Supernova Remnants (SNRs)

Seminars on X-ray AstronomyPhysics 8.971

November 1, 2007Claude R. Canizares

The remnants of supernovae are THE major sources ofchemical enrichment in the universe and significant

sources of energy in galaxies

http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html

Supernovae also produce all the stellar-masscompact objects (neutron stars & black holes)

And, they are beautiful to look at!

Chandra X-ray image of Cas ACredit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.

Some facts about Supernovae and SupernovaRemnants

• ~ 1 supernova explodes every 30-50 years in our Galaxy• ~ 1 supernova explosion occurs every second somewhere in the

universe• Remnants of supernovae are visible for up to 100,000 yrs

(primarily in radio and X-ray bands)• Roughly ~200 SNRs identified in our Galaxy• ~100,000,000 supernovae in Galaxy’s history• Supernovae are sources of

– Most heavy element enrichment of the universe– Heating of galaxy interstellar medium– Many (most) cosmic rays– All neutron stars and stellar-mass black holes– Triggered star formation

e.g. see Burrows, 2000 Nature 403, 727

Supernova Explosions• Triggered by the collapse of ~ Msun object, either

• degenerate Fe-rich core of a massive (>8 Msun) YOUNG star• “core collapse” supernova• bounce ejects most of the mass• forms neutron star or black hole

• accreting C-O white dwarf in binary system (OLD star)• massive thermonuclear “deflagration” (“slow” explosion)• total “incineration” of star with no remnant

• Classified in two “types” based on optical spectrum• Type 1 - No hydrogen lines --> Absence of H-rich outer

layers in progenitor star• Type 1a -- accreting WD progenitor• Type 1b -- core progenitor that lost it’s outer envelope

• Type 2 - Yes hydrogen lines --> core collapse

Gravitational energy released during corecollapse:

!

E "GM

2

R1

#GM

2

R2

"GM

2

R2

,R2

<< R1

M " Msun = 2x1033gm

R "10km =105cm

$ E ~ 1053erg

This is 1000x what the sun would radiate over the entireage of the universe!

Most energy comes out as neutrinos, but ~10% percentemerges as kinetic energy of ejecta: ~10-20 Msun x (109

cm s-1) => 1052 erg

U.C. Berkeley

Core collapses,bounces, emits hugeneutrino pulse

Layers from Si shelloutward ejected at5,000-10,000 km s-1

providing most of theheavy elements inthe universe

Type 2, core collapse supernova

http://csep10.phys.utk.edu/astr162/lect/supernovae/type1.html

Relatively ~uniformconditions make this asclose to a universal“standard candle” as wehave in cosmology.

Used to measure theacceleration of theuniverse!

Type 1a supernova: a “standard candle”

Three Phases of SNREvolution

1. “Free” Expansion Phase• Mass of ejecta >> Swept-up mass• Energy losses are negligible• Lasts few hundreds to thousands yrs

2. Adiabatic Phase• Swept up mass dominates• Energy losses still small• Lasts tens of thousands of yrs

3. Radiative Phase• Radiative losses important

Eventually SNR dissipates, mixes and merges withinterstellar medium

www.eng.vt.edu

www.lightandmatter.com/.../3vw/ch03/ch03.html

Shock-heating of circum-stellar material

Expanding stellar ejecta is likea piston moving at supersonicvelocities

e.g. v >> vsound~ (kT/mp)1/2

Supersonic shock front

vsound

vplane >> vsound

Physics of a strong shocks (highly supersonic)

vshock >> vsound ; need only use conservation of energy, momentum (pressureequilibrium) and mass flow to derive “jump” conditions across shock front

(e.g. see McKee & Hollenback 1980 Ann Rev Astron Ap 18, 219)

!

"ovo

= "svs

P0

+ "0v0

2

= Ps+ "

svs

2

1

2v0

2+ 5

3P0

= 1

2vs

2+ 5

3Ps

Mass conservation

Momentum/pressure conservation

Energy conservation

“piston” shocked gas shock front unshocked gas

!

"s,v

s,T

s

!

"0,v0,T0

Physics of a strong shocks (highly supersonic)

vshock >> vsound ; need only use conservation of energy, momentum and massflow to derive “jump” conditions across shock front

(e.g. see McKee & Hollenback 1980 Ann Rev Astron Ap 18, 219)

!

"ovo

= "svs

P0

+ "0v0

2

= Ps+ "

svs

2

1

2v0

2+ 5

3P0

= 1

2vs

2+ 5

3Ps

Mass conservation

Momentum/pressure conservation

Energy conservation

“piston” shocked gas shock front unshocked gas “flowing” toward shock front

!

"s,v

s,T

s

!

"0,v0,T0

!

then (for perfect gas)

"s

= 4"0

kTs

= 316

µvs

2, where µ = mean particle mass

Analyze in frame moving with shock front

For vs ~ 1-5000 kms-1

Ts ~ 107 - 108 K

=> X-rays dominate!

Deceleration of ejecta drives a second shock “backwards”heating the ejecta (“reverse shock” in the moving frame)

“gaseous piston” “reverse” shock front primary shock front unshocked gas

Shocked circum-stellar matter:

hotter, less dense

Shocked stellar ejecta:

cooler, denser,

rich in heavy elements

Shocks in ionized gas with magneticfields also accelerate protons andand electrons to relativistic energiesgiving synchrotron radiation and“cosmic rays” (high energy particles)

SN observed in 1572, probably Type 1a, no collapsed remnant has been seen

X-ray Image: Chandra Observatory

PrimaryShockfront (hottestregion)

Mix of circumstellar matterand stellar ejecta heatedby “reverse shock”

Distance ~2.4 kpc

Dia ~ 8.5 arcmin

~ 6 pc = 2 1019 cm

Mean expansion velocity

~ 7700 km s-1

Mass ~few Msun

Mean density

~few particles cm-2

Tycho’s SNR (1572)Colors related to temperatureand composition

Cas A: Remnant of core collapse (Type 2 or 1b) SN

Dist: 3 kpc

Age: ~300 yr Dia: 5’ = 5 pc

~25 Msun

Rich in HeavyElements

shockPrimary

Ejecta heatedby “reverse”shhock

Colors related totemperature andcomposition

Cas A

Collapsed stellarRemnant(Neutron star or Black Hole?)

Hwang et al. 2000 ApJ

Chandra X-ray spectrum of Cas A

An Older Core Collapse SNRSNR E 0102-72

Dist = 60 kpc (in SMC)Age ~ 1000 yr;Dia ~ 10pc;M ~ 15-25 Msun

Chandra Grating Spectrometer of SNR E0102-72

Flanagan et al. 2004

E0102-72

O VIII (O+7) Ly α

E0102-72O VII(O+6)

O VIII(O+7)

More ionized atoms on outside: evidencefor “reverse” shock propagating intoexpanding ejecta Flanagan et al. 2004

Doppler Shifts

1800 kms-1

900 kms-1

-900 kms-1

-1800 kms-1

Flanagan et al. 2004

Pulsar-powered SNRs• Young core-collapse SNRs with active radio

and/or X-ray pulsar at center• Relativistic particles and waves dominate

emission (synchrotron) from radio to X-ray• Called “plerions” or center-filled SNRs (vs.

“shell” SNRs) [Greek: pleres = “full”]

OpticalThe Crab NebulaSN 1054

Crab Pulsar: 33 msec period

Dist ~ 3 kpc

Dia ~ 5 arcmin ~ 3 pc

X-ray

Optical

Crab Nebula & Pulsar

(Credits: X-ray: NASA/CXC/ASU/J.Hester et al.; Optical:NASA/HST/ASU/J. Hester et al.)

pulsar

Crab Nebula is powered by rotational energy

!

I ~ Mr2 moment of inertia of neutron star

E = 12I" 2 rotational energy

dE

dt= I"

d"

dt energy loss

for M = Msun,r =10 km, " = 2# /33 msec

and 1

"

d"

dt=10$11

s$1 (observed slow down rate)

then dE

dt~ 1038erg s-1 or 100,000 x Lsun

vs. observed Crab luminosity = 5 1037 erg s-1

A cosmic, relativistic dynamo!

SN1987A in the Large Magellanic Cloud

Before After

SN1987a ~20 years later

Optical (Hubble)

X-ray

(Credit: X-ray: NASA/CXC/PSU/S.Park& D.Burrows.;Optical: NASA/STScI/CfA/P.Challis)

Optical (stars)

(Digitized Sky Survey)X-ray (hot, enriched gas)

(Chandra: NASA,CXC, SAO)

Antenna Galaxy: Colliding galaxies trigger a “starburst” leading to thousands of supernovae

Credit: NASA/CXC/Eureka Scientific/M.Roberts et al.

SNR G11.2-0.3

Thank you

Questions?