I read that two huge black holes collided or merged and so it created gravitational waves billion years ago , So now we are able to detect it & detected it. So what is the speed of gravitational wave ? Is it faster than light ? and are there many more to be detected ?
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$\begingroup$ Have you tried Wikipedia? en.wikipedia.org/wiki/Gravitational_wave $\endgroup$– Peter ErwinCommented Sep 14, 2016 at 9:09
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$\begingroup$ There are probably many more to be detected; another merger was detected three months later (announced this past June). $\endgroup$– Peter ErwinCommented Sep 14, 2016 at 9:11
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Gravitational waves travel at the speed of light.
There are many possible sources of gravitational waves. The two confirmed detections so far (14 Sep 2016) are merging black hole binary systems, but sources of (detectable) gravitational waves may include merging neutron stars, short period binaries containing neutron stars or white dwarfs, gamma ray bursters or supernovae.
For a brief introduction see Gravitational Wave Sources at the ALIGO site.
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$\begingroup$ But why? Space expands faster than the speed of light, why can't it ripple it faster too? And if a gravity wave is caused by massive materia interacting in a lumpy star going supernova, or in two massiv material neutron stars colliding, then the GW should move slower because massive materia cannot move that fast. That's my intuition anyway. $\endgroup$ Commented Sep 14, 2016 at 15:24
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1$\begingroup$ @LocalFluff The detected waves were used to infer the initial and final masses of the merging BHs. As GR is fully compliant with causality, that tells you straight away that GWs do not travel faster than light. The speed of the wave and the speed of the object producing it are not directly linked (as indeed they are not in electromagnetism). $\endgroup$– ProfRobCommented Sep 14, 2016 at 15:51