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Galaxy Evolution and Gravitational Waves, Part II

4 Apr 2014, 01:05 UTC
Galaxy Evolution and Gravitational Waves, Part II
(200 words excerpt, click title or image to see full post)

This post is a continuation from Part I last week. It turns out that there is another way to detect gravitational waves (GWs) without laser interferometers such as LIGO: once again, through pulsars, except this time in a way that directly demonstrates the presence of gravitational waves nearby the earth. (And it will be particularly suited for supermassive black hole GW detection, as I’ll explain later.) This method is entirely different from the indirect method I spoke of earlier that won Russell Hulse and Joseph Taylor the Nobel Prize in Physics in 1993, but it too relies on the fact that pulsars emit very regular pulses. Imagine a distant (single) pulsar rotating like a lighthouse and sending trains of regular pulses propagating through space and eventually reaching us. Because the timing, and thus the distance, between lightspeed-propagating pulses is very regular, these interstellar radio waves themselves are like a very long ruler! Should there be a stretching of space at or around the earth, a careful pulsar astronomer will find that the number of pulses received per second (typically on the order of a thousand per second) decreases slightly, then increases slightly, as a gravitational wave stretches the fabric of spacetime back and forth. (Note that the gravitational wave I’m referring to otherwise has nothing to do whatsoever with the ...

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