The LIGO/Virgo Scientific Collaboration recently announced the detection of a compact object binary merger , GW190412 , as the first asymmetric binary black hole ( BBH ) merger with mass ratio q \approx 0.25 .
Other than the mass ratio , this BBH has shown to have a positive effective spin of around \chi _ { eff } \approx 0.28 .
Assuming a field formation channel , associating this effective spin to either the primary or the secondary BH each has its implications : If the spin of the BBH comes form the primary BH , it would imply that the angular momentum transport in the formation of massive BHs operates such that high spin massive BHs are born abundantly .
If , on the other hand , the spin is due to the secondary BH through tidal spin up processes , one has to note that such processes have very short delay times and low local star formation rate at sufficiently low metallicities .
We show that the predicted merger rate density from this channel is \lesssim 0.3 ~ { } Gpc ^ { -3 } yr ^ { -1 } and in tension with the rather high local merger rate of such systems which we estimate from this single event to be \sim 2.5 ^ { +3.5 } _ { -0.5 } ~ { } Gpc ^ { -3 } yr ^ { -1 } ( 90 % confidence interval ) .
Large natal kicks ( v \gtrsim 500 { km / s } ) would be required to get such BBHs with in-plane spin component to account for the marginal detection of precession in GW190412 .
However , this would only exacerbate the tension as the estimated local merger rate would be further decreased .
Similarly , the formation of such systems through the dynamical assembly is exceedingly rare , leaving this system a dilemma hard to account for with the currently accepted paradigms of BBH formation .