April Monthly Meeting – 3D map of the Universe to understand the cosmic expansion history

Our meetings include brief business, a main presentation and items of astronomical news or learning from members.

The April Main Item will be: 3D map of the Universe to understand the cosmic expansion history by Dr Rossana Ruggeri.
Synopsis below.

The April 2023 meeting is planned to be a face-to-face meeting; attendees can also join in online via Zoom. Details emailed to members. Guests/visitors can contact us for Zoom details at .
Visitors are welcome to join our face-to-face or online meetings.

Synopsis – 3D map of the Universe to understand the cosmic expansion history

The expansion of the universe is accelerating, and we do not yet have a compelling explanation for it. In this talk I will present the science I am leading within the Dark-Energy-Spectroscopic-Instrument (DESI) collaboration, to understand the physical mechanism behind this accelerated expansion.

By observing the sky with the DESI-telescope we create a 3D map of the Universe’s structures, such as galaxies, from the nearby universe to a distance of some billion light-years. In the next 4 years, we will complete a survey of 30 million galaxies, beating the largest survey to date by an order of magnitude.

To test gravity I will combine the two key observations to map out the Universe, which are deep images of the sky and surveys of galaxy positions (observed by DESI). The first indicates how the light of distant galaxies is deflected, as it passes massive clumps of matter (gravitational lensing). The second describes how the light emitted by galaxies shifts towards longer wavelengths. This tells us how much the Universe has expanded in the time it took for that light to reach Earth, allowing us to build a 3D map of the galaxy distribution (large-scale structure).

By combining lensing and the large-scale-structure, we can simultaneously study how gravity affects light and matter, and therefore understand if the recent acceleration is due to dark energy or to modified gravity