Missing words: mass hydrogen burning electrostatic repulsion. gravitationally hydrogen temperature protostar

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1 Instructions Fill in the blanks of each frame using the list of missing words given. Cut out each frame and arrange them on your page in order, then stick them down. The first two frames are already in the right order. Missing words: mass hydrogen burning electrostatic repulsion gravitationally hydrogen temperature protostar Brown Dwarf PE KE nuclear fusion electrons Gas and dust, mainly made up of atoms with some helium atoms, are dispersed thinly throughout space. If the mass is high enough, in the centre of the cloud, hydrogen atoms are stripped of their. The nuclei have enough energy to overcome their and fuse together. Each atom is attracted to each other, and so is pulled together, creating a dense region, which attracts more and more atoms. When the temperature is high enough, the cloud glows dimly, forming a. The fusing of two atoms is called. Sometimes this is called, but it isn t burning as we know it. A large, spherical cloud forms. The decreases, and the and increase. If the cloud doesn t have enough, it remains in this way for the rest of its life, and is called a.

2 Instructions Answer the questions or follow the instructions in each frame in the spaces provided. 1. What is nuclear fusion? 2. Write down the 3 nuclear equations described in the previous frame in the space below. 2 hydrogen nuclei/protons join together to form a deuterium nucleus, a positron, and a neutrino. The deuterium nucleus fuses with another proton to form a helium-3 nucleus. Two of these helium-3 nuclei fuse to form a helium-4 nucleus, and two more protons. 4. Up to which element can nuclear fusion occur? Elements heavier than this undergo nuclear fission instead. What happens in nuclear fission? 3. What happens to the mass difference between the initial 4 protons and the helium atom created?

3 Instructions: Fill in the gaps with the words in the bottom right corner (words may be used more than once). Also, illustrate the descriptions in each frame. Once starts, the star is no longer known as a protostar, but is called a. A star is a low-mass, dim main sequence star. It transports energy from its core to the surface by alone. A medium sized main sequence star transports energy via, through the. The energy is transported further through the by, to the surface. When the energy reaches the surface, which is called the, it is radiated out into space. Missing Words kinetic sizes main sequence star The energy that travels from the core to the star s surface gives surrounding atoms more energy. The atoms start moving away from the star s centre, causing the star to expand, and creating an outward. This acts against the pull of the, and for most of the star s life, the two are balanced. Stars will have collected different amounts of gas, so are different. What happens next depends on the initial size of the star at the start of its life. radiation pressure fusion Red Dwarf convection radiative zone gravity photosphere radiation convection zone

4 Instructions: In this exercise, you will describe the death of a low-mass star in your own words. The pictures are arranged in order and are there to guide you. Cut them out and stick them on your page, and write a description to go with each image. Make sure you answer every question with each image in your descriptions. 1. What is the maximum size of a low-mass star? 2. What happens to the amount of hydrogen and helium in the core of a main sequence star towards the end of its life? 3. What happens to fusion? 1. What happens to the balance between the outward radiation pressure and the gravitational inward pull? 2. What happens to the radius of the star? 1. As the star collapses, what happens to the pressure and temperature of the core? 2. The star then expands again. What causes this expansion? 1. What happens next to the size of the star? 2. What type of star does it become? 1. What happens to the outer layers and the core? 2. When the temperature gets high enough, what happens to the helium in the core? 1. What happens to the fusion process, and why? 2. What then happens to the core? 1. What happens to the outer layers of the star? 2. What happens to the total mass? 1. The star then cools and shrinks. What causes the star to stop shrinking? 2. What is the star now called? 1. What happens to the remaining heat of the star? 2. Once the heat has all gone, what happens to the star?

5 Instructions The diagrams are in the right order, but the descriptions to go with each one aren t. Cut out each diagram and caption, and match the correct description to each diagram, and finish off each description.

6 When the star runs out of the element it is fusing in the core, the core contracts. This raises the temperature and pressure sufficiently such that. When the core is mostly made up of iron nuclei (which cannot fuse together), nuclear fusion finally stops and the star begins to collapse for the last time. The collapse of the star recoils and bounces back outwards because the iron nuclei The core contracts due to gravity, growing hotter and denser so that heavier nuclei can begin to fuse. This temporarily stops any further collapse because For a larger mass star, instead of swelling into a Red Giant, it swells into a A black hole is formed instead of a neutron star if the star was approximately 15 times more massive than the Sun. The collapse of the star would be so great that not even neutrons can withstand the high pressures. The core collapses into a singularity and is so dense that not even light can. The collapse of the star recoils and bounces back outwards because the iron nuclei The remaining core left over from the supernova can form Pulsars are. We can observe the pulses of radiation when Neutron stars spin very rapidly, turning one revolution in seconds. They can have enormous All of the naturally occurring elements in the Universe are created by just nuclear fusion. Elements above iron are created when The shockwave sweeps material out from the star, and the material is flown out into the Universe in a huge explosion called a. A neutron star is made up entirely of neutrons, which are created because A star with a high mass remains as a main sequence star for a shorter amount of time than a low mass star. This is because

7 Answers The Birth of a Star Gas and dust, mainly made up of hydrogen atoms with some helium atoms, are dispersed thinly throughout space. Each atom is gravitationally attracted to each other, and so is pulled together, creating a dense region, which attracts more and more atoms. A large, spherical cloud forms. The GPE decreases, and the KE and temperature increase. When the temperature is high enough, the cloud glows dimly, forming a protostar. If the cloud doesn t have enough mass, it remains in this way for the rest of its life, and is called a Brown Dwarf. If the mass is high enough, in the centre of the cloud, hydrogen atoms are stripped of their electrons. The nuclei have enough energy to overcome their electrostatic repulsion and fuse together. The fusing of two atoms is called nuclear fusion. Sometimes this is called hydrogen burning, but it isn t burning as we know it. Nuclear Fusion 1. Nuclear fusion is a process where lighter nuclei join together to form a heavier nuclei, e.g. 4 hydrogen nuclei become one helium nucleus The mass difference is converted into energy and released. 4. Elements up to Iron can undergo nuclear fusion. In nuclear fission, heavier nuclei split into lighter nuclei. Main Sequence Star A medium sized main sequence star transports energy via radiation, through the radiative zone. The energy is transported further through the convection zone by convection, to the surface. When the energy reaches the surface, which is called the photosphere, it is radiated out into space. Once fusion starts, the star is no longer known as a protostar, but is called a main sequence star. A Red Dwarf star is a lowmass, dim main sequence star. It transports energy from its core to the surface by convection alone.

8 The energy that travels from the core to the star s surface gives surrounding atoms more kinetic energy. The atoms start moving away from the star s centre, causing the star to expand, and creating an outward radiation pressure. This acts against the pull of the gravity, and for most of the star s life, the two are balanced. Stars will have collected different amounts of gas, so are different sizes. What happens next depends on the initial size of the star at the start of its life.

9 Death of a Low Mass Star If the star is less than 4 times the mass of the Sun, it is a lowmass, or small star. Towards the end of the star s life, it begins to run out of hydrogen fuel to fuse together, and the core is mostly made of helium. Nuclear fusion in the core therefore temporarily stops. There is no longer anything generating an outward pressure to counteract the gravitational inward pull. This makes the outer layers of the star begin to collapse inwards again. As before, this makes the temperature and pressure increase. The temporary heat creates outward pressure again and counteracts the inward force of gravity, pushing the outer layers of the star outwards. The star ends up expanding much more than it did before, and it becomes about a hundred times bigger than it s ever been in its life. It has turned into a Red Giant. While the outer layers of the Red Giant continue to expand, the core is still contracting so the temperature continues to increase. The temperature gets high enough for helium to start fusing together, forming a heavier element, carbon. No further fusion takes place, as there is not enough mass to compress the carbon further to fuse together. The core remains stabilised. Large amounts of matter are ejected from the outer layers of the Red Giant, until only about 20% of the star s initial mass remains. As it can t produce any more heat, it radiates away the remaining heat for billions of years. Once the heat has all gone, it sits as a cold dark mass, called a Black Dwarf. The star then begins to cool and shrinks until the gravitational pull is balanced by the repulsion of the electrons at the core. It stops shrinking and becomes a White Dwarf, which is about half as massive as the Sun, but only slightly bigger than the Earth.

10 Death of a High Mass Star A star with a high mass remains as a main sequence star for a shorter amount of time than a low mass star. This is because they are more massive, so the temperatures and pressures are far greater, and the fuel gets used up much more quickly, even though there is more of it. The core contracts due to gravity, growing hotter and denser so that heavier nuclei can begin to fuse. This temporarily stops any further collapse because an outward pressure is produced when nuclear fusion takes place. The collapse of the star recoils and bounces back outwards because the iron nuclei get crushed together but the electrostatic repulsive force between them overcome the gravitational force. For a larger mass star, instead of swelling into a Red Giant, it swells into a Red Supergiant just a larger version of a Red Giant. When the star runs out of the element it is fusing in the core, the core contracts. This raises the temperature and pressure sufficiently such that heavier elements begin to fuse. This happens for heavier and heavier elements. When the core is mostly made up of iron nuclei (which cannot fuse together), nuclear fusion finally stops and the star begins to collapse for the last time. All of the naturally occurring elements in the Universe are created by just nuclear fusion. Elements above iron are created when an explosive shockwave is created. The shockwave travels through the star s outer layers, heating the material it encounters to a high enough temperature that they begin to fuse to form new elements. The shockwave sweeps material out from the star, and the material is flown out into the Universe in a huge explosion called a supernova.

11 The remaining core left over from the supernova can either form a neutron star, or if it s massive enough, can form a black hole. A neutron star is made up entirely of neutrons, which are created because of the extremely high pressure of the remaining core. Electrons are forced to combine with protons, forming the neutrons. Neutron stars spin very rapidly, turning one revolution in seconds, and can have enormous electric and magnetic fields. Pulsars are neutron stars that pulse with electromagnetic radiation.we can observe the pulses of radiation when the magnetic pole crosses our line of sight. A black hole is formed instead of a neutron star if the star was approximately 15 times more massive than the Sun. The collapse of the star would be so great that not even neutrons can withstand the high pressures. The core collapses into a singularity and is so dense that not even light can escape its gravitational pull.