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DTSTART;TZID=America/New_York:20231107T110000
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SUMMARY:Fluid stabilization in slowly expanding cosmological spacetime
DESCRIPTION:General Relativity Seminar \nSpeaker: David Fajman (Vienna) \nTitle: Fluid stabilization in slowly expanding cosmological spacetime \nAbstract: Relativistic fluids are known to form shocks during their evolution from near-homogeneous initial data. In expanding spacetimes\, shock formation is suppressed\, if the expansion is sufficiently strong. We refer to this effect as fluid stabilization. The occurrence of this phenomenon depends on features of the fluid and has implications for our understanding of structure formation and cosmological evolution. While the effect is well studied in the regime of accelerated expansion\, in recent years it has been shown that fluid stabilization occurs as well in spacetimes with slower expansion rates. In this talk we present different recent results on fluid stabilization in slowly expanding spacetimes and aspects of the methods involved in the respective proofs. \n  \nTalk via Zoom\, broadcast in G10 \n 
URL:https://cmsa.fas.harvard.edu/event/gr_11723/
LOCATION:Hybrid – G10
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-11.07.23.png
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20231114T110000
DTEND;TZID=America/New_York:20231114T120000
DTSTAMP:20260426T015214
CREATED:20240223T052212Z
LAST-MODIFIED:20240223T052212Z
UID:10002814-1699959600-1699963200@cmsa.fas.harvard.edu
SUMMARY:Quasi-Local Mass in a Binary Black Hole Merger
DESCRIPTION:General Relativity Seminar \nSpeaker: Daniel Kolb (Max Planck Institute) \nTitle: Quasi-Local Mass in a Binary Black Hole Merger \nAbstract: One of the major open problems in classical general relativity is how one should define the mass of a finite region of space. In this talk\, we will investigate a promising definition proposed by Wang and Yau in 2009. A closed 2-surface bounding the region of interest is embedded isometrically into Minkowski space. The mass is then calculated by comparing the extrinsic geometries. The Wang-Yau mass has many desirable properties\, but it has previously not been calculated for surfaces in dynamical spacetimes. To remedy this\, we will discuss how the Wang-Yau mass can be computed in practice and extend the definition to surfaces important in black hole dynamics: their quasi-local horizons. Finally\, we look at how this mass behaves in a merger of black holes.
URL:https://cmsa.fas.harvard.edu/event/gr_111423/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20231128T110000
DTEND;TZID=America/New_York:20231128T120000
DTSTAMP:20260426T015214
CREATED:20240223T051146Z
LAST-MODIFIED:20240223T051146Z
UID:10002813-1701169200-1701172800@cmsa.fas.harvard.edu
SUMMARY:Remarkable symmetries of rotating black holes
DESCRIPTION:General Relativity Seminar \nSpeaker: David Kubiznak (Charles University) \nTitle: Remarkable symmetries of rotating black holes \nAbstract: It is well known that the Kerr geometry admits a non-trivial Killing tensor and its ‘square root’ known as the Killing-Yano tensor. These two objects stand behind Carter’s constant of geodesic motion as well as allow for separability of test field equations in this background. The situation is even more remarkable in higher dimensions\, where a single object — the principal Killing-Yano tensor — generates a tower of explicit and hidden symmetries responsible for integrability of geodesics and separability of test fields around higher-dimensional rotating black holes. Interestingly\, similar yet different structure is already present for the slowly rotating black holes described by the `magic square’ version of the Lense-Thirring solution\, giving rise to a geometrically preferred spacetime that can be cast in the Painleve-Gullstrand form and admits a tower of exact rank-2 and higher rank Killing tensors whose number rapidly grows with the number of spacetime dimensions.
URL:https://cmsa.fas.harvard.edu/event/gr_112823/
LOCATION:MA
CATEGORIES:General Relativity Seminar
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