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Til bevillingsoversigt

The anisotropic local universe and the sources of high energy cosmic rays.

Carlsbergfondets postdoc-stipendier i Danmark


The universe is believed to be statistically isotropic and homogenous on large scales. However, the local Universe is anisotropic. Under the current standard model, this should extend only ~100 Mpcs. However, various surveys of the local universe suggest that the local group of galaxies is part of a bulk flow that stretches significantly beyond 100 Mpcs, beyond which data is sparse. My project is about a) quantifying this anisotropy/resultant bulk flow within the context of the standard model of cosmology, b) testing if similarly large bulk flows are more common than we think in the Universe, c) quantifying the implications of the fact that we are in the middle of a rare bulk flow on observations and their interpretations, and d) the implications of this anisotropy on cosmic ray physics.


The current standard model of cosmology, which assumes the existence of cold dark matter and dark energy, is built on evidence gathered from observations of the cosmic microwave background, which is a picture of the early Universe, as well as Type 1a Supernovae. The data have so far been interpreted in the context of this assumed homogeneity and isotropy on large scales. If it indeed turns out that the local Universe is incompatible with this assumption, our understanding of cosmology will need to be reevaluated. Many searches looking for the sources of ultra-high energy cosmic rays test against a null hypothesis of isotropy. This may lead to a misclassification of the anisotropy of the local universe, as the discovery of sources that correlate with the local structure.


My present ongoing projects explore various facets of this problem. I am looking to augment current all-sky two-dimensional surveys of the local universe with photometric redshift data to allow analysis with an approximate 3rd dimension. With this, I intend to measure the structure growth rate in the local universe. Simultaneously I am looking at the largest catalogue of type 1a SNe for a dipolar modulation in the acceleration, which might hint at a significantly larger bulk flow than previously believed. I am also currently constructing maps of the local structure to be used as null hypothesis in searches for the sources of ultra-high energy cosmic rays.


Tools developed in the past for high energy physics and cosmology, such as neural networks and machine learning, have later been adopted in various other fields for the analysis of large quantities of complex multidimensional data. To process the terabytes of data, that make up modern surveys and simulations of the Universe, we employ cutting edge computational methods, involving GPUs and distributed processing. Though academic, it is possible that methods I develop for my work will find applicability in fields of more human significance. At the very least, our place in the Universe is a question of philosophical importance to humanity.