Topic 4.2 - Galaxies Flashcards

1
Q

What are the four main types of of galaxies classified based on their appearance from Earth?

A
  1. Spiral
  2. Barred spiral
  3. Elliptical
  4. Irregular
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2
Q

Describe a spiral galaxy.

A

Flattened disk-shaped systems such as Andromeda Galaxy and M81

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3
Q

Describe a barred-spiral galaxy.

A

Similar to a spiral galaxy but with a bright ‘bar’ running through the nucleus from which spiral arms emerge

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4
Q

Describe an elliptical galaxy.

A

Relatively smooth spheroidal distributions of stars, showing a gradual decrease in brightness from the centre outwards

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5
Q

Describe an irregular galaxy.

A

Very little structure or symmetry

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6
Q

Explain how spiral, barred-spiral, and elliptical galaxies are distinguished further by assigning a number or a letter.

A

Spiral, barred-spiral, and elliptical galaxies are sub-classified by letters a, b or c depending on the strength of the nuclear bulge and ‘opens’ of the spiral arms. For example Sa galaxies have a predominant nucleus and tightly wound arms; Sc galaxies have a relatively small nucleus and open arms. Elliptical galaxies are assigned on numbers 0-7 depending on their shape (E0 is almost circular and E7 is highly elongated)

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7
Q

What type of galaxy is the Milky Way?

A

Spiral

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8
Q

What is a local group?

A

In similar way that stars are found in large collections, the galaxies themselves are grouped on both small and large scales. The Milky Way is in The Local Group

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9
Q

How many galaxies are in The Local Group and what is its size?

A

The Local Group comprises of about 50 galaxies and is about 3 Mpc across

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10
Q

Name 4 things The Local Group contains

A
  1. The Andromeda Galaxy (M31) - a giant spiral galaxy and the largest in the Group
  2. The Large and Small Magellanic Clouds (two irregular companion galaxies to ours)
  3. The Triangulum Galaxy (M33) - a spiral galaxy
  4. Several satellite and dwarf galaxies such as Pisces Dwarf and Aquarius Dwarf
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11
Q

Who is famous for classifying different types of galaxy?

A

Edwin Hubble 1920’s

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12
Q

What is a cluster?

A

On a larger scale, galaxies are found in gravitational agglomerations called clusters that often contain a giant elliptical galaxy in their central region

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13
Q

What is the nearest large grouping of galaxies to us?

A

The Virgo Cluster which contains 2000 galaxies (its centre lies 15-20 Mpc away)

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14
Q

What is a superclusters?

A

On an even larger scale, clusters collect together in superclusters. These are also held together by gravity

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15
Q

Name the members of the Virgo supercluster.

A
  1. Our Local Group of galaxies
  2. The Virgo Cluster
  3. The Fornax Cluster
  4. The Coma Cluster
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16
Q

How do galaxies ‘shine’?

A

They emit starlight

17
Q

What’s an active galactic nucleus?

A

Region in the centre of some galaxies emitting huge amounts of radiation. Not just visible light Radio, infra red, UV, X-rays, Gamma rays.

18
Q

What are the 3 types of nebula?

A
  1. Emission
  2. Reflecting
  3. Dark
19
Q

What are the two types of star clusters and where are they found?

A
  1. Globular (in halo)

2. Open (in disk)

20
Q

What are the 4 main types of active galactic energy?

A
  1. Radio galaxies
  2. Seyfert galaxies
  3. Quasars
  4. Blazars
21
Q

Describe radio galaxies.

A
  • Mainly elliptical
  • Intense sources of radio waves
  • They emit more than a million times more energy at radio wavelengths than normal galaxies
22
Q

Describe Quasars.

A
  • Far away
  • High redshift
  • They’re centres of other galaxies
  • Give off UV, infra-red, X-ray, high energy gamma
  • Their compact appearance make them look like stars
  • They give off lots of radio waves
23
Q

Describe Blazars.

A
  • They’re compact Quasars
  • Jets from Blazars are generally closely lined up to our direction from the galaxy
  • They emit the same as Quasars