Planets Elsewhere?

download Planets Elsewhere?

of 20

  • date post

    23-Feb-2016
  • Category

    Documents

  • view

    52
  • download

    0

Embed Size (px)

description

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. Who Orbits Whom?. - PowerPoint PPT Presentation

Transcript of Planets Elsewhere?

Introductory Astronomy

Planets Elsewhere?Protoplanetary Disks and universality suggest many stars have planetsFirst discovery in 1988. Now 853 around 672 starsFinding planets is tough: dim, small, near bright star. 32 planets in 28 systems detected by imaging1NAAP simulations1Who Orbits Whom?Planet and Star orbit common center of mass

One detection by Astrometry2Binary star simulatorInfluence of Planets on Sun Simulator

2How Fast?3498 planet in 386 systems detected by radial velocity measurementsExtrasolar simulator3Transiting PlanetsIf planet eclipses star can observe light curveShape of curve helps find size, mass, even properties of atmosphere of planet290 planets in 235 systems detected via transitKepler has 2321 candidate planets in 1290 systems4Simulator Again4Other MethodsGravitational lensing of starlight by planet. 16 planets in 15 systemsTransit Timing Variation uses discrepancies in transit times of eclipsing planet to predict others in same system

5What 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 findMigration is common as are strongly interacting orbits

6

What Are They Like?Taking selection bias into account, super Earths outnumber JupitersSome SuperJupitersKepler-16b orbits two stars7

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 PhysicsWhy dont nuclei break up under electric repulsion?A strong attractive force binds nucleonsShort-range since atoms do not collapse9

Nuclear EnergyRearranging nucleons recover nuclear energyIn large nuclei distant nucleons barely attractBreaking up fission or emission recover electromagnetic energy Heats planets powers reactors

10

Fusion?In small nuclei, less attractive interactionsLiberate nuclear energy by fusion to HeliumProblem: Hydrogen is all protonsStrong interactions cannot change a proton to a neutron

11Weak InteractionsSomething can do this!And the inverseA free neutron decays in 15min Weak nuclear force mediates this decay

12

Some Questions and AnswersCan a force change one particle into another?Is a neutron just a tiny Hydrogen atom? What is ? Are there any rules?Conservation LawsMass-EnergyMomentumAngular MomentumElectric ChargeElectron NumberWeak interaction: rare13YesNoParticle PhysicsParticleQNe1000-1101-10001-10-100Antiparticle: same mass opposite chargesNeutrinos almost massless, weakly interactingDiscovered as missing energy in decay14

Pp simulator

14Solar Energyp-p chain is source of Solar Energy

Sun could last

15Had 1e-19J/atom for 10^4y, so this is 10^7 more15What it TakesTo initiate fusion, protons must overcome electric repulsionOne proton must inverse decay before highly unstable breaks upRequires temperatures of - only in core Inefficient because weak process required 16How Do We Know?Theory (Eddington, Bethe 1932) firstDavis, Bahcall (1968): Detect thePro: Penetrate SunCon: Penetrate detectorFlux at Earth: Put a tank with of Chlorine in Homestake Gold Mine

Requires high-energy produced in other processesExpect one atom per six days 17Where Are the Neutrinos?Flux Found is less than predictionsIs Solar Model wrong?Is detector model wrong?Decided in 2001 by SNO: particle physics

18

More Particles, More ChargesParticleQNeNNMass10009350000938-11000.5110100?-10101060010?-100117770001?19Masses in MeV/c2, worry about that later

Limits on nu masses but not important.19So What?Neutrinos change spontaneously en routepp process produces When they arrive, 1/3 are This implies, in particular, that neutrinos are not massless although light.20

MpRp =MsRs

R = Rs +Rp = Rs(1 +Ms/Mp)

Rs = (Mp/M)R

Rs = (MX/M) 7.79 1012m = 7.44 109m

GMsMpR2

=Msv2sRs

v2s =GMpRsR2

=GM

R

MpM

2

vs =rGM

R

MpM

= vX(MX/M) = 12.5m/s

104 y

107 y

1019 J

6 107 J

6.4 1018 kg/s

L = 3.83 1026W

1015m

n! p+ + e + e

e

E = mc2

e

e+

n

n

p

p

n

e

e

p+ + p+ ! d+ + e+ + ed+ + p+ ! 3He2+

3He2+ + 3He2+ ! 4He2+ + p+ + p+

4p+ ! 2+ + 2e+ + 2e + 4.3 1012 J

1011 y

2He

106K

1011em2 s

e

380m3

37Cl + e ! 37Ar + e

e

p

n

e

e

e

e