Transcript What are Gravitational Waves? - Glasgow Experimental Particle

Institute for Gravitational Research
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Director: Jim Hough
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+ 4 Academic Staff
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+ Joint academic staff member with Astronomy Group (Graham Woan)
+ 8 Research Assistants / Hon Research Fellow
+ 6 Postgraduate Research Students (1 joint with Astronomy Group)
+ 7 Technical, Engineering and Research Associate support staff
+ Secretary
Aim:
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To observe gravitational waves using laser interferometric techniques
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on earth (GEO 600, Advanced LIGO, EURO), and
in space (LISA)
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Gravitational waves
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Propagating ripples in the curvature of spacetime causing timevarying strains in space
Produced in the form of
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Bursts
 Compact binary coalescences: NS/NS, NS/BH, BH/BH
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Stellar collapse (asymmetric) to NS or BH
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Black hole interactions
Continuous waves
 Pulsars
 Binary orbits long before coalescence
 Low mass X-ray binaries (e.g. SCO X1)
 Modes and Instabilities of neutron stars
Stochastic background
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Interactions in the early Universe
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The gravitational waves spectrum
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As in the electromagnetic case, gravitational wave signals cover a wide range
of frequencies. Ground-based detectors are noise-limited to operation above
~10 Hz ; space-based detectors are required for lower frequency observations
Gravity
gradient
wall
ADVANCED GROUND - BASED
DETECTORS
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Effect of a gravitational wave
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Modulation of the proper distance between free test particles
A gravitational wave of amplitude h, will produce a strain L  h
L 2
between masses a distance L apart
Detection conveniently done by monitoring the distance between “free”
masses using laser interferometry to measure the fluctuations in relative
length of two approximately orthogonal arms formed between suitably
“isolated” mirrors
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Detectability ?
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The 1st generation detectors under construction are optimised for the “audio
band” – above 10Hz
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These may well make the first detections
Plans for 2nd generation interferometers (2006?) are well advanced, and plans
for 3rd generation detectors (2010?) are now being considered
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Each generation is planned to have improved by  10 in amplitude,  100 in energy
and  1000 in volume of space searched
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These should make frequent detections
LISA is being developed for a launch around 2011 as a joint ESA-NASA mission
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LISA will open the low-frequency window (below 1Hz), where it must make many
detections, some of which will be at very high signal-to-noise ratios
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Interferometrically sensed
gravitational wave detectors
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5 detector systems approved / now being developed worldwide:
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LIGO (USA) - 2 detectors of 4km arm length + 1 detector of 2km arm
length - Washington State and Louisiana
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VIRGO (Italy/France) - 1 detector of 3km arm length - Cascina, near Pisa
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GEO 600 (UK/Germany) - 1 detector of 600m arm length - Hannover
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TAMA 300 (Japan) - 1 detector of 300m arm length - Tokyo
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LISA - Spaceborne detector of 5 x 106 km arm length
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GEO 600
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GEO 600
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Initial GEO 600 strategy:
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to build a low cost detector of comparable sensitivity to the initial
LIGO and VIRGO detectors
to take part in gravitational wave searches in coincidence with these
systems
Unique GEO 600 design technology to make this possible:
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Advanced suspension technology for low thermal noise
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Advanced optics configuration – signal recycling
Disadvantage:
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for geographical reasons the GEO armlength (600m) cannot be
extended to the 3/4kms of VIRGO/LIGO
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Monolithic silica suspensions
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GEO600 is the first interferometer to use such suspensions to reduce
thermal noise
The technology offers ~10 x lower noise than the alternative designs
that are used in the other initial interferometers
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Advanced interferometry
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One of the fundamental limits
to interferometer sensitivity is
photon shot noise
mirror
Power recycling effectively
increases the laser power
Signal recycling – a Glasgow
invention – trades bandwidth
for improved sensitivity
beamsplitter
laser and
injection
optics
mirror
detector
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With signal recycling the
frequency and bandwidth
of the optimum sensitivity
are easily adjustable
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Timescales - first detectors
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GEO and LIGO
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TAMA
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Main interferometer under development during 2001 / 2002
First coincident run took place over New Year 2002
Further runs planned for summer and autumn 2002
Data exchange with LIGO agreed : GEO is a member of the LIGO I
Consortium based on data exchange
some data taking for periods over past year and coincidence with
LIGO and GEO soon
VIRGO
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First operation scheduled for 2003
Data exchange agreement being discussed
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GEO and LIGO begin to work!
Strain sensitivity of GEO interferometer
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GEO not yet configured with final
optics and signal recycling still to
be installed
Preliminary result from Glasgow
analysis of GEO data: upper limit
for GW from PSR - J1939+2134
h0 < 10-20
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Preliminary snapshots of GEO
and LIGO noise spectra
As expected, the initial
performance of GEO and of
LIGO is still some way from
their design sensitivities, but
noise studies and improvements
are progressing well
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From initial to Advanced LIGO
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Signal recycling is added to
upgrade the interferometer
hrms = h(f) f ~10 h(f)
configuration
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Initial interferometers
GEO 600 style silica
suspension technology and
multiple stage pendulums
Open up wider band
replace the current wire-loop
15 in h
~3000 in rate
single stage suspensions
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Sapphire optics are proposed
for low thermal noise (small
Advanced interferometers
Reshape
noise
mechanical dissipation) and
high optical power handling
(high ratio of conductivity to
dn/dT)
Kip S. Thorne
California Institute of Technology
used with permission
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The Glasgow rôle in Advanced LIGO
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Technologies under development in GEO are
essential ingredients of Advanced LIGO
In recognition of this, LIGO have offered GEO
partnership in Advanced LIGO for a very
modest financial contribution
Glasgow is undertaking key elements of the
enabling research for Advanced LIGO, with the
IGR R&D programme being coordinated by the
LIGO Scientific Collaboration working with the
LIGO laboratory
LIGO Hanford
The IGR:
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was invited to undertake an experimental investigation of signal recycling applied to
suspended-optics interferometers (based in our new JIF-funded laboratory)
is centrally involved in the development of GEO fused-silica suspension technology
for application in Advanced LIGO
cooperates in the investigations into mechanical losses in fused-silica and sapphire
mirrors for use in Advanced LIGO
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Preparing for post-Advanced LIGO
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The IGR plans research in
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materials/Thermal Noise research for future detectors – e.g. Euro
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direct measurement of thermal noise in samples with
inhomogeneous loss
novel interferometry
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silicon at low temperature
new signal recycling interferometer topologies
all reflective interferometer systems
… and is also engaged on ESA TRP-funded contracts on
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optical bench design and construction for SMART 2
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phase readout systems for LISA
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Timescales
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Advanced LIGO
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Suspensions developed from GEO
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Interferometry developed from GEO
GEO upgrade
2006-2009
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Silicon test masses at low temperature
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All reflective interferometry
EURO development
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2003-2009
£4M
£12M+
Long baseline, based on GEO upgrade?
SMART 2 and LISA
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2008 onwards
£6M
2006/2011
£12M+
Optical design and construction
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Conclusion
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The IGR has a clear 15 year strategy for the initiation and
development of the field of gravitational wave astronomy
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GEO proves advanced technology and takes part in initial gw searches
The contribution of GEO technology buys the UK a pivotal position in
the development and use of Advanced LIGO
Glasgow expertise in high precision interferometry and in ultra-stable
optical construction techniques ensures a prominent rôle in the space
gravitational wave detector, LISA, and in its precursor demonstrator
mission, SMART 2
The evolution of GEO to an upgraded system allows proving of
emerging technologies and materials
An upgraded GEO places the UK in a compelling position to play a
lead rôle in a large scale European detector in the post-Advanced
LIGO era
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