# Abstracts Colloquium July 11, 2012

**Petya Nedkova** (University of Sofia)

*Exact black hole solutions in five dimensions*

Higher dimensional gravity admits a much wider variety of black hole solutions compared to the 4-dimensional case. Solutions with non-trivial topology have been obtained (black rings, black lenses), as well as balanced multi-black hole configurations (bi- and di- rings, black saturns). Another class of solutions distinctive for the higher dimensional gravity are the so called black holes on gravitational instantons. In this talk I will review the basic exact black hole solutions to the 5-dimensional Einstein and Einstein-Maxwell equations with a flat and Kaluza-Klein asymptotic. Their properties will be discussed, as well as their classification in the context of the corresponding uniqueness theorems. Systematic construction of exact solutions is possible in the vacuum case, and in some subclasses of Einstein-Maxwell when the field equations reduce to integrable sigma-models, and I will discuss the relevant solution generation methods.

**Joachim Vogt** (Jacobs University Bremen)

*Magnetosphere-Ionosphere Coupling in Models and Multi-Spacecraft Data*

The dynamics of the Earth's space environment is manifested in space weather phenomena such as auroral lights and geomagnetic storms. Among the compartments of the geospace system that control space weather are various magnetospheric regions such as the dayside magnetopause, the magnetotail, and the radiation belts, as well as the auroral acceleration region and the polar ionosphere. In this context, the term magnetosphere-ionosphere (M-I) coupling refers to the complex interplay of these regions in geospace that are typically associated with energy conversion on large scales. The presentation reviews physical principles of M-I coupling, and then addresses the potential and limitations of multi-spacecraft missions for studies of the dynamical M-I system. Special four-point data analysis techniques were designed in the preparation phase of the Cluster mission for a number of generic analysis tasks such as gradient estimation, boundary analysis, and wave identification. Recent additions to the arsenal of multi-point methods include the wave surveyor technique for fast identification of the dominant wave mode, and three spacecraft methods based on planar reciprocal vectors. Particular emphasis will be on data from Cluster and Themis but we will also discuss potential applications in the context of the forthcoming Swarm mission.

**Kostas Kokkotas** (University of Tuebingen)

*The violent phases of a neutron star's life*

Neutron stars are the most compact massive objects in the universe with yet unknown equation of state. During their lifetime they have violent periods during which they are primary sources for gravitational wave, x-ray and gamma-ray astronomy. We will present recent results concerning the dynamics of fast rotating neutron stars and magnetars (neutron stars with extreme magnetic fields). Our analysis suggests that the signals (electromagnetic or gravitational) during the violent phases carry information about the details of their interior, the crust, the spin period and the strength of the magnetic field.

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