The LIGO/Virgo collaboration has reported the detection of GW190412 , a black hole-black hole ( BH-BH ) merger with the most unequal masses to date : m _ { 1 } = 24.4 – 34.7 { ~ { } M } _ { \odot } and m _ { 2 } = 7.4 – 10.1 { ~ { } M } _ { \odot } , corresponding to a mass ratio of q = 0.21 – 0.41 ( 90 \% probability range ) .
Additionally , GW190412 ’ s effective spin was estimated to be \chi _ { eff } = 0.14 – 0.34 , with the spin of the primary BH in the range a _ { spin } = 0.17 – 0.59 .
Based on this and prior detections , \gtrsim 10 \% of BH-BH mergers have q \lesssim 0.4 .
Major BH-BH formation channels ( i.e. , dynamics in dense stellar systems , classical isolated binary evolution , or chemically homogeneous evolution ) tend to produce BH-BH mergers with comparable masses ( typically with q \gtrsim 0.5 ) .
Here we test whether the classical isolated binary evolution channel can produce mergers resembling GW190412 .
We show that our standard binary evolution scenario , with the typical assumptions on input physics we have used in the past , produces such mergers .
We provide an explicit example of an unequal mass BH-BH merger , which forms at low metallicity ( Z = 0.002 ; \sim 10 \% { ~ { } Z } _ { \odot } ) from two massive stars ( M _ { ZAMS, 1 } = 77 { ~ { } M } _ { \odot } and M _ { ZAMS, 2 } = 35 { ~ { } M } _ { \odot } ) and results in a BH-BH merger with m _ { 1 } = 27.0 { ~ { } M } _ { \odot } , m _ { 2 } = 9.9 { ~ { } M } _ { \odot } ( q = 0.37 ) , with primary black hole spin a _ { spin } = 0.19 and an effective spin parameter \chi _ { eff } = 0.335 .
For this particular model of the input physics the overall BH-BH merger rate density in the local Universe ( z \sim 0 ) is : 73.5 { ~ { } Gpc } ^ { -3 } { ~ { } yr } ^ { -1 } , while for systems with q < 0.21 , 0.28 , 0.41 , { and } 0.59 the rate density is : 0.01 , 0.12 , 6.8 , { and } 22.2 { ~ { } Gpc } ^ { -3 } { ~ { } yr } ^ { -1 } , respectively .
The results from our standard model are consistent with the masses and spins of the black holes in GW190412 , as well as with the LIGO/Virgo estimate of the fraction of unequal-mass BH-BH mergers .