论文标题
小心GW190412的现场形成解释
Being Careful with the Field Formation Interpretation of GW190412
论文作者
论文摘要
Ligo/处女座的科学合作最近宣布检测紧凑的物体二进制合并GW190412，是第一个以质量比$ q \ yboty.25 $的不对称二进制黑洞（BBH）合并。除质量比以外，该BBH的阳性有效自旋约为$χ_ {\ rm eff} \ oft0.28 $。假设有一个田间形成通道，将这种有效自旋与主要BH或次级BH相关联，每个BH具有其含义：如果BBH的自旋形成主要BH，则对BH形成中角动量传输的效率产生了影响。另一方面，旋转是由于二次BH通过潮汐旋转过程引起的，则必须注意，（i）此类过程的延迟时间很短，并且（ii）随后，它们的局部合并速率由BBH的假定形成金属性以局部恒星形成速率确定。我们表明，该通道的预测合并速率密度为$ \ Lessim 0.3〜 \ rm gpc^{ - 3} yr^{ - 1} $，并且与我们从单个事件中估计的此类系统的相当高的本地合并速率紧张，我们估计，$ \ sim 1.7^{+2.5} {+2.5} _ {+2.5} _ {+2.5} _ { - 1.4}} - { - 1.4}} yr^{ - 1} $（90 \％置信区间，并假设观察时间为50天）。要获得具有平面旋转组件的此类BBH，以说明GW190412中的进度的边际检测，需要大型纳塔尔踢（$ v \ gtrsim 500 \，{\ rm km/s} $）。但是，这只会加剧张力，因为估计的本地合并率将进一步降低。同样，通过动力组装形成此类系统非常罕见，这使该系统难以解决当前接受的BBH形成范式。
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.
