Planets Elsewhere?
• Protoplanetary Disks and universality suggest
many stars have planets
• First discovery in 1988. Now 853 around 672
stars
• Finding planets is tough: dim, small, near
bright star. 32 planets in 28 systems detected
by imaging
1
Who Orbits Whom?
• Planet and Star orbit common center of mass
• One detection by Astrometry
2
How Fast?
• 498 planet in 386 systems detected by radial
velocity measurements
3
Transiting Planets
• If planet eclipses star can observe light curve
• Shape of curve helps find size, mass, even
properties of atmosphere of planet
• 290 planets in 235 systems detected via
transit
• Kepler has 2321 candidate planets in 1290
systems
4
Other Methods
• Gravitational lensing of starlight by planet. 16
planets in 15 systems
• Transit Timing Variation uses discrepancies in
transit times of eclipsing planet to predict
others in same system
5
What Have We Found?
• 1-40% of (Sunlike) stars
have planets. Planets are
ubiquitous!
• Our methods are most
sensitive to hot Jupiters
so these are mostly what
we find
• Migration is common as
are strongly interacting
orbits
6
What Are They Like?
• Taking selection bias
into account, super
Earths outnumber
Jupiters
• Some SuperJupiters
• Kepler-16b orbits two
stars
7
The Sun Shines – but How?
• Sun is big and hot so luminous
• How does it stay hot?
• Chemical (rearrange electrons electromagnetic) burning
produces
per atom, or
per kg.
• Need to burn
so
run out in
• Kelvin-Helmholtz (gravitational)
energy would last
8
Nuclear Physics
• Why don’t nuclei break
up under electric
repulsion?
• A strong attractive force
binds nucleons
• Short-range
since atoms do not
collapse
9
Nuclear Energy
• Rearranging nucleons
recover nuclear energy
• In large nuclei distant
nucleons barely attract
• Breaking up – fission –
or emission recover
electromagnetic energy
• Heats planets powers
reactors
10
Fusion?
• In small nuclei, less
attractive interactions
• Liberate nuclear energy
by fusion to Helium
• Problem: Hydrogen is all
protons
• Strong interactions
cannot change a proton
to a neutron
11
Weak Interactions
• Something can do this!
• And the inverse
• A free neutron decays
in 15min
• Weak nuclear force
mediates this decay
12
Some Questions and Answers
• Can a force change one
particle into another?
Yes
• Is a neutron just a tiny
Hydrogen atom? No
• What is ?
• Are there any rules?
13
• Conservation Laws
–
–
–
–
–
Mass-Energy
Momentum
Angular Momentum
Electric Charge
Electron Number
• Weak interaction: rare
Particle Physics
Particle
14
Q
Ne
1
0
0
0
-1
1
0
1
-1
0
0
0
1
-1
0
-1
0
0
• Antiparticle: same mass
opposite charges
• Neutrinos almost
massless, weakly
interacting
• Discovered as missing
energy in decay
Solar Energy
• p-p chain is source of
Solar Energy
• Sun could last
15
What it Takes
• To initiate fusion, protons must overcome
electric repulsion
• One proton must inverse decay before
highly unstable
breaks up
• Requires temperatures of
- only in core
• Inefficient because weak process required
16
How Do We Know?
• Theory (Eddington, Bethe
1932) first
• Davis, Bahcall (1968):
Detect the
• Pro: Penetrate Sun
• Con: Penetrate detector
• Flux at Earth:
17
• Put a tank with
of
Chlorine in Homestake
Gold Mine
• Requires high-energy
produced in other
processes
• Expect one atom per six
days
Where Are the Neutrinos?
• Flux Found is less than
predictions
• Is Solar Model wrong?
• Is detector model
wrong?
• Decided in 2001 by
SNO: particle physics
18
More Particles, More Charges
Particle
19
Q
Ne
Nμ
Nτ
Mass
1
0
0
0
935
0
0
0
0
938
-1
1
0
0
0.511
0
1
0
0
?
-1
0
1
0
106
0
0
1
0
?
-1
0
0
1
1777
0
0
0
1
?
So What?
•
•
•
•
20
Neutrinos change spontaneously en route
pp process produces
When they arrive, 1/3 are
This implies, in particular, that neutrinos are
not massless although light.