Complete the worksheet on differences between fusion and fission… You will need to think back to the end of year 9 to help!!

LO’s - To be able to explain the stages in a star’s life cycle and how these stages are dependent upon its mass. Understand the processes that keep a star stable during its phases and why this processes ceases.

The Story of a Star The Story of a Star

Made of Star Dust.... The universe has had 4 generations of stars, When the largest of these past generations die they explode in a supernova! The remnants, are mostly gases and bits of dust. These are attracted towards each other by gravity and create nebulae. All solar systems start off as nebulae.

Nebulae come in different shapes and sizes and are mostly hydrogen and dust.

Protoplanetary Disk.... Dust pulled towards centre and starts to spin around, lots of energy VERY hot! Enough to ‘ignite’ the sun. All this 4.4 BILLION years ago. Most of the dust forms the sun and some that is left outside forms the planets.

Twinkle, Twinkle, Little Star ... Hubble Heritage image of Sagittarius Star field. Note that along the horizontal axis, the image is 13.3 light-years across. Ask audience what they notice by looking at this image. Hopefully they will notice the different colors. You can then ask them what the different colors mean [different temperatures] Image from http://heritage.stsci.edu/public/Oct22/sgr1/sgrtable.html. The sun is one of many billions of stars in space! What do you notice about these stars?

Twinkle, Twinkle, Little Star ... Hubble Heritage image of Sagittarius Star field. Note that along the horizontal axis, the image is 13.3 light-years across. Ask audience what they notice by looking at this image. Hopefully they will notice the different colors. You can then ask them what the different colors mean [different temperatures] Image from http://heritage.stsci.edu/public/Oct22/sgr1/sgrtable.html. Stars are different! Most obviously they have different colours which indicate different temperatures

is the Sun? Are all stars the same? Our Sun is quite average, it’s about in the middle in terms of size and temperature of the stars we have seen. All stars are different and we classify them using different names. Our sun is a Main Sequence Star. Stars go through phases in their life just like we go through; baby, child, teenager etc. Remember star evolution is SLOW! Millions/billions of years it is only by studying distant stars we can see how they form from a nebula to a main sequence and beyond...

Main Sequence Star

Matter is pulled towards the centre of the star due to its weight. Compacted particles in the centre get very hot, about 15 million degrees in the centre. Once a star is hot and small enough it will ‘ignite’. All Main Sequence Stars are undergoing a process called fusion. When the Sun was young, like all stars, it was nearly 100% hydrogen. As fusion takes place hydrogen atoms fuse together and release energy. The hydrogen then changes into helium and is used up. Energy released from fusion opposes the inward force of gravity so the star does not expand or contract!

The Death of a Star Once a star has exhausted its supply of hydrogen it will leave the main sequence. Its fate is now dependant on the mass of the star. And the will of the emperor

Red Giant

Stars burn a succession of elements towards the end of their life. Iron is the most stable element and cannot be fused further. Instead of releasing energy, it uses energy.

The fate of small stars… White Dwarf Black Dwarf

The fate of large stars… Supernova Movie clip; red giant goes supernova

Neutron Star

Black Hole

Teacher notes This three-stage animation explains how we know black holes exist, and where, even though they cannot be seen.

Supernova Remnants: Cas A Optical X-ray Cas A is 300 years old. The remnant is about 10 light-years in diameter, and 10,000 light-years away. X-ray: outer shock wave is from the initial supernova explosion ripping through the interstellar medium at 10 million miles per hour. Temperatures may reach 50 million degrees. The inner shock is the ejecta from the SN heating up the circumstellar shell, heating it to 10 million degrees The optical image of Cas A shows matter with a temperature of about ten thousand degrees. Some of these wisps contain high concentrations of heavy elements and are thought to be dense clumps of ejected stellar material. Cas A x-ray and optical images from http://chandra.harvard.edu/photo/0237/

Your Task Read through the text ‘The Story of a Star’ Learning Objectives By the end of this lesson you should… Be able to explain the stages in a star’s life cycle Understand the processes that keep the star stable throughout its stable phases Know what causes a star to leave a stable phase Know how the fate of a large star differs from the fate of a small star Your Task Read through the text ‘The Story of a Star’ Highlight any important terms and facts Use the information to fill in the ‘Stellar Evolution’ flow chart In the boxes write down the stage of the star and a brief description of it In the clouds write down the process that causes the change in the star. Finished that? Colour in the arrows blue that show the star contracting Colour in the arrows red that show the star expanding Highlight on your flow chart the route our Sun will take as it evolves

Learning Objectives By the end of this lesson you should… Be able to explain the stages in a star’s life cycle Understand the processes that keep the star stable throughout its stable phases Know what causes a star to leave a stable phase Know how the fate of a large star differs from the fate of a small star Small Stars Hydrogen runs out, star swells and begins to fuse helium. Star is cooler and red. Fusion of hydrogen nuclei produces heat and light. Outward forces balanced by inward gravitational pull. To help students complete stages – could be printed off and offered as a hint sheet Helium runs out causing the star to cool and contract. Gravity causes gases to spiral together.

Large Stars Gravity causes gases to spiral together. Learning Objectives By the end of this lesson you should… Be able to explain the stages in a star’s life cycle Understand the processes that keep the star stable throughout its stable phases Know what causes a star to leave a stable phase Know how the fate of a large star differs from the fate of a small star Large Stars Gravity causes gases to spiral together. A very small, dense core is left. Hydrogen runs out, star swells and begins to fuse helium. Star is cooler and red. Fusion of hydrogen nuclei produces heat and light. Outward forces balanced by inward gravitational pull. Helium runs out causing the star to contract, this collapse causes a supernova explosion.