Year: 2021
Type: article
Abstract: ABSTRACT The nucleus of our nearest, large galactic neighbour, M31, contains an eccentric nuclear disc – a disc of stars on eccentric, apsidally aligned orbits around a supermassive black hole (SMBH). Previous studies of eccentric nuclear discs considered only an isolated disc, and did not study their dynamics under galaxy mergers (particularly a perturbing SMBH). Here, we present the first study of how eccentric discs are affected by a galactic merger. We perform N-body simulations to study the disc under a range of different possible SMBH initial conditions. A second SMBH in the disc always disrupts it, but more distant SMBHs can shut off differential precession and stabilize the disc. This results in a more aligned disc, nearly uniform eccentricity profile, and suppression of tidal disruption events compared to the isolated disc. We also discuss implications of our work for the presence of a secondary SMBH in M31.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: G2586609609, G2796167598, MRI Collaborative Consortium: Acquisition of a Shared Supercomputer by the Rocky Mountain Advanced Computing Consortium, G4958434179, MRI Collaborative Consortium: Acquisition of a Shared Supercomputer by the Rocky Mountain Advanced Computing Consortium, G8929392486, SURPRISINGLY IN MORE THAN TWENTY PERCENT OF NEARBY ELLIPTICAL GALAXIES THE DISTRIBUTION OF STARS ORBITING THE CENTRAL SUPERMASSIVE BLACK HOLE IS STRONGLY ASYMMETRIC. IN THESE GALAXIES THE STARS ARE ON APSIDALLY-ALIGNED ORBITS IN AN ECCENTRIC NUCLEAR DISK. LONG THOUGHT TO BE EXOTIC THIS CONFIGURATION IS QUITE COMMON IN OUR LOCAL UNIVERSE. DESPITE THE PREVALENCE OF ECCENTRIC DISKS HOWEVER THEIR DYNAMICS HAVE BEEN LARGELY OVERLOOKED. NAIVELY ONE MIGHT EXPECT THAT PACKING ORBITS SO CLOSELY TOGETHER WOULD MAKE THEM VIOLENTLY UNSTABLE TO GRAVITATIONAL SCATTERING OR THAT DIFFERENTIAL PRECESSION WOULD WIPE OUT THEIR LARGE-SCALE APSIDAL-ALIGNMENT.WE HAVE RECENTLY IDENTIFIED A NEW DYNAMICAL MECHANISM WHICH STABILIZES ECCENTRIC NUCLEAR DISKS (MADIGAN ET AL. 2016) THUS EXPLAINING THEIR OBSERVED UBIQUITY. THE STABILIZING MECHANISM PRODUCES OSCILLATIONS OF ORBITAL ECCENTRICITIES OF STARS IN THE DISK PUSHING MANY STARS EXTREMELY CLOSE TO THE BLACK HOLE. IF THESE DISKS FORM IN GAS-RICH MERGERS AS IS FOUND IN COSMOLOGICAL SIMULATIONS THERE WILL BE AN ENHANCED RATE OF STELLAR TIDAL DISRUPTION EVENTS (TDES) FOLLOWING THE MERGER. IN A PRELIMINARY CALCULATION WE SHOW THE TDE RATE IS INITIALLY SO HIGH THAT THE NUCLEUS WOULD APPEAR AS AN AGN OR AS A CHANGING-LOOK-QUASAR. WE THEREFORE SUGGEST THAT ACCRETION OF DENSE STELLAR MATERIAL MAY CONTRIBUTE SIGNIFICANTLY TO THE GROWTH OF SUPERMASSIVE BLACK HOLES; IF SO THIS COULD EXPLAIN THE PRESENCE OF SUPERMASSIVE BLACK HOLES IN THE EXTREMELY EARLY UNIVERSE Z>7 AS WELL AS THE PEAKING OF QUASAR ACTIVITY AROUND Z~2 WHEN THE GALAXY MERGER RATE PEAKS. OUR MODEL CAN ALSO EXPLAIN THE RECENTLY OBSERVED PREFERENCE OF TDES IN POST-MERGER POST-STARBURST (K+A) GALAXIES. HERE WE PROPOSE TO QUANTIFY THESE CALCULATIONS. WE WILL ALSO UNDERTAKE A STATISTICAL ANALYSIS OF THE LITERATURE TO DETERMINE THE TRUE OCCURRENCE RATE OF ECCENTRIC NUCLEAR DISKS.LONG AFTER THE MERGER AND THE K+A PHASE ECCENTRIC DISKS NO LONGER DIRECTLY PRODUCE TDES. HOWEVER A STABLE ECCENTRIC DISK CREATES A NON-AXISYMMETRIC POTENTIAL WHICH IN MANY WAYS MIMICS THAT OF A BINARY SUPERMASSIVE BLACK HOLE SYSTEM. TORQUES FROM THE DISK POTENTIAL IN ANALOGY WITH THE ECCENTRIC KOZAI-LIDOV MECHANISM WILL PRODUCE HIGH ECCENTRICITY ORBITS IN THE OLDER BACKGROUND STELLAR POPULATION. THIS WILL RESULT IN HYPER-VELOCITY STARS AND BINARIES. WE WILL SHOW THAT THE LATTER CAN ACCOUNT FOR THE CURRENTLY UNEXPLAINED DISTRIBUTION OF UNUSUAL CA-RICH SUPERNOVAE OBSERVED OFFSET FROM THEIR HOST GALAXIES. SINCE AN ECCENTRIC DISK CAN LAST>GYR THIS MECHANISM ALSO SIGNIFICANTLY INCREASES PREDICTED EVENT RATES OF EXTREME-MASS RATIO INSPIRALS OF COMPACT STELLAR REMNANTS INTO SUPERMASSIVE BLACK HOLES A PRIME TARGET FOR GRAVITATIONAL WAVE OBSERVATORIES.
OpenAlex ID: W3095830952