J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 1 Accretion of Stellar Winds in the Galactic Centre Jorge Cuadra, S. Nayakshin, V. Springel, T. Di Matteo MPA, Garching MNRAS 360, L55 (2005) MNRAS 366, 358 (2006)

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 2 (From the GC group in Köln) Bright Stars around a Dim Black Hole

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 3 Young Massive Stars in the GC ● ~ 30 Wolf-Rayets at distances < 0.5 pc – Strong winds, up to few × Msun / yr / star. – Distributed in two discs. Genzel et al 2003

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 4 Revnivtsev et al 2004 Sgr A* Luminosity ● Very dim (~10 36 erg/s) – Caused by low mass supply and radiatively inefficient accretion. ● But it was brighter before. – Hard X-ray reflection from Sgr B2 indicates high luminosity just 350 yr ago. – Star formation Myrs ago, in an AGN-like disc. (eg, Nayakshin & Cuadra 2005) Narayan 2002

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 5 Previous Models of Stellar Winds in the Galactic Centre ● Coker & Melia (1997) fixed grid hydrodynamics. ● Rockefeller et al (2004) SPH simulation. – Finite number of fixed sources (do not follow orbits). ● Quataert (2004) 1-d analytical model. – Infinite number of sources, isotropically distributed. ● In all these models neither cooling nor angular momentum are important.

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 6 Springel 2005 Gadget-2: SPH / N-body code ● Solves gravitational and hydrodynamical forces. ● Lagrangian code. ● New version has sink particles: accretion. ● We added source particles: wind emission.

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 7 Simulations with Moving Stars: Importance of Angular Momentum ● Disc and spherical configurations. stars Angular Momentum of the Gas Accretion Rate

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 8 ● WR winds ~ 1000 km/s. ● Cooling time: t cool  v wind 5.4 ● New observations: wind velocities ~ 300 km/s for some stars. – t cool ~ 15 years < dynamical time scale! –  These winds can cool. Cooling of Winds Paumard et al 2001, also Martins et al 2006

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 9 Simulating the Galactic Centre ● Use 30 Wolf-Rayets / LBV candidates. (Paumard et al 2006) – Measured 2d positions and 3d velocities. ● 3d positions set putting stars in the discs. – Stellar wind properties measured for some stars. (Paumard et al 2001, Martins et al 2006) ● Total mass loss rate ~ M Sun / yr. ● Try different assumptions for stars not analysed yet. – Start the simulations ~1200 yr ago and let it evolve until the present time.

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 10 Simulating the Galactic Centre: Accretion Rate ~ few  M Sun /yr, but Variable Particles in the inner 0.05'' are accreted. Variability caused by the stellar orbits. Even with circular orbits, cold clumps produce a variable accretion rate.

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 11 Simulating the Galactic Centre: Variable Luminosity on yr Scales ● Viscous time-scale will smooth the accretion rate, but peaks survive. ● Due to non-linear accretion physics, may give rise to strong variability in X-rays. Yuan et al (2004) 50 years sampling

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 12 Simulating the Galactic Centre: Paschen alpha emission Scoville et al 2003

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 13 Uncertainty on the mass loss rates Decreasing the outflow from the “slow wind stars” from to M Sun /yr.

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 14 Future extensions ● Even more realistic model of the stellar population. – IRS 13E as a cluster, 16SW as a binary. – LBV variability? ● Include the mini-spiral. ● Feedback from the black hole. – Different AGN modes? ● Use these results as outer boundary conditions for studies of the inner accretion flow.

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 15 Conclusions ● Observations allow us, for the first time, to model the mass feeding of a super-massive black hole. We have developed a method to do so. ● Dynamics of the stellar system and stellar winds properties have a strong influence on the accretion onto the black hole. ● Cool gas clumps coexist with the hot X-ray emitting gas in the inner arc-second. ● Variable accretion rate: Sgr A* probably is energetically important for the Galactic centre on long time-scales.

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 16

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 17 Simulating the Galactic Centre: Cold and Hot Gas in the Inner Region

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 18

J. Cuadra – Accretion of Stellar Winds in the Galactic Centre – IAU General Assembly – Prague – p. 19 Star Formation in a Disc AGN discs become grav unstable at large radius. (Paczyński; Kolykhalov & Sunyaev; Shlosman & Begelman; Collin & Zahn; Goodman et al; Levin) In the GC, need M d ~ 10 4 M Sun. Star formation for Q < 1. Nayakshin & Cuadra ‘05 Nayakshin, Cuadra, Springel, in prep