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ASTRASTR 1120: Stars & Galaxies1120: Stars & Galaxies

Prof. Prof. JuriJuri ToomreToomre TA: TA: LiciaLicia RayRayLecture 23 Fri 5 Mar 04Lecture 23 Fri 5 Mar 04zeus.colorado.edu/astr1120zeus.colorado.edu/astr1120--toomretoomre

Stellar windsStellar windsfrom hot starfrom hot star

Today’s “Bizarre” EventsToday’s “Bizarre” Events

•• Today look at Today look at white dwarfswhite dwarfs in binary in binary systemssystems

•• Supernova can createSupernova can create neutron starsneutron stars•• ConsiderConsider “pulsars”“pulsars” –– fast spinning neutron fast spinning neutron

stars with fierce magnetic fieldsstars with fierce magnetic fields

•• Review Set 2Review Set 2 available today: available today: LiciaLicia Ray Ray runs review session next Wed night, runs review session next Wed night, second midsecond mid--term exam next Fridayterm exam next Friday

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Binary Systems: The Binary Systems: The AlgolAlgol ParadoxParadox

•• AlgolAlgol is a binary system consisting of a 3.7 is a binary system consisting of a 3.7 solar mass main sequence star and a 0.8 solar mass main sequence star and a 0.8 solar mass red giant. Why is this strange?solar mass red giant. Why is this strange?

•• A.A. A 3.7 star should have become a red giant before a 0.8 solar mass star

•• B.B. Binary stars usually have the same mass•• C.C. 0.8 solar mass stars usually never become

red giants

A.A.

AlgolAlgol Binary SystemBinary System

•• A.A. Binary stars can Binary stars can have different masses have different masses but usually ARE but usually ARE formed at the same formed at the same time. The more time. The more massive star should massive star should have had a shorter have had a shorter main sequence main sequence lifetimelifetime

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What happened?What happened?

•• The 0.8 solar mass star once The 0.8 solar mass star once was more massive (3.0), with was more massive (3.0), with a 1.5 mass companiona 1.5 mass companion

•• As it became a red giant, it As it became a red giant, it swelled and poured material swelled and poured material onto its companion (lost 2.2)onto its companion (lost 2.2)

•• The red giant (0.8) is now The red giant (0.8) is now less massive than its less massive than its companion (3.7)companion (3.7)

•• Future: when the other star Future: when the other star goes red giant, it may pour goes red giant, it may pour gas back…?gas back…?

Binary Mass ExchangeBinary Mass Exchange

3.03.0 1.51.5

--2.22.2

0.80.8 3.73.7

early MSearly MS

nownow

““Core collapse”Core collapse”SUPERNOVASUPERNOVA

““Rapid disassembly” Rapid disassembly” of elements in coreof elements in core

Neutrons Neutrons & neutrinos& neutrinos

Neutron degeneracyNeutron degeneracypressurepressure stiffens thestiffens thecollapsing core collapsing core ------plus push of plus push of escaping neutrinosescaping neutrinos

envelope bounces !envelope bounces !

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Only supernova Only supernova explosionexplosion creates creates elements heavier elements heavier than iron:than iron:

magic of magic of nucleosynthesisnucleosynthesis

Expanding SN Expanding SN shells, and what shells, and what is left behind?is left behind?

SUPERNOVA SUPERNOVA –– what a “new star” !what a “new star” !

•• Exploding remnant Exploding remnant of massive star of massive star disperses heavy disperses heavy elements through elements through the galaxythe galaxy

•• Inside may be a Inside may be a neutron starneutron star –– a a remnant core of remnant core of pure neutrons!pure neutrons!

Crab Nebula (M1),Crab Nebula (M1), first seen as SUPERNOVA first seen as SUPERNOVA on 4 July 1054 from China on 4 July 1054 from China ---- visible in daytimevisible in daytime

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CrabCrabNebulaNebulaSNRSNR

infraredinfrared

radioradio

opticaloptical

xx--rayray

Was Crab SN recorded in Chaco?Was Crab SN recorded in Chaco?….and nothing recorded in Europe!….and nothing recorded in Europe!

•• PetroglyphPetroglyph from from Chaco Canyon:Chaco Canyon:

•• Correct configuration Correct configuration relative to the new relative to the new moon for the Crab moon for the Crab SupernovaSupernova

•• You can check this You can check this on your on your SkyGazerSkyGazerplanetarium softwareplanetarium software

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How do SN and stellar winds touch us?How do SN and stellar winds touch us?•• All heavy elementsAll heavy elements are are

created and dispersed created and dispersed through the galaxy by starsthrough the galaxy by stars

•• Without supernovae, Without supernovae, nothing heavier than nothing heavier than carbon is madecarbon is made

•• WE ARE STAR STUFF !WE ARE STAR STUFF !

•• Our atoms were once Our atoms were once parts of stars that died parts of stars that died more than 4.6 billion years more than 4.6 billion years ago, whose remains were ago, whose remains were swept up into the solar swept up into the solar system when the Sun system when the Sun formedformed Fierce winds and Fierce winds and ejectaejecta

Observing SupernovaeObserving Supernovae

•• About 1 per century per About 1 per century per galaxy (none in Milky galaxy (none in Milky Way since 1604) Way since 1604)

•• Bright explosion visible Bright explosion visible for weeks/months for weeks/months -- some some visible in daytime!visible in daytime!

•• Remnant visible for Remnant visible for 100,000+ years as huge 100,000+ years as huge bubbles and “veils”bubbles and “veils”

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Veil Nebula Veil Nebula ---- HSTHST Tycho’sTycho’s SNR now SNR now –– ChandraChandra(exploded in 1572)(exploded in 1572)

Supernova Remnants (SNR) as veils in skySupernova Remnants (SNR) as veils in sky

Supernovae in Supernovae in Other GalaxiesOther Galaxies

•• Bright enough to be seen Bright enough to be seen as a sudden, bright point as a sudden, bright point in other galaxiesin other galaxies

•• Many amateur and pro Many amateur and pro astronomers monitor astronomers monitor nearby galaxies nightly to nearby galaxies nightly to catch themcatch them

•• 1 per 100 years per 1 per 100 years per galaxygalaxy means that if you means that if you monitor 100 galaxies, see monitor 100 galaxies, see ~ 1 supernova per year)~ 1 supernova per year)

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Supernova Light CurvesSupernova Light CurvesBright Candles in Sky to Bright Candles in Sky to Measure DistanceMeasure Distance

(Type I)

(Type II)

SN 1987 A: nearest one since 1604SN 1987 A: nearest one since 1604

•• Exploded in the Large Exploded in the Large MagellanicMagellanic Cloud Cloud (small companion galaxy to Milky Way)(small companion galaxy to Milky Way)

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Supernova SN 1987 ASupernova SN 1987 A

•• Precursor: massive Precursor: massive blue star (!?)blue star (!?)

•• Ring structure: Ring structure: illuminated remnants illuminated remnants of an earlier stellar of an earlier stellar wind?wind?

•• EjectaEjecta are now are now starting to hit this starting to hit this region region -- brighteningbrightening

Final fate ofFinal fate ofmassive starsmassive stars

Neutron starNeutron star

Black holeBlack hole

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““CompactCompactobjectsobjects””

all charmingall charmingbut bizarre!but bizarre!

Neutron starsNeutron stars

more massive,more massive,smaller in size!smaller in size!

star with astar with acrystal crust!crystal crust!

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Next Stellar EventsNext Stellar Events

•• Continue reading ofContinue reading of Chap 18: Bizarre Stellar Chap 18: Bizarre Stellar GraveyardGraveyard

•• ReRe--read 18.3 read 18.3 Neutron StarsNeutron Stars, and pulsars with , and pulsars with some care nowsome care now

•• Look overLook over Review Set 2Review Set 2. . Second midSecond mid--term term examexam next Fri 12 March, and review session next Fri 12 March, and review session next Wed eveningnext Wed evening

•• Observatory Night # 4Observatory Night # 4 next Tues 9 Marnext Tues 9 Mar