Conveners
Tuesday afternoon
- Brynmor Haskell (Università degli Studi di Milano)
Tuesday afternoon
- Brynmor Haskell (Università degli Studi di Milano)
The geometry of the X-ray emission region in accreting black holes has been a subject of debate for over three decades. Despite extensive spectral and timing data, no consensus has emerged on the structure of these regions. The launch of the Imaging X-ray Polarimetry Explorer (IXPE) at the end of 2021 marked a major advancement in X-ray astronomy, as it is the first satellite specifically...
Very long baseline interferometry observations can now resolve event-horizon angular scales for at least 2 supermassive black holes, M87 and Sagittarius A. What is more, these observations give us access to resolved polarimetry, that constitute a particularly powerful tool for the diagnostic of the accretion flow and magnetic fields in the compact region. I will discuss how the polarization...
We study spectra produced by weakly accreting black hole systems using the GRMHD simulations. We highlight the role of large temperature fluctuations, which characterise the GRMHD solutions, in shaping the broadband spectrum and find that this effect can explain the SED observed in the active nucleus of galaxy M87. We apply our model to VLBI images of this active nucleus, but find that the...
We explore off-equatorial acceleration of electrically charged matter near a magnetized black hole with the aim of understanding the boundaries between the regions of stable, plunging, and escaping motion. As a generalisation of the Innermost Stable Circular Orbit (ISCO), the concept of the radius of the Innermost Stable Spherical Orbit (ISSO) determines the inner rim of inclined...
We present first results from Spritz, a general-relativistic magnetohydrodynamics (GRMHD) code developed for high-precision simulations of binary neutron star (BNS) mergers using nuclear equations of state. Spritz is designed with a focus on robustness and accuracy, incorporating high-order shock-capturing schemes and support for tabulated equations of state, allowing for the inclusion of...
It has been known since the 70’s that accretion disks are unstable above an accretion rate of ~10% Eddington. Yet, despite the several accreting systems known, only a handful of stellar mass black holes have been showing clear signs of accretion disk instabilities. Through an unprecedented multi-wavelength campaign of a highly accreting neutron star, it has been recently shown that the whole...
The energy released in the collapse of the core of a massive star are believed to produce a wide range of astrophysical transients including core-collapse (type Ib, Ic, II) supernovae and long duration gamma-ray bursts. A number of engines have been proposed to extract the energy released in the collapse and power an energetic explosion. All of the proposed engines are likely to occur in...
In this talk, I will report on some of the largest (in terms of simulation domain size) and longest (in terms of duration) 3D general relativistic radiation magnetohydrodynamic simulations of super-critical accretion onto black holes. The simulations are all set for a rapidly rotating ($a_* = 0.9$), stellar-mass ($M_\mathrm{BH} = 6.62 M_\odot$) black hole. The simulations vary in their target...
We performed the first simulations of accretion onto the compact objects in the Reissner-Nordström (RN) space-time. The results could not be more different for the two cases. For a black hole, just as in the familiar Kerr case, matter overflowing the cusp plunges into the black hole horizon. For the naked singularity, the accreting matter forms an inner structure of toroidal topology and...
We investigated a novel pulsar planet detection method based on radio emissions produced by the interaction of a terrestrial planet with the pulsar wind.
Using the PLUTO code, we simulate relativistic magnetohydrodynamics of an Earth-sized planet ensconced in a highly relativistic pulsar wind. We achieved a Lorentz factor of approximately 6 or a pulsar wind speed of approximately 98.5\% of...
We present preliminary results of our attempt to build a physically consistent model for the active nucleus of the galaxy M87, based on the GRMHD simulations. Our model simultaneously reproduces the broad-band spectrum and intensity maps, offering a unified explanation of these observations. In our solution, most of the radiation observed at frequencies above 100 GHz originates from the inner...
We present a new pseudo-Newtonian potential for the gravity around a
Reissner–Nordström naked singularity and perform numerical simulations of matter encircling such object. Simulations with our potential reproduce exactly the radial dependence of the Keplerian orbital frequency, with the orbital angular velocity vanishing at the zero gravity radius and showing a maximum at 4/3 of that...
I will present magnetohydrodynamic (MHD) simulations of a binary black hole (BBH) system embedded within a magnetized active galactic nucleus (AGN) disk, aiming to explore the accretion dynamics and the formation of outflows. Unlike traditional models that assume a circumbinary accretion disk around the binary, our approach allows the interaction between the binary system and the surrounding...
