • Like our own Milky Way, all spiral galaxies have a nuclear bulge, and at least 2 spiral or propeller-shaped arms, with a halo of gas, dust, stars, and globular clusters.

  • Spiral galaxies are classified as Sa, Sb, or Sc depending on the size of the nucleus & how tightly the arms are wrapped.


Galaxy classification

M104 – the Sombrero Galaxy, an Sa type,large nucleus & very tight spiral arms.


Galaxy classification

The Andromeda Galaxy, M81, is a type Sb.It has a medium nucleus & less tight arms.


Galaxy classification

This type Sc has a small nucleus and very

open arms.


Barred spiral galaxies

Barred Spiral Galaxies

  • Barred Spiral galaxies (SB) are classified just like ordinary spiral galaxies: SBa, SBb, SBc.

  • Our own Milky Way is probably an SBb type galaxy, similar to Andromeda, but with a central bar.


Galaxy classification

The bar is very noticeable in this SBc type.


Galaxy classification

In a barred

spiral, the

arms don’t

“grow”

directly

from the

nucleus.

This is NGC

1365.


Irregular galaxies

Irregular Galaxies

  • Several famous galaxies are irregular and have no definite shape.

  • The Large & Small Magellanic Clouds, and the Cartwheel Galaxy are irregular.

  • These galaxies are full of regions of new star formation!


Irregular galaxies 2

Irregular Galaxies 2

  • Irregular galaxies are often the result of collisions between galaxies.

  • Our own Milky Way cut a single smaller galaxy like a buzz saw blade.

  • The Large & Small Magellanic Clouds are the “chips” left over from that round of cannibalism.


Galaxy classification

The Large Magellanic Cloud.


Galaxy classification

The Cartwheel

Galaxy.


Now you try hubble s scheme

Now you try Hubble’s scheme.

  • Homework: Classify the 15 galaxies on the handout.


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