Unit 4

Question 1

What is a galaxy?

Answer 1

A massive collection of stars bound together by gravity and all orbiting a common centre

Question 2

How many stars are there in the milky way?

Answer 2

Aproximately 250 billion

Question 3

State the names of the two satellite galaxies of the Milky Way

Answer 3

Large Magellanic Cloud

Small Magellanic Cloud

Question 4

Label the diagram of the milky way

What is the diameter and thickness of the bulge

What is the diameter and thickness of the entire milky way (the disk)

Answer 4

The disk (the whole milky way) is 30,000 pc (30 kpc) in diamter and 1-2 kpc thick

The bulge is 16 kpc in diameter and 4 kpc thick

Question 5

What is the problem caused to astronomers by clouds of gas in the solar system

How can this problem be overcome

Answer 5

Clouds of gas in the solar system absorb the light that is coming towards us by stars in the spiral arms. This stops us from being able to see the arms properly

To overcome this astronomers looks at the stars by filtering for 21cm radio waves which are emitted from hydrogen atoms in the stars, as these can pass through the clouds.

Question 6

Which type of galaxy is this, explain how you know.

Answer 6

This is an eliptical galaxy. This is becuase it is a spheriod group of stars

Question 7

Which type of galaxy is this, explain how you know this?

Answer 7

This is a barred spiral galaxy. This can be seen becuase there is a central bar with sprial arms projecting out from it

Question 8

What type of galaxy is this, explain how you know this

Answer 8

This is a spiral galaxy, this can be seen becuase there is a spherical centre (nucleus) with spiral arms radiating out from it.

Question 9

Give an example of:

1. A spiral galaxy
2. A barred spiral galaxy

Answer 9

1. Andromeda
2. The Milky Way

Question 10

What is the Hubble Tuning Fork diagram

Answer 10

This is a diagram which is used to classify the galaxies

Question 11

What is the local group

State 5 galaxies that are contained within the local group

Answer 11

The local group is a group of galaxies that are all held together by their gravitational attraction to each other

Galaxies:

The Milky Way

Andromeda (the largest galaxy in the group)

Triangulum galaxy

Large Magellanic cloud

Small Magellanic cloud

Question 12

What is a cluster

What normally lies at the centre of a cluster

Answer 12

A cluster is a group of local groups that are all held together by gravity

They usually have one or more giant elliptical galaxies at the centre, providing the gravitational force to hold the other galaxies around them.

Question 13

What is a supercluster?

Which supercluster are we a part of?

Answer 13

A supercluster is a large group of galactic clusters that are held together by gravity.

We are part of the Virgo supercluster.

Question 14

What is an Active Galaxy

Answer 14

Most galaxies orbit around a supermassive black hole in the centre. Active Galaxies are galaxies where matter is currently falling into the supermassive black hole in the centre rather than orbiting around it.

In these galaxies the supermassive black hole is known as an Active Galactic Nucleus

The material that falls into the black hole heats up and emits electromagnetic waves as it falls.

Question 15

Describe the 4 main types of Active galaxy

Answer 15

1. Radio galaxy - These are galaxies that emit radio waves as the material falls into the black hole
2. Seyfert galaxy - these are galaxies where the falling material has enough energy to emit waves from infra-red to x-rays as the material falls into the centre of the universe
3. Quasar - Massive galaxies where material is falling into the centre of the the supermassive black hole. They are only seen very far away so occured a long time ago
4. Blazar - similar to a quazar but situated much closer to us and one of its electromagnetic jets pointing straight at us, they therefore appear much brighter than quazars

Question 16

Who discovered quazars

Answer 16

Ciril Hazar and John Bolton found the first quazar in 1962. Then Maarten Schmidt used its spectrum to work out the speed of recession (47,000,000 m/s away from the Earth), proving that it was very far away.

Question 17

Define the term cosmology

Answer 17

The study of the origin and development of the universe

Question 18

What is the doppler effect?

Explain why red shift and blue shift occur

Answer 18

The doppler effect is the changing of the wavelength (and therefore colour) of the light emitted by an object when that object is moving towards or away from you.

Red shift is when the light moves towards the red end of the spectrum (the wavelength becomes longer) this happens when the galaxy is moving away from us

Blue shift is when the light oves towards the blue end of the spectrum (wavelength becomes shorter) this happens when a galaxy is moving towards us

Question 19

Explain how to use the doppler effect to find the velocity (speed) of a galaxy moving relative to us

Example: what is the speed of recession of a galaxy with an original wavelenth of 300nm and a new wavelength of 300.001 nm.

Answer 19

The equation for redshift is shown in the image

lambda = new wavelength (m - meters)

lambda0 = original wavelength (m - meters)

c = speed of light (3x10⁸ m/s - meters per second)

v = speed of recession of the galaxy (m/s - meters per second)

This means that the speed of recession can be found

Example:

First of all convert nanometers into meters. 1 nm = 1x10^-9 m

Then put the numbers into the formula

v = (3x10⁸ x (300.001x10^-9 - 300x10^-9))/300x10^-9

v = 1000 m/s

Question 20

Explain why the Andromeda galaxy is blue shifted

Answer 20

The andromeda galaxy is blue shifted becuase it is moving towards us. This is becuase the gravitaional force between Andromeda and The Milky Way is pulling the two galaxies towards each other at a rate that overcomes the expansion of the universe

Question 21

What is hubbles law?

Explain how it can be used to find out how far away a galaxy is.

Answer 21

Hubbles law states that the distance of a galaxy from the earth is proportional to the speed of recession of the galaxy.

v = Hd

v = speed of recession (km/s - kilometers per second)

H = Hubbles constant (km/sMpc)

d = the distance of the galaxy from the earth (Mpc - mega parsec)

To find the distance of a galaxy away from the earth first use the doppler shift to find the recession speed in km/s. Then rearrange the Hubbles law equation to give

d = v/H

Then put in the numebers to find the distance in Mpc

Question 22

Describe the big bang

Answer 22

The big bang is the theory that all of space, time and matter all started off in one place and exploded outwards.

Question 23

Describe 3 bits of evidence for the big bang

Answer 23

1. Galactic red shifts - the further away a galaxy is the the more ded shifted the light is, meaning that it is travelling faster. This impleis that all of the galaxies started in the same place.
2. Cosmic microwave background radiation - During the big bang gamma rays were predicted to be released. As time and space has streched the waves have also stretched, so now the gamma rays are longer microwaves that can be detected coming from all directions at once
3. Proportions of hydrogen (75%) and helium (25%) in the universe - the probotions of hydrogen and helium are the same as in the center of a star. This follows the theory that at the begining of the big bang the entire universe was one large fusing star (big bang nucleosynthesis)

Question 24

State two satellites that have been used to study the Cosmic Microwave Background Radiation (CMBR) and give the date they were launched

Answer 24

1. The COsmic Backround Explorer (COBE) - 1989
2. The Wilkinsin Microwave Anisotropy Probe (WMAP) - 2001

Question 25

What is dark matter?

Describe the effect that dark matter has on the universe

Answer 25

Dark matter is matter that cannot be seen or felt except because it exerts a gravitational force on surrounding objects

Dark matter is important becuase stars at the edge of the galaxy are rotating around the galactic nucleus at a much faster rate than expected, implying a that there is a greater gravitational force in galaxies compared to theat from the matter that we can see.

Question 26

What is gravitational lensing?

Answer 26

This is when light passing passed an object with a large gravitational field is pulled towards and therefore bent by the object as it passes by. This focuses the light and allows us to see objects much further away in more detail.

Question 27

What is dark energy?

Explain how dark energy is affecting the universe

Answer 27

Dark energy is energy in the universe that we cannot detect and know very little about

Dark energy affects the universe becuase the expansion of the universe is accelerating. The energy to cause this acceleration is the dark energy

Question 28

Describe the two possible fates of the universe

Explain what will decide which of these fates will occur

Answer 28

1. Big crunch - the gravitational force of the universe will slow down the expansion of the universe and eventually it will contract back to a single point. This creates a cyclical universe as another big bang will happen, causing the process to repeat, this is called the cyclical universe
2. Big Yawn - The univers continues to expand forever untli eventually it is so spread out that no energy can be transferred from one place to another. This causes the universe to die a ‘heat death’

The big crunch will happen if the effect of gravity (from dark matter) has a greater effect than the effect of expansion (from dark energy). The big Yawn will happen if the effect of expansion outweights the effect of gravity.