LISA A Mission to detect and observe Gravitational Waves O. Jennrich, ESA/ESTEC on behalf of the...

LISA

LISAA Mission to detect and observe Gravitational Waves

O. Jennrich, ESA/ESTEC

on behalf of the LISA Science Team

LISA 2Réunion LISA-France, Collège de France, 20/21 Janvier 2005

What are Gravitational Waves?

Gravitational waves are predicted by GR (Einstein, 1915)

Propagate with the speed of light

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


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, …


Hulse-Taylor Binary PSR1913+16

Einstein prediction

tP [s]

Observed loss of energy matches prediction of GW emission to betterthan 0.3%

Indirect evidence of gravitational waves

Outside any detector band


The Effect of a Gravitational Wave

GW change the distance between free-falling test masses


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


LISA Verification Binaries

0.60.794U1626-67

600.105CC ComW Uma

23.04U1820-30LMXB

Strain h (10-23)

f (mHz)

SourceClass

1000.24KPD 1930+2752

600.26KPD 0422+4521WD+sdB

> 200.14WD 2331+290

400.14WD 1704+481

200.16WD 1101+364

400.38WD 0957-666WD+WD

Strain h (10-23)

f (mHz)

SourceClass

30.72GP Com

41.16CP Eri

101.24V803 Cen

101.36CR Boo

201.79HP Lib

201.94AM CVn

93.2KUV05184-0939

603.5RXJ1914+245

406.2RXJ0806.3+1527AM CVn

Galactic binaries (100pc – 1000pc)

Instrument verfication sources

Guranteed detection!

0.60.794U1626-67

600.105CC ComW Uma

23.04U1820-30LMXB

Strain h (10-23)

f (mHz)

SourceClass

1000.24KPD 1930+2752

600.26KPD 0422+4521WD+sdB

> 200.14WD 2331+290

400.14WD 1704+481

200.16WD 1101+364

400.38WD 0957-666WD+WD

Strain h (10-23)

f (mHz)

SourceClass

30.72GP Com

41.16CP Eri

101.24V803 Cen

101.36CR Boo

201.79HP Lib

201.94AM CVn

93.2KUV05184-0939

603.5RXJ1914+245

406.2RXJ0806.3+1527AM CVn


LISA Verification Binaries


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


Evidence for 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


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


Evidence for (S)MBH binaries

During the collision of Galaxies MBH will interact

After merging, MBH binaries can exist


Evolution of (S)MBH binaries

B Schutz (AEI)


GW from SMBH

Time series of the GW amplitude

h

h+

-10-22

0

1022

-10-22

0

1022

S Hughes (CalTech)


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 Einstein’s Theory of Relativity

Determine the population of ultra-compact binaries in the Galaxy

Probe the physics of the early universe

NASA/CXC/MPE/S. Komossa et al.K. Thorne (Caltech) NASA, Beyond Einstein


LISA Mission Concept

Cluster of 3 spacecraft in a heliocentric orbit

Trailing the Earth by 20° (50 Million kilometer)

Equilateral triangle with 5 Million kilometer arm length

Inclined with respect to the ecliptic by 60°


The LISA Orbit

Constellation counter-rotates during the course of one year


The LISA Orbit


LISA layout

main transpondedlaser beams

referencelaser beams

Diffraction widens the laser beam

to many kilometers

– 0.7 W sent, 70 pW received


LISA optical scheme “one-way” measurements

– Each received laser is individually recombined with a local laser

– Phasemeasurement occurs locally

Additional measure-ments on the back-side of the proof masses


LISA layout



Diffraction widens the laser beam

to many kilometers


Michelson with a 3rd arm, Sagnac

Capable to distinguish both

polarizations of a GW

Orbital movement

provides

directionality


Using phase modulation due to orbital motion is equivalent to aperture synthesis

Gives diffraction limit = / 1 AU

Measurements on detected sources:

- ~ 1’ – 1o - (mass,distance) 1%

Wave(f = 16 mHz)

Angular Resolution with LISA


LISA layout



Diffraction widens the laser beam to many kilometers


Michelson with a 3rd arm, Sagnac

Capable to distinguish bothpolarizations of a GW

Orbital movement providesdirectionality

Laser beams reflected off free-flying test masses


Ensuring free-fall


Ensuring free-fall

“Drag-free” control 10-15 m/(s2 Hz)

– Not truly “drag-free”, hence named DRS

Needs tight control of

– Magnetic cleanliness

– Electro-static noise (patch field effect, charging, …)

– Gravity gradient

Ground tests can only demonstrate 10-13 m/(s2 Hz)

LISA PF as technology demonstrator


LISA layout


Spacecraft Layout


Payload layout


Optical layout


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 to remove Doppler shift before transmission to the ground

– USO transmitted as laser sideband (~2 GHz) to be stabilised on armlength

main beams

reference beams


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

LISA Interferometry

main beams

reference beams


Instrumental Noise

Armlength penalty:

5 Million kilometer

Acceleration noise: 10-15 m/(s2 Hz)

Quality of drag-free control,

gravity gradient noise

Shot noise: 70 pW 10-5 cycles/Hz


LISA Launch and Cruise Delta IV launches all three spacecraft Each spacecraft is attached to its own propulsion

module– Propulsion Module V = 1.22 km/sec

– Propulsion module incorporates a bipropellent (N2

O4 / hydrazine) system and a Reaction Control System for attitude control

13 month cruise phase


Status of LISA today

Proposed to ESA 1993, approved as a Cornerstone Mission 1996

Collaborative ESA/NASA mission with a 50/50 sharing ratio

– ESA: Responsibility for the payload I&T, 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)

Launch foreseen in the 2012/2013 timeframe

LISA PF in 2008

– Approved by ESA’s SPC in June 04 (160 M€)

– Europe: LISA Technology Package (LTP)

– US: Disturbance Reduction System (DRS)

LISA A Mission to detect and observe Gravitational Waves O. Jennrich, ESA/ESTEC on behalf of the...

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