november 25, 2002gustavus adolphus college catch the gravity wave: searching for einstein’s...

November 25, 2002 Gustavus Adolphus College

Catch the Gravity Wave:Searching for Einstein’s

Elusive Prediction

Rauha Rahkola, University of Oregon


Special Relativity

• Physics works the same in different reference frames

• Speed of light is constant in all frames

&

General Relativity

– “generalizes” to frames of reference with a0– “special” because a=0


MASS CAUSES SPACE TO CURVE

Einstein’s predictions using GR:

What General Relativity tells us…

verified

– Perihelion shift of Mercury (twice what Newton predicted)

1916

– Light rays are bent near a massive star 1919

– Gravitational waves 1998???


Gravitational Waves

Einstein describes GWs:• Propagate information

(gravitational field) at the speed of light

• Source of energy loss• Two polarizations– ’+’ and ‘×’• Alter the dimensions of space

perpendicular to axis of propagation

Rendering of space stirred by two orbiting black holes:

MOVING MASS CAUSES SPACE TO CURVE DYNAMICALLY


Exaggerated Picture of the Effects of Gravitational Radiation

THIS IS YOUR BRAIN

LIGO

THIS IS A GRAVITY WAVE

Time

THIS IS YOUR BRAIN IN A GRAVITY WAVE

ANY QUESTIONS?


PSR 1913+16:Evidence for GWs

• Slight energy loss (semi-stable orbits)

– r, , T

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

• Circumstantial evidence – not a detection of gravity waves


Sources of Gravity-WavesAll sources have two things in common:• they’re dynamic• they’re asymmetric

Credits: Steve Snowden (supernova remnant);

Kip Thorne (binary black hole diagram)

Supernovae

Binary end-stage

More?


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 about 350 LIGO Science Collaboration members worldwide.


Laser

Beam Splitter

End Mirror End Mirror

ScreenViewing

Sketch of a Michelson Interferometer


Recycling Mirror

Optical

Cavity

4 km or2-1/2

miles

Beam Splitter

Laser

Photodetector

Fabry-Perot-Michelson with Power Recycling


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


What Limits Sensitivityof Interferometers?

• Seismic noise & vibration limit at low frequencies

• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies

• Quantum nature of light (Shot Noise) limits at high frequencies

• Myriad details of the lasers, electronics, etc., can make problems above these levels

Sensitive region


LIGO Observatories


LIGO Schedule

1996 Construction Underway (mostly civil)

1997 Facility Construction (vacuum system)

1998 Interferometer Construction (complete facilities)

1999 Construction Complete (interferometers in vacuum)

2000 Detector Installation (commissioning subsystems)

2001 Commission Interferometers (first coincidences)

2002 Sensitivity studies (initiate LIGO I Science Run)

2003+ LIGO I data run (one year integrated data at h ~ 10-21)

2006+ Begin ‘Advanced LIGO’ installation


What UofO does for LIGO

• Data Characterization (separating the signal from the noise)– monitor the instrument (Global Diagnostics System) – monitor the environment (Physics Environment Monitoring System) – real-time programs to monitor data (Data Monitoring Tool) – track down glitches, frequency resonances (Noise Studies)

• Data Reduction– Start with ~4Mb / s– Reduce to ~1Gb / week (output)

• Data Analysis– Search for correlations between output & the environment– Search for GWs associated with Gamma Ray Bursts (GRBs)


Searching for GWsusing GRBs as triggers

• Gamma ray bursts (GRBs) are high-energy, short duration E/M radiation from extra-galactic sources

Why do we care?

• Gravitational Wave Bursts (GWBs) are possibly emitted from same source as GRBs

• Most probably, GWBs emitted before GRBs

So, we can look for GWs specifically during times we see GRBs!

• GRB sources may be energetic enough to produce GWs that LIGO can see even now


Correlating output fortwo interferometers

Goal: We want to see if evidence for GWs exist in both interferometers simultaneously

• 1 GW Time-domain cross-correlation

• Several GWs Frequency-domain cross-correlation

• Signal is too low for one c.c. value to be significant

…but …

• A distribution of cross-correlation values is stationary over time…

… except in the presence of gravity waves!


SURF’ing w/ LIGO(Catch the Wave, Man!)

• LIGO’s summer undergraduate research fellowship

• Work with a staff scientist @ Caltech or one of the observatories

• 2 ½ months w/ stipend (housing provided at the observatories)

• Spaces are limited – apply now!


Recent Undergraduate Projects

2002 (38 projects)• Mapping of Synthetic Sapphire Optical Absorption at 1064nm• Noise Characterization in the LIGO Livingston 4-km Interferometer• An Improved Template Matching Algorithm for LIGO• An Improved Actuator for Earth-Tide Compensation• Characterization of Glitches in LHO Interferometers

2001 (24 projects)• Automated Measurement of Sideband Power in the 2K

Interferometer• Tool Development for External Trigger Driven Burst Detection• Core Optics Auto-Alignment Sequencer

2000 (25 projects)• Commissioning the Tidal Compensation Servo• Wavefront Sensing for the 40m LIGO Prototype


Benefits for Students

• Learn some general relativity• Probe into current topics in astrophysics and

cosmology (or other fields of physics)• Hone/Increase your programming skills• Experience one of the rising “new” fields of

physics


Summary

• Gravity waves are a consequence of general relativity– Transfer information (curvature of space) at light speed– But, they need a lot of energy (mass) to be produced

• LIGO is a broadband method of detecting gravity waves– Limited by seismic noise (low freq), shot noise (high freq)– Goal is to be sensitive to 1:10-21

• We can look for associations between gravity waves and gamma ray bursts– Use correlated output from two (or more) interferometers– Test the null hypothesis for distributions of cross-correlations

• Plenty of research opportunities for undergraduates (& graduates!)– SURF program (see handout)– Possibly at a graduate school near you! (LIGO home page)– Also hiring operators on site

november 25, 2002gustavus adolphus college catch the gravity wave: searching for einstein’s...

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