Wednesday Colloquium


"Cosmic-Ray driven strong outflows from disk galaxies"

Michał Hanasz (Center for Astronomy, Nicolaus Copernicus University, Toruń)

Recent theoretical studies indicate that cosmic rays play an important role in regulating the evolution of the interstellar medium and efficiency of star formation. I will present numerical models of galactic winds driven by cosmic rays (CRs) produced in supernova remnants in massive star-forming disk galaxies. We assume that type II supernovae deposit 10% of their energy into the ISM as cosmic rays. With a typical Galactic diffusion coefficient for CRs (3 × 1028 cm2 s−1), we demonstrate that this process alone can trigger the local formation of a strong low-density galactic wind maintaining vertically open magnetic field lines. Driven by the additional pressure gradient of the relativistic fluid, the wind speed can exceed 103 km s−1, much higher than the escape velocity of the galaxy. The global mass loading, i.e., the ratio of the gas mass leaving the galactic disk in a wind to the star formation rate, becomes of order unity once the system has settled into an equilibrium. We conclude that relativistic particles accelerated in supernova remnants alone provide a natural and efficient mechanism to trigger winds similar to observed mass-loaded galactic winds in high-redshift galaxies. These winds also help in explaining the low efficiencies for the conversion of gas into stars in galaxies, as well as the early enrichment of the intergalactic medium with metals. This mechanism may be at least of similar importance to the traditionally considered momentum feedback from massive stars and thermal and kinetic feedback from supernova explosions.


"On the interplay between the heartbeat oscillations and wind outflow in the microquasar IGR J17091-3624"

Mikolaj Grzędzielski (Center for Theoretical Physics, PAN, Warsaw)

In 2011, the black hole candidate IGR J17091-3624 exhibited in some characteristic states, bright outbursts and strong quasi-periodic oscillations of luminosity (on timescales of tens of seconds), so called 'heartbeat state. That process may be modeled by the radiation instability driven by the domination of radiation pressure and enhanced heating of the plasma. Despite that the mean accretion rate in this source is probably below the Eddington limit, such oscillations will still have large amplitudes. As the observations show, that the wind may occures in some states. Wind helps to stabilize the hearbeat outbursts. We use the hydrodynamical GLADIS code to model the disk and X-Ray radiation. We examined the data archive from Chandra and XMM-Newton satellites to find the observed limitations on the wind physical properties, such as its velocity and ionization state and investigated the long term evolution of this source, spanned over about 600 days of observations. Our model requires a substantial wind component, to heartbeat variability explain the proper variability pattern, and even complete suppression of flares in some states. The wind mass loss rate extracted from the data is in good quantitative agreement with our scenario.


"Variability of accreting black holes connected with the shocks in the low angular momentum flows"

Petra Suková (Center for Theoretical Physics, PAN, Warsaw)

We derive the conditions for shock formation in a quasi-spherical, slightly rotating flows. We verify the results of semi-analytical, stationary calculations with the time evolution studied by numerical hydro-simulations, and we study the oscillations of the shock position. We also study the behaviour of flows with varying specific angular momentum, where the ’hysteresis’ type of loop is found when passing through the multiple sonic points region. Our results are in agreement with the timescales and shapes of the luminosity flares observed in Sgr A*. These or similar models may also be applicable for the Galactic stellar mass black holes, like GX 339-4, where periodic oscillations of X-ray luminosity are detected.