Topic 4.2 - Galaxies Flashcards
What are the four main types of of galaxies classified based on their appearance from Earth?
- Spiral
- Barred spiral
- Elliptical
- Irregular
Describe a spiral galaxy.
Flattened disk-shaped systems such as Andromeda Galaxy and M81
Describe a barred-spiral galaxy.
Similar to a spiral galaxy but with a bright ‘bar’ running through the nucleus from which spiral arms emerge
Describe an elliptical galaxy.
Relatively smooth spheroidal distributions of stars, showing a gradual decrease in brightness from the centre outwards
Describe an irregular galaxy.
Very little structure or symmetry
Explain how spiral, barred-spiral, and elliptical galaxies are distinguished further by assigning a number or a letter.
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)
What type of galaxy is the Milky Way?
Spiral
What is a local group?
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
How many galaxies are in The Local Group and what is its size?
The Local Group comprises of about 50 galaxies and is about 3 Mpc across
Name 4 things The Local Group contains
- The Andromeda Galaxy (M31) - a giant spiral galaxy and the largest in the Group
- The Large and Small Magellanic Clouds (two irregular companion galaxies to ours)
- The Triangulum Galaxy (M33) - a spiral galaxy
- Several satellite and dwarf galaxies such as Pisces Dwarf and Aquarius Dwarf
Who is famous for classifying different types of galaxy?
Edwin Hubble 1920’s
What is a cluster?
On a larger scale, galaxies are found in gravitational agglomerations called clusters that often contain a giant elliptical galaxy in their central region
What is the nearest large grouping of galaxies to us?
The Virgo Cluster which contains 2000 galaxies (its centre lies 15-20 Mpc away)
What is a superclusters?
On an even larger scale, clusters collect together in superclusters. These are also held together by gravity
Name the members of the Virgo supercluster.
- Our Local Group of galaxies
- The Virgo Cluster
- The Fornax Cluster
- The Coma Cluster
How do galaxies ‘shine’?
They emit starlight
What’s an active galactic nucleus?
Region in the centre of some galaxies emitting huge amounts of radiation. Not just visible light Radio, infra red, UV, X-rays, Gamma rays.
What are the 3 types of nebula?
- Emission
- Reflecting
- Dark
What are the two types of star clusters and where are they found?
- Globular (in halo)
2. Open (in disk)
What are the 4 main types of active galactic energy?
- Radio galaxies
- Seyfert galaxies
- Quasars
- Blazars
Describe radio galaxies.
- Mainly elliptical
- Intense sources of radio waves
- They emit more than a million times more energy at radio wavelengths than normal galaxies
Describe Quasars.
- 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
Describe Blazars.
- They’re compact Quasars
- Jets from Blazars are generally closely lined up to our direction from the galaxy
- They emit the same as Quasars
