SCIENCE CONTENT/ TEACHER CURRICULUM LINK RESOURCE PLANET EARTH AND BEYOND – ASTRONOMICAL SYSTEMS.

NATURE OF SCIENCE – UNDERSTANDING, INVESTIGATING,

COMMUNICATING, PARTICIPATING AND CONTRIBUTING. PHYSICAL WORLD – INQUIRY STARDOME OBSERVATORY & PLANETARIUM AND CONCEPTS. FACTS, RESOURCES AND ACTIVITIES ON...

As prerequisites to this resource we recommend the previous resources: Stellar Star Brightness; Star Colours; Spectroscopy; The 3). Family Portrait Stars (parts 1, 2, and particularly The Hertzsprung-Russell Diagram

Just like people, stars are born, go through different life stages, and eventually die. This resource introduces the Hertzsprung-Russell diagram (HRD) which is a scatter plot of stars at every phase of the life cycle – rather like a human family portrait. A family portrait is a ‘snapshot’ in time that might have grandparents, parents, teenagers and Stars are babies. Comparing a new portrait with an old one of a generation ago, we’d find the original classified by two grandparents now absent, having been key properties: replaced by the original parents. Likewise, the temperature and teenagers will have become parents, babies luminosity. The HRD teenagers, and there will be a new crop of is a plot of these properties. babies. Some of the people will be different, but there will still be grandparents, parents, teenagers, and babies – and so it is with stars. A star’s initial The HRD, or ‘stellar family portrait’, helps us mass is its DNA, understand stars and what happens as they Australia Telescope National Facility determining its age and eventually die. evolutionary The diagram plots stars’ (surface) path, life span, star. When a star is born it enters the MS and and end state. temperatures against their luminosities (see spends the next 90% of its life in almost the same figure). Temperature runs from right to left on spot. It follows that 90% of stars at any one time the x-axis and corresponds to colour and spectral are MS stars. On the class (O,B,A,F,G,K, or M). Luminosity, shown HRD stars appear logarithmically on the y-axis (each step 10 times A star’s position on the MS is determined by its in distinct groups brighter than previous), represents the actual, mass: higher mass = brighter, bluer, hotter, short reflecting the different intrinsic brightness of the stars. It reveals clear lifespans; lower mass = dimmer, redder, cooler, life stages of stars groupings of stars with common Lum-Temp long lifespans. (stages of stellar evolution). correlations representing different stages of stellar Once an MS star has fused all its core hydrogen into life! These groups also align closely to 5 luminosity helium, it quickly (in stellar terms) moves to another classes, from Supergiants (I) to Main Sequence (V). group, its mass determining its path (see figure). Our Sun sits near the centre of the ‘Main Sequence (MS)’ band All stars spend proportionately much less time which runs from lower right to upper left. By definition, a star in each successive stage. that fuses hydrogen into helium in its core, is a Main Sequence Check out these other resources... en.wikipedia.org/wiki/Stellar_evolution atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_postmain.html atnf.csiro.au/outreach//education/senior/cosmicengine/stars_hrdiagram.html atlasoftheuniverse.com/hr.html starinabox.lco.global/

Main sequence stars make up 90% of stars we We need to know the intrinsic luminosities but don’t see that many with the unaided eye. Why of stars to plot them on the HRD. Discuss the might this be? Which stars are the problem? factors involved in determining these correctly.

Blue means bright and red means DISCUSSION dim doesn’t it? Not always. POINTS The red stars at the HRD’s top right STARDOME.ORG.NZ are brilliant. How can this be? 09 624 1246 ACTIVITY

STARDOME OBSERVATORY & PLANETARIUM

HELPS stellar analysesThe 4 stages of stellar evolution Do your own stellar analyses using the HRD. (simplified): 1 Main Sequence (core fusion WHAT YOU'LL NEED H=>He {hydrogen burning}). 2 Red Giants & Super Giants Night Sky phone app for students (e.g.: Star Walk, Sky Safari, Stellarium, (inert helium-rich core, shell Google Sky) surrounding core fusing The HRD as per this resource (or on-line) for individual students. H=>He).. star expands, surface Large sheet of paper or whiteboard for a classroom HRD display where cools, luminosity increases all results can be plotted and details shown. due to increased surface area. 3 Horizontal Branches (core WHAT TO DO fusion He=>C&O, shell H=>He). • On a clear night pick a number of prominent stars in the sky 4a Asymptotic Giant Branch • Identify them with your night sky app (inert C&O core, successive • Look-up Luminosity & Temperature & Mass using the units shown on the shells burn He & H).. shells

HRD (Wikipedia is good) destabilise => Star ‘dies’ and > Consider ‘look-ups’ by independent parties (it’s easy to accidentally cheat) becomes a White Dwarf with Planetary Nebula • Record the stars on the attached table OR • Plot the stars on the HRD 4b Super Giants (successive ‘Stars (part 3 – the shells burning heavier Primarily from your HRD plot, and also from our resource elements => an inert iron and the helps below where necessary, work out the following inside stories)’ core).. eventual supernova and record your answers on the table: and cataclysmic collapse into • Determine evolutionary stage (Main Sequence, Red Giant, Supergiant Neutron Star or Black Hole (and branch if possible)) with supernova remnant • Deduce internal processes (fuel being used, core state, shell burning?)

• Determine the heaviest elements produced by end of life. • Determine star’s end state (White Dwarf? Neutron Star? HIGHLY Black Hole?) RECOMMENDED

• Record your stars (and your deduced details) on-line activity from on the classroom HRD display. Las Cumbres Observatory

• Compare your answers with on-line data Have students go wild with this as a and discuss reasons for deviations separate activity. They can create their own hypothetical star of a particular mass, and gathering as much information as possible from the activity, write their star’s life story for a report back to class. starinabox.lco.global/

It all ends quickly for a supergiant! Credit: Swinburne University of Technology and send it to us. take a photo of your activity we'd love to see it! [email protected] STARDOME.ORG.NZ 09 624 1246 TEMPLATE stellar analyses

DATA TABLE

Luminosity Stage of Internal STAR Temp (K) Elements up to End State (sols) Evolution processes

Sun 1.00 5,750 MS Core H=>He C & O White Dwarf

STARDOME.ORG.NZ 09 624 1246