4.2: Galaxies

Question 1

Who suggested the most widespread system of classifying galaxies

Answer 1

Edwin Hubble in 1920’s

Question 2

What are the 4 type of galaxy

Answer 2

• spiral (S)
• barred spiral (SB)
• elliptical (E)
• irregular (Irr)

Question 3

Describe a spiral galaxy

Answer 3

Flattened disk-shaped systems e.g. Andromeda

Question 4

Describe a barred spiral galaxy

Answer 4

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

Question 5

Describe an elliptical galaxy

Answer 5

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

Question 6

Describe an irregular galaxy

Answer 6

Very little structure or symmetry

Question 7

How are S and SB galaxies distinguished further

Answer 7

By sub-classifying them with letters a,b or c depending on the strength of the nuclear bulge and ‘openness’ of the spiral arms (Sa galaxies have big nuclear and tightly wound arms, Sc galaxies have small nucleus and open arms)

Question 8

How are E galaxies distinguishe further

Answer 8

By sub-classifying then with numbers 0-7 depending on their shape (E0 is almost circular and E7 is highly elongated)

Question 9

What do later versions of Hubbles scheme include

Answer 9

Lenticular galaxies (S0) as a class between ellipticals and spirals

Question 10

What is Hubble’s classification scheme shown on

Answer 10

A tuning fork diagram. It was first published in 1936 in his book The Realm of the Nebulae

Question 11

When was the galaxy zoo launched and what is it

Answer 11

Launched in July 2007 and is a web-based project that has invited members of public to access images of galaxies in order to classify them

Question 12

What galaxy type is the Milky Way

Answer 12

SBb

Question 13

What does the local group included

Answer 13

• the andromeda galaxy
• the LMC and SMC
• the Triangulum Galaxy
• several satellite and dwarf galaxies such as Pisces Dwarf and Aquarius Dwarf

Question 14

How far across is the local group

Answer 14

3 Mpc

Question 15

What supercluster is local group part of

Answer 15

The Virgo Supercluster

Question 16

What are active galaxies/active galactic nuclei

Answer 16

Galaxies that emit vast amounts of energy at wavelengths other than those of visible light

Question 17

What are the 4 main types of active galaxy/active galactic nuclei

Answer 17

• radio galaxies
• seyfert galaxies
• quasars
• blazars

Question 18

Describe radio galaxies

Answer 18

• discovered in 1950s
• mainly elliptical galaxies
• intense sources of radio waves
• radio emissions often originate from symmetrical pairs of ‘lobes’ that lie on opposite sides of the galaxy

Question 19

Describe seyfert galaxy

Answer 19

• discovered by carl seyfert in 1943
• spiral galaxy
• have extremely compact but bright nuclei
• have strong emission lines in their spectra
• show strong and often variable emissions of radiation at IR and X-ray wavelengths

Question 20

Describe quasars

Answer 20

• discovered by radio astronomers in 1963
• compact appearance make the look star-like
• emit huge quantities of energy from X-rays to (sometimes)radio waves
• high redshifts reveal quasars are some of most distant objects in universe

Question 21

Describe Blazars

Answer 21

• discovered in 1970s
• appear star-like
• lie much closer than quasars
• emir strongly in all regions of spectrum from Radio to gamma-rays
• can vary in optical brightness in a timescale of 1/2 days

Question 22

How do astronomers believe AGNs are powered

Answer 22

By matter falling onto a supermassive black hole that lies at the centre of the galaxy