Strong Gravity News & Events

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From Infinitely Large to Infinitely Small

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Gr@v member António P. Morais gave a talk at Escola Secundária José Régio in Vila do Conde with title "Do Infinitamente Grande ao Infinitamente Pequeno - uma jornada pelas interações fundamentais na natureza". António was an invited speaker to participate in a sequence of seminars entitled "A Biblioteca convida...", and presented to 11th and 12th grade Science and Technology students the four fundamental interactions in nature and how have they shaped our Universe.

Strong Gravity
Cosmology
High Energy Physics
Astrophysics
Celestial Mechanics

Critical behavior of a domain wall collapse

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Speaker
Taishi Ikeda (Nagoya U.)
Event date
Venue
GAP room
Event type
Seminars
Abstract: Gravitational collapse is the one of the most important phenomena of gravity. About 20 years ago, Choptuik discovered a critical collapse in the massless scalar system. After this discovery, many author have shown that the critical behavior appears in the many systems, and it contains to the rich phenomena. In particular, Okawa et al showed the massive scalar system, which has the typical length scale, has a non trivial phase diagram with respect to the critical collapse. In this study, we consider the spherically symmetric domain wall collapse. Because this system also has the typical length scale in the action, it is expected that this system also has the non trivial phase diagram. In order to analyze non-trivial phase diagram of this system, we study the gravitational collapse of this system around threshold of the BH formation. In this talk, as a first step of this study, I will show that the type II critical collapse appears in some parameter region in this system.
Strong Gravity

The first "Alberto" Prize

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The first "Alberto" prize, awarded to a young researcher in the area of General Relativity by the SPRG was presented in the IX Black Holes Workshop to Jorge Rocha, currently at the University of Barcelona. The award is a hologram of an image of Albert Einstein, which was produced by Pedro Pombo and Emanuel Santos, at the U. Aveiro.

Strong Gravity

The spacetime around neutron stars and astrophysical observables

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Speaker
Georgios Pappas (GRIT - CENTRA - IST)
Event date
Venue
GAP room
Event type
Seminars
Abstract: Compact objects in general and neutron stars (NSs) in particular open a window to some of the most extreme physics we can find in nature. On the one hand in the interior of NSs we can find matter in very extreme densities, exceeding nuclear densities and anything we can probe in the laboratory, while on the other hand NSs are related to the strongest gravitational fields next only to those found in black holes. Therefore studying NSs gives us access to both supranuclear densities and strong gravity and can be used to get information and test our theories of matter (equation of state) and gravity. The properties of the structure of NSs are encoded on the spacetime around them and by studying the astrophysical processes that take place around NSs we can map that spacetime.Here we will talk about the properties of NS structure and how they are related to the properties of the spacetime around them. We will also talk about the relation of these properties to astrophysical observables. Finally we will extend our discussion to the case of scalar-tensor theory of gravity.
Strong Gravity
Astrophysics

A journey into a black hole

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Gr@v's Ph.D. student (in collaboration with IST-Lisbon) Pedro Cunha produced a short movie illustrating a voyage into a black hole, and in particular the lensing effects visualized by an observer undergoing such journey. The journalist Catarina Lázaro (voice) and Gr@v researcher C. Herdeiro (scientific advising) collaborated in the movie, which will have a premiere on December 3rd 2016 at "Observatório Geofísico e Astronómico da Universidade de Coimbra".

Strong Gravity
Astrophysics

General parametrization of axi-symmetric black holes in metric theories of gravity

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Speaker
Roman Konoplya (Theoretische Astrophysik Tübingen (TAT)
Event date
Venue
GAP room
Event type
Seminars
Abstract: Following previous work of ours in spherical symmetry, we here propose a new parametric framework to describe the spacetime of axisymmetric black holes in generic metric theories of gravity. In this case, the metric components are functions of both the radial and the polar angular coordinates, forcing a double expansion to obtain a generic axisymmetric metric expression. In particular, we use a continued-fraction expansion in terms of a compactified radial coordinate to express the radial dependence, while we exploit a Taylor expansion in terms of the cosine of the polar angle for the polar dependence. These choices lead to a superior convergence in the radial direction and to an exact limit on the equatorial plane. As a validation of our approach, we build parametrized representations of Kerr, rotating dilaton, and Einstein-dilaton-Gauss-Bonnet black holes. The match is already very good at lowest order in the expansion and improves as new orders are added. We expect a similar behavior for any stationary and axisymmetric black-hole metric.
Strong Gravity