Imaging and spectroscopy with HST show that LBQS 0103 - 2753 ( V = 17.8 , z = 0.848 ) is a binary quasar with a separation of 0 ^ { \prime \prime } . 3 or 2.3 kpc .
This is by far the smallest separation binary quasar reported to date .
The two components have very different spectra , including the presence of strong broad absorption lines ( BALs ) in component A only .
The emission-line redshifts , based on the broad high ionization C IV lines , are z _ { A } = 0.834 and z _ { B } = 0.858 ; their difference is 3900 km s ^ { -1 } in velocity units .
The broad C IV lines , however , are probably not a good indicator of systemic redshift ; and LBQS 0103 - 2753 A and B could have a much smaller systemic redshift difference , like the other known binary quasars .
If the systemic redshift difference is small , then LBQS 0103 - 2753 would most likely be a galaxy merger that has led to a binary supermassive black hole .
There is now one known 0 ^ { \prime \prime } . 3 binary among roughly 500 QSOs that have been observed in a way that would reveal such a close binary .
This suggests that QSO activity is substantially more likely for black hole binaries at spacings \sim 2 kpc than at ~ { } \sim 15 to 60 kpc .
Between 1987 and 1998 , the observed Mg II BAL disappeared .