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Summary:
This is the homepage of the of the weekly Astrophysics journal club at the Division of Particle physics and astrophysics at the University of Helsinki. The meetings are of an unofficial nature and the main driver is to get together and discuss recent interesting papers. This meeting differs from the Seminar series in that people are not expected to talk about their own research and in that no credits will be awarded to students. The meetings are open to everyone and the aim is to stimulate discussion about recent results and provide the possibility to
 learn about research that is not necessarily connected to one's own field of expertise.

All topics are welcome ranging from planetary science to larger scales involving stellar
 astrophysics, Milky Way studies, galaxies and cosmology.
The only requirement is that the
 presented papers should be interesting to a wider audience and that they should be presented 
in such a way that also a non-expert can follow the presentation. In the meetings we discuss one paper each week for about 45 minutes.
 All meetings are in English.

Location: Conference room C310 on the third floor.

Time: Thursdays at 10.15-11.00am during term time.

Speakers: Please contact Peter Johansson, Mikael Granvik or Clif Kirkpatrick if you want to present a paper.

Present Program: The next talk will be on the 5th of December

Presenter: Pauli Pihajoki:
Paper title: Evidence for anisotropy of cosmic acceleration
Authors: Colin, J., Mohayaee, R. Rameez, M., Sarkar, S.
Reference: 2019, A&A, 631, 13

Abstract: Observations reveal a "bulk flow" in the local Universe which is faster and extends to much larger scales than are expected around a typical observer in the standard ΛCDM cosmology. This is expected to result in a scale-dependent dipolar modulation of the acceleration of the expansion rate inferred from observations of objects within the bulk flow. From a maximum-likelihood analysis of the Joint Light-curve Analysis catalogue of Type Ia supernovae, we find that the deceleration parameter, in addition to a small monopole, indeed has a much bigger dipole component aligned with the cosmic microwave background dipole, which falls exponentially with redshift z: q0 = qm + qd.n̂ exp(-z/S). The best fit to data yields qd = -8.03 and S = 0.0262 (⇒d ̃ 100 Mpc), rejecting isotropy (qd = 0) with 3.9σ statistical significance, while qm = -0.157 and consistent with no acceleration (qm = 0) at 1.4σ. Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of "dark energy" in the Universe. 


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