Type%Ia(Supernovae(as(Cosmological(

probes(

Astrophysics(Part(2(Essay(2012/13(Nic(Walton(

Richard(McMahon(

Is(Dark(Energy(the(21st(century(Ether?(

(The(Discovery(that(the(

Expansion(of(the(Universe(is(AcceleraLng(

(not(Dark(Energy)((

•  1998(ScienLfic(breakthrough(of(the(year(

•  2011:(Nobel(Prize(Physics((

Before(the(discovery(of(the(AcceleraLng(Universe(

DES%UK,(London,(2012(Sep(28( 4(

AYer:(Nobel(Prize(Awards(2011(IOA(Team(with(Saul(Perlmu\er((Our(Glorious(Leader(and(The(Master)(

(

DES%UK,(London,(2012(Sep(28( 5(

•  The(discovery(of(the(acceleraLng(expansion(of(the(Universe(is(considered(as(significant(as(the(discovery(of(the(expansion(itself(and(the(detecLon(of(the(cosmic(microwave(background(radiaLon.((

•  AcceleraLng(expansion(was(first(discovered(through(observaLons(of(distant(Type%Ia(supernovae(over(a(range(of(redshiYs.((

•  This(measurement(relied(on(the(assumpLon(that(Type%1a(supernovae(can(be(used(as(standard(isable)(candles.((

SN(1987A((•  The(first(naked(eye(SN(

since(SN(1572((Cass(A)(and(SN(1604((Kepler’s(SN)(

Light(curves(of(Supernovea(

•  Type(1a(are(the(brightest(‘normal’(SN.((•  News(flash:(more(luminous(SN(have(been(recently(discovered(

Spectral(ClassificaLon(of(Supernova(•  Example(opLcal(

spectra(of(four(supernovae,(all(about(1(week(old,(with(types(indicated(in(parentheses.(The(Si(II(line(is(used(to(idenLfy(type(Ia(spectra.((

•  Type(II(supernova(have(strong(Balmer(Hydrogen(lines(

The(nearby(SN(Ia(sample(

•  Evidence(for(good(distances?(How(are(distances(derived?((

•  How(does(the(uncertainty(in(the(local(present(day(value(of(the(expansion(constant(Ho(effect(the(results?(

The(data(have(a(nice(gaussian(error(distribuLon(of(0.16(mag((8%)((

How(do(we(find(distant(Supernova?(~1000(galaxies(per(image(

Figure(4(from(Spectra(and(Hubble(Space(Telescope(Light(Curves(of(Six(Type(Ia(Supernovae(at(0.511(<(z(<(1.12(and(the(Union2(CompilaLon(R.(Amanullah(et(al.(2010(ApJ(716(712(((((RedshiY(z=(1.124(

VLT/ISAAC(J%band(observaLons(of(the(distant(SN(Ia,(2001gn((north(is(up(and(east(is(to(the(leY).(On(the(leY,(we(show(a(27''(wide(and(51''(high(image(with(the(SN;(in(the(middle(we(show(the(reference(image,(which(was(taken(two(years(later.(The(images(on(the(right(are(the(subtracLon(between(the(two(and(show(the(SN(with(a(signal%to%noise(raLo(of(10.(Each(image(is(the(result(of(10(hr(of(integraLon(in(good(condiLons.(The(image(quality(in(the(leY%hand(image(is(FWHM(=(039.(

Background(•  Type%Ia(supernovae(result(when(carbon%oxygen(white(dwarfs(in(

binary(systems(accrete(mass(from(companion(stars,(reach(a(criLcal(mass(and(explode.((

•  However,(the(relaLonships(that(allow(the(calibraLon(of(their(peak(luminosiLes(using(light%(curve(shapes(and(colours,(and(hence(permit(them(to(be(used(as(cosmological(probes,(remain(purely(empirical.(e.g.(no(unique(Theory(

•  As(the(available(samples(of(type%Ia(supernoave(increase(in(size(and(quality(the(constraints(they(provide(on(the(history(of(cosmic(acceleraLon(should(become(correspondingly(more(staLsLcally(precise.((

•  However,(it(is(possible(that(the(precision(will(be(limited(by(errors(in(the(empirical(calibraLng(relaLonships.(

•  (It(is(therefore(important(that(the(validity(of(these(relaLonships(is(both(verified(and(understood.((

RelaLve(to(empty(Universe(

Empirical(Light(curve(stretch(correcLon(factor(

•  Light&curves&of(nearby,(low%redshiY(type(Ia(super(novae(measured(by(Mario(Hamuy(and(coworkers(

•  Note(the(range(in(peak(brightness((•  ((a)&Absolute(magnitude(plo\ed(against(

Lme((in(the(star’s(rest(frame)(before(and(aYer(peak(brightness.(The(great(majority((not(all(of(them(shown)(fall(neatly(onto(the(yellow(band.((

•  The(figure(emphasizes(the(relaLvely(rare(outliers(whose(peak(brightness(or(duraLon(differs(noLceably(from(the(norm.(The(brightest(supernovae(fade((more(slowly(than(the(faintest.(&

•  (b)&Simply(by(stretching(the(Lme(scales(of(individual(light(curves(to(fit(the(norm,(and(then(scaling(the(brightness(by(an(amount(determined(by(the(required(Lme(stretch,(one(gets(all(the(type(Ia(light(curves(to(match.(

From(Perlmu\er,(2003,(Physcis(Today(

Uncertainty(due(to(stretch(correcLon(

From(Howell(et(al,(2007,(ApJL,(667,(L37(

Distribution is no symmetric and could vary with redshift

Your(essay(should(include(the(following(points:((

1.  What(are(the(different(types(of(supernova(and(what(evidence(is(there(that(type%Ia(supernovae(are(standard(isable)(candles?((

2.  Review(the(experimental(background(to(the(discovery(of(the(acceleraLng(expansion(of(the(Universe(and(how(the(observaLonal(strategy,(sample(sizes(and(errors(have(improved(over(the(last(decade.((

3.  How(can(observaLons(of(type%Ia(supernovae(be(used(to(disLnguish(between(compeLng(theories(of(the(origin(of(the(acceleraLng(expansion?((

4.  Where(is(progress(needed(to(ensure(systemaLc(effects(are(not(the(limiLng(factor(for(future(surveys?((

1998(ScienLfic(breakthrough(of(the(year(

•  Nobel(Prize(Physics(2011(

Some(Credits(and(Bibliography(•  Wikipedia(and(as(cited(by(Wikipedia(•  Stan(E.(Woosley,("Supernova,"(in(AccessScience,(©McGraw%Hill(

Companies,(2008(h\p://accessscience.com/content/Supernova/669600(