11. Observing TDEs in the era of LSSTKatja Bricman, 2020, objavljeni povzetek znanstvenega prispevka na konferenci Opis: The upcoming Large Synoptic Survey Telescope (LSST) will observe ~18000 square degrees of the Southern sky and is expected to discover thousands of transients every night due to its large coverage of the sky and its observing strategy. Being an exceptional transient hunter, we expect the LSST to increase the current observed sample of Tidal Disruption Events (TDEs) by a factor of ~1000 in 10 years of survey duration. TDEs are one of the most promising phenomena in the study of dormant supermassive black holes (SMBHs) in the Universe, and if their observed optical light curves are sampled frequently enough, TDEs can serve as indicators of SMBH mass. We present our simulations of TDE observations with the LSST, the resulting SMBH mass distributions of observed TDEs, and the efficiency of different proposed observing strategies of the LSST in finding these rare transients. Ključne besede: Tidal Disruption Events, Supermassive black holes, sky surveys Objavljeno v RUNG: 04.01.2021; Ogledov: 2534; Prenosov: 0 Gradivo ima več datotek! Več... |
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13. TDEs with LSSTKatja Bricman, 2018, objavljeni povzetek znanstvenega prispevka na konferenci Opis: The Large Synoptic Survey Telescope (LSST) is an upcoming ground-based survey telescope in Chile, which will produce a multi-color survey of 18000 square degrees of the Southern Sky during its 10 years of observations. Due to its large coverage of the sky and its observing strategy it will be a perfect tool in search for transient astrophysical events, including rare Tidal Disruption Events (TDEs). TDEs occur when a star passes close by a supermassive black hole (SMBH) in a center of a galaxy and gets disrupted by its tidal forces. These events emit a bright flare of light, which can be observed to cosmological distances.
In the seminar I will provide an overview of the LSST and TDEs, and present the preliminary results on the estimated absolute rates of TDE detection in 10 years of LSST operations, which were obtained by simulations of TDE light curves with an end-to-end LSST simulations framework. Ključne besede: Tidal Disruption Events, Supermassive Black Holes, Sky Surveys Objavljeno v RUNG: 04.01.2021; Ogledov: 2924; Prenosov: 64 Celotno besedilo (1009,99 KB) |
14. A study of stellar debris dynamics during a tidal disruption eventAurora Clerici, 2020, doktorska disertacija Opis: The number of observed tidal disruption events is increasing rapidly with the advent of new surveys. Thus, it is becoming increasingly important to improve TDE models using different stellar and orbital parameters.
We study the dynamical behaviour of tidal disruption events produced by a massive black hole like Sgr A* by changing different initial orbital parameters, taking into account the observed orbits of S stars. Investigating different types of orbits and penetration factors is important since their variations lead to different timescales of the tidal disruption event debris dynamics, making mechanisms such as self-crossing and pancaking act strongly or weakly, thus affecting the circularisation and accretion disk formation.
We have performed smoothed particle hydrodynamics simulations. Each simulation consists in modelling the star with $10^5$ particles, and the density profile is described by a polytrope with $\gamma$ = 5/3. The massive black hole is modelled with a generalised post-Newtonian potential, which takes into account relativistic effects of the Schwarzschild space-time.
Our analyses find that mass return rate distributions of solar-like stars and S-like stars with same eccentricity have similar durations, but S-like stars have higher mass return rate, as expected due to their larger mass. Regarding debris circularisation, we identify four types of evolution, related to the mechanisms and processes involved during circularisation: in type 1 the debris does not circularise efficiently, hence a disk is not formed or is formed after relatively long time; in type 2 the debris slowly circularises and eventually forms a disk with no debris falling back; in type 3 the debris relatively quickly circularises and forms a disk while there is still debris falling back; finally, in type 4 the debris quickly and efficiently circularises, mainly through self-crossings and shocks, and forms a disk with no debris falling back. Finally, we find that the standard relation of circularisation radius $r_{\rm circ} = 2r_{\rm t}$ holds only for $\beta = 1$ and eccentricities close to parabolic. Ključne besede: 07.05.Tp Computer modeling and simulation, 95.30.Lz Hydrodynamics, 98.35.Jk Galactic center, bar, circumnuclear matter, and bulge, 98.62.Js Galactic nuclei (including black holes), circumnuclear matter, and bulges, 98.62.Mw Infall, accretion, and accretion disks Objavljeno v RUNG: 29.09.2020; Ogledov: 3812; Prenosov: 84 Celotno besedilo (37,55 MB) |
15. Black holes, gravitational waves and fundamental physics: a roadmapLeor Barack, Tanja Petrushevska, Andreja Gomboc, Katja Bricman, Aurora Clerici, Christopher Eckner, Nada Ihanec, Gabrijela Zaharijas, 2019, pregledni znanstveni članek Opis: The grand challenges of contemporary fundamental physics—dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem—all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions.
The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature.
The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics. Ključne besede: black holes, gwverse Objavljeno v RUNG: 24.06.2019; Ogledov: 3710; Prenosov: 0 Gradivo ima več datotek! Več... |
16. Simulations of Tidal Disruption Events Observations with the LSSTKatja Bricman, 2017, magistrsko delo Opis: The Large Synoptic Survey Telescope (LSST) will produce a multi-colour survey of 25000 square deg of the Southern sky during its 10 years of operations. It will observe over 20 billion galaxies and a similar number of stars, map the Solar System and the Milky Way, and probe dark matter and dark energy. In addition, it will discover thousands of transients every night, including new classes of objects, which have not yet been observed. Due to its large coverage of the sky it will be a perfect tool for the search of rare Tidal Disruption Events (TDEs), which occur when a star passes close by a supermassive black hole and gets disrupted by its tidal force. Afterwards the stellar debris fall back to the black hole, initially at a rate exceeding
the Eddington rate, producing an outflow, which releases a flare of energy. When the fallback rate subsides below the Eddington rate, the gas accretes onto the black hole via accretion disk. The LSST simulation framework enables us to simulate observations of different types of objects with the LSST. In this work, we include TDEs in the LSST simulation framework, estimate the number of detected TDEs, and simulate their light curves using a theoretical model, which predicts a t^(-2.6) light curve decline with time in the outflow phase and a t^{-0.4} decline in the disk phase. We also take a closer look at the distribution of the detected TDEs over cosmological redshift and black hole mass. Ključne besede: Astronomical observations, Large Synoptic Survey Telescope, Tidal Disruption Events, Black Holes, simulations Objavljeno v RUNG: 17.10.2017; Ogledov: 4456; Prenosov: 0 Gradivo ima več datotek! Več... |
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20. Horizon Shells and BMS-like soldering transformationsMatthias Blau, Martin O'Loughlin, 2016, izvirni znanstveni članek Opis: We revisit the theory of null shells in general relativity, with a particular
emphasis on null shells placed at horizons of black holes. We study in detail the considerable
freedom that is available in the case that one solders two metrics together across null
hypersurfaces (such as Killing horizons) for which the induced metric is invariant under
translations along the null generators. In this case the group of soldering transformations
turns out to be infinite dimensional, and these solderings create non-trivial horizon shells
containing both massless matter and impulsive gravitational wave components. We also
rephrase this result in the language of Carrollian symmetry groups. To illustrate this
phenomenon we discuss in detail the example of shells on the horizon of the Schwarzschild
black hole (with equal interior and exterior mass), uncovering a rich classical structure
at the horizon and deriving an explicit expression for the general horizon shell energy-
momentum tensor. In the special case of BMS-like soldering supertranslations we find a
conserved shell-energy that is strikingly similar to the standard expression for asymptotic
BMS supertranslation charges, suggesting a direct relation between the physical properties
of these horizon shells and the recently proposed BMS supertranslation hair of a black hole. Ključne besede: Black Holes, Classical Theories of Gravity, Space-Time Symmetries Objavljeno v RUNG: 10.03.2016; Ogledov: 4864; Prenosov: 0 Gradivo ima več datotek! Več... |