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Recent calculations agree that a merging pair of supermassive black holes can emit enough gravitational waves to eject themselves from a galaxy. Could NGCC 1277, a small galaxy with a 17 billion solar-mass black hole (see the Nature article), be the result of such an ejection? The black hole would have had to drag along, or gather up, enough additional matter to form/constitute the small galaxy. Is this plausible, or at least possible? |
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A scenario like how you describe is definitely consistent with results form numerical relativity. The key point is that almost half of the total power radiated by the gravitational waves in a merger event is radiated during the last half-orbit of the inspiraling holes. This makes the gravitational wave profile's power heavily asymmetric, which causes a net momentum to be imparted to the merged BH. Interestingly, this 'kick velocity' is typically relativistically small, but astronomically large, and, like you said, can often be faster than the escape velocity from the galaxy (note that, in contrast to intuition with the solar system, the masses of the central SMBH are typically between 1/10 and 1/100 of the total mass of the galaxy, so the effect of the SMBH on things like escape velocity is smaller than you would think), while retaining any stars and gas bound to the central object with an escape velocity less than the kick velocity. That said, I'm no observationalist, so I can't tell you much about the features of this particular system. The details of this qualitative description are computationally beyond what is appropriate for stack exchange (unless someone cleverer than me can throw something quantitative together), so I have to leave the description qualitative. |
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