The Signature Of The Stars Worksheet (Page 6 of 6) in pdf

The Signature Of The Stars Worksheet Page 6

The Expanding Universe

Extension: T ype 1 a S upernovas

Type 1 a s upernovas a re i ncredibly b right a nd a lmost a ll i dentical, t wo c haracteristics t hat m ake t hem v ery u seful f or s tudying t he u niverse

on t he l argest ( and o ldest) s cale.

The d istances t o T ype 1 a s upernovas c an b e d etermined u sing t wo d ifferent m ethods: b rightness a nd r edshift. F or n earby T ype 1 a s upernovas b oth

methods g ive t he s ame r esult; h ence, H ubble’s l aw i s a s traight l ine. H owever, a s w e l ook a t m ore d istant

Type 1 a s upernovas, t he l ine b egins t o c urve.

F igure 6

s hows h ow t he b rightness o f T ype 1 a s upernovas c hanges w ith r edshift.

Figure 6

C osmologists u se a p arameter c alled z t o i ndicate r edshift. T he h igher t he v alue o f z , t he h igher t he r edshift.

11. Predictions b ased o n d ifferent m odels a re s hown i n

F igure 6

. T he b ottom l ine d escribes a f lat u niverse, w hich c ontains o nly

mass a nd z ero v acuum e nergy. T he d otted l ine d escribes a n e mpty u niverse, a nd t he t op l ine i s t he l ine o f b est f it. W hat k ind o f

universe d oes t he l ine o f b est f it d escribe?

12. Type 1 a s upernovas l ook d immer t han e xpected f or a g iven r edshift. T his o bservation s uggests a n e xpanding u niverse i n

which t he e xpansion i s i ncreasing o ver t ime, t hat i s, a ccelerating. T he d ark e nergy m odel p roposes t hat t he u niverse h as a

vacuum e nergy t hat e xerts a n egative p ressure, c ausing t he u niverse t o e xpand f aster a s i t a ges. W hat d oes t his m ean f or t he

future o f t he u niverse?

Activity 2