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What If We Could Listen to the Stars?

Fred Raab

LIGO Hanford Observatory

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LIGO’s Mission is to Open a New Portal on the Universe

In 1609 Galileo viewed the sky through a 20X telescope and gave birth to modern astronomy» The boost from “naked-eye” astronomy revolutionized humanity’s

view of the cosmos & astronomers have “looked” into space to uncover the natural history of our universe

LIGO’s quest is to create a radically new way to perceive the universe, by directly listening to the vibrations of space itself

LIGO consists of large, earth-based, detectors that will act like huge microphones, listening for the most violent events in the universe

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LIGO (Washington) LIGO (Louisiana)

The Laser InterferometerGravitational-Wave Observatory

Brought to you by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 500 LIGO Scientific Collaboration members worldwide.

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2998 km

(+/- 10 ms)

CIT

MIT

LIGO Laboratories Are Unique National Facilities

Observatories at Hanford, WA (LHO) & Livingston, LA (LLO)

Support Facilities @ Caltech & MIT campuses

LHO

LLO

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Part of Future International Detector Network

LIGO

Simultaneously detect signal (within msec)

detection confidence locate the sources

decompose the polarization of gravitational waves

GEO VirgoTAMA

AIGO

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Big Questions for 21st Century Science

Images of light from Big Bang imply 95% of the universe is composed of dark matter and dark energy. What is this stuff?

The expansion of the universe is speeding up. Is it blowing apart?

There are immense black holes at the centers of galaxies. How did they

form?

What was it like at the birth of space and time?

WMAP Image of Relic Light from Big Bang

Hubble Ultra-Deep Field

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A Slight Problem

Regardless of what you see on Star Trek, the vacuum of interstellar space does not transmit conventional

sound waves effectively.

Don’t worry, we’ll work around that!

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John Wheeler’s Picture of General Relativity Theory

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General Relativity: A Picture Worth a Thousand Words

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The New Wrinkle on Equivalence

Not only the path of matter, but even the path of light is affected by gravity from massive objects

Einstein Cross

Photo credit: NASA and ESA

A massive object shifts apparent position of a star

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Gravitational Waves

Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy

Rendering of space stirred by two orbiting black holes:

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Gravitational Collapse and Its Outcomes Present LIGO Opportunities

fGW > few Hz accessible from earth

fGW < several kHz interesting for compact objects

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Supernova: Death of a Massive Star

•Spacequake should preceed optical display by ½ day

•Leaves behind compact stellar core, e.g., neutron star, black hole

•Strength of waves depends on asymmetry in collapse

•Observed neutron star motions indicate some asymmetry present

•Simulations do not succeed from initiation to explosions

Credit: Dana Berry, NASA

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The “Undead” Corpses of Stars:Neutron Stars and Black Holes

Neutron stars have a mass equivalent to 1.4 suns packed into a ball 10 miles in diameter, enormous magnetic fields and high spin rates

Black holes are the extreme edges of the space-time fabric

Artist: Walt Feimer, Space Telescope Science Institute

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Gravitational-Wave Emission May be the “Regulator” for Accreting Neutron Stars

•Neutron stars spin up when they accrete matter from a companion

•Observed neutron star spins “max out” at ~700 Hz

•Gravitational waves are suspected to balance angular momentum from accreting matter

Credit: Dana Berry, NASA

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Catching WavesFrom Black Holes

Sketches courtesy of Kip Thorne

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Detection of Energy Loss Caused By Gravitational Radiation

In 1974, J. Taylor and R. Hulse discovered a pulsar orbiting a companion neutron star. This “binary pulsar” provides some of the best tests of General Relativity. Theory predicts the orbital period of 8 hours should change as energy is carried away by gravitational waves.

Taylor and Hulse were awarded the 1993 Nobel Prize for Physics for this work.

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Sounds of Compact Star Inspirals

Neutron-star binary inspiral:

Black-hole binary inspiral:

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How does LIGO detect spacetime vibrations?

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Important Signature of Gravitational Waves

Gravitational waves shrink space along one axis perpendicular to the wave direction as they stretch space along another axis perpendicular both to the shrink axis and to the wave direction.

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Laser

Beam Splitter

End Mirror End Mirror

ScreenViewing

Sketch of a Michelson Interferometer

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Core Optics Suspension and Control

Local sensors/actuators provide damping and control forces

Mirror is balanced on 1/100th inchdiameter wire to 1/100th degree of arc

Optics suspended as simple pendulums

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How Small is 10-18 Meter?

Wavelength of light, about 1 micron100

One meter, about 40 inches

Human hair, about 100 microns000,10

LIGO sensitivity, 10-18 meter000,1

Nuclear diameter, 10-15 meter000,100

Atomic diameter, 10-10 meter000,10

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Vacuum Chambers Provide Quiet Homes for Mirrors

View inside Corner Station

Standing at vertex beam splitter

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And despite a few difficulties, science runs started in 2002…

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Binary Neutron Stars:S1 Range

Image: R. Powell

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Binary Neutron Stars:S2 Range

Image: R. Powell

S1 Range

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Binary Neutron Stars:Initial LIGO Target Range

Image: R. Powell

S2 Range

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What’s next? Advanced LIGO…Major technological differences between LIGO and Advanced LIGO

Initial Interferometers

Advanced Interferometers

Open up wider band

ReshapeNoise

Quadruple pendulum

Sapphire optics

Silica suspension fibers

Advanced interferometry

Signal recycling

Active vibration isolation systems

High power laser (180W)

40kg

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Binary Neutron Stars:AdLIGO Range

Image: R. Powell

LIGO Range