The Big Bang

Question 1

The Expanding Universe

Answer 1

Almost all of the galaxies are moving away from each other with the further galaxies moving fastest.

Question 2

Models of the Universe

Answer 2

• With the help of the newly invented telescope, Galileo observed four moons orbiting Jupiter. This confirmed that not everything orbited the Earth and supported Copernicus’ idea that planets orbit the sun.
• The Roman Catholic Church did not support Galileo’s model as they believed that the Earth was at the centre of the Universe and it was a very long time before it was accepted.
• In the 17th century, Newton was working on his theory of universal gravitation which suggested that all bodies attract one another.
• Today, we believe that gravitational collapse is prevented because the Universe is constantly expanding as a result of the Big Bang.

Question 3

Red shift

Answer 3

• When a source of light is moving away from an observer, its wavelength appears to increase which shifts towards the red end of the spectrum - red shift.
• When a scientist looks at light from the Sun, there is a pattern of lines across the spectrum. This same pattern is observed when they look at light from distant stars but it is closer to the red end of the spectrum.
• Scientists can use this information from red shift to work out the age of the Universe.

Question 4

What is a Nebula?

Answer 4

A nebula is a swirling cloud of gas and dust.

Question 5

How does a star form?

Answer 5

• Nebula clouds are pulled together by gravity and, as the spinning ball of gas starts to get hot, it glows.
• This protostar cannot be seen in a dust cloud.
• Gravity causes the star to become smaller, hotter and brighter and after millions of years, the core temperature is hot enough for nuclear fusion to take place.
• As hydrogen nuclei join together to form helium nuclei, energy is released and the star continues to shine while there is enough hydrogen.

Question 6

What do the isotopes of hydrogen create?

Answer 6

Helium + Neutron + Energy

Question 7

Why do small stars shine longer?

Answer 7

Small stars shine for longer because they have less hydrogen but use it up at a slower rate and what happens at the end of a star’s life depends on its size.

Question 8

What happens to a medium-sized star at the end of its life?

Answer 8

• A medium-sized star, like the sun, becomes a red giant.
• While the core contracts, the outer part cools, changes colour from yellow to red and expands.
• Gas shells, called planetary nebulas are thrown out.
• The core becomes a white dwarf shining very brightly but cools to become a black dwarf.

Question 9

What happens to large stars at their end of its life?

Answer 9

• Large stars become red supergiants.
• As the core contracts and the outer part expands, the core suddenly collapses to form a neutron star and there is an explosion called a supernova.
• Neutron stars are very dense
• Remnants from a supernova can merge to form a new star
• The core of the neutron star continues to collapse, becoming even more dense and could form a black hole.

Question 10

Black hole

Answer 10

A black hole has a very large mass concentrated in a small volume so it has a very large density and its large mass has a very strong gravitational pull