Starbursts near supermassive black holes: young stars in the Galactic Centre, and gravitational waves in LISA band

By Y. Levin. 2006

259 citations recorded by the source corpus.

We propose a scenario in which massive stars form in a self-gravitating gaseous disc around a supermassive black hole (SMBH). We analyse the dynamics of a disc forming around an SMBH, in which the angular momentum is transported by turbulence induced by the disc's self-gravity. We find that once the surface density of the disc exceeds a critical value, the disc fragments into dense clumps. We argue that the clumps accrete material from the remaining disc and merge into larger clumps; the upper mass of a merged clump is a few tens to a few hundreds of solar mass. This picture fits well with the observed young stellar discs near the SgrA* black hole in the Galactic Centre. In particular, we show how the masses and spatial distribution of the young stars, and the total mass in the Galactic Centre discs can be explained. However, explaining the origin of the several young stars closest to the black hole (the S-stars) is more problematic: their orbits are compact, eccentric, and have random orientation. We propose that the S-stars were born in a previous starburst(s), and then migrated through their parent disc via type-I or runaway migration. Their orbits were then randomized by the Rauch–Tremaine resonant relaxation. We then explore the consequences of the star formation scenario for AGN discs, which are continuously resupplied with gas. We argue that some compact remnants generated by the starburst will get embedded in the disc. The disc-born stellar mass black holes will interact gravitationally with the massive accretion disc and be dragged towards the central black hole. Merger of a disc-born black hole with the central black hole will produce a burst of gravitational waves. If the central black hole is accreting at a rate comparable to the Eddington limit, the gas drag from the accretion disc will not alter significantly the dynamics of the final year of merger, and the gravitational waves should be observable by Laser Interferometer Space Antenna (LISA). For a reasonable range of parameters such mergers will be detected monthly, and that the gravitational-wave signal from these mergers is distinct from that of other merger scenarios. Also, for some plausible black hole masses and accretion rates, the burst of gravitational waves should be accompanied by a detectable change in the optical luminosity of the central engine.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9dc4f5404f1102b6d39b51495f0618afcda0e953

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

Citations in the corpus

Rapid and Bright Stellar-mass Binary Black Hole Mergers in Active Galactic Nuclei (2016, background): “Further, massive stars can form near galactic centers, e.g., in AGN disks (Goodman & Tan 2004; Levin 2007; McKernan et al. 2012; Stone et al. 2016), providing an additional source of black holes to the nucleus.”
Dynamics of Protoplanetary Disks (2010, unknown): “Writing κ = κ0T β c , one finds that α can be expressed as an explicit function of just the surface density and angular velocity (Levin 2007), α ∼ σ κ0 ( µmp γkB )4−β (Q0πG) 6−2β Σ4−2βΩ2β−7.”
Black hole mergers: can gas discs solve the ‘final parsec’ problem? (2009, background): “However in AGN discs the opposite occurs (i.e.β ≪ 1), and these discs are expected to fragment rather easily (Goodman2003; Nayakshin 2006; Nayakshin et al. 2007; Levin 2007).”
CHALLENGES IN FORMING PLANETS BY GRAVITATIONAL INSTABILITY: DISK IRRADIATION AND CLUMP MIGRATION, ACCRETION, AND TIDAL DESTRUCTION (2011, methodology): “Recent analytic studies (Levin 2007; Rafikov 2009; Cossins et al. 2010; Zhu et al. 2010b) have shown that irradiation may even suppress fragmentation beyond 50 AU.”
Tearing up the disc: misaligned accretion on to a binary (2013, background): “We also note that the maximum sustainable accretion rate in a critically self-gravitating disc is a strong function of radius (see Levin 2007; Harsono, Alexander & Levin 2011).”
AN EXTREMELY TOP-HEAVY INITIAL MASS FUNCTION IN THE GALACTIC CENTER STELLAR DISKS (2009, background): “It is currently debated whether the S-stars formed in the disk(s) and subsequently migrated to the central arcsecond (Levin 2007; Löckmann et al. 2008), or whether they formed outside the central few parsecs, were injected into near-parabolic orbits by massive perturbers and were then captured by…”
Doing Science with eLISA: Astrophysics and Cosmology in the Millihertz Regime (2012, background): “…mechanism, other proposed channels for EMRI are tidal disruption of binaries that pass close to the central black hole (Miller et al., 2005), and creation of massive stars (and their rapid evolution into black holes) in the accretion discs surrounding the central massive black hole (Levin, 2007).”
THE RUNTS OF THE LITTER: WHY PLANETS FORMED THROUGH GRAVITATIONAL INSTABILITY CAN ONLY BE FAILED BINARY STARS (2009, background): “(Levin 2007), where H = cs/Ω is the disk scaleheight.”
Intermediate mass black holes in AGN discs – I. Production and growth (2012, background): “…a population of stars and compact objects (collectively nuclear cluster objects, NCOs) that can migrate within and accrete from the disk (e.g. Ostriker 1983; Syer, Clarke & Rees 1991; Artymowicz et al. 1993a; Goodman & Tan 2004; Levin 2007; Nayakshin & Sunyaev 2007; McKernan et al. 2011a,b).”
STRONG MASS SEGREGATION AROUND A MASSIVE BLACK HOLE (2008, background): “There are indications that star formation deep in the potential well of a MBH can be very different from that in the field (Levin & Beloborodov 2003; Milosavljević & Loeb 2004; Paumard et al. 2006; Levin 2007).”
Massive black hole binary mergers within subparsec scale gas discs (2008, methodology): “Motivated by the good agreement between the decay rate obtained from our simulations, and that predicted analytically by Ivanov et al. (1999), we combine their formalism with that of Levin (2007) to calculate the maximum decay rate that can be obtained due to a self-gravitating disc.”
A DISK OF YOUNG STARS AT THE GALACTIC CENTER AS DETERMINED BY INDIVIDUAL STELLAR ORBITS (2008, background): “These models typically result in stars on circular orbits as would be the case for the slow build up of a gas disk that is circularized before there is sufficient mass for gravitational instabilities to set in (Milosavljević & Loeb 2004; Nayakshin & Cuadra 2005; Levin 2007).”
Stellar Dynamics and Stellar Phenomena Near a Massive Black Hole (2017, background): “3.2.3), and the non-geodetic drag by an accretion disk is negligible (Narayan 2000; Levin 2007).”