The Universe

Question 1

what is cosmology?

Answer 1

Cosmology is the study of the COSMOS – in other words, the universe.

Question 2

What is the universe?

Answer 2

The universe is all existing matter, energy, space and time considered as a whole extending to the cosmic horizon.

Question 3

what is the big bang theory?

Answer 3

▪ Before the Big Bang there was no universe, no space, no time. There simply was nothing as we know it. Absolutely nothing but energy.
▪ This energy was located in one single point of infinite density. During the Big Bang, it began to expand extremely quickly. All of the mass and energy in the universe today is still equal to this and there is evidence that the universe is continuing to expand.
▪ Cosmologists believe the universe began about 13.7 billion years ago with a massive explosion. This is considered a ‘no cause’ event.

Question 4

what is the dark ages?

Answer 4

the last time when empty space really was empty; no planets, no suns, no galaxies, no life

Question 5

Timeline of order in which celestial elements were formed

Answer 5

1. Big Bag and Inflation
2. 10-32 second - cosmic inflation ends
3. 10-6 second - protons formed
4. 300,000 years - first elements formed
5. 400,000 years - cosmic background radiation
6. 100 million years - first starts form
7. 500 million years - earliest known galaxy
8. 4 billion years - start formation peaks
9. 9 billion years - our solar system formed
10. 13.8 billion years - now

Question 6

Evidence for the Big Bang?

Answer 6

▪ All galaxies are moving away from each other (still expanding) – this is demonstrated by red shift in light coming from distant stars. This suggests that the universe is expanding and that, if you extrapolate backwards, the universe had a beginning.
▪ Cosmic background is present everywhere and the levels exactly fit predictions based on calculations of the universe being 14 billion years old.
▪ Levels of helium in the universe are too high to have only formed by collapsing stars so must have been formed in the Big Bang explosion.

Question 7

what is the doppler effect?

Answer 7

Doppler effect - as waves move towards you the frequency is perceived to be higher with shorter wavelength (blue shift) as it moves away frequency is perceived to be lower with longer wavelength (red shift) – although it isn’t changing!

Question 8

Other Universe Models?

Answer 8

▪ Aristotle 380BC - Earth was at the centre of the universe, and that the sun, stars, moon, and planets all revolve around the earth in 55 concentric orbits.
▪ Copernicus 1540 AD - suggested that the sun was stationary at the centre of the universe and that all other bodies revolved around it in circular paths.
▪ And then the telescope was invented and the movement of all the visible stars could be studied…
▪ Steady State model - the universe is infinite and has always existed more or less like it is now…. And it will continue to be this way….

Question 9

What is next for the universe?

Answer 9

• the big freeze
• the big rip
• the big crunch
• the big bounce

Question 10

what is a star?

Answer 10

▪ Stars are massive, luminous spheres of plasma held together by gravity

Question 11

what is the big freeze?

Answer 11

the universe will keep expanding and cooling as it has done and at some point the energy will be too dissipated to sustain life. As existing stars run out of fuel and cease to shine, the universe will slowly grow darker, one star at a time and there will be nothing but black holes. Also called heat death or maximum entropy)

Question 12

what is the big rip?

Answer 12

is similar, in the future the distances in the universe will become infinite. At a point where the ratio between dark energy pressure and its density become less than -1 , the universe will be pulled apart.

Question 13

what is the big crunch?

Answer 13

If the universe begins to recontract it will form a hot, dense state similar to that immediately after the Big Bang

Question 14

what is the big bounce?

Answer 14

The Big Bounce describes a scenario of the universe expanding and then contracting – so the Big Bang was caused by the last contraction of the universe.

Question 15

what is apparent magnitude?

Answer 15

Apparent magnitude is a measure of the brightness of a star as it appears on Earth – but this isn’t a fair comparison as some stars are very distant.

Question 16

what is absolute magnitude?

Answer 16

Absolute magnitude is a measure of the brightness of a star if it was 10 parsecs from the Earth – better comparison.

Question 17

what is the Hertzsprung – Russell Diagram?

Answer 17

A Hertzsprung–Russell or H–R diagram is a plot of star brightness (measured as luminosity) against star temperature/colour.

Question 18

why is the Hertzsprung – Russell Diagram important?

Answer 18

It enables astronomers to classify the type of star they are looking at and helps them to determine many of its characteristics like how old it is, its surface temperature and the stage of its life cycle.

Question 19

what does the colour of star tell you?

Answer 19

The colour of a star is related to its temperature: blue stars are the hottest and red stars are the coolest. Stars are given a spectral class letter based on their temperature and colour.

Question 20

what is the luminosity of the star?

Answer 20

Stars also vary in brightness, this is called luminosity. The scale of luminosity is based around our Sun, which is given a luminosity of 1. Stars that are brighter than the Sun have a luminosity of greater than 1 and stars that are less bright than the Sun are given a luminosity of less than 1.

Question 21

what is nuclear fusion?

Answer 21

• Stars obtain their energy through a process called nuclear fusion. This occurs when two atoms combine (or fuse) to create a new element. Because it is so hot inside the cores of stars, hydrogen atoms have enough energy to fuse together to form helium and an enormous amount of energy is released in the process. The gravitational collapse of matter triggers enormous levels of heat and pressure which triggers a nuclear fusion reaction.
• the fusion of four Hydrogen nuclei to form Helium includes a loss of mass, but this is converted into a huge amount of energy (gamma radiation)

Question 22

how is matter formed?

Answer 22

• Formation of hydrogen and helium occurred first after the Big Bang. Other elements must be formed as a result of the lifecycle of stars.
• When the star’s supply of hydrogen is used up, it begins to convert helium into oxygen and carbon. If the star is massive enough, it will continue until it converts carbon and oxygen into neon, sodium, magnesium, sulphur and silicon. Eventually, these elements are transformed into calcium, iron, nickel, chromium, copper and others until iron is formed.

Question 23

what do low mass starts tend to be?

Answer 23

cooler and less bright

Question 24

what do high mass starts tend to be?

Answer 24

hotter and brighter

Question 25

what determies what happens to a star?

Answer 25

What happens to a star depends on its initial mass.

Question 26

The life cycle of stars?

Answer 26

▪ Stars begin their lives as clouds of dust and gas called nebulae.
▪ The gravity of a passing star or the shock wave from a nearby supernova may cause the nebula to contract.
▪ Matter in the gas cloud will begin to coalesce into a dense region called a protostar.
▪ As the protostar continues to condense, it heats up. Eventually, it reaches a critical mass and nuclear fusion begins.
▪ This begins the main sequence phase of the star. It will spend most of its life in this stable phase.
▪ The lifespan of a star depends on its size.
▪ Very large, massive stars burn their fuel much faster than smaller stars. Their main sequence may last only a few hundred thousand years. Smaller stars (average star) will live on for billions of years because they burn their fuel much more slowly.
▪ Eventually, the star’s fuel will begin to run out. It will expand into what is known as a red giant.
▪ Massive stars will become red supergiants. This phase will last until the star exhausts its remaining fuel.
▪ At this point, the pressure of the nuclear reaction is not strong enough to equalise the force of gravity and the star will collapse.
▪ Most average stars will blow away their outer atmospheres to form a planetary nebula. Their cores will remain behind and burn as a white dwarf until they cool down. What will be left is a dark ball of matter known as a black dwarf.
▪ If the star is massive enough, the collapse will trigger a violent explosion known as a supernova.
▪ If the remaining mass of the star is about 1.4 times that of our Sun, the core is unable to support itself and it will collapse further to become a neutron star. The matter inside the star will be compressed so tightly that its atoms are compacted into a dense shell of neutrons.
▪ If the remaining mass of the star is more than about three times that of the Sun, it will collapse so completely that it will literally disappear from the universe. What is left behind is an intense region of gravity called a black hole.

Question 27

the loop cycle of a star?

Answer 27

▪ The nebula that was expelled from a star may continue to expand for millions of years.
▪ Eventually, the gravity of a passing star or the shock wave from a nearby supernova may cause it to contract, starting the entire process all over again.
▪ This process repeats itself throughout the universe in an endless cycle of birth, death, and rebirth. It is this cycle of stellar evolution that produces all of the heavy elements required for life.

Question 28

Main Sequence Stars?

Answer 28

The main sequence is the point in a star’s evolution during which it maintains a stable nuclear reaction. It is this stage during which a star will spend most of its life. Our Sun is a main sequence star. A main sequence star will experience only small fluctuations in luminosity and temperature.

Question 29

Red Giants?

Answer 29

A red giant is a large star that is reddish or orange in colour. It represents the late phase of development in a star’s life, when its supply of hydrogen has been exhausted and helium is being fused. This causes the star to collapse, raising the temperature in the core. The outer surface of the star expands and cools, giving it a reddish colour. Betelgeuse in Orion is an example of a red supergiant star.

Question 30

White Dwarfs?

Answer 30

A white dwarf is the remnant of an average-sized star that has passed through the red giant stage of its life. Nuclear fusion no longer takes place. The core glows because of its residual heat. Eventually the core will radiate all of its heat into space and cool down to become a black dwarf. White dwarf stars are very dense. Their size is about the same as that of the Earth, but they contain as much mass as the Sun. They are extremely hot, reaching temperatures of over 100,000 degrees.

Question 31

Brown Dwarfs?

Answer 31

During the process of star formation, some protostars never reach the critical mass required to ignite the fires of nuclear fusion. A brown dwarf is a giant ball of gas that is too massive to be a planet but not massive enough to be a star.

Question 32

Binary Stars?

Answer 32

Many stars in the universe are part of a multiple star system. A binary star is a system of two stars that orbit around a common point

Question 33

Quasars?

Answer 33

It is thought that a quasar is produced by super massive black holes consuming matter in an acceleration disk. As the matter spins faster and faster, it heats up. The friction between all of the particles would give off enormous amounts of light to other forms of radiation such as x-rays.

Question 34

Pulsars?

Answer 34

A pulsar is a rapidly spinning neutron star. A neutron star is the highly compacted core of a dead star, left behind in a supernova explosion. This neutron star has a powerful magnetic field which causes the neutron star to emit strong radio waves and radioactive particles from its north and south poles.

Question 35

Black Holes?

Answer 35

▪ Black holes are formed from the cores of super massive stars and can best be described as regions of space where so much mass is concentrated that nothing, not even light, can escape the gravitational pull.
▪ It is infinitely small and infinitely dense, yet it contains the same amount of mass as the original star. This is what is known as a singularity and it defines the centre of the black
hole.

Question 36

what are galaxies?

Answer 36

Galaxies are enormous collections of stars, planets, gases and dust that are bound by gravity. They are usually orbiting a black hole.

Question 37

what are galaxies classified as?

Answer 37

Today, galaxies are classified according do their shapes, divided into four main groups: spiral, barred spiral, elliptical, and irregular

Question 38

How did our solar system form?

Answer 38

From a dense cloud of interstellar gas and dust. The cloud collapsed, possibly due to the shockwave of a nearby exploding star, called a supernova. When this dust cloud collapsed, it formed a solar nebula – a spinning, swirling disk of material.

Question 39

what are planets?

Answer 39

Planets are large objects that orbit stars. They do not produce their own light.

Question 40

what are Terrestrial Planets?

Answer 40

composed primarily of rock and metal and have very high densities. They tend to be relatively small in size, have slow periods of rotation and few moons.
▪ The terrestrial planets in our solar system are Mercury, Venus, Earth, and Mars.

Question 41

what are gas giants?

Answer 41

They are Jupiter, Saturn, Uranus, and Neptune. Gas giants are composed mainly of hydrogen and helium. They have low densities , tend to have a very fast period of rotation, have ring systems and a large number of moons. it is believed that the ring systems may have formed from old moons that were pulverised by the tidal forces of the planets’ gravity.

Question 42

what are planetoids?

Answer 42

Planetoids is a name given to a group of objects that are too large to be asteroids and too small to be planets. Thousands of these objects are known to be orbiting the outer regions of our solar system in an area known as the Kuiper Belt. In fact, many astronomers believe that the planet Pluto and its moon Charon may actually be Kuiper belt objects and not planets.