LISA
http://www.esa.int/science/lisa
October 3, 2005
LISA Laser Interferometer Space Antenna
Status of Gravitational Physics Program
Jo van den Brand
NIKHEF – SAC Meeting April 2006
Introduction
Einstein gravity :
Gravity as a geometry
Space and time are physical objects
8
G T
Gravitational waves
• Dynamical part of gravitation, all space is filled
• Very large energy, almost no interaction
• Ideal information carrier, almost no scattering or attenuation
• The entire Universe has been transparant for GWs, all
the way back to the Big Bang
LISA
Gravitational waves `squeeze’ space: small effects
Proper distance between x
and x
+dx
Plane GW propagating in z-direction Define
Wave equation
Amplitude, frequency and duration
Bar detectors: IGEC collaboration
Built to detect gravitational waves from compact objects
LISA
Mini-GRAIL: a spherical `bar’ in Leiden
Interferometric detectors: an international dream
GEO600 (British-German) Hanover, Germany
LIGO (USA)
Hanford, WA and Livingston, LA
TAMA300 (Japan) AIGO (Australia), VIRGO (French-Italian)
LISA
Network of Interferometers
LIGO
detection confidence
GEO Virgo
TAMA
AIGO locate the sources
decompose the polarization of
gravitational waves
Interferometer as GW detector
Principle: Measure distances between free test masses
– Michelson interferometer
– Test masses = Interferometer mirrors
– Sensitivity: h = L/L
– We need large interferometer – For Virgo L = 3 km
2 L hL 2
L hL
Suspended
mirror Suspended
mirror
Beam splitter
Light
Virgo: CNRS+INFN
( ESPCI-Paris, INFN-Firenze/Urbino, INFN-Napoli, INFN-Perugia, INFN-Pisa, INFN-Roma,LAL-Orsay,
LAPP-Annecy, LMA-Lyon, OCA-Nice)
+ NIKHEF joining
LISA
Interferometer Concept
As a wave passes, the arm lengths
change in different
ways….
…causing the interference pattern
to change at the
photodiode Suspended
Masses
VIRGO Optical Scheme
Laser 20 W
Input Mode Cleaner (144 m)
Power Recycling
3 km long Fabry-Perot Cavities
Output Mode
Cleaner (4 cm)
LISA
Virgo – inside the central building
Mirror suspension
High quality fused silica mirrors
• 35 cm diameter, 10 cm thickness, 21 kg mass
• Substrate losses ~1 ppm
• Coating losses <5 ppm
• Surface deformation ~l/100
Superattenuators
Possible contributions:
Virgo+ will use
monolithic suspension
Input-mode cleaner
suspension
NIKHEF: Linear alignment of VIRGO
N W
EOM
Phase modulation of input beam
Demodulation of photodiode signals at different output beams
– => longitudinal error signals
Quadrant diodes in output beams
– => Alignment information
– (differential wavefront sensing)
Anderson-Giordano technique
– 2 quadrant diodes after arm cavities
LISA
Linear alignment setup
Sensitivity evolution
LIGO started
commissioning first
arm in 1999
LISA
Virgo compared to LIGO
Virgo-LIGO joint analysis
Working group for burst and inspiral events
Up to now work on simulated data :
– Project “1a”: Compare analysis pipelines on the same data sets.
– Project “2b”: Study the advantages of 3 sites for astrophysical sources
– Sky location, Detection efficiency
3 talks and papers (GWDAW9 and Amaldi 6)
Burst from galactic
center
LISA
Virgo- Bars joint analysis
AURIGA, ROG
Burst events and Stochastic signals
Project starting with software injection
– 4 hours of data
– Plan for analysis C6 &C7
Detection of Periodic Sources
• Pulsars in our galaxy: “periodic”
• search for observed neutron stars
28 Radio Sources
h ~ GIf 2 e /cr < 10 -24
LISA
Periodic Sources – all sky search – Roma / NIKHEF
• Doppler shifts
• Frequency modulation: due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes
• Amplitude modulation: due to the detector’s antenna pattern.
• The original frequency is 100 Hz and the maximum variation fraction is of the order of 0.0001
• Note the daily variations.
• Because of the frequency
variation, the energy of the
wave doesn’t go in a single
bin, so the SNR is highly
reduced.
Optimal detection by re-sampling procedure
• Use a non-uniform sampling of the received data: if the sampling frequency is proportional to the (varying) received frequency, the
samples, seen as uniform, represent a constant frequency sinusoid and the energy goes only in one bin of their FFT.
• Every point of the sky (and every spin-down or spin-up behavior) needs a particular re-sampling and FFT.
Original data:
The frequency is varying, we sample non-uniformly
(about 13 samples per period).
The non-uniform samples, seen as uniform, give a perfect sinusoid and the
periodogram of the
1 year FFT length (number of points) 3.1E+10
Sky points 3.1E+13
Spin-down points (1st ) 3.1E+06
Spin-down points (2nd ) 3.2E+02
Freq. points (500 Hz) 1.6E+10
Total points 4.8E+32
ALL SKY SEARCH
enormous computing challenge
LISA
VIRGO - Next steps
2006: Commissioning + data taking
– Alignment, controls,…
– A science run by the end of 2006 (coincidence with LIGO-S5) ?
2007
– Data taking/Commissioning/Upgrades
2008-9: Virgo +
– 50W laser, New electronics, New mirrors ? (not yet decided)
2011(?): Advanced Virgo
– 200W laser? New beam geometry? New mirrors?...
Third generation detector
Rüdiger, ‘85
Two order of magnitude compared to initial Virgo
Underground site
Multiple interferometers:
– 3 Interferometers; triangular configuration?
– 10 km long
– 2 polarization + redundancy
Design study part of ILIAS & FP7
Construction: 2010-16 ?
LISA
Gravitational wave antenna in space - LISA
– 3 spacecraft in Earth-trailing solar orbit separated by 5 x10
6km.
– Measure changes in distance between fiducial masses in each spacecraft
– Partnership between NASA and ESA
– Launch date ~2016+
Complementarity of Space- & Ground- Based Detectors
Rotating Neutron Stars
Difference of 10
4in wavelength:
Like difference between X-rays and IR!
VIRGO LISA
LISA will see all the compact white-dwarf and
LISA
LISA – Technical contributions NL
SRON
Test equipment for position sensor read-out electronics in on-ground tests of the satellite system
Simulation software modules of the position sensors, used in system simulations
TNO-TPD
Test equipment of the Laser Optical Bench
Decaging Mechanism (TBC)
Bradford Engineering
Cold Gas propulsion (TBC)
NIKHEF
ASIC development for read-out electronics
LISA Science Goals & Sources
Observational Targets:
• Merging supermassive black holes
• Merging intermediate- mass/seed black holes
• Gravitational captures by supermassive black holes
• Galactic and verification binaries
• Cosmological backgrounds Science Objectives:
• Determine the role of massive black holes in galaxy evolution, including the origin of seed black holes
• Make precision tests of Einstein’s Theory of Relativity
• Determine the population of ultra- compact binaries in the Galaxy
• Probe the physics of the early
universe
Primordial gravitational waves
LISA Production: fundamental physics in the early universe - Inflation, phase transitions, topological defects
- String-inspired cosmology, brane-world scenarios
Spectrum: slope, peaks give masses of key particles & energies of transitions.
A TeV phase transition would have left radiation in LISA band.
Logistics
SRON
– Netherlands Institute for Space Research
Radboud Universiteit Nijmegen
– Department of astrophysics
NIKHEF
– National institute for nuclear and particle physics
Vrije Universiteit - Amsterdam
– Subatomic physics group
Interest expressed by astronomy groups of both Leiden & Utrecht Universities
Henk Jan Bulten & Gijs Nelemans (RUN) – DAST
LISA
Summary
Collaborate on LISA and VIRGO
– Component of our particle-astrophysics initiative
– Exciting new physics program at NIKHEF
NIKHEF commitment
– NIKHEF
– Thomas Bauer, Harry van der Graaf, Jan Willem van Holten – Sipho van der Putten – OIO
– VU
– Jo van den Brand, Henk Jan Bulten, Tjeerd Ketel – Gideon Koekoek - AIO
– Technical impact
– Mechanical engineering, Electronics and ASIC design, GRID
Negotiate with SRON, LISA and VIRGO
– Define responsibilities
LISA Pathfinder
TM1 Optical bench
Sensor housings
Dimensions: 640 mm x 375 mm x 375 mm
Goal: demonstrate free-fall of a proofmass, i.e. isolation from non- gravitational disturbances.
Method: laser interferometry between two proof masses (PMs)
LISA
Evidence for Gravitational Waves
PSR 1913+16
– R. Hulse, J. Taylor (1974)
– 2 neutron stars
– 1 Pulsar → get the orbital parameters
– Orbital period decreases
– Energy loss due to GW emission
– Good agreement with GR
GW Source: Coalescing Binary
End of the life of compact binary systems
– Neutron Stars or Black Hole
Rare events:
– ~ 0.1 event/year (@20Mpc) ±1 order of magnitude
Typical amplitude (NS-NS): h ~ 10
-22@20 Mpc
“Known” waveform
– Search with matched filtering
– General Relativity test
– Standard candles: get the distance from the waveform
– Coincidence with short gamma ray burst?
LISA
Rotating asymmetric neutron star
GW Amplitude function of the unknown asymmetry
–
ε = star asymmetry = ??
–
Upper limit set by the pulsar spin down
A few pulsars around a few 100 Hz
–
Only 800 pulsars plotted out of 10
9in the galaxy
Weak signal but could be integrated for months
–
But a complex problem due to the Doppler effect
–
CPU issues
GW Source: pulsars
6
2 2
45 27
10 200
10 10 10
3
Hz f cm
g I r
h kpc zz
f (Hz)
N
GW source : Supernovae
Non-spherical star collapse
Impulsive events
– Duration < 10ms
Waveform and amplitude difficult to predict
h << 10
-21@ 10 Mpc (?)
Rates:
– 10/year in the Virgo cluster
Required coincidences
– GW, Optic, neutrino detectors
Example of expected
waveforms
LISA
Virgo: What for?
First (?) direct observation of gravity waves
Better understanding of gravity
–
GW produce in high density area
–
Strong field
–
Tests GR
Open a new window on the universe
–
GW very weakly absorbed
–
Standard candle: Hubble constant
–
GW + Gamma Ray Bursts?
–
Supernova understanding?
–
Neutron stars/black hole physics?
–
Early universe picture??
Pushing interferometer techniques to their limits
The future ?
LISA
Next Virgo steps
2006
– Interferometer restart: 1 Month
– New sensitivity curve: February ?
– Recycled ITF commissioning: 3 Months
– Start data taking during weed-ends and nights
– Noise hunting: 4 Months
– Start a Science Run (NS-NS horizon around 15/2.5 Mpc?)
– Data taking > 30% of the time
2007
– A possible shutdown to fix problems
– Commissioning and noise hunting
– Nominal sensitivity
– Data taking > 50% of the time
Virgo+
Independent changes
– Same optical layout
– Monolithic suspension
– 50 W laser
– “Short” shutdown
“Low” cost upgrades
– 1-2 M€
Installation: early 2008
Virgo Virgo+ (a) Virgo+ (b)
NSNS 12 (31) 46 (114) 22 (56) BHBH 58 (145) 234 (584) 116 (291)
Inspiral Range (Mpc): averaged (optimal orientation )
LISA
Advanced Virgo
Target sensitivity improvement:
–
One order of magnitude compared to Virgo
Time scale: Shutdown around 2011
Bigger changes compared to Virgo+:
–
New beam topology:
– Flat beam? Change the beam waist? Signal recycling??
–
Progress on internal thermal noise:
– Material? Coating? Monolithic suspension?
–
Newtonian noise subtraction?
–
…
But Smaller Changes than Advanced LIGO
–
keep the seismic isolation.
A possible sensitivity
LISA: How to go to low frequencies
Space detector to remove the seismic noise
Low frequencies:
– 10
-4-1 Hz
Complementary to ground
based ITF
Taking data in 2016?
• Spatial interferometer (NASA-ESA)
• 3 satellites, arm length = 5.10
6km
LISA
Summary
The Gravitational waves physics is new & exciting
The detectors sensitivity is improving fast
Virgo close to start a first Science run
More progress to come soon…
LISA Science Goals & Sources
Observational Targets:
• Merging supermassive black holes
• Merging intermediate- mass/seed black holes
• Gravitational captures by supermassive black holes
• Galactic and verification binaries
• Cosmological backgrounds Science Objectives:
• Determine the role of massive black holes in galaxy evolution, including the origin of seed black holes
• Make precision tests of Einstein’s Theory of Relativity
• Determine the population of ultra- compact binaries in the Galaxy
• Probe the physics of the early
universe
LISA
LISA Interferometry
“LISA is essentially a Michelson Interferometer in Space”
However
– No beam splitter
– No end mirrors
– Arm lengths are not equal
– Arm lengths change continuously
– Light travel time ~17 seconds
– Constellation is rotating and
translating in space
VIRGO & Lisa – Technical activities
Linear alignment of Virgo
– Keep mirrors and input beam aligned
Monolithic suspension of Virgo mirrors
– Reduce thermal noise
Recycling mirror for Virgo+
– Improve mirror suspension
Lisa electronics
– Drag-free control readout
LISA
Present Virgo noise budget
Control noise
Developments
Present developments
–
More modules needed
– Installation of 9
thquadrant diode (maybe 10
th) – Spares needed
–
New Annecy local oscillator boards, compatible with alignment
– Phase shifters for standard photodiodes
Possible developments
–
Substitute Si diodes with InGaAs diodes
– Better quantum efficiency – Lower bias voltage
– => higher power capability
lower noise
Reduction of electronics noise
Better preamplifier: 5 pA/rtHz -> 1.6 pA/rtHz (?)
DC signals: pre-amplification / pre-shaping
–
Fast quadrant centering system
– (Napoli is working on that)
– LA noise limits sensibility (especially at low frequencies)
LISA
LISA key technology
Test-mass position sensing:
Capacitive sensing.
Drag-Free control.
FEEP micro-Newton thrusters. NIKHEF and SRON develop ASICS for electronic readout of all LISA signals
Low noise, high resolution ADCs
NIKHEF 2 – 3 ASIC designers
+ 2 FTE support
LISA science: massive black hole mergers
MBH = 0.005M
bulgeLISA
Massive black hole mergers
[Merritt and Ekers, 2002]
Several observed phenomena may be attributed to MBH
binaries or mergers
– X-shaped radio galaxies (see figure)
– Periodicities in blazar light curves (e.g. OJ 287)
– X-ray binary MBH:
NGC 6240
See review by Komossa
[astro-ph/0306439]
EMRI - capture orbits
Stellar-type black holes (10 M
) sometimes fall into supermassive holes.
Orbits complicated, can have 10
4or more cycles, provide detailed
examination of black-hole geometry.
Tests of black-hole no-hair theorems, strong-field gravity.
Filtering the data to find these orbits in a huge parameter space
Dealing with source confusion
Challenges:
– Computing the orbits
Typical EMRI event: 10 M BH
LISA