The Lifecycle of Stars
Introduction Did you know that, just like us, stars are born, grow older and die? This presentation will guide you through some of the stages in a star’s life and suggest observations that you can make for yourself with the naked eye, binoculars or a small telescope. Where you see this symbol there are exercises that you should complete.
Real stars, real lives… The Sun DO NOT, EVER LOOK DIRECTLY AT THE SUN Task – answer these questions: What colour is the Sun? How large is it compared to the Earth? Is it a special star?
Our Sun is a yellow dwarf star It is in the main sequence Task: What do these terms mean? Find out.
Orion Learn to find this constellation in the night sky In the winter, you will find it to the south soon after dark By observing this constellation you will see many of the stages in the lifecycle of different stars Homework Task: Observe Orion
What comes first? A star forms when gravity pulls together enough gas and dust to create extremely large temperatures and pressures Nuclear fusion reactions begin in the centre when pressure is high enough to force together Hydrogen nuclei (despite electrostatic repulsion) to eventually form Helium What is a region of gas and dust in space called? Find out
Star Birth There are typically three types of regions in space where new stars form. These are examples of each of them: The Pleiades The Horsehead Nebula The Ring Nebula Find out 1.what type of object each of these is and 2. what they have to do with young stars
Find your own nebulae Practical Task: Look for Orion’s ‘sword’ hanging from his belt You will see that the sky around it looks fuzzy These are the nebulae M42 and M43 – see the next slide to locate them
Look for M42 and M43…
Hot, young stars in M42
A long and stable life? The life of a star is a tough one It is a constant battle between the pull of gravity inwards and expansion of matter and radiation outwards In ‘Main Sequence’ stars these forces are in balance
Joining the ‘Main Sequence’ This is a Hetzsprung-Russell Diagram – find out what it tells you
When nuclear fuel runs low, gravity eventually begins to win… The matter inside the star gets more compressed and hotter This allows new types of nuclear fusion to take place using heavier elements This makes the star hotter still, so expansion wins for a while A dying Yellow Dwarf becomes a RED GIANT
Practical Task – Find Betelgeuse. What colour is it? Betelgeuse is actually a red supergiant. Our Sun will never get this big.
Death of a star Once the final stages of nuclear fusion are exhausted, the red giant collapses Remnants of the star’s atmosphere are blasted into space forming a PLANETARY NEBULA At its centre, the star’s core remains as a hot WHITE DWARF These are a thousand times smaller than the Sun and usually hard to see
The Dog Star Getting ambitious? Then follow the diagonal line of Orion’s ‘belt’ to find Sirius, the ‘Dog Star’
Sirius Sirius A is a very bright star – the brightest in the night sky. It is a white star with a second, dimmer white dwarf called Sirius B orbiting it. Why is it so bright? Find out!
Dead Stars The remnants of burnt out white dwarfs are called – wait for it – black dwarfs Here’s one. Can you see it?
Big Stars Practical Task: Find Rigel. What colour is it?
Rigel Rigel is a Blue Supergiant It won’t last as long as the Sun When it finally collapses it will cause a SUPERNOVA explosion and turn into a neutron star or a black hole
Re-birth When a star goes supernova, it scatters atoms of newly formed elements back into space Gradually, gravity pulls them together and the whole cycle of creation begins again…
Task complete