认真做好GW190412油田地层解释
Being Careful with the Field Formation Interpretation of GW190412
摘要：
LIGO/Virgo科学合作组织最近宣布探测到一个紧凑物体双星合并，GW 190412，这是第一个质量比为$q\approx0.25$的非对称双星黑洞（BBH）合并。除了质量比之外，该BBH已经显示出具有大约$χ_{\rm eff}\approx0.28$的正有效自旋。假设一个场形成通道，将这个有效自旋与初级BH或次级BH相关联，每个都有其含义：如果BBH的自旋来自初级BH，它会影响BH形成过程中角动量输运的效率。另一方面，如果自旋是由于次级黑洞通过潮汐自旋上升过程引起的，则必须注意：（i）这种过程具有非常短的延迟时间，（ii）随后，它们的局部合并速率由假定的BBH形成金属丰度下的局部恒星形成速率决定。我们表明，从这个通道的预测合并率密度是$\lesssim 0.3~\rm Gpc^{-3} yr^{-1}$和张力与相当高的本地合并率等系统，我们估计从这个单一的事件是$\sim 1.7^{+2.5}_{-1.4}~\rm Gpc^{-3} yr^{-1}$（90\%的置信区间，并假设50天的观测时间）。需要大的出生反冲（$v\gtrsim 500\,{\rm km/s}$）来获得这种具有面内自旋分量的BBH，以解释GW 190412中进动的边缘检测。然而，这只会加剧紧张局势，因为估计的当地合并率将进一步下降。类似地，通过动力学组装形成这样的系统是非常罕见的，这使得这个系统很难用目前公认的BBH形成范式来解释。
英文摘要：
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 $q\approx0.25$. Other than the mass ratio, this BBH has shown to have a positive effective spin of around $χ_{\rm eff}\approx0.28$. 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 has consequences for the efficiency of angular momentum transport in the formation of the BH. If, on the other hand, the spin is due to the secondary BH through tidal spin-up processes, one has to note that (i) such processes have very short delay-times, and (ii) subsequently, their local merger rate is determined by local star formation rate at assumed formation metallicity of the BBH. We show that the predicted merger rate density from this channel is $\lesssim 0.3~\rm Gpc^{-3} yr^{-1}$ and in tension with the rather high local merger rate of such systems which we estimate from this single event to be $\sim 1.7^{+2.5}_{-1.4}~\rm Gpc^{-3} yr^{-1}$ (90\% confidence interval, and assuming 50 days of observing time). Large natal kicks ($v\gtrsim 500\,{\rm km/s}$) would be required to get such BBHs with an 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.
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