Mapping the Universe and unraveling the mysteries of dark energy
Edinburgh is part of an international collaboration using the Dark Energy Spectroscopic Instrument (DESI) to create a 3D map of the universe and learn about the nature of dark energy.
A five-year quest to map the Universe and unravel the mysteries of dark energy has officially begun. By gathering light from some 30 million galaxies, DESI will create a 3D map of the universe with unprecedented detail. Seeing how structure in the Universe has evolved with time will help understand the repulsive force associated with dark energy that drives the acceleration of the expansion of the universe across vast cosmic distances.
DESI is an international science collaboration located at Kitt Peak National Observatory near Tucson, Arizona, and managed by the Lawrence Berkeley National Laboratory (Berkeley Lab) with primary funding from the U.S. Department of Energy (DOE) Office of Science.
The formal start of DESI’s five-year survey follows a four-month trial run of its custom instrumentation that captured spectra from four million galaxies - more than the combined output of all previous spectroscopic surveys.
How does DESI work?
The DESI instrument includes 5,000 robotically controlled optical fibres to gather spectroscopic data from an equal number of objects in the telescope’s three-degree field of view. On any given night, the optical fibres align to collect light from galaxies as this is focused by the telescope mirror. From there, the light is fed into a bank of spectrographs and cameras for further processing and study.
Spectra collected by DESI are the components of light corresponding to the colors of the rainbow. Their characteristics, including wavelength, reveal information such as the chemical composition of objects being observed as well as information about their relative distance and velocity. As the Universe expands, galaxies move away from each other, and their light is shifted to longer, redder wavelengths. The more distant the galaxy, the greater its ‘redshift’. By measuring galaxy redshifts, DESI researchers will create a 3D map of the Universe.
Dark energy – and more
The map detailing the distribution of galaxies is expected to yield new insights on the influence and nature of dark energy, which makes up around 70% of the energy in the universe today. Researchers also hope to learn about the degree to which gravity follows the laws of general relativity that form the basis of our understanding of the cosmos.
The universe is expanding at a rate determined by its total energy contents. The DESI instrument will be able to take snapshots of any set time - today, yesterday, 1 billion-years-ago, 2 billion-years-ago - to enable scientists to figure out the energy content in these snapshots and see how it is evolving.
But at the same time, the instrument is so powerful that other cosmological experiments can be carried out in parallel, allocating some fibres to take spectra from faint stars in nearby dwarf galaxies, measuring their orbital velocities and hence learning about the distribution of dark matter in these galaxies.
An international team, including colleagues from the School’s Institute for Astronomy have collaborated on this project for more than a decade. Edinburgh’s expertise stems from the Institute’s work on the influential Two-degree Field Galaxy Redshift Survey (2dFGRS) for which the School of Physics & Astronomy's Professor John Peacock was jointly awarded the Shaw Prize for Astronomy in 2014. More recently, a significant expansion of the Institute for Astronomy has brought two new faculty members with a strong interest in DESI: Florian Beutler, who is an expert in statistics of galaxy clustering, and Sergey Koposov, who is an expert in using local dwarf galaxies to understand galaxy formation.