My understanding of GW is that they ripple the fabric of the space-time just as accelerating charged particle emits electromagnetic radiation, accelerating massive objects produce gravitational radiation in the form of gravitational waves.

The observed waves was produced from collision of two black holes which then merged to a spinning more massive black hole.

Question 1 : How do gravitational waves escape from black holes even if the light can not? For a logical explanation I assume GW do not come from inside of a black hole and they are emitted as the space-time is distorted with mass.

Question 2 : Suppose a hypothetical single, non-spinning star. Does such a star produce GW?

  • $\begingroup$ the first question seems naive , but it is not trivial even the BHs collide at both $\frac c 2$ ... It will be interesting to compare the answers to the others on the BHs. $\endgroup$
    – user46925
    Feb 13, 2016 at 15:38
  • $\begingroup$ I know the new discovery is exciting, but it's best to do a little research on your own before posing a question in haste. If you just read the wikipedia on gravitational waves I believe it will answer at least your second question - of which the answer is no. The answer to the first question I believe involves the event horizon. Space is warped outside the event horizon from which energy can escape - including gravitational energy. $\endgroup$
    – docscience
    Feb 13, 2016 at 16:58

1 Answer 1


Suppose a hypothetical single, non-spinning star. Does such a star produce GW?

No more than a nonmoving boat floating in a perfectly still ocean produces water waves. Gravitational waves are produced by things actively disturbing the spacetime around them.

More technically, there needs to be a time-varying system with nonzero quadrupole or higher moment. A perfectly spherical object expanding and contracting does not produce gravitational waves, nor do two point masses moving along a line toward and away from each other. However, two masses orbiting each other have a nonzero quadrupole moment and so produce waves.

I assume GW do not come from inside of a black hole

Indeed most of the signal we see clearly does not. The initial "inspiral" portion of the waveform (where the amplitude of the wave is slowly building up) is generated when there are two distinct black holes orbiting one another. It is the combined system, not either black hole individually, that generates the waves.

After merger, we see the "ringdown" phase (where the waveform rapidly diminishes back toward the noise floor). This pattern is produced when the event horizons have merged, so there's only one black hole. Still, the waves don't have to "escape" from inside the black hole. At this point, the black hole has not settled down into a stationary state. The horizon itself, and the surrounding spacetime, are in some sense still vibrating.


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