Gravitational Waves at the AEI [email protected] Bernard Schutz.

Gravitational Waves at the AEI

[email protected]

Bernard Schutz

Bernard F Schutz Albert Einstein Institute

12 March 2004

AEI Ferienkurs: Astrophysical Relativity

2

Themes• General relativity impacts astrophysics broadly today:

black holes, neutron stars, gravitational lensing, cosmology, gravitational waves.

• Our main interest is in gravitational waves and their sources, mainly black holes and neutron stars.

• We are involved with detector development (GEO600, LIGO, LISA) and with numerical simulations of gravitational wave emission from black hole and neutron star collisions.


12 March 2004


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Astrophysical Relativity GroupsNumerical Relativity (Rezzolla)• Simulations of black hole and

neutron star dynamics, mergers• Prediction of gravitational wave-

forms• ~20 active scientists• Peyote and Belladonna clusters

provide one of the most powerful computational facilities available to any numerical relativity group worldwide.

Gravitational Waves (Papa)• Astrophysics of GW sources• Data analysis for GEO, LIGO,

and VIRGO detectors• Designing LISA analysis system• ~15 active scientists• Merlin cluster, 1.3 Tflops peak

speed, 18 TB of data storage. Expect to replace it this year with a facility 5 times as fast.

• Einstein@Home project

Theoretical Gravitational Wave Physics (Chen) Design of advanced detectors. Gravitational wave data analysis. 5 scientists.


12 March 2004


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Gravitational Wave Detection• Gravitational waves are the most important prediction of Einstein

that has not yet been verified by direct detection. The Hulse-Taylor pulsar system PSR1913+16 gives very strong indirect confirmation of the theory.

• Gravitational waves carry huge energies, but they interact very weakly with matter. These properties make them ideal probes of some of the most interesting parts of the Universe, now that we have learned how to make sufficiently sensitive detectors.

• Unlike in most of electromagnetic astronomy, gravitational waves will be observed coherently, following the phase of the wave. This is possible because of their relatively low frequencies (most interest is below 10 kHz). This makes detection strategies very different: instead of bolometric (energy) detection in hardware, gravitational wave detection will be by data analysis, in software.


12 March 2004


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GW physics across the spectrum

810low

high

f

f

A chirping system is a GW standard candle: if positionis known, distance can be

inferred.

3/2

1~

2

1RGMGf


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Polarisation• Gravitational waves have 2 independent polarisations, illustrated

here by the motions of free “test” particles.

• They follow the motions of the source projected on the sky.• Interferometers are linearly polarised detectors.• A measurement of the degree of circular polarisation determines

the inclination of a simple binary orbit. If the orbit is more complex, as for strong spin-spin coupling, then the changes in polarisation tell what is happening to the orbit.


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Worldwide Interferometer Network


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Large Interferometers: the 1st Generation


12 March 2004


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GEO: Advanced Technology• GEO beats disadvantage of

shorter baseline with advanced technology for controlling noise and adjusting bandwidth.

• GEO is the only 1st-gen detector that can go narrow-band; will do best all-sky pulsar searches.

• GEO’s technology will be used to make the Advanced LIGO upgrade. GEO responsible for suspensions and lasers. Funded by Max Planck Society and PPARC.

• GEO upgrade to GEO-HF, also now funded by Max Planck Society and PPARC, will happen end of this decade.


12 March 2004


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LIGO performance in September 2005

S5 data taking run is underway: At Design Sensitivity for 18 months!

Binary Inspiral Range 11 Mpc!


12 March 2004


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Data: Massive Volume, Massive Analysis• The LSC records hundreds

of terabytes of data per year. Most of this is “housekeeping”. Signal data around 500 GB/y.

• AEI responsible for pulsar searches, contributes to others

• All-sky surveys for pulsars very demanding: Einstein@Home giving us 40 Tflops delivered, continuous.

• LIGO and GEO have jointly developed data analysis software and are doing joint analysis of current data for upper limits.

• New software have come from this:– Triana quick-look system (Cardiff)– Coherent demodulation code (AEI)– Hough-transform hierarchical

methods for all-sky surveys (AEI)

• Grid efforts increasing: GriPhyN, DataGrid, Triana/GridOneD


12 March 2004


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Merlin Cluster

• 180 dual-processor Athlon nodes

• 1.6 GHz clock speed

• 1.3 Tflop peak speed

• Storage capacity 18 TB

Maria Alessandra Papa


12 March 2004


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Observe from Ground or Space?

• Ground detectors –- Can only observe at f > 1 Hz because of gravity noise on Earth; can’t be screened.- Events are rare, catastrophic.- Likely:

* neutron-star in-spiral (gamma-ray bursts?)* black-hole in-spiral* neutron stars

- First detections are likely to be made from the ground.

• Space detectors –- Required for f < 1 Hz- Many strong sources- Many known sources- Expected:

* Massive BH mergers* Small BHs larger

ones* Known binaries

- Genuine tests of general relativity are possible because of high S/N.

Detectors are complementary


12 March 2004


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LISA


12 March 2004


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LISA in Orbit


12 March 2004


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LISA Sources• Supermassive black holes in galactic centers• Binary star systems in the Galaxy

LISA Organization

• Joint ESA-NASA project (50-50 sharing)• Development guided by LISA International

Science Team (LIST); 3 of the 14 European members are from AEI.


12 March 2004


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Gravitational Waves from Black Holes • Generically, there are 3

regimes in which black holes radiate:– Orbital in-spiral: post-

Newtonian approximations or point-particle orbits.

– Plunge/merger after the last stable orbit: numerical simulations or point-particle orbits.

– Ring-down of the disturbed black hole as it settles down to a Kerr hole: perturbation theory of black holes.

(Kip Thorne)


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Plunge and Merger Radiation• In the point-particle limit, we can calculate the orbit and the

radiation reaction. But for two holes of comparable mass, we need numerical simulations. This is a major activity at the AEI, as well as at many other centers.

• GR is complex. First-order formulations of the vacuum field equations can contain 50 variables or more at each grid point. The largest supercomputers are still not big enough. Coordinate choices are very difficult and codes are so far not as robust as we would like.

• Recent breakthroughs at the AEI and in 4 other groups around the world have produced first full orbit simulations, merger simulations, believable waveform predictions. But much work still to be done.


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LISA Data Analysis

• ESA and NASA are now developing the LISA DA system, much genuine research needed to solve source confusion problem.

• AEI played a leading role in specifying the goals of the system, and is now helping to coordinate the European collaboration: 50 institutes in 7 countries.

• At AEI we will increasingly concentrate effort in this area, expect to make 4-5 postdoctoral appointments in the next few years, support several PhD students.


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IMPRS Gravitational Waves

• Started this year, jointly with AEI/Hannover.• Unique: only course in world where students get

postgrad courses in detectors, theory, data analysis, and numerical work.

• Will take in ~5 students per year for a 3-year award.

• See AEI website for application procedure.

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Gravitational Waves at the AEI [email protected] Bernard Schutz.

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