ǂA ǂstudy of stellar debris dynamics during a tidal disruption event

dissertation

A. Clerici (Author), Andreja Gomboc (Mentor)

Abstract

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.

Keywords

hydrodynamics;galactic nuclei;accretion;computer simulations;dissertations;

Data

Language:	English
Year of publishing:	2020
Typology:	2.08 - Doctoral Dissertation
Organization:	UNG FPŠ - Graduate School
Publisher:	[A. Clerici]
UDC:	524(043.3)
COBISS:	30226691
Views:	2694
Downloads:	71
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	Slovenian
Secondary title:	Studij dinamike zvezdne snovi med dogodkom plimskega raztrganja
Secondary abstract:	\v Stevilo opa\v zenih dogodkov plimskih raztrganj hitro nara\v s\v ca zahvaljujo\v c novim pregledom neba. Zato postaja vedno pomembneje, da izbolj\v samo modele dogodkov plimskih raztrganj in dobimo teoreti\v cne napovedi za razli\v cne zvezdne in orbitalne parametre. V tej disertaciji smo prou\v cevali dinami\v cno obna\v sanje snovi ob plimskih raztrganjih zvezd v bli\v zini masivne \v crne luknje, kakr\v sna je Sgr A* v sredi\v s\v cu na\v se Galaksije, pri \v cemer smo spreminjali za\v cetne orbitalne parametre in upo\v stevali opazovane orbite S zvezd. Prou\v cevanje razli\v 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-pre\v ckanje in splo\v s\v 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 opi\v se politropni model z $\gamma = 5/3$. Vpliv masivne \v crne luknje smo modelirali s posplo\v senim post-Newtonskim potencialom, ki upo\v steva relativisti\v cne efekte Schwarzschildovega prostor-\v casa. Na\v se analize ka\v zejo, da imajo porazdelitve hitrosti vra\v canja snovi za zvezde podobne Soncu in za zvezde podobne S-zvezdam pri enaki ekscentri\v cnosti podoben \v cas trajanja, vendar imajo S-zvezde vi\v sjo vrednost histrosti vra\v canja snovi, kot je pri\v cakovano zaradi njihove ve\v 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 u\v cinkovito in posledi\v cno disk ne nastane ali pa nastane po relativno dolgem \v casu; pri tipu 2 se ostanki zvezde cirkularizirajo po\v casi in s\v casoma tvorijo disk, pri \v cemer ne ostane ni\v c snovi, ki bi \v se padala proti disku; pri tipu 3 se ostanki zvezde relativno hitro cirkularizirajo in tvorijo disk, vendar ostane \v se nekaj snovi, ki pada na disk; pri tipu 4 pa se ostanki zvezde hitro in u\v cinkovito cirkularizirajo, ve\v cinoma zaradi samo-pre\v ckanja in udarnih valov, in tvorijo disk, pri \v cemer ne ostane ni\v 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 ekscentri\v cnosti blizu paraboli\v cni.
Secondary keywords:	vesolje;središča galaksij;hidrodinamika;plimsko raztrganje;akrecija;računalniške simulacije;disertacije;
URN:	URN:SI:UNG
Type (COBISS):	Doctoral dissertation
Thesis comment:	Univ. v Novi Gorici, Fak. za podiplomski študij
Pages:	115 str.
ID:	12049932