lonely black holes of the cosmos

There have been several interesting candidates for binary supermassive black holes found recently.
New data suggests one of the recently announced candidates is probably not a binary.

A recent press release from NOAO suggested that SDSS J153636.22+044127.0 might be a close binary supermassive black hole. (Nature paper here, subscription required).
The object was picked from the Sload Digital Sky Survey catalog of active galactic nuclei based on its extreme spectral properties.

click to embiggen

The observation was of a double peaked broad emission line spectrum, and Todd and Tod suggested that the best interpretation of the data was of two black holes, separated by about 0.1 pc (0.3 light years), orbiting each other with relative velocity of about 3,500 km/sec; the black holes having a mass of about 20 million and billion solar masses respectively.

Binary black holes are interesting, both in and of themselves as, for example, gravitational radiation sources for LISA, and as tracers of galaxy mergers and structure formation in cosmology.

But... the history of AGN observation has a long history of people seeing peculiar multi-peaked broad emission lines and hoping to have found something exotic like a close binary black hole.
Unfortunately, accretion disks around single black holes can mimic this signature, effectively due to disk limb brightening - depending on the viewing geometry, the emission lines may be seen preferentially from the edges and possibly center of the line of sight, rather than uniformly from the disk, giving a characteristic double or triple horned emission line feature - such lines can also be variable, depending on the disk structure, if the disk is blobby, or elliptical, or perturbed by a companion.
Similar features can also be seen from non-equilibrium structures like the rapidly evolving debris from tidally disrupted stars around black holes.

Arp 102B (click to embiggen)

Previous examples include Arp 102B

Arp102B spectrum (Halpern and Filippenko Nature 331, 46 (1991)

and 3C390.3

3C390.3 - Chandra image from Krawczynski's Group at WU

Now, very quickly, a group from UC Berkeley has taken additional spectra of SDSS J1536+0441, and in an Astronomer's Telegram (1955) they show new spectra, showing a third peak, and, more importantly, no shift in the position of the peaks over the 10+ month baseline between this spectrum and the previous spectrum by Todd and Tod.

click to embiggen

It does not move.

This strongly tests the binary supermassive black hole model, and the original model posed in the Nature paper fails. If it is a binary the system parameters are quite different and the orbit is longer.
More likely it is a single black hole with its disk aligned to show the triple peaked emission line, of the Arp 102B/3C390.3 class.

But, never despair, there are other interesting binary black hole candidates out there, and currently they're being discovered faster than the binary model parameters are being tested.
Eventually one of them will move...

(cf Julianne at CV)