Egwald: Topics in Astronomy and Cosmology
Elmer G. Wiens
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Topics in Astronomy and Cosmology
Astronomy is the Universe taking a selfie.
The following astronomy web pages present some topics in Astronomy.
1. Curvature of Space: The cosmological principle states that the Universe is homogeneous and isotropic on large scales. Three cosmological models of the spatial
constituent of the Universe that conform to this principle are hypersurfaces in a 4-dimensional space with uniform positive, zero, and negative curvature.
The space of each model is specified by systems of coordinates that locate an object, and by a metric that determines the distance between objects
2. Globular Clusters: Globular clusters consist of tens, to hundreds of thousands of mainly low mass, old low-metal stars bound together by their mutual gravitational attraction in a
dense, slowly rotating sphere that orbits the center of a galaxy. The stars in these clusters formed when the Universe was still young, from huge clouds of abundant
hydrogen and helium gas that collapsed under each cloud's internal gravity.
3. Gravitational Lensing: Gravitational lensing refers to the perceived influence of a celestial object's gravity on light passing by the object. The object's
mass bends spacetime, bending light's path, and focusing its measured brightnes. As predicted by Einstein's Theory of General Relativity,
the foreground object acting as a lens may generate multiple images or ring-images of the background object's emitted light.
4. Stellar Collapse: Stars that stop generating energy through nuclear fusion die. Smaller stars transform into white dwarf stars. Larger stars collapse
to form neutron stars or black holes.
Much larger stars may blow apart. Various coordinate transformations of the Schwarzschild metric are used to calculate geodesic trajectories of particles and radiation at various
radii about stellar objects collapsing from self-gravitation. Within a black hole, the mechanics of stellar collapse are modelled with the geodesics of the Robertson-Walker metric (FLRW).
5.Links and References