Dennis Ugolini, Trinity University Bite of Science Session, TEP 2014 February 13, 2014 Catching the Gravitational Waves

Gravity Misconception #1: Mass Pulls on Mass physicscentral.com/coloringbook On Earth: In general:

Digression: Mirages 1.Light travels by fastest possible route 2.Light travels faster in hotter air hot air not as hot air Your brain interprets light as if it had always been traveling in the direction it arrived blue sky

Gravitational Lensing “Einstein Cross” The bending of light rays Real quasar Galaxy Image of quasar

Warped Space-Time Einstein’s theory of general relativity says that smaller masses travel toward larger masses, not because of an attractive force, but because space is warped toward the larger object.

Gravity Misconception #2: Instantaneous Action Einstein also found that changes in the curvature of space-time will propagate outwards at the speed of light.

Gravity Misconception #3: GR Explains Everything Compact binary mergers But if we can measure the ripples in space-time curvature that reach Earth, we can learn about strong-field general relativity experimentally.

Other Sources  Supernovae?  Dark matter?  Dark energy?  Background from Big Bang?  Who knows what else?

Why are We So Confident? Neutron Binary System PSR   17 / sec ~ 8 hr In 1975, Russell Hulse and Joseph Taylor were cataloguing pulsars when they found something unusual – a pulsar that periodically stopped!

How Big Are They? km  Size in terms of strain, h = ΔL/L  Imagine two neutron stars, each with the mass of our sun, but as big as San Antonio’s Loop 410 freeway  They are in the Virgo cluster of galaxies, about 60 million light years away  They are about to collide, and are spinning around each other 400 times per second (!?!)

That’s REALLY Small! SunEarth L = 1.5 × m Δ L = m h ~ is equivalent to the distance from the Earth to the Sun changing by the width of a single atom!

Interferometry  Uses light interference to measure length difference between the two arms  Each arm is a reflective cavity, effectively increasing arm length

The LIGO Project LIGO: Laser Interferometer Gravitational-Wave Observatory  US project to build GW observatories  Detection, followed by astronomy of gravitational waves  830 collaborators from dozens of institutions  Funded by US National Science Foundation

LIGO-G SMU Physics Seminar, March 29,

The LIGO Observatories LIGO Hanford Observatory (LHO) (4km and 2km in same vacuum) LIGO Livingston Observatory (LLO)

The LIGO beam tubes must be kept at one trillionth of atmospheric pressure! Vacuum System

17 SMU Physics Seminar, March 29, 2010 LIGO-G SeismicInternal thermal Shot noise and pole frequency

Suspended Test Masses Optics are 25 cm diameter, 10 cm thick, 10.7 kg, of high purity fused silica. They must have less than 1 part per million absorption losses. The optics are suspended to attenuate seismic motion above the pendulum frequency.

Length Sensing and Control  Each optic has five magnet and coil assemblies (four on the back, one on the side)  The magnet blocks light from the LED, giving position  Current through the coil creates a magnetic field, allowing mirror control

New Optic Suspensions 40 kg fused silica optics Quadruple suspension with reaction mass Last stage suspended by fused silica ribbons

The Need for Advanced LIGO  Goal: factor of ten improvement in sensitivity at all frequencies  x10 increase in sensitivity = x1000 volume of sky searched  Inspiral event rate from one every few years to one every few days!  Resolution improved for astronomy  Transition began Oct E-LIGO Initial LIGO

Future Timeline ?? LIGO ’05’06’07’08’09’10’11’12’13’14’15’16 S4S5 VSR1VSR2VSR3 S6 GEO-HF VSR4VSR5 S7S8 GEO Virgo Advanced LIGO → Advanced Virgo → AstroWatch

Interferometry Video Interferometer/Interferometer.html

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