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To associate the stages in the death of (i) solarmass and (ii) heavier stars with planetary nebulae and supernovae. To show an awareness of the main components of the HR diagram and relate these to stellar death. To describe the end-products of stars: white dwarfs (for solar-mass stars); neutron stars (for heavier stars) and black holes (for even heavier stars!). To understand how astronomers provide evidence for neutron stars (pulsars) and black holes. To show an awareness of the main components of the HR diagram and relate these to stellar death This is a hertzprung russel diagram. A log scale of the luminosity of the star (or absolute magnitude) is plotted against the spectral class (or decreasing temperature – non linear scale) There is a band down the middle with 90% of the stars – main sequence. These ‘burn’ hydrogen Stars at the end of their life are on either side Sketch a diagram of an HR diagram in your books. Annotate it appropriately. Try and do it from memory If you are struggling use the internet to help If you complete this try and describe what the diagram tells us about the birth and death of a star? Eventually the star burns up the hydrogen in its core and burns the hydrogen in its outer core or shell. It becomes brighter and expands to a red giant. Helium is now being burnt by the star. At this point different scenarios present themselves depending on the mass of the star. If the star has a very small mass it shrinks to a red dwarf, burning its hydrogen and helium. If a star, such as our Sun, has under 4 solar masses it will grow to a red giant and eventually puff away its outer layers before shrinking to a white dwarf, of under 1.5 solar masses. If the star has between 4 and 25 solar masses it will grow to a red super giant and explode as a supernova, leaving a neutron star the size of Earth. If it has over 25 solar masses it will again explode as a supernova but will produce a black hole. Read and make summary notes. Highlight important info A supernova is the brightest event in space. There are two types of supernova: 1 Similar to a nova where a dwarf takes material from a giant. This time the explosion destroys the dwarf. Typically this takes place when the mass of the white dwarf is over 1.4 solar masses. 2 When a star has a mass greater than 8 solar masses. The red giant swells so much it collapses in on itself. These are dramatic events as once they explode the core forms a neutron star or a black hole. The light curve shows a drastic increase in brightness before receding to a small luminance after a few months. A planetary nebula is usually seen in the region of a supernova for years, sometimes centuries afterwards. Read and make summary notes. Highlight important info A star between 4 and 25 solar masses will grow to a red super giant and explode as a supernova, leaving a neutron star smaller than the size of Earth. These stars are compressed so much that they are composed entirely of neutrons, parts of the atom without electrical charge. This is the equivalent of the size of the Sun in the same area as a city or the human population on Earth fitting inside an area the size of a sugar cube. Neutron stars rotate rapidly after formation, typically spinning between fractions of a second and half a minute. We can detect this because they emit radio pulses, and the ones we detect are known as pulsars. Radio astronomy has also detected brightness and temperature from neutron stars, and astronomers have used x-ray astronomy to detect them when matter from companion stars falls onto neutron stars. Read and make summary notes. Highlight important info No astronomer has ever seen a black hole, largely because there is too much material surrounding it and also because it is black as the name suggests. Most astronomers accept they exist but there is a lot about them that we don't know. When a very large star explodes, the mass condenses so much that is collapses in on itself. The gravity is still present. It appears to pull in any material in the vicinity. Once matter goes past the boundary of a black hole (called the event horizon) it cannot escape back out again; not even light can escape which travels at 300,000 kilometres a second. Evidence from black holes comes from binary stars that get their solar material pulled into the hole. This often forms an accretion disc of matter circling the area. It orbits so fast it is hot enough to give off x-rays which we can measure. The black hole forces such a gravitational force on these particles it can push them light years away, perpendicular to the disc in the form of particle jets travelling near to the speed of light. It is thought that most galaxies have a super massive black hole in their centre. Research about some of our ‘known’ black holes and neutron stars. Obtain some images if possible and how we can tell they are there