Observing Massive Black Hole Binaries with LISA

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Observing Massive Black Hole Binaries with LISA

• Robin T. Stebbins
• U.S. Project Scientist
• Physics and Astrophysics of Supermassive Black
  Holes
• Bishops Lodge, Santa Fe
• 14 July 2006

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LISA Overview

• The Laser Interferometer Space Antenna (LISA) is
  a joint ESA-NASA project to design, build and
  operate a space-based gravitational wave
  detector.
• The 5 million kilometer long detector will
  consist of three spacecraft orbiting the Sun in a
  triangular formation.
• Space-time strains induced by gravitational waves
  are detected by measuring changes in the
  separation of fiducial masses with laser
  interferometry.

• LISA is expected to detect signals from merging
  supermassive black holes, compact stellar objects
  spiraling into supermassive black holes in
  galactic nuclei, thousands of close binaries of
  compact objects in the Milky Way and possibly
  backgrounds of cosmological origin.

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Science
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Science Objectives and Sources

• Supermassive black holes (105-107 M?)
• Located at centers of proto-galactic structures
  and galaxies
• Can trace black hole merger history and galaxy
  formation, can test extreme gravity in the
  dynamical regime, could map dark energy with
  electromagnetic counterparts
• Reach zgt10
• 10s - 100s /yr
• Intermediate mass black holes (102-105 M?)
• Located in stellar clusters or small dark matter
  halos or wherever they may have formed
• Can trace hierarchical build up of massive black
  holes and formation of galactic structure
• Reach z10-20
• Events rates are highly uncertain, but could be
  substantial

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Equal-Mass Binaries
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Science Objectives and Sources

• Extreme mass ratio inspirals (10 M? spiraling
  into 106 M?)
• Stellar-mass black holes in dense galactic nuclei
  captured by central supermassive black holes
• Sample stellar populations and densities in
  galactic cores, most severe test of GR
• Reach z1
• Several 10s, or more
• Close binaries of white dwarfs, neutron stars,
  stellar-mass black holes
• Close binaries of compact objects in the Milky
  Way, and beyond
• Compile demographics of compact objects, known
  sources can be used to verify the instrument
• Reach Milky Way, extragalactic
• 11,000 in Milky Way, remainder a confusion
  background
• Other exotic sources like cosmological
  backgrounds, strings,boson stars, etc.

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Unequal-Mass Binaries
Smallest M2 for detectable BH coalescence signal
at z 1, for 1 yr observation and S/N 5.
Courtesy P. Bender.
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Science Products

• LISAs highest level product will likely be a
  source catalog, updated periodically over the 5
  yr lifetime, or 8 yr extended lifetime.
• What astrophysical parameters can be measured?
• Sky position
• Distance
• Orientation
• Chirp mass, individual masses if chirping
• Spin magnitudes and orientations
• Merger time
• How well can the parameters be estimated?
• Monte Carlo study by Scott Hughes and Ryan Lang,
  MIT
• 10,000 binaries with M1 1 x 106 M?, M2 3 x
  106 M?, at z 1
• Randomly distributed sky position, orbit
  orientation, spin magnitude and orientation

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Parameter Estimation
Ryan Lang and Scott Hughes, MIT
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Mission Concept
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Mission Concept Overview

• Measure time-varying strain in space-time by
  interferometrically monitoring changes in three
  long reference arms.
• Three spacecraft in a triangular formation orbit
  the Sun, 20 behind the Earth.
• The three arms
• Form an equilateral triangle with 5 million
  kilometer long sides
• Are defined by six proof masses, located in pairs
  at the vertices of the triangle
• Are monitored interferometrically to achieve a
  usable measurement bandwidth from 3x10-5 to 1 Hz
• The proof masses are protected from disturbances
  by careful design and drag-free operation
  (i.e., the mass is free-falling, but enclosed and
  followed by the spacecraft).
• Lasers at each end of each arm operate in a
  transponder mode. Optical path difference
  changes, laser frequency noise, and clock noise
  are determined by comparing the frequencies of
  the returned and local laser beams.
• Three arms measure both polarizations of
  quadrupolar waves. Source direction is decoded
  from amplitude, frequency, and phase modulation
  caused by annual orbital motion.

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Instrument Concept

• Six free-falling proof masses define the measured
  lengths, and an interferometric ranging system
  measures changes in their separation.
• Interferometry Measurement System
• Laser subsystem with frequency and amplitude
  stabilization
• Ranging measurement using local and return laser
  beams
• Frequency noise correction
• Disturbance Reduction System
• Proof masses
• Enclosures with sensing, actuation, discharging,
  caging
• Control systems for spacecraft and proof mass
• Micronewton thrusters based on ion spray
• Spacecraft and payload design features to reduce
  disturbances

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Sciencecraft

• Three interacting spacecraft make up the
  science instrument
• Multiple combinations of one-way measurements.

• Drag-free control protects the proof masses from
  the ambient environment and reduces the
  disturbances on the proof masses from the
  spacecraft.

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Sciencecraft
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Distance Measurement Concept

• The distance monitoring system is a continuous
  ranging system, like spacecraft tracking, using
  optical frequencies.
• The ranging system senses
• Inter-spacecraft doppler motions
• Temporal variations of laser frequency
• Time variations of the optical pathlength between
  proof masses (gravitational waves show up here)
• Time variations in the ultra-stable oscillator
  frequency
• The phasemeter measures the accumulated phase as
  a function of time.
• The science signal appears as a millihertz phase
  modulation on a megahertz fringe signal.

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Optical Assembly
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Optical Bench
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Disturbance Reduction System

• Gravitational Reference Sensor
• Proof mass
• Electrostatic and optical sensing
• Electrostatic actuation
• Charge control
• Microthrusters
• Liquid metal ion emitters
• Neutralizers
• Control Laws
• Attitude and position for two proof masses and
  the spacecraft.
• Articulation angle between telescopes

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DRS Hardware
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Programmatics
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Programmatic Overview

• LISA is currently in Formulation Phase (Phase A)
  at NASA, subject to an NRC panels review of
  Beyond Einstein in 2007/2008 time frame
• Current NASA cost is 1.4B, full life cycle,
  including Pathfinder. Cost share is expected to
  be 60/40 NASA/ESA.
• Current launch date is 2017. Science operations
  start in 2019, nominally end in 2024. Extendable
  to 2027.
• LISA Pathfinder - ESA-led mission with ESA and
  NASA (ST-7) payloads
• Demonstrate disturbance reduction technologies
  and local interferometry
• L1 halo orbit
• Preliminary Design Review complete, engineering
  models complete and qualified, entering the
  Implementation Phase (Phase C/D)
• 250M from Europe, 90M from NASA
• Launch October 2009, operations complete in 2011.
• Current activities of the LISA Project
• Technology development
• Formulation study design trades, architecture
  refinement
• Cost savings/simplifications

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Technology
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Gravitational Reference Sensor

• The Pathfinder GRS is the LISA GRS.
• The technology has been fully developed and
  verified on the ground for Pathfinder.
• Additional measurements on ground are desirable
  to characterize the electronics at low frequency
  for LISA.
• Pathfinder validates the GRS on orbit.

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Microthrusters

• Three thruster technologies are being
  independently developed and verified on the
  ground for Pathfinder.
• Pathfinder demonstrates two microthruster
  technologies in flight.
• We are developing lifetime improvements beyond
  those demonstrated by Pathfinder.

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IMS Technology Development
LPF proto-flight laser
Prototype model of LPF optical block
FPGA-based phasemeter
Frequency stabilization cavity
Prototype position sensitivity
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Summary

• LISA can
• Directly detect extreme gravitational
  interactions of intermediate and massive black
  holes out to the era of galaxy formation, and
  beyond.
• Probe the history of galaxy and proto-galaxy
  mergers.
• Test scenarios for the formation of supermassive
  and intermediate-mass black holes.
• LISA can probe the environment around galactic
  engines.
• Test General Relativity in extremely relativistic
  situations with great accuracy.
• The mission concept is well-developed.
• Conceptual design is mature.
• Formulation is very advanced.
• Design optimizations under study, investigating
  cost savings.
• The Project is underway
• Formulation Phase has started in both U.S. and
  Europe.
• Science community is growing.
• Technology development is progressing.
• Demonstration flight is in implementation.

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Parameter Estimation
Ryan Lang and Scott Hughes, MIT
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Parameter Estimation
Ryan Lang and Scott Hughes, MIT