This week there is a large gathering of extragalactic astronomers here at at Lawrence Berkeley National Lab (LBNL) to attend a conference on the Dark Energy Spectroscopic Instrument (DESI), a new experiment that will be commissioned on a large telescope on Kitt Peak National Observatory (KPNO) in Arizona.
With a team now 500 people strong, the focussed goal is to measure the relative positions and orientations of millions of galaxies in order to study properties of the early universe.
One can get at a straightforward understanding of this project by considering galaxy shapes. Galaxies are complicated objects with billions of stars. Even so, from a distance galaxies mostly take on oval shapes. These oval-shaped galaxies that we see on a typical pictures can face any which way. This turns out to be the case when one views galaxies within regions of space in which one can see only hundreds of examples at a time, but not millions.
On such scales indeed there is not any preferred order to their placement and orientation on the sky. Even so, when we consider now extending the image to include millions of galaxies, an interesting pattern emerges. Galaxies on very large scales start to form a dot-to-dot picture. Tracing the dots leads one to discover that galaxies are situated in a massive structure with thin filaments and the nodes that connect them similar to a 3D spider web.
We measure the average distances between these ‘strings’ of galaxies, similar in this analogy to measuring the average distances between the threads of a spider’s web. In this way, we are able to discern the conditions present in the early universe which led to this favored average distance being embedded into space itself. DESI will be mounted onto the 4-meter Mayall Telescope at KPNO in fall of this year.
