A close supermassive black hole binary in Centaurus A?

Abstract

The Event Horizon Telescope (EHT) project has recently published a high-resolution picture of the Centaurus A galaxy core, where a supermassive black hole (SMBH) is supposed to be located. This picture has been accompanied with interpretation difficulties. In particular, the expected central SMBH and its accretion disk are not detected, the conical forward plasma jet seems hollow and its bended shape is difficult to explain. We argue that this image could in fact reveal the existence of two SMBHs, instead of one. Within this alternative interpretation, the black holes and their disks become visible on the image, the curved jet shapes may more easily be explained and the jets display no dark spine. The putative SMBH binary system shows a projected separation distance of ∼0.4-0.7 milliparsec. This is 700 times narrower than the NGC 7674 SMBH binary, so far the visually-identified system with the shortest such distance (0.35 pc). The orbital period can be inferred to lie in the 101 to 10−1 yr magnitude range. The image suggests a double helical jet structure that, if real, would support the lower end of this estimation range. If confirmed by future observations, this close SMBH binary in Centaurus A will be of great interest as a testing ground for SMBH binary dynamics models and plasma jet studies.