sign in sign up
<<
Home , Binary pulsar

2/25/13

The Binary

Gravitaonal waves Predicon of general relavity:

• perturbaons to curvature of me • propagate at

Analogy: dropping a stone (perturbaon) in a pond (spaceme) produces waves (spaceme ripples) that propagate away from the source

1 2/25/13

Gravitaonal waves Sources:

• non- axisymmetric moons of… • massive bodies… • moving close to the speed of light

strong gravitaonal waves

Rotang black hole: NO (axisymmetric)

Rotang neutron with a “mountain” on surface: YES

Binary : YES …strong if the binary is so close that v ~ c

2 2/25/13

Strongest sources of gravitaonal waves:

• merging binaries of compact objects • black hole – black hole (either or supermassive) • black hole – • neutron star – neutron star

Ongoing experiments to detect gravitaonal waves from these sources directly on Earth

No direct detecons yet: but there is strong indirect evidence that gravitaonal waves exist

3 2/25/13

The “Binary Pulsar”

1974: Joe Taylor & Russell Hulse discover a binary pulsar • two neutron stars in a binary • one of them is observed as a radio pulsar • Nobel Prize 1993

Why is this system excing? Pulses from a rotang neutron star are very regular: a near-perfect clock

Radio pulses emied when the neutron star Timing of pulses can is at the “far” side of measure the size of orbit have further to the orbit (+special travel: arrive “late” relavisc effects)

4 2/25/13

No gravitaonal waves:

Orbit is exactly periodic: me between closest approaches to Earth is fixed

Gravitaonal waves: • orbit shrinks (loss of energy) • smaller orbit has shorter period • me between closest approaches gets less with me

5 2/25/13

Through 1988, binary pulsar moment of closest approach got less by 8 seconds

Matches the predicon of gravitaonal wave emission in general relavity

Latest ming measurements

Weisberg et al. (2010)

6 2/25/13

Rao between GR predicon and measurements for this system: 0.997 +/- 0.002

This system, and others discovered subsequently, best tests of general relavity to date: agree with expectaons to few tenths of a percent

Highly confident gravitaonal waves exist, even though we haven’t detected them (yet!)

7