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Gravitational Waves and LIGO

What is a Gravitational Wave? What are the sources of GW? How can we detect them? LIGO Problems with detection What can we learn from them?. Gravitational Waves and LIGO. EINSTEIN VS NEWTON. Newtonian Gravity.

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Gravitational Waves and LIGO

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  1. What is a Gravitational Wave? • What are the sources of GW? • How can we detect them? • LIGO • Problems with detection • What can we learn from them? Gravitational Waves and LIGO

  2. EINSTEIN VS NEWTON

  3. Newtonian Gravity • Force is proportional to the mass of the bodies and inversely proportional to thee square of their separation. • Is this enough? • Not really. • What is the effect of a very rapid change? • Ex. 2 stars collide or a star explodes – there is a change in the mass distribution, the presence or absence of a star where there was one before has to be communicated throughout the whole universe. • There is no way for that information to take some finite amount of time and hence with Newton's view on gravity the entire universe knows instantaneously. • Problem of action at a distance

  4. Einstein! • Special Relativity (1906) • Distances in space and time change between observers moving relative to one another but the space time interval remains invariant. (speed of light =c) • ds^2 = dx^2 + dy^2 – c^2 * dt^2 • Hence space and time are not viewed as separate but rather 4D space-time. • (1916) included the effect of gravitation. • Gravity is described as a “warpage” of space time. • Ex. Bowling ball on rubber sheet (fabric)

  5. What are Gravitational Waves and where do they come from?? • You can describe GW as “ripples in space time” • They are produced by massive objects traveling at near relativistic speeds. • Some examples are: I The binary orbit of two black holes II A merge of two galaxies III Two neutron stars in an inspiral and orbit.

  6. Compare EM and G radiation: • The most common source of GW is two massive objects orbiting each other. • The equation for amplitude in the Earth Sun System is: EM • accelerating charge • Accelerating mass Gravitational • So a typical amplitude of a GW would be • This shows that you need massive bodies traveling at high speed to create any significant form of gravitational radiation. • Hence terrestrial sources are too weak.

  7. Detecting GW • When there is an acceptable source of GW. • This direct detection is the goal of several large experiments around the world. • Why would we want to detect GW? • They provide more information about systems. • They give us information we can’t see with light or radio waves • The provide a test for Einstein’s Theory of Relativity. • The great challenge of this type of detection is the small effect the waves have on the detector. And as we saw before, amplitude falls off inverse of the distance from the source • Hence the detectors in LIGO must be very sensitive.

  8. LIGO • LIGO – Laser Interferometer Gravitational Wave Observatory. • Each consists of two light storage arms which are 4 km in length and 90 degrees to each other. • The GW causes the phase difference to vary by: • Stretching • Compressing • TWO LOCATIONS • Hanford, WA. • Livinston, LA • LIGO is sponsored by the NSF • $365 Million. • Largest and most ambitious project funded by the NSF

  9. LIGO – how does it work? • Pre-stabilized laser emits a 10W beam and is passed through a beam splitter. • As a GW passes the space-time fabric is altered. • This length change will cause the light currently in the cavity to be slightly out of phase with the incoming light. • If the beam is out of phase, some light will arrive at the photo diode indicating a signal

  10. Problems with Detection • Interferometry is limited by three fundamental noise sources. • Seismic noise • Thermal • Shot LIGO I – Noise Floor To Reduce some of these noise sources: • The Beam Tube must be in a high vacuum to minimize phase noise. • All optical components must be in high vacuum • Seismic Isolation Stack

  11. What can we Learn from GW? • Space-time of the universe is filled with vibrations: Einstein’s Symphony. • LIGO will provide basic tests for General Relativity and test the invariant speed of light. • Learn more about the history of the universe. • We can learn more about things that are unable to be seen with light or radio waves. • Allows for new and exciting discoveries.

  12. Einstein@Home! • Check this: • http://einstein.phys.uwm.edu/ How to get involved? • Einstein@Home is a program that uses your computer's idle time to search for spinning neutron stars (also called pulsars) using data from the LIGO and GEO gravitational wave detectors. • Einstein@Home is a World Year of Physics 2005 project supported by the American Physical Society (APS) and by a number of international organizations.

  13. References • http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GenRelativity.html • http://imagine.gsfc.nasa.gov/docs/features/topics/gwaves/gwaves.html • http://en.wikipedia.org/wiki/Gravitational_wave • http://einstein.phys.uwm.edu/ • http://astrogravs.gsfc.nasa.gov • http://lisa.jpl.nasa.gov/documents/ppa2-09.pdf • http://www.ligo.caltech.edu • http://www.geo600.uni-hannover.de/ • http://www.virgo.infn.it/ • http://tamago.mtk.nao.ac.jp/ • http://www.anu.edu.au/Physics/ACIGA/

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