Tag Archives: accretion

Going NUTs

Posted on by

By Paul I. Jefremov and Volker Perlick.

Among all known solutions to Einstein’s vacuum field equation the (Taub-)NUT metric is a particularly intriguing one. It is that metric that owing to its counter-intuitive features was once called by Charles Misner “a counter-example to almost anything”. In what follows we give a brief introduction to the NUT black holes, discuss what makes them interesting for a researcher and speculate on how they could be detected should they exist in nature.

paul jefremov-and-volker

Volker Perlick and Pavel (Paul) Ionovič Jefremov from the Gravitational Theory group at the University of Bremen in Germany. Volker is a Privatdozent and his research interests are in classical relativity, (standard and non-standard) electrodynamics and Finsler geometry. He is an amateur astronomer and plays the piano with great enthusiasm and poor skills. Paul got his diploma in Physics at the National Research Nuclear University MEPhI in Moscow, 2014. Now he is a PhD Student in the Erasmus Mundus Joint Doctorate IRAP Programme at the University of Bremen. Beyond the scientific topics in physics his interests include philosophy in general, philosophy of science, Eastern and ancient philosophy, religion, political and social theories and last but not the least organic farming.

The NUT (Newman–Unti–Tamburino) metric was obtained by Newman, Unti and Tamburino (hence its name) in 1963. It describes a black hole which, in addition to the mass parameter (gravito-electric charge) known from the Schwarzschild solution, depends on a “gravito-magnetic charge”, also known as NUT parameter. If the NUT metric is analytically extended, on the other side of the horizon it becomes isometric to a vacuum solution of Einstein’s field equations found by Abraham Taub already in 1951. However, for an observer who is prudent enough to stay outside the black hole, the Taub part is irrelevant.

At first sight, the existence of the NUT metric seems to violate the uniqueness (“no-hair”) theorem of black holes according to which a non-spinning uncharged black hole is uniquely characterised by its mass. Actually, there is no contradiction because Continue reading →

Pulsed Gravitational Waves

Posted on by
timothyjwalton

Timothy J. Walton occupies some quantum state between a physicist and a mathematician, having obtained his PhD from the physics department at Lancaster University in 2008 but now masquerading as a lecturer in mathematics at the University of Bolton.

by Timothy J. Walton.

Applying techniques from classical electrodynamics to generate new gravitational wave perturbations

I must begin with a confession: I don’t view myself as a gravitational physicist. Despite my PhD at Lancaster University involving a formulation of relativistic elasticity and an awful lot of differential geometry, my research thus far has been within the realm of classical and quantum electrodynamics. But it was precisely within that domain, along one particular avenue of investigation, where the first seeds of an idea were sown. Following my earlier work on a class of exact finite energy, spatially compact solutions to the vacuum source-free Maxwell equations – pulsed electromagnetic waves – describing single cycle pulses of laser light [1], together with Shin Goto at Kyoto University in Japan and my former PhD supervisor Robin Tucker at Lancaster University, a new question arose: “do pulsed gravitational waves exist?’’

As I recall, this question was posed and began to take root during one of the regular meetings I have with Robin. Within my institution, I am fortunate enough Continue reading →

Accreting onto almost Kerr-de Sitter black holes

Posted on by

Read the full article for free* in Classical and Quantum Gravity:
Bondi-type accretion in the Reissner-Nordström-(anti-)de Sitter spacetime
Filip Ficek 2015 Class. Quantum Grav. 32 235008
arXiv: 1509.07005
*until 30/12/15

Filip Ficek

Filip Ficek is a graduate student in Theoretical Physics at Jagiellonian University.

In spite of numerous investigations, accretion flows onto the Kerr black hole are still not fully understood, especially for radially dominated flows, where aside from a very specific case of an ultra-hard fluid, general solutions are not known. Some insight may be provided by considering a simpler problem instead, namely spherically symmetric, steady accretion in Reissner-Nordström spacetimes. It is well known that rotating Kerr black holes and charged Reissner-Nordström black holes feature similar horizon and causal structures. In fact, it is common to treat a Reissner-Nordström black hole as a toy model of an astrophysical black hole. If we also take into account the cosmological constant, we may suppose, that accretion solutions in Reissner-Nordström-(anti-)de Sitter spacetime will Continue reading →