- #1

JD_PM

- 1,131

- 158

- TL;DR Summary
- I want to understand how does GR predict the existence of gravitational waves.

I am reading the following paper on the basic physics of a binary black hole merger: https://arxiv.org/ftp/arxiv/papers/1608/1608.01940.pdf

Imagine two black holes orbiting each other until a point they merge.

As you can see in Figure 1, the wave period is decreasing and thus the frequency of oscillation increases. Then, around time 0.43 s there is a drop of the frequency. I interpret this drop as the acceleration of the system being zero (the two orbiting black holes merge and the resulting black hole has a lower velocity).

This is what I have in mind: two black holes orbit each other and they are being accelerated. Thus they will emit gravitational radiation; spacetime is getting curved more and more as time passes and that means that waves of greater amplitude and frequency are being generated (these are the gravitational waves if I am not mistaken). It makes sense for me that the frequency increases as they approach; the waves become more energetic (shorter wavelength greater frequency. The same happens with light; for instance, gamma rays are more energetic than X-Rays and thus higher frequency).

My question is:

Why aren't Livingston and Hanford detectors showing a more progressive increase in frequency? Shouldn't we expect a final clearly higher peak (when the two black holes are just about to merge and thus where the spacetime gets more bent)?

I am starting with GR and gravitational waves so please point out any mistakes you see in my interpretation above.

Imagine two black holes orbiting each other until a point they merge.

As you can see in Figure 1, the wave period is decreasing and thus the frequency of oscillation increases. Then, around time 0.43 s there is a drop of the frequency. I interpret this drop as the acceleration of the system being zero (the two orbiting black holes merge and the resulting black hole has a lower velocity).

This is what I have in mind: two black holes orbit each other and they are being accelerated. Thus they will emit gravitational radiation; spacetime is getting curved more and more as time passes and that means that waves of greater amplitude and frequency are being generated (these are the gravitational waves if I am not mistaken). It makes sense for me that the frequency increases as they approach; the waves become more energetic (shorter wavelength greater frequency. The same happens with light; for instance, gamma rays are more energetic than X-Rays and thus higher frequency).

My question is:

Why aren't Livingston and Hanford detectors showing a more progressive increase in frequency? Shouldn't we expect a final clearly higher peak (when the two black holes are just about to merge and thus where the spacetime gets more bent)?

I am starting with GR and gravitational waves so please point out any mistakes you see in my interpretation above.