LISA

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LISA

• A Mission to detect and observe Gravitational
  Waves

O. Jennrich, ESA/ESTECLISA Project Scientist
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What are Gravitational Waves?

• Gravitational waves are predicted by GR
  (Einstein, 1915)
• Propagate with the speed of light
• Change the distance between freely falling test
  masses
• Quadrupole waves, two polarisations
• Bondi (1957) GW are physical, i.e. they carry
  energy, momentum and angular momentum
• Small coupling to matter, hence almost no
  absorption or scattering in the Universe
• Small amplitude, small effects
• Ideal tool to observe
• distant objects
• centre of galaxies
• Black Holes
• early Universe

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Sources of GW

• Any mass distribution that is accelerated in a
  non-spherical symmetric way (waving hands,
  running trains, planets in orbit,)
• Large masses necessary
• Neutron star binary system, Black Holes,

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Hulse-Taylor Binary PSR191316

• Observed loss of energy matches prediction of GW
  emission to (0.13 0.21)
• Indirect evidence of gravitational waves
• Frequency 70 µHz, amplitude 710-23 ? outside
  detector sensitivity

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What are the sources?

• Useful frequency range stretches over 8 decades

• Asymmetrical collapse of a supernova core

• Coalescence of compact binary systems (NS-NS,
  NS-BH)

• Inspiralling white dwarf binaries

• Compact binaries (early evolution)

• BH formation, BH-BH coalescence, BH binaries

• Ground based detectors observe in the audio band

• Only a space borne detector can overcome the
  seismic barrier

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LISA Verification Binaries

• Galactic binaries (100pc 1000pc)
• Instrument verfication sources
• Guranteed detection!

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LISA Verification Binaries
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At the Edge of a Black Hole

• Capture by Massive Black Holes
• By observing 10,000 or more orbits of a compact
  object as it inspirals into a massive black hole
  (MBH), LISA can map with superb precision the
  space-time geometry near the black hole
• Allows tests of many predictions of General
  Relativity including the no hair theorem

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Evidence for Super Massive Black Holes

• Stellar motions in the vicinity of Sgr A.
• The orbital accelerations of stars close to the
  Galactic centre allow placing constraints on the
  position and mass of the central supermassive
  black hole

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Mergers of Massive Black Holes

• Massive black hole binaries produce gravitational
  waves in all phases of their evolution
• Signal-to-noise of 1000 or more allows LISA to
  perform precision tests of General Relativity at
  ultra-high field strengths

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Evidence for (S)MBH binaries

• During the collision of Galaxies MBH will interact

• After merging, MBH binaries can exist

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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Evolution of (S)MBH binaries
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Summary of LISA Science Goals

• Merging supermassive black holes
• Merging intermediate-mass/seed black holes
• Gravitational captures
• Galactic and verification binaries
• Cosmological backgrounds and bursts

• Determine the role of massive black holes in
  galaxy evolution
• Make precision tests of Einsteins Theory of
  Relativity
• Determine the population of ultra-compact
  binaries in the Galaxy
• Probe the physics of the early universe

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LISA Mission Concept

• Cluster of 3 spacecraft in a heliocentric orbit
• Spacecraft shield the test masses from external
  forces (solar wind, radiation pressure)
• Allows measurement of amplitude and polarisation
  of GW

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LISA Mission Concept

• Cluster of 3 spacecraft in a heliocentric orbit
• Trailing the Earth by 20 (50 million kilometers)
• Reducing the influence of the Earth-Moon system
  on the orbits
• Keeping the communication requirements
  (relatively) standard

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LISA Mission Concept

• Cluster of 3 spacecraft in a heliocentric orbit
• Trailing the Earth by 20 (50 million kilometers)
• Equilateral triangle with 5 million kilometers
  arm length
• Results in easily measurable pathlength
  variations
• Orbit is still stable enough to allow for mission
  duration gt5years

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LISA Mission Concept

• Cluster of 3 spacecraft in a heliocentric orbit
• Trailing the Earth by 20 (50 million kilometers)
• Equilateral triangle with 5 million kilometers
  arm length
• Inclined with respect to the ecliptic by 60
• Required by orbital mechanics

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The LISA Orbit

• Constellation counter-rotates during the course
  of one year
• Phase modulation (Doppler) and amplitude
  modulation (antenna pattern) give directionality
• Synthetic aperture diffraction limit ?? ?/
  1 AU
• Measurements on detected sources
• ?? 1 1, ?(mass,distance) ? 1

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LISA optical scheme
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LISA Interferometry

• Each beam (reference and main) is separately
  heterodyned with the local laser on a photodiode
  
• 12 signals 6 from the main beams plus 6 from
  the reference beams
• Beat signals from the reference beams are used
  to phase-lock the lasers in the same spacecraft
• Armlength changes slowly over a range of several
  1000 km per year due to orbital mechanics
• Fringe rate of several MHz makes interferometer
  self calibrating based on laser wavelength
• No calibration procedure necessary during
  operation
• Need Ultrastable Oscillator as common clock
• USO transmitted as laser sideband (??2 GHz)
  serve as common clock

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LISA Interferometry

• 18 beat signals
• 6 beat signals from main beams
• 6 beat signals from reference beams
• 6 beat signals from USO sideband signals
• Linear combinations of signals
• Cancel laser and USO noise and keep instrumental
  noise and the GW signal
• Cancel the GW signal and laser and USO noise and
  keeps the instrumental noise
• LISA can distinguish a stochastic gravitational
  wave background from instrumental noise

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Instrumental Noise
Acceleration noise 310-15 m/(s2 ?Hz)Quality of
drag-free control, gravity gradient noise
Armlength penalty 5 Million kilometer

• Shot noise 70 pW ? 10-5 cycles/?Hz

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Payload layout
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Optical layout
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LISA Launch and Cruise

• Atlas V launches all three spacecraft

• Each spacecraft is attached to its own propulsion
  module
• Propulsion Module ?V 2.9 km/sec
• Propulsion module incorporates a bipropellent (N2
  O4 / hydrazine) system and a Reaction Control
  System for attitude control

• 13 month cruise phase

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Status of LISA today

• Collaborative ESA/NASA mission with a 50/50
  sharing ratio
• ESA Responsibility for the payload IT, 50 of
  the payload (nationally funded)
• NASA 3 S/C, launcher, ground segment (DSN),
  mission ops
• Science ops will be shared
• Data analysis by two independent teams (Europe
  and US) TBC
• Preparation for data analysis have just started
  Mock LISA Data Challenge
• Launch foreseen in the 2015 timeframe
• LISA PF in 2009
• Approved by ESAs SPC in June 04 (160 M)
• Europe LISA Technology Package (LTP)
• US Disturbance Reduction System (DRS)
• Recent descoping AOCS and thrusters only

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Status of LISA

• Recent developments in ESA and NASA
• ESAs SPC demanded review of the programmatic
  situation in 2008
• Affects LISA and Solar Orbiter
• Boundary conditions are not yet set
• NASAs budget request for FY 2007 has start of
  the development of LISA indefinitely deferred
• But technology and science studies are ongoing
• Selection of one of LISA, ConX, JDEM later this
  decade, (2008?)
• Project works on somewhat reduced funding in the
  US, limited effects on the ESA formulation study
  phase

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