Transcript Supernova Neutrinos

Neutrino Astronomy:
Seeing the Cosmos in a
Matthew Malek
Imperial College London
Advances in Astronomy
17-April-2010
 Light
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Outline
• Introduction
– Ways of looking at the sky
– What is this neutrino thing, anyway?
• What has been done in astronomy with neutrinos?
– Solar neutrinos
– Supernova 1987a
• What are we doing now?
– Supernovae: Bursts and relics
– Point sources: AGN, GRB, etc.
– High energy neutrino astronomy
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How Do We Look At The Sky?
• For most of our history, humanity could only
observe space via visible light…
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How Do We Look At The Sky?
Hale-Bopp in IR (Palomar)
SNR in Centaurus (Chandra)
• Then came other messengers:
– Infrared, X-ray, Microwave, Gamma rays, et cetera…
CMB (WMAP 2008)
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Astrophysics
with cosmic rays
GeV -rays
Astrophysics
with photons
Protons @1021 eV
point as far as 40Mpc
X-rays
Visible
IRB
CMB
Radio
How Else Can We Look?
e+e-

Halzen, Ressell & Turner
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What Is This
“Neutrino” Thing?
…and why do we care?
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A Brief History of Neutrinos
N1 → N2 + e-
• 1910s - 1920s: Studies of nuclear β decays
Did not appear to conserve energy!
nuclei
electron
• 1930: Wolfgang Pauli postulated Neutrinos in order to save energy conservation
N1 → N2 + e- + 
“I have done a terrible thing. I have postulated a
particle that cannot be detected”
 has no charge, no mass, very feeble interaction, just a bit of energy
• 1956:  finally discovered by Cowan and Reines.
Used nuclear reactor as source of neutrinos.
Nobel prize 1995
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Neutrino Interactions
•  only interact ‘weakly’ – how weak is this?
•  mean free path
(i.e., average distance travelled before interacting) is:
~ 1 light year of lead!
• 1 light year ~ 1016 m = 10,000,000,000,000,000 m
neutron
Interaction
n + e→ p + e –
u
u
d
d
d(-1/3)
proton
u(2/3)
W
e–
Mediated by W boson
e
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Cosmic Gall
Neutrinos they are very small.
They have no charge and have no mass
And do not interact at all.
The earth is just a silly ball
To them, through which they simply pass,
Like dustmaids down a drafty hall
Or photons through a sheet of glass.
They snub the most exquisite gas,
Ignore the most substantial wall,
Cold-shoulder steel and sounding brass,
Insult the stallion in his stall,
And, scorning barriers of class,
Infiltrate you and me! Like tall
And painless guillotines, they fall
Down through our heads into the grass.
At night, they enter at Nepal
And pierce the lover and his lass
From underneath the bed – you call
It wonderful; I call it crass.
– by John Updike (1960)
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Why Study Neutrinos?
• Second only to the photon in abundance
• Produced in the Big Bang in numbers comparable to photons
• Neutrinos are crucial to understanding how the Sun shines
• Neutrinos provide a unique window into exploding stars
(supernovae)
• Neutrino astronomy: used to study distant objects
• Recent surprise: neutrinos have non-zero mass!
We don’t know what the mass is but it is less than:
0.00000000000000000000000000000001 g
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Sources of Neutrinos
• Atmospheric – from cosmic rays
• Artificially created (reactors, accelerators)
• Natural background radiation (from rocks, etc.)
• Solar – from nuclear reactions within the sun
• Supernovae – core collapse of massive stars
}
• Cosmic  background – relics from Big Bang
• Other sources: AGNs? GRBs?
2002 Nobel Physics prize!
200
Ray Davis & Masatoshi Koshiba share with Riccardo Giacconi
for “pioneering contributions to astrophysics”.
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Solar Neutrinos:
Dawn of a
 Era!
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What Makes The Sun Shine?
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What Makes The Sun Shine?
In The Mine,
But Looking At The Stars…
• First solar neutrino detector:
• Homestake mine, S. Dakota
• Ray Davis, Brookhaven
• 1967 – 1998
• 615 tons of C2Cl4
(cleaning fluid!)
• “Radiochemical” detector:
e + 37Cl → 37Ar* + eGood News:
First discovery of solar !
Bad News:
Far fewer than anticipated!
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Some Questions Remain
Q1: How do you know the neutrinos came from the sun?

A: Need a different
type of neutrino
telescope!
• Cherenkov detectors
find  via emitted light
• Can be water, ice, salt…
• Some directional
information is preserved
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Directionality Is Key
The KamiokaNDE detector (Masatoshi
Koshiba) first to prove  seen from Sun

e

22,385 Solar  events
(14.5 events/day)
The Sun (seen in neutrino “light”)
Water Filling At Super-Kamiokande
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What About The Missing
+0.20
1.0 - 0.16
7.6 +1.3 SNU
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?
1.01±0.13
+9
128 -7 SNU
- 1.1
Experiments
+7
71 - 6
0.55±0.08
Theory
7Be
pp
71±6
8B
CNO
0.47±0.02
2.56 ±0.23
37Cl Homestake
Kamioka
0.35±0.02
H2O
SuperK
C.C. D2O N.C.
SAGE 71Ga GALLEX
(+GNO)
Q2: The so-called “Solar Neutrino Problem” (1967 - 2001)
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Q3: …but what does this teach us about the Sun??
Neutrino telescopes give us a
look inside the sun
• Photons (light) take about
1,000,000 years to leave
• Neutrinos exit “instantly”
Based on solar , we know:
1. Fusion powers the Sun
2. SSM originally verified only by 
(later aided by helioseismology)
3. “pp” neutrinos strongly
correlate with solar light output
4. Other, rarer,  types give different information
For instance, from 8B solar  measurements, we know the temp.
at the core of the Sun is: 1.5 x 107 K ± 1%
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Supernova Neutrinos:
Things That Go BOOM
In The Night
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Supernova Progenitors
Main
Sequence
Accreting White Dwarf
Carbon
deflagration
supernova
Supergiant
H core
m > 8 M?
Red
Giant
C & O core
He & H shells
He core
+ H shell
Images taken from:
http://astron.berkeley.edu/~bmendez/ay10/2000/cycle/cycle.html
“ Onion” Shells
(H,He,C,O,Ne,Si,Fe)
Core
Collapse!
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Supernova Classification
Classify by spectral lines:
Type II
Supernova
Got
Hydrogen?
Type I
Supernova
(Got Silicon?)
NOTE:
Spectral class ≠Mechanism
Type Ib
Supernova
Type Ia
Supernova
Got
Helium?
Type Ic
Supernova
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Supernova Neutrino Emission:
Start of Collapse
• Electrons captured on nuclei produce
e via:
e– + A(N,Z) → e + A(N+1,Z-1)
• Mean free path of neutrinos > core size
• Neutrinos escape promptly
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Supernova Neutrino Emission:
Neutrino Trapping
• Core density increases as collapse continues
• Mean free path of
 shrinks w/ increasing
density
• Neutrinos trapped by scattering off nuclei:
 + A(N,Z) →  + A(N,Z)
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Supernova Neutrino Emission:
Shock Wave Formation
•
•
Inner core reaches nuclear densities
Neutron degeneracy halts gravitation attraction
Inner core rebounds, causing shock wave
Shock wave propagates through infalling outer core
•
Larger
•
•
-sphere; s still emitted from outer core
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Supernova Neutrino Emission:
Neutronization Burst
•
•
Shock slows infalling matter and separates nucleons
Shock loses energy (8 MeV) per dissociated nucleon
→ eventually stalls (revives how?)
•
Electrons captured on dis. protons produce e via:
e– + p → e + n
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Supernova Neutrino Emission:
Neutrino Cooling
• Egrav → Etherm, about 1046 Joules
• T  40 MeV  500,000,000,000 K
• (Room temperature = 300 K  1/40 eV)
• Proto-neutron star cools, producing

• Unlike previously, all 6 types are generated
• Neutron star (or black hole?) left behind
What Can  Teach Us About
Supernovae?
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Neutrinos ()
• 99% of the energy from a
core-collapse supernova is
released as neutrinos
Photons ()
• Only 1% energy appears as 
(+ tiny fraction as kin. energy)
•  emitted during SN, giving
unique insight into the
process of a supernova &
neutron star formation
• Light () emitted hours later,
largely from decay of
radioactive elements produced
in the supernova’s shock wave
•  carry information direct
from core; no scattering!
•  scatters in dense, turbulent
gas, losing information about
its source
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Finding Supernovae Neutrinos
• To date, only SN  burst came from
Sanduleak -69o 202 in Large Mag. Cloud
• Spotted on 23-Feb-1987, it is now more
famously known as Supernova 1987a
• 19 (or 20) SN neutrinos seen in two
water Cherenkov experiments:
• 11 (or 12) at KamiokaNDE
• 8 at the competing IMB
• Hundreds of papers written analysing
these few neutrinos!
• Today, a SN burst from the galactic centre (10 kpc) could provide up to 10,000 events!
• Additionally, because  are emitted first, they can be a useful early warning system
for astronomers. SNEWS exists to alert astronomers of a nearby supernova.
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Finding Supernovae Neutrinos
Problem:
Cannot predict when
next SN burst arrives!
→ Waiting > 20 years
Semi-Solution:
 never stop moving…
so the cosmos should
be filled with a diffuse
background of  from
all the supernovae that
have ever exploded!
→ Look for it whilst
waiting!
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Supernova Relic Neutrinos
• SRN should be an isotropic
background composed of  from
all SN explosions
• Predictions obtained by taking 
spectrum from single SN and
redshifting according to SN rate
Solar 8B
Solar hep
Atmospheric e
SRN
predictions
• Natural energy window to search
• Massive stars – with relatively short lives – die in core-collapse
• Thus, SN rate is a good tracker of star formation rate!
→ Birth of  cosmology??
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SRN Search Results
Total background
(Atm. + decay e)
Decay
electrons
Atmospheric e
• SRN signal would manifest as distortion of BG
• No such signal seen yet → some models ruled out
• The search continues!
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The Expanding
Universe of
Neutrino
Astronomy:
Other Topics &
Observatories
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Other Sources of Cosmic

Thus far, only source of extra-solar  is SN1987a.
Other possible types include:
• High E: Collisions of galactic cosmic rays
produce ±, which decay into  (& other things…)
• Ultra-High E: From collisions of extra-galactic
cosmic rays (see slide 5 and last year’s talk)
• Ultra-Low E: Relics from the Big Bang, with
temperature of 1.9 K (equiv. E = 1.7×10−4 eV)
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Looking for Cosmic

There are many different neutrino telescopes.
An [incomplete] list includes:
• High E: AMANDA, ANTARES, NESTOR,
ICECUBE
• Ultra-High E: ANITA, GLUE, RICE, SALSA,
Pierre Auger Observatory
• Ultra-Low E: No current experiments.
(Energy is too low for detection w/ current tech.)
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High Energy Cosmic

• Likely to correlate to point sources, such as
Gamma Ray Bursts, Active Galactic Nuclei, etc.
• Searches by Super-K, MACRO, etc. find nothing...
• A typical search
involves a catalog
(e.g., BATSE)
• Check for an excess
of  events around
the time of the GRB
GRB 080916C imaged by Fermi LAT
High Energy Cosmic :
New Dedicated Observatories
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ANTARES[*] is located in the Mediterranean.
It uses 885 eyes, in strings 450 m high to
search for upgoing high energy cosmic 
[*] Astronomy with a Neutrino Telescope
and Abyss Environmental RESearch
The Sky In High Energy Cosmic 
• Each point shows one  event in ANTARES
• Downgoing events cut to remove cosmic rays
• Since 2006, all events consistent with atmospheric 
– Thus far, no cosmic  sources found…
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High Energy Cosmic :
New Dedicated Observatories
• IceCube is an ice Cherenkov
observatory at the South Pole,
covering 1 km3 of ice
• It replaces and incorporates
the former AMANDA-II expt.
• Again, galactic map shows no
sign of sources… yet!
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Ultra-High Energy Cosmic
• UHE  intrinsically interesting,
if discovered
– Where do they come from?
– What process creates them?
• Unusual detection techniques
– GLUE: Uses lunar limb as target
and searches for radio emission
– ANITA: Flies in a balloon over
Antarctica and looks for radio
pulses in the ice
– Pierre Auger Observatory:
Uses the Andes as target.
Searches for horizontal events
with high EM component

:
Current Search Results
Ultra-High Energy Cosmic
• Again, no sources discovered (yet)
• GZK  seem a “guaranteed” source,
from cosmic rays colliding with CMB
• Wait and see…
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Summary
• Neutrino astronomy has opened up a fascinating new
window for looking at the cosmos
• Solar neutrinos are well established and have taught us
much about stellar astrophysics
• Supernova neutrinos have given us a glimpse into the
death of massive stars and the formation of neutron stars;
we are ready and waiting for the next burst!
• Supernova relic neutrinos must exist. When found, they
will open the door to “Neutrino Cosmology.” Exciting!!
• Many high energy neutrino telescope coming online now
• Ultra-high energy neutrinos remain elusive.
Check back in one, five, ten years…
→ Extremely interesting time to be doing  astronomy!