LISA Science

Items 1-3 and 7: `guaranteed science'. Items 4-6: uncertain, but potential big payoffs.

Source physics astronomy LISA design
1. Exotic binary stars Precision tests of weak field General Relativity.

(P,e,r,a,M) known from optical/IR or radio observations for some sources.

  • f=2/P ?
  • harmonics if e nonzero
  • Polarization vs orbit orientation,
  • h(r,a,M1,M2)
  • Several known calibrators, e.g. RXJ1914.4+2456
  • Guaranteed thousands of sources
  • =largest sample of objects at frontiers of stellar evolution:
  • W UMa binaries
  • WD-WD post common envelope systems (SN Ia?)
  • Cataclysmic variables in quiescence
  • Close exchange binaries in globular clusters
  • NS-NS binaries (incl close, non-PSR) -gamma-ray bursts?
  • NS-BH binaries
  • BH-BH binaries (undetectable electromagnetically!)
  • Confusion limit sets

    `sky noise'

    2. 1-10^4 Msun black holes scattered into 10^6-10^8 Msun black holes in galactic nuclei Waveforms can be computed exactly by perturbation theory.
  • Presision test of strong-field GR
  • Map full Kerr geometry
  • Precision test of No Hair Theorem
  • Masses of scattered black holes depend upon IMF and mass segregation in central parsec of galactic nuclei.

    Event rate depends on rate of scattering into loss cone. (triaxiality, bars, Brownian wandering of black hole)

    Provides census of M, a/M, spin directions of black holes in non-active nuclei (e.g. M31, M32).

    In active nuclei, accretion disk drag can compete with gravitational radiation reaction to determine rate of orbital decay: surface mass density of inner accretion disk.

    Clean pure gravitaional two-body problem: no tomographic inversion (X-ray Fe lines) or gas-dynamic modeling (QPOs)

    sets :
  • h floor
  • mission duration (event rate and to beat Galactic binary confusion noise)
  • 3.Mergers of 10^6-10^8 Msun black h in the nuclei of merging galaxies For lower-mass holes, detectable anywhere in universe with S/N of thousands.
  • Ring-down is precision test of horizon dynamics in strong-field time-dependent General Relativity.
  • Merger waveform will be precision test of numerical Relativity (S/N much higher than LIGO stellar-mass BH mergers)
  • Cosmic censorship -will new horizon form all cases?
  • Final truth check on AGN models and velocity dispersion rises in non-AGN:
  • Are the things in the middle black holes or dense star clusters?
  • Are precessing radio jets due to binary black holes?
  • Merging rate of BHs depends on:

  • Merging rate of galaxies z=0-10, convolved with
  • Formation history of supermassive black holes, convolved with
  • Rate of dynamical friction in loss-cone regime
  • To reach supermassive >10^7Msun, argues for
  • Push low frequency below 10^-4 Hz
  • Long mission duration
  • 4. Formation of supermassive black holes Easily detectable if formed by
  • runaway merging in dense star cluster with compact objects
  • nonaxiymmetric collapse of dense gas cloud.
  • Undetectable if grown by gas accretion from small seed.

    5. Cosmic Backgrounds All waves produced since Planck era reach LISA! Frequency range corresponds to horizon scale at Electroweak symmetry breaking (100GeV).

    Consensus for baryogenesis at Electroweak transition: requires first-order phase transition.

  • Strongly first order: LISA detects GWs, gets Nobel prize
  • Weakly first order: LISA doesn't
  • Really long shots: strings, nonstandard inflation, QCD phase transition

    6. Discover dark matter If dark matter in galaxy halos is 10^4-10^6 Msun black holes (Ostriker-Lacey) reaching to radii where dynamical friction is important: bright sky!
    7. The Unknown and Unexpected