PKS 2131-021

PKS 2131-021 is quasar and a BL Lacerate object, producing an astrophysical jet. lt is located in the constellation Aquarius and classified as a blazar, a type of active galactic nucleus whose relativistic jet points in the direction towards Earth.

Redshift estimation for PKS 2131-021
The redshift of PKS 2131-021 is 1.285, estimating the quasar to be located about 8.5 billion light-years away. For more consistency according to researchers, they applied a cosmological parameters of H0 = 71 km s−1 Mpc−1, Ωm = 0.27, ΩΛ = 0.73. On this model, the comoving coordinate distance of PKS 2131−021 is 3.97 Gpc, with an angular diameter distance of 1.74 Gpc, and luminosity distance of 9.08 Gpc.

Black hole observation
Observations of its radio emission spanning a 45-year duration show epochs of periodic brightness variations. These nearly sinusoidal brightness changes have been interpreted as evidence of orbital motion of a binary black hole. The orbital separation of the two black holes is inferred to be 200 to 2000 AU. The periodic variability in the light curve indicates that the pair orbit each other about every two years, at a distance so close that they will merge in about 10,000 years (as viewed from the Earth).