Unit 4 Galaxies Flashcards

1
Q

How did Edwin Hubble classify galaxies?

A

Based upon appearance.
Spiral (S) - flat discs such as Andromeda.
Barred Spiral (SB) - similar to a spiral but with a bar running through the nucleus from which spiral arms emerge.
Elliptical (E) - Relatively smooth spheroidal distribution of stars, showing a gradual decrease in brightness from the nucleus outwards.
Irregular (Irr) - very little structure or symmetry.

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2
Q

How did Hubble use numbers or letters to help classify galaxies?

A

Elliptical - numbers 1-7 with E0 being circular and E7 being a long narrow ellipse.
Spiral - letters a-c with a being many tight spirals and c being few, spaced spirals.
Barred Spiral - letters a-c with a being many tight spirals and c being few, spaced spirals.
S0 - lenticular (between elliptical and spiral).

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3
Q

What is Hubble’s Tuning Fork?

A

The diagram showing galaxies shapes and classifications.

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4
Q

What classification of galaxy is the Milky Way?

A

Traditionally it has been an Sb type but there is increasing evidence to suggest a well defined bar which would make it an SBb.

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5
Q

What is the Local Group?

A

The group of galaxies which our galaxy belongs to. It is made up of about 50 galaxies spread over a distance of about 3 Mpc. Examples of galaxies in our local group include Anromeda, Triangulum and Aquarius Dwarf.

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6
Q

How many neighbouring groups of galaxies are there within 10 Mpc of ours?

A

5 other groups of galaxies.

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7
Q

What is a cluster?

A

A cluster is a group of galaxies gravitationally bound that often contain a giant elliptical galaxy at the centre. Our nearest cluster is the Virgo Cluster about 15-20 Mpc away. It includes about 2000 galaxies.

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8
Q

Give an example of a nearby cluster.

A

Virgo Cluster
Fornax Cluster
Coma Cluster

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9
Q

What is a supercluster?

A

A supercluster is a group of clusters. Our Local Group, the Virgo Cluster, Fornax Cluster and Coma Cluster are all part of the Virgo Supercluster.

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10
Q

What are active galaxies?

A

Galaxies that emit wavelengths other than visible light, mostly X-ray and radio waves. These are the most powerful energy sources in the universe.

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11
Q

What is thought to be the source of the energy for active galaxies?

A

Their energy source is thought to be an extremely small nucleus, also known as active galactic nuclei (AGNs).

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12
Q

There are four main types of active galaxy, what are they?

A

Radio Galaxies, Seyfert Galaxies, Quasars and Blazars.

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13
Q

What are Radio Galaxies?

A

They are mainly elliptical galaxies that emit more than 1 million times the radio waves than a normal galaxy. The radio waves originate from symmetrical pairs of lobes that lie on opposite sides of the galaxy.

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14
Q

What are Seyfert Galaxies?

A

Seyfert Galaxies are spiral galaxies with extremely compact and bright nuclei. They have strong emission lines in their spectra and show strong and often variable emission of radiation at IR and X-ray wavelengths.

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15
Q

What are Quasars?

A

Galaxies that appear like stars but emit huge amounts of X-rays to radio waves. Their red shifts show that they are some of the most distant objects in the Universe.

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16
Q

What are Blazars?

A

Appear star like but are much closer than quasars. Emit strongly in the region from radio waves to gamma rays. Their brightness can vary on a timescale of one to two days.

17
Q

What is the widely believed view on AGNs?

A

That they are all the same just viewed from different angles. Probably a black hole.