Studij dinamike zvezdne snovi med dogodkom plimskega raztrganja

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 timein type 2 the debris slowly circularises and eventually forms a disk with no debris falling backin type 3 the debris relatively quickly circularises and forms a disk while there is still debris falling backfinally, 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.v Stevilo opav zenih dogodkov plimskih raztrganj hitro narav sv ca zahvaljujov c novim pregledom neba. Zato postaja vedno pomembneje, da izboljv samo modele dogodkov plimskih raztrganj in dobimo teoretiv cne napovedi za razliv cne zvezdne in orbitalne parametre. V tej disertaciji smo prouv cevali dinamiv cno obnav sanje snovi ob plimskih raztrganjih zvezd v bliv zini masivne v crne luknje, kakrv sna je Sgr A* v srediv sv cu nav se Galaksije, pri v cemer smo spreminjali zav cetne orbitalne parametre in upov stevali opazovane orbite S zvezd. Prouv cevanje razliv cnih vrst orbit in parametrov trka je pomembno, saj le-ti vplivajo na v casovno skalo dinamike ostankov plimskih raztrganj, na jakost mehanizmov, kot sta samo-prev ckanje in splov sv citev, ter s tem na cirkularizacijo in nastanek akrecijskega diska. Simulacije smo izvedli z metodo hidrodinamike zglajenih delcev. V simulacijah smo zvezdo modelirali z $10^5$ delci in gostotnim profilom, kot ga opiv se politropni model z $gamma = 5/3$. Vpliv masivne v crne luknje smo modelirali s posplov senim post-Newtonskim potencialom, ki upov steva relativistiv cne efekte Schwarzschildovega prostor-v casa. Nav se analize kav zejo, da imajo porazdelitve hitrosti vrav canja snovi za zvezde podobne Soncu in za zvezde podobne S-zvezdam pri enaki ekscentriv cnosti podoben v cas trajanja, vendar imajo S-zvezde viv sjo vrednost histrosti vrav canja snovi, kot je priv cakovano zaradi njihove vev cje mase. Glede cirkularizacije ostankov smo identificirali v stiri tipe razvoja, ki so povezani z mehanizmi in procesi med cirkularizacijo: pri tipu 1 se ostanki zvezde ne cirkularizirajo uv cinkovito in poslediv cno disk ne nastane ali pa nastane po relativno dolgem v casupri tipu 2 se ostanki zvezde cirkularizirajo pov casi in sv casoma tvorijo disk, pri v cemer ne ostane niv c snovi, ki bi v se padala proti diskupri tipu 3 se ostanki zvezde relativno hitro cirkularizirajo in tvorijo disk, vendar ostane v se nekaj snovi, ki pada na diskpri tipu 4 pa se ostanki zvezde hitro in uv cinkovito cirkularizirajo, vev cinoma zaradi samo-prev ckanja in udarnih valov, in tvorijo disk, pri v cemer ne ostane niv c snovi, ki bi padala proti disku. Ugotovili smo tudi, da standardna zveza, da je cirkularizacijski polmer enak dvakratniku plimskega polmera, $r_{circ} = 2r_t$ , velja le za parameter trka $beta = 1$ in ekscentriv cnosti blizu paraboliv cni

Black holes, gravitational waves and fundamental physics: a roadmap

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'