LIGO-G020518-01-W What If We Could Listen to the Stars? LIGO Hanford Observatory

LIGO-G020518-01-W

What If We Could Listen to the Stars?

LIGO Hanford Observatory

LIGO: Portal to Spacetime 2LIGO-G020518-01-W

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




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.


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


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


LIGO Laboratory & Science Collaboration

LIGO Laboratory (Caltech/MIT) runs observatories and research/support facilities at Caltech/MIT

LIGO Scientific Collaboration is the body that defines and pursues LIGO science goals» >400 members at 44 institutions worldwide (including LIGO Lab)

» Includes GEO600 members & data sharing

» Working groups in detector technology advancement, detector characterization and astrophysical analyses

» Memoranda of understanding define duties and access to LIGO data


Big Question: What is the universe like now and what is its future?

New and profound questions exist after nearly 400 years of optical astronomy

» 1850’s Olber’s Paradox: “Why is the night sky dark?”» 1920’s Milky Way discovered to be just another galaxy» 1930’s Hubble discovers expansion of the universe; Zwicky finds shortage of

luminous matter in galaxy clusters» mid 20th century “Big Bang” hypothesis becomes a theory, predicting origin of

the elements by nucleosynthesis and existence of relic light (cosmic microwave background) from era of atom formation

» 1960’s First detection of relic light from early universe» 1970’s Vera Rubin documents “missing mass”, a.k.a. “dark matter” in

individual galaxies» 1990’s First images of early universe made with relic light» 2003 High-resolution images imply universe is 13.7 billion years old and

composed of 4% normal matter, 24% dark matter and 72% dark energy; 1st stars formed 200 million years after big bang.

We hope to open a new channel to help study this and other mysteries


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


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!


John Wheeler’s Picture of General Relativity Theory


General Relativity: A Picture Worth a Thousand Words


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


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:

LIGO-G020518-01-W

What Phenomena Do We Expect to Study With LIGO?


Gravitational Collapse and Its Outcomes Present LIGO Opportunities

fGW > few Hz accessible from earth

fGW < several kHz interesting for compact objects


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


Supernovae

time evolution

The Brilliant Deaths of Stars

Images from NASA High EnergyAstrophysics Research Archive


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


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


Catching WavesFrom Black Holes

Sketches courtesy of Kip Thorne


Sounds of Compact Star Inspirals

Neutron-star binary inspiral:

Black-hole binary inspiral:


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.


Searching for Echoesfrom Very Early Universe

Sketch courtesy of Kip Thorne

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How does LIGO detect spacetime vibrations?


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.


Laser

Beam Splitter

End Mirror End Mirror

ScreenViewing

Sketch of a Michelson Interferometer


Sensing the Effect of a Gravitational Wave

Laser

signal

Gravitational wave changes arm lengths and amount of light in signal

Change in arm length is 10-18 meters,

or about 2/10,000,000,000,000,000

inches


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


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


Suspended Mirror Approximates a Free Mass Above Resonance


Vacuum Chambers Provide Quiet Homes for Mirrors

View inside Corner Station

Standing at vertex beam splitter


Why is Locking Difficult?

One meter, about 40 inches

Human hair, about 100 microns000,10

Wavelength of light, about 1 micron100

LIGO sensitivity, 10-18 meter000,1

Nuclear diameter, 10-15 meter000,100

Atomic diameter, 10-10 meter000,10

Earthtides, about 100 microns

Microseismic motion, about 1 micron

Precision required to lock, about 10-10 meter


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


Binary Neutron Stars:S1 Range

Image: R. Powell


Binary Neutron Stars:S2 Range

Image: R. Powell

S1 Range


Binary Neutron Stars:Initial LIGO Target Range

Image: R. Powell

S2 Range


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


Binary Neutron Stars:AdLIGO Range

Image: R. Powell

LIGO Range


Stops on walking tour:» Show camera images on screen 2 in auditorium

» Weber Bar

» Beam Tube enclosure & tube segment

» Overpass

» Control Room


Camera shots

These are images that come off of the optics inside the vacuum chambers

We use a fat beam to minimize dispersion as the beam travels

The graininess that you see is due to slight imperfections in the mirrors

When we lose lock, the reflections disappear as the light ceases to resonate in the arms


Weber Bar

One of four bars that Joseph Weber ran simultaneously in 1969 and afterwards to detect grav waves

Weber pioneered the field at the University of Maryland Bar is a gift to LIGO from UM 5-ft length, 3-ft diameter, 6500 pounds of Al alloy A grav wave would stretch the atoms out of their positions. They would then recoil from the

elastic inter-atomic forces. This effect, taken over all the atoms in the bar, would produce a ringing in the bar like what occurs in a tuning fork. These vibrations would be transmitted to the piezo crystals that are glued to the top of the bar and amplified up to a measurable voltage

Bars are narrow-band detectors. Weber searched for GW waves at 1660 Hz in his 1969 paper

Using a different bar in 1966, Weber showed that he could measure a stretch in the bar that was the width of an atom (strain of 10^16).

1969 and subsequent reports of successful detections were not corraborated LIGO is a broad-band microphone, sensitive to a range of frequencies. Separate mirrors yield

a longer baseline and greater sensitivity. Interferometry is a more sensitive technology


Beam Tube Segment

Tube construction was undertaken by CBI 1-foot width 3/8” low-hydrogen steel was robotically spiral-welded at the Pasco facility into

60-foot sections Sections were trucked to the site and welded together in a portable clean room that moved

down the arms Each section was leak-checked, as were the completed tubes Each tube was baked out through electrical heating (~200 C) for ~one month Tubes are insulated and covered by several hundred concrete beam tube enclosures Arms are held at about a trillionth of an atmosphere of vacuum Beams from two interferometers run side-by-side in the tube Tube diameter can accommodate additional beams Bellows are inserted periodically on the arms to allow for expansion/contraction. Horizontal supports hold the tube up


Overpass

Light stays in the arms for roughly a millisecond during lock ~100 round trips of the light in the arms shrinks and sharpens the dark fringe, increasing

our sensitivity Largest-amplitude ground motion is the earth tides, which stretch the arms by ~1/3 mm

each tidal cycle. We control the laser wavelength and use fine actuators at the end stations to make sure

that the light sees a consistent arm length The microseism is smaller than the tides, somewhat less than a micron, but is much faster

(~micron per second). Microseisms are produced by the energy of ocean waves which couples into the sea floor and moves out across land masses

We use the voice coil actuators to hold off the microseism. We are implementing a feed-forward strategy to use the tidal actuators to offset the microseism as well

We have seismometers in each building and we monitor a host of other environmental effects


Control Room

Separate control stations for each interferometer All interferometer control is delivered from here via computers ~12,000 data channels send data to the control room. A small subset of these are data

from the interferometer itself Additional computers are dedicated to the vacuum system, the electronic log and data

monitoring The room next door collects and stores data as it comes in. The Linux cluster in the

auditorium building can hold terabytes of data and can be accessed by collaborators for analysis of fresh data.

Data is written to tape and archived at Caltech

Documents

LIGO-G020518-01-W What If We Could Listen to the Stars? LIGO Hanford Observatory