ASTR 1040 Accel Astro:ASTR 1040 Accel Astro: Stars & Stars & GalaxiesGalaxies

Prof. Juri Toomre TA: Nick FeatherstoneProf. Juri Toomre TA: Nick Featherstone

Lecture 17 Tues 13 Mar 07Lecture 17 Tues 13 Mar 07zeus.colorado.edu/astr1040-toomrezeus.colorado.edu/astr1040-toomre

Cas A SNRCas A SNRVLA - radioVLA - radio

Today in Bizarre-LandToday in Bizarre-Land

• Massive stars end life withMassive stars end life with supernova supernova explosionexplosion, leaving behind either , leaving behind either neutron neutron starstar or or black holeblack hole

• Pulsars Pulsars –– fast spinning neutron starsfast spinning neutron stars with with fierce magnetic fields; gradually slow downfierce magnetic fields; gradually slow down

• Synchrotron radiationSynchrotron radiation makes the light seen makes the light seen as pulses – and thus Crab nebula + pulsar as pulses – and thus Crab nebula + pulsar shines (and pulses) brightly in many shines (and pulses) brightly in many wavelengthswavelengths

Things to doThings to do

• Respond to discussion (Thur) onRespond to discussion (Thur) on “we are “we are made of star stuff, and how does it come made of star stuff, and how does it come about”about”

• Observatory Night 4 Observatory Night 4 tonighttonight, 8pm+ (signup), 8pm+ (signup)• Read Read 18.4 Black Holes18.4 Black Holes carefully for Thur carefully for Thur

lecturelecture

• Evening ReviewEvening Review tomorrow 7-9pm, prepare tomorrow 7-9pm, prepare for for Second Mid-Term ExamSecond Mid-Term Exam on Fri 16 Mar on Fri 16 Mar (Review Sheet # 2 still available)(Review Sheet # 2 still available)

• Helium nucleus (2 protons) is Helium nucleus (2 protons) is absorbedabsorbed, energy is released, energy is released• Elements are created going up periodic table inElements are created going up periodic table in ssteps of 2teps of 2

Fusion by Fusion by “helium-capture”“helium-capture” (alpha-particles ) (alpha-particles ) burns C, O, Ne, Mg, Si ..burns C, O, Ne, Mg, Si ..

REMINDERREMINDER““layers of onion”layers of onion”

““Onion-shell fusion burning” stops with Onion-shell fusion burning” stops with

IRON IRON (Fe, 26 protons )(Fe, 26 protons )

Iron does NOT Iron does NOT release energyrelease energy when it fuses ! when it fuses !

FUSIONFUSION FISSIONFISSION

CARTOONCARTOON

Several fatesSeveral fatesfor massive starfor massive star

1.1. Strong winds Strong winds shrinkshrinkstar, may end as star, may end as WHITE DWARFWHITE DWARF

2.2. Or core burns to Fe, Or core burns to Fe, eventually sudden eventually sudden CORE COLLAPSECORE COLLAPSE ! !

SUPERNOVASUPERNOVA

REMINDERREMINDER

““Core collapse”Core collapse” (massive star)(massive star) SUPERNOVASUPERNOVA

““Rapid disassembly” Rapid disassembly” of elements in coreof elements in core neutrons neutrons + neutrinos+ neutrinos

Neutron degeneracyNeutron degeneracypressurepressure stiffensstiffenscollapsing corecollapsing core --- --- + + push of neutrinospush of neutrinos

envelope `bounces’ !envelope `bounces’ !SHELL BLOWS OFFSHELL BLOWS OFF

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

magic of magic of nucleosynthesisnucleosynthesis

SN shells, andSN shells, andwhat is left atwhat is left atcenter ?center ?

““Core Collapse SUPERNOVA”Core Collapse SUPERNOVA”

• Exploding remnant Exploding remnant of of massive starmassive 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 -- visible in daytimeon 4 July 1054 from China -- visible in daytime

SNR: SNR: Crab Crab NebulaNebula M1M1

4 July 10544 July 1054

Crab SNRCrab SNRcompositecompositeOct 06:Oct 06:Spitzer (IR), Spitzer (IR), Chandra (X), Chandra (X), Hubble (V)Hubble (V)

Observing SupernovaeObserving Supernovae

• About 1 per century per About 1 per century per galaxy (none in Milky galaxy (none in Milky Way since 1604 – Kepler) Way since 1604 – Kepler) [1572 – Brahe; 1054 – [1572 – Brahe; 1054 – Crab; 1004 – brightest]Crab; 1004 – brightest]

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

• RemnantRemnant visible for visible for 10,000+ years as huge 10,000+ years as huge bubbles and “veils” – bubbles and “veils” – longer in radiolonger in radio

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

• Petroglyph from Petroglyph from Chaco CanyonChaco Canyon::

• Correct position Correct position relative to new relative to new moon for Crab moon for Crab Supernova, but Supernova, but some doubtsome doubt

• Check this on your Check this on your SkyGazer SkyGazer softwaresoftware

Clicker review – red giantsClicker review – red giants

• The The main source of energymain source of energy for a star as it for a star as it grows in size to become a grows in size to become a red giantred giant is is _______ ._______ .

• A.A. gravitational contraction gravitational contraction

• B.B. hydrogen fusion in a shell around core hydrogen fusion in a shell around core

• C.C. helium fusion in the core helium fusion in the core

• D.D. hydrogen fusion in the core hydrogen fusion in the core

B.B.

Neutron starsNeutron stars

More massive,More massive,smaller in sizesmaller in size! !

Star with aStar with acrystal crust !crystal crust !

Idea of neutron starsIdea of neutron starsfirst suggested infirst suggested in1930s (Landau, Zwicki, 1930s (Landau, Zwicki, Baade, Oppenheimer)Baade, Oppenheimer)… … but seemed likebut seemed like

wild dreamingwild dreaming

..

Favorite Postcard: Favorite Postcard: SizeSize of Neutron Stars of Neutron Stars

• Structure determined by Structure determined by gravity vs. neutron gravity vs. neutron degeneracy pressuredegeneracy pressure

• Size ~ 10 kmSize ~ 10 km. More . More massive, smaller !!massive, smaller !!

• Crushing gravity at its Crushing gravity at its surface, so not a nice surface, so not a nice neighbor …or place to neighbor …or place to visit …. as tourist – try visit …. as tourist – try Big Apple instead.Big Apple instead.

Neutron star over NYC !Neutron star over NYC !

QUEENSQUEENS

BROOKLYNBROOKLYN

STATEN STATEN ISLANDISLAND

BRONXBRONX

MANMAN

Observing the`First’ Pulsar: Observing the`First’ Pulsar: BIG discoveryBIG discovery

• Jocelyn BellJocelyn Bell : : Cambridge (UK) Cambridge (UK) graduate student in graduate student in 1967 (+ 1967 (+ Anthony Anthony HewishHewish) discovered ) discovered pulsars by accident pulsars by accident

• Little Green Men Little Green Men (LGM) ? (LGM) ? Just WHAT Just WHAT could cause signalcould cause signal??

1.3 sec period1.3 sec period

““Pulsar”Pulsar” = rotating= rotating neutron starneutron star

Fierce magnetic fields Fierce magnetic fields + sizzling electrons + sizzling electrons + fast rotation+ fast rotation finest “lighthouse”finest “lighthouse”

Thomas Gold 1968Thomas Gold 1968

Pulsars and Neutron StarsPulsars and Neutron Stars

Pulsars are lighthouses Pulsars are lighthouses in our Galaxy!in our Galaxy!

Why pulsars spin so fast:Why pulsars spin so fast:Vast shrinking conserves angular momentumVast shrinking conserves angular momentum

• Collapse to a neutron Collapse to a neutron star star increases both increases both rotation and magnetic rotation and magnetic fieldsfields

• Newly collapsed Newly collapsed neutron stars can neutron stars can rotate rotate hundreds to hundreds to thousands of times thousands of times per second per second !!

Mystery resolvedMystery resolved when when pulsar discovered in pulsar discovered in Crab Nebula (knownCrab Nebula (knownto be supernova remnant)to be supernova remnant) -- Messier 1 or M1 !-- Messier 1 or M1 !

The Crab pulsar also The Crab pulsar also pulses in visual lightpulses in visual light

Spinning Bowling Ball DemoSpinning Bowling Ball Demo

Neutron Star in the LabNeutron Star in the Lab

+ Sound on the Web+ Sound on the Web

““Pulsar”Pulsar” = rotating= rotating neutron starneutron star

Fierce magnetic fields Fierce magnetic fields + sizzling electrons + sizzling electrons + fast rotation+ fast rotation finest “lighthouse”finest “lighthouse”

REMINDERREMINDER

SYNCHROTRONSYNCHROTRON RADIATIONRADIATION

SynchrotronSynchrotron radiationradiation

beaming frombeaming fromneutron starneutron star … … and many and many other energeticother energeticplaces (quasars)places (quasars)

““scream from electronsscream from electrons”” spiralling along magnetic spiralling along magnetic fields – like in particlefields – like in particleacceleratorsaccelerators

Synchrotron RadiationSynchrotron Radiation

• Fast electrons in Fast electrons in strong magnetic strong magnetic fieldsfields neutron neutron stars, black holesstars, black holes

• Different shapeDifferent shape from thermal from thermal radiation: radiation: emits at emits at all wavelengths,all wavelengths, strongest in radiostrongest in radio

Visible vs. X-ray emissionVisible vs. X-ray emission

• Thermal lightThermal light from from starsstars visible and IRvisible and IR

• Synchrotron lightSynchrotron light from from neutron neutron starsstars X-ray X-ray and radioand radio

Visible lightVisible light

X-ray lightX-ray light

Visible Light vs. RadioVisible Light vs. Radio Thermal vs. SynchrotronThermal vs. Synchrotron

Elliptical galaxy -- visibleElliptical galaxy -- visibleSame galaxy -- radioSame galaxy -- radio

SN: SN: CrabCrabNebulaNebula M1M1

4 July 10544 July 1054

Back toBack tofamousfamousfriend !friend !

Crab’s pulseCrab’s pulsepatternspatterns

x-rayx-ray

visiblevisible

radioradio

CrabCrabNebulaNebulaSNRSNR

infraredinfrared

radioradio

opticaloptical

x-rayx-ray

ChandraChandraX-ray viewX-ray viewof Crabof Crabcentercenter

Crab pulsar at work: Crab pulsar at work: Nov 00 – Apr 01Nov 00 – Apr 01

Chandra X-rayChandra X-ray HST VisibleHST Visible

Gradual slowing Gradual slowing down of down of pulsar rotationpulsar rotation

Energy emittedEnergy emittedin pulses comesin pulses comesfrom from rotationalrotationalkinetic energykinetic energy

(Listen to pulsars(Listen to pulsars from our website)from our website)