Post on 29-Apr-2019
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
An Older Core Collapse SNRSNR E 0102-72
Dist = 60 kpc (in SMC)Age ~ 1000 yr;Dia ~ 10pc;M ~ 15-25 Msun
E0102-72O VII(O+6)
O VIII(O+7)
More ionized atoms on outside: evidencefor “reverse” shock propagating intoexpanding ejecta 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 ~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