A Candidate Sub-Parsec Supermassive Binary Black Hole System

Understand

We identify SDSS J153636.22+044127.0, a QSO discovered in the Sloan Digital Sky Survey, as a promising candidate for a binary black hole system.

• This QSO has two broad-line emission systems separated by 3500 km/sec.
• The redder system at z=0.3889 also has a typical set of narrow forbidden lines.
• The bluer system (z=0.3727) shows only broad Balmer lines and UV Fe II emission, making it highly unusual in its lack of narrow lines.