The Binary Black Hole Model for Mrk 231 Bites the Dust

Understand

Mrk 231 is a nearby quasar with an unusually red near-UV-to-optical continuum, generally explained as heavy reddening by dust (e.g., Leighly et al.

• 2014).
• Yan et al.
• 2015 proposed that Mrk~231 is a milli-parsec black-hole binary with little intrinsic reddening.