LISA Science

LISA Science

Bernard Schutzfor the

LISA International Science Team

Albert Einstein Institute – Max Planck Institute for Gravitational Physics, Golm, Germany

andCardiff University, Cardiff, UK

http://www.aei.mpg.de

[email protected]

http://www.aei.mpg.de/

http://www.aei.mpg.de/

Bernard F Schutz Albert Einstein Institute

20 July 2002

LISA Science: 4th LISA International Symposium

2

LISA• Joint mission: NASA and

ESA have exchanged Letters of Agreement.

• NASA: both JPL and GSFC participate

• Launch planned 2011• Technology mission

SMART-2 will be launched by ESA in 2006 with experiment packages from Europe and USA.

• 20-member science team called LIST (LISA International Science Team), chaired by T Prince and K Danzmann.

• LIST working groups involve the wider community, give input on design, data analysis, and scientific goals.


20 July 2002


3

Science drivers and current issues• Merging supermassive black holes (SMBH) in galactic centers

– Formation, evolution, relation to galaxy formation and mergers, indicators from other observations, cosmological information, numerical modelling

• Signals from gravitational capture of small BHs by SMBHs– Event rates, evolution of clusters near SMBHs, modelling of very complex

waveform (radiation-reaction), signal extraction from background of distant events, accuracy of tests of BH uniqueness theorems of general relativity

• Survey of all galactic binaries with sufficiently short periods – Population statistics, confusion by large population at lower frequencies,

confusion limit on signal extraction, information extraction from observations

• Backgrounds, astrophysically generated and from the Big Bang– Strength and spectrum of astrophysical backgrounds, production of early-

universe radiation, relation to fundamental physics (string theory, branes, …)

• Bursts, unexpected sources– Formation of BHs of intermediate to large mass, possible sources in dark matter


20 July 2002


4

Black holes, white dwarfs, Big Bang

10-4 10-3 10-2 10-1 100

Frequency (Hz)

10-23

10-22

10-21

10-20

10-19

10-18

Detection threshold (S/N = 5)

for a 1-year observation

Binary confusion limit

2 x 106 Mo B Hs at z=1

10 Mo + 106 Mo BH

2 x 104 Mo BH s

RXJ1914.4+2456

4U1820-30

h

10

5

0

-5

-10

-15

mg w

gw = 10-10


20 July 2002


5

Issue: LISA measurement theory(Estabrook, Tinto, Armstrong; Dhurandhar &

Vinet) • LISA is not just one interferometer. All estimates of LISA

sensitivity until now have used just one interferometer. • Estabrook et al have shown that there are many

combinations of the 12 signals measured on-board LISA that cancel laser frequency noise and that therefore are clean enough to detect gws. These represent ways of using all the information returned by the 3 arms.

• Dhurandhar and Vinet (gr-qc/0112059) have shown that the set of all such combinations has the mathematical structure of a module.

• Different combinations have different antenna patterns. Data analysis can switch from one combination to another if a particular source moves into a “hole” in the first pattern.


20 July 2002


6

Possible sensitivity improvement


20 July 2002


7

A 2.6 106 M Black Hole in our Galaxy

LISA’s most exciting goal is to study the formation, growth, space density and surroundings of massive black holes, which are observed in most nearby galaxies. Here is our own!

(Eckart & Genzel)


20 July 2002


8

Other evidence for MBHs• Velocity fields are

measured using – Maser lines– Stellar velocity

dispersion– X-ray iron lines

• More distant MBHs make jets in AGNs and QSOs, but most are quiet

• Twin MBHs: 3C75

(Sterl Phinney)


20 July 2002


9

Issue: BH Merger Simulations• Improving all the time:

– More stable forms of the field equations– Gauge conditions improved– Run times lengthening– Initial data improving: subtle

• Still hungry for computer time. The Discovery Channel funded AEI’s longest simulation to date, and its visualization.

C:\Program Files\quickTime\QuickTimePlayer.exe C:\bfs\images\simulations\discoverychannel\comp-bh3-20.mpeg


20 July 2002


10

• 3PN-E1B-ISCO and QC3/QC4 parameters are very close, but PN not converging …

Comparisons with PNComparisons with PN

(Baker, Campanelli, Lousto, Takahashi 02)

Going byond QC4 …• Longer numerical simulations!

• Comparisons with FN needed!

(work in progress … AEI)


20 July 2002


11

Issue: Cosmology with SMBH Mergers

• Position uncertainties of SMBH mergers are significant, error boxes of order several degrees likely. This dominates uncertainty in range too, makes it impossible on position alone to find galaxy in which merger took place.

• Cosmology with SMBHs. If the merger can be associated with a galaxy or cluster, then the uncertainty in position is drastically reduced, the distance error is reduced to ~0.1% (dominated by random velocities of galaxies), and the distance can be compared with the redshift. This would allow tracking of the acceleration history of the Universe.


20 July 2002


12

1 yr before plunge:

r=6.8 rHorizon

185,000 cycles left,

S/N ~ 100

1 mo before plunge:

r=3.1 rHorizon

41,000 cycles left,

S/N ~ 20

1 day before plunge:

r=1.3 rHorizon

2,300 cycles left,

S/N ~ 7

heff

Gravitational capture example10M/106M circular equatorial orbit, fast spin

[Finn/Thorne]

f (Hz)


20 July 2002


13

Issue: How well can we study gravitational captures?

• Potential for very fundamental results, mapping spacetime near a Kerr black hole

• Nightmare for matched filtering:– Very large parameter space for orbits, perhaps

1030 or more distinguishable sets of parameters– Filters not yet understood, because radiation-

reaction problem in strong-field Kerr not solved– Approximate, hierarchical scheme needed

• Filtering must be good, because:– Signals from galactic WD binaries need to be

removed– More distant capture events provide background,

a kind of Olbers limit


20 July 2002


14

Galactic binaries• All compact-object binaries (WD, NS, BH) in

galaxy with large enough frequency will be observed.

• Population statistics will make very important contribution to understanding binary evolution and even stellar evolution.

• Coupled with GAIA (ESA Cornerstone mission follow-on to Hipparcos), LISA can help define spatial structure and stellar distribution of Galaxy.

• For f < 0.001 Hz, only nearest binaries will be resolved; most form an anisotropic noise. Even at higher frequencies, binary signals must be removed accurately to see other weak sources.


20 July 2002


15

Issue: cosmological background

• One of the most fundamental goals of GW detection is the cosmological background from the Big Bang. Best observational evidence we are likely to get about fundamental physics. LISA limit around gw ~ 10-10.

• Standard inflation predicts very weak radiation (gw < 10-14), but some brane scenarios and some scenarios of symmetry breaking can produce observable radiation.

• Backgrounds from astrophysical sources restrict observing range. Possible window around 1 Hz.


20 July 2002


16

LISA follow-on mission• Clear from present science studies that

there are three areas where we want to go beyond LISA.1. Cosmological background2. Angular position improvement for SMBH

mergers3. Intermediate frequency band: 0.1-1.0 Hz

• Relevant now, especially if current LISA could be a component of the next one. Team trying to design in long lifetime, 10 years or more.

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LISA Science

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