Physics 2C Lecture 27

Physics 2c Lecture 27

Some fun stuff

This is extra material, not tested on any exam! Making gravity waves

Imagine the yellow mass to explode. As it explodes, the distortion of space time disappears, and a wave ripple propagates through space like a wave on water. Gravity waves

A gravity wave passing you stretches space. Think of it as an oscillatory pulling of a square cloth along its two diagonals. Gravity wave detection

A gravity wave passing you stretches space. This is measured as a distance difference between the two arms of the Michelson interferometer.

In addition, there’s another interferometer in Italy, called VIRGO, and more are being built in Japan, Australia, .... Arial view LIGO principle Gravity wave signal at mid station is ½ the amplitude of the end station. Coincidence of two signals required to discriminate against noise.

Sensitivity vs frequency

10-19m

To set the scale, the diameter of a proton is roughly 10-15m !!! LIGO Science

● So far only science impact via non-observation of gravity waves.

– Constraint on shape of Neutron star.

– Constraint on gamma ray burst origin.

● Planning for upgrade of instrument by 2014

– “We anticipate that this new instrument will see gravitational wave sources possibly on a daily basis, with excellent signal strengths, allowing details of the waveforms to be observed and compared with theories of neutron stars, black holes, and other astrophysical objects moving near the speed of light," says Jay Marx of the California Institute of Technology, executive director of the LIGO Laboratory. And if that isn’t futuristic enough …

● http://lisa.nasa.gov/

● A gravitational wave observatory in space! Switching topic Radio Astronomy The dish is the size of a small mountain, or lake. Diffraction Limit

Two sources 1,2 can be resolved as long as their diffraction patterns don't overlap too much.

Diffraction Limit Diffraction Limit - example photo -

For circular apertures, Rayleigh criterion becomes:

θmin ≥ 1.22 λ/D D = aperture diameter The ALMA Telescope Array

http://www.almaobservatory.org/ MERLIN, an array of radio telescopes across Britain. EVN Interferometry on a global Scale

http://www.evlbi.org/ Radio telescopes throughout the world do interferometry together. EVN Interferometry on a global Scale

http://www.evlbi.org/ Radio telescopes throughout the world do interferometry together. EVN Press Release from October 4th 2004

Object as viewed by MERLIN Same object as viewed by EVN VLA in New Mexico & Satellite HALCA

HALCA has only 8m diameter

http://en.wikipedia.org/wiki/HALCA

Comparing resolution of a Quasar with VLA and a combo of VLA and HALCA Top is image from earth based VLBI

Bottom image is a zoom of the image once HALCA is added to the interferometry.

Excellent angular resolution is especially important when studying binary objects, and/or the physics of Active Galactive Nuclei, where people are trying to understand the physics that produces the “gigantic jets” observed. Spectr-R

On September 27, 2011, the Spektr-R telescope started scientific observations capturing its "first light" from the brightest natural radio source in the sky known as Cassiopeia A, an ancient exploded star.

http://www.russianspaceweb.com/ spektr_r_mission.html