We look into the abundance of Dual AGN in the largest hydrodynamical simulation from the EAGLE project .
We define a Dual AGN as two active black holes ( BHs ) with a separation below 30 kpc .
We find that only 1 per cent of AGN with L _ { HX } \geq 10 ^ { 42 } \mbox { erg } ~ { } \mbox { s } ^ { -1 } are part of a Dual AGN system at z = 0.8 - 1 .
During the evolution of a typical binary BH system , the rapid variability of the hard X-ray luminosity on Myr time-scales severely limits the detectability of Dual AGN .
To quantify this effect , we calculate a probability of detection , t _ { on } / t _ { 30 } , where t _ { 30 } is the time in which the two black holes are separated at distances below 30 kpc and t _ { on } , the time that both AGN are visible ( e.g .
when both AGN have L _ { HX } \geq 10 ^ { 42 } \mbox { erg } ~ { } \mbox { s } ^ { -1 } ) in this period .
We find that the average fraction of visible Dual systems is 3 per cent .
The visible Dual AGN distribution as a function of BH separation presents a pronounced peak at \sim 20 kpc that can be understood as a result of the rapid orbital decay of the host galaxies after their first encounter .
We also find that 75 per cent of the host galaxies have recently undergone or are undergoing a merger with stellar mass ratio \geq 0.1 .
Finally , we find that the fraction of visible Dual AGN increases with redshift as found in observations .