Large-scale peculiar velocities in the universe
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866912943816310784 |
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| author | Tsagas, Christos G. Perivolaropoulos, Leandros Asvesta, Kerkyra |
| author_facet | Tsagas, Christos G. Perivolaropoulos, Leandros Asvesta, Kerkyra |
| contents | Observations have repeatedly confirmed the presence of large-scale peculiar motions in the universe, commonly referred to as ``bulk flows''. These are vast regions of the observable universe, typically spanning scales of several hundred Mpc, that move coherently with speeds of the order of several hundred km/sec. While there is a general consensus on the direction of these motions, discrepancies persist in their reported sizes and velocities, with some of them exceeding the predictions of the standard $Λ$CDM model. The observed large-scale peculiar-velocity fields are believed to have originated as weak peculiar-velocity perturbations soon after equipartition, which have subsequently grown by structure formation and by the increasing inhomogeneity of the post-recombination universe. However, the evolution and the implications of these bulk velocity fields remain poorly understood and they are still a matter of debate. For instance, it remains a challenge for the theoreticians to explain the high velocities measured by several bulk-flow surveys, like those recently reported using the CosmicFlows-4 data. Such extensive and fast velocity fields could have played a non-negligible role during structure formation and they might have also ``contaminated'' our observations. After all, in the history of astronomy, there are examples where relative-motion effects have led us to a serious misinterpretation of reality (shortened abstract due to length limits). |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2510_05340 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Large-scale peculiar velocities in the universe Tsagas, Christos G. Perivolaropoulos, Leandros Asvesta, Kerkyra Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology Observations have repeatedly confirmed the presence of large-scale peculiar motions in the universe, commonly referred to as ``bulk flows''. These are vast regions of the observable universe, typically spanning scales of several hundred Mpc, that move coherently with speeds of the order of several hundred km/sec. While there is a general consensus on the direction of these motions, discrepancies persist in their reported sizes and velocities, with some of them exceeding the predictions of the standard $Λ$CDM model. The observed large-scale peculiar-velocity fields are believed to have originated as weak peculiar-velocity perturbations soon after equipartition, which have subsequently grown by structure formation and by the increasing inhomogeneity of the post-recombination universe. However, the evolution and the implications of these bulk velocity fields remain poorly understood and they are still a matter of debate. For instance, it remains a challenge for the theoreticians to explain the high velocities measured by several bulk-flow surveys, like those recently reported using the CosmicFlows-4 data. Such extensive and fast velocity fields could have played a non-negligible role during structure formation and they might have also ``contaminated'' our observations. After all, in the history of astronomy, there are examples where relative-motion effects have led us to a serious misinterpretation of reality (shortened abstract due to length limits). |
| title | Large-scale peculiar velocities in the universe |
| topic | Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2510.05340 |