Modelling the light-curves of objects tidally disrupted by a black hole

Tidal disruption by massive black holes is a phenomenon, during which a large part of gravitational energy can be released on a very short time-scale. The time-scales and energies involved during X-ray and IR flares observed in Galactic centre suggest that they may be related to tidal disruption events. Furthermore, aftermath of a tidal disruption of a star by super-massive black hole has been observed in some galaxies, e.g. RX J1242.6-1119A. All these discoveries increased the demand for tools for tidal disruption study in curved space-time. Here we summarise our study of general relativistic effects on tidal deformation of stars and compact objects.Comment: 2 pages, to appear in the proceedings of the JENAM 2008, Symposium 7: "Grand Challenges in Computational Astrophysics

Tidal Capture by a Black Hole and Flares in Galactic Centres

We present the telltale signature of the tidal capture and disruption of an object by a massive black hole in a galactic centre. As a result of the interaction with the black hole's strong gravitational field, the object's light curve can flare-up with characteristic time of the order of 100 sec \times (M_{bh} / 10^6 M_{Solar}). Our simulations show that general relativity plays a crucial role in the late stages of the encounter in two ways: (i) due to the precession of perihelion, tidal disruption is more severe, and (ii) light bending and aberration of light produce and enhance flares seen by a distant observer. We present our results for the case of a tidally disrupted Solar-type star. We also discuss the two strongest flares that have been observed at the Galactic centre. Although the first was observed in X-rays and the second in infra-red, they have almost identical light curves and we find it interesting that it is possible to fit the infra-red flare with a rather simple model of the tidally disrupted comet-like or planetary object. We discuss the model and possible scenarios how such an event can occur.Comment: 3 pages, 1 figur

Clumps of material orbiting a black hole and the QPOs

Clumps of material orbiting a black hole may be disturbed, somewhat like comets in the Kuiper belt, to relatively small periastron orbits. Each periastron passage changes the orbital parameters in such a way that the orbit becomes more and more eccentric and the angular momentum approaches the critical value for tidal capture. When this value is reached, the body is suddenly caught by the relativistic potential to the last periastron (occurring at two Schwarzschild radii for a non rotating black hole). In this process the transfer of orbital into internal energy heats the body before it makes a few more turns toward the horizon of the black hole. Because of strong relativistic effects this last bright message from the object is seen as a quasi-periodic flare. Assuming that a black hole may be fed by a large number of such small debris we calculate light curves expected from such events. We investigate the resemblance of the Fourier spectra of such light curves with those of observed QPOs.Comment: 3 pages, 6 figure

Opredelitev dveh genov za membranski transport v genomu parazita Plasmodium yoelii

Malaria, an infectious disease caused by parasites from the Plasmodium genus, is one of the leading causes of death and morbidity worldwide and puts almost half of the world population at risk. Due to the emergence and rise of resistance to the insecticides and antimalarial drugs, there is a great need for a vaccine. So far whole sporozoite based immunization has been shown to be the most effective in experimental settings. Genetically attenuated parasites (GAP) have demonstrated significant protection in rodent models of malaria. The ideal GAP would arrest late in the liver stage of the malaria life cycle and provide sterile immunity in the host. However, the route and method of sporozoite administration have not been optimized yet. Intravenous injection (IV) is currently the only effective route of administration, that has been able to induce strong protective immune response. The preferred route is intradermal injection (ID), but several studies have shown that it induces lower immunity compared to IV injection. In order to improve the ID route of administration and determine the suitability of chosen genes as vaccine candidate genes, we aimed to generate mutant parasite lines of two promising membrane transporter genes, mfs6 and ctr2 of P. yoelii. We generated fluorescently tagged and deletion mutants of candidate genes with different biomolecular methods for functional analysis. We also characterized the expression and localization of fluorescently tagged proteins in the blood stage. These lines can be further used to determine expression and localization of tagged genes in the liver stage by infecting hepatocytes in vitro. Deletion mutant parasite lines need to be fully confirmed or further genetically characterized before use for route of administration experiments. Generated transgenic lines can then be used for studying route of administration and generation of GAP vaccine candidates in murine models of malaria.Malarija, nalezljiva bolezen, ki jo povzročajo paraziti rodu Plasmodium, je ena od glavnih vzrokov smrti in obolevnosti po svetu. Ogroža skoraj polovico svetovnega prebivalstva. Zaradi pojava odpornosti proti insekticidom in antimalarijskim zdravilom nujno potrebujemo cepivo. Do sedaj se je za najbolj učinkovito izkazalo poskusno cepljenje s celimi sporozoiti. V mišjih modelih malarije so najboljšo stopnjo zaščite dosegli z genetsko oslabljenimi sporozoiti. Razvoj popolnega genetsko oslabljenega sporozoita bi se ustavil v pozni jetrni stopnji življenjskega kroga parazita in tako sprožil imunski odziv, ki bi zagotovil popolno in trajno zaščito pred okužbo s parazitom malarije. Vseeno pa je za uspešnost samega cepiva potrebno razviti še optimalni način dajanja cepiva. Trenutno je edini preizkušen učinkoviti način vnosa cepiva, ki sproži močan imunski odziv, z intravenozno injekcijo. Vnos z intradermalno injekcijo je bolj zaželjen, vendar pa so testi pokazali, da sproži šibkejši imunski odziv v primerjavi z intravenoznim vnosom. Mutantske parazitske linije mfs6 in ctr2 P. yoelii smo ustvarili zato, da bi izboljšali intradermalni vnos cepiva ter hkrati določili ustreznost izbranih genov kot kandidatnih genov za cepivo proti malariji. S pomočjo različnih biomolekularih metod smo ustvarili parazite s fluorescentno označenima izbranima genoma ter parazite z izbitima genoma. Opredelili smo izražanje in lokalizacijo izbranih genov v krvni stopnji življenjskega kroga parazita. Pridobljene parazitske linije se lahko uporabijo za opredelitev in lokalizacijo označenih genov v jetrni stopnji tako, da se z njimi okuži jetrne celice in vitro. Mutantske linije z izbitimi geni je potrebno najprej potrditi in genetsko opredeliti, preden se jih lahko uporabi v poskusih optimizacije vnosa cepiva. Te transgene parazitske linije se lahko nato uporabi za nadaljnje raziskovanje načina vnosa cepiva, kot tudi za razvoj genetsko oslabljenih parazitov oziroma kandidatnega cepiva v mišjih modelih malarije

Do flares in Sagittarius A* reflect the last stage of tidal capture?

In recent years the case for the presence of 3-4 10^6 M_sun black hole in our Galactic Center has gained strength from results of stellar dynamics observations and from the detection of several rapid X-ray and IR flares observed in the Sagittarius A* from 2000 to 2004. Here we explore the idea that such flares are produced when the central black hole tidally captures and disrupts a small body - e.g. a comet or an asteroid.Comment: 6 pages, 9 figures, acknowledgments added, to appear in the Proceedings of the Albert Einstein's Century International Conference, Paris 200

Unveiling the Secrets of Gamma Ray Bursts

Gamma Ray Bursts (GRBs) are unpredictable and brief flashes of gamma rays that occur about once a day in random locations in the sky. Since gamma rays do not penetrate the Earth's atmosphere, they are detected by satellites, which automatically trigger ground-based telescopes for follow-up observations at longer wavelengths. In this introduction to Gamma Ray Bursts we review how building a multi-wavelength picture of these events has revealed that they are the most energetic explosions since the Big Bang and are connected with stellar deaths in other galaxies. However, in spite of exceptional observational and theoretical progress in the last 15 years, recent observations raise many questions which challenge our understanding of these elusive phenomena. Gamma Ray Bursts therefore remain one of the hottest topics in modern astrophysics.Comment: 20 pages, 11 figures, review article, draft version, final version will appear in Contemporary Physic