Dark Energy Spectroscopic Instrument

Dark Energy Spectroscopic Instrument. It is a state-of-the-art multi-object spectrograph mounted on the Mayall Telescope at Kitt Peak National Observatory in Arizona. The project is led by the Lawrence Berkeley National Laboratory with significant contributions from a large international collaboration of institutions. Its primary mission is to create the largest three-dimensional map of the universe to date, probing the effects of dark energy and the expansion history of the cosmos.

Overview

The instrument represents a major leap in astrophysics and cosmology, building upon the legacy of previous surveys like the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic Survey. Funded primarily by the United States Department of Energy's Office of Science, it involves over 75 research institutions worldwide, including University College London and the French Alternative Energies and Atomic Energy Commission. The project's design and construction phase concluded in 2019, with the main five-year survey commencing in 2021. It operates by simultaneously capturing the spectra of thousands of galaxies and quasars each exposure, an unprecedented capability enabled by its innovative robotic positioner system.

Scientific goals and design

The core scientific objective is to measure the Hubble constant and the growth rate of cosmic structures with extreme precision, thereby constraining the properties of dark energy. It aims to achieve this by precisely mapping the baryon acoustic oscillations (BAO) imprinted in the large-scale structure of the universe and by measuring redshift-space distortions. The survey is designed to cover one-third of the sky, targeting tens of millions of objects. This vast dataset will allow scientists to test competing theories of cosmic acceleration, including modifications to Albert Einstein's theory of general relativity and the potential evolution of the cosmological constant.

Instrumentation and technology

The heart of the instrument is a focal plane containing 5,000 robotic positioners, each capable of placing a fiber-optic cable within microns of a target's position on the sky. These fibers feed light to ten identical spectrographs located in a climate-controlled room below the telescope dome. Each spectrograph uses a combination of high-efficiency volume phase holographic gratings and state-of-the-art CCD detectors developed at Lawrence Berkeley National Laboratory. The system can observe 5,000 objects simultaneously over a wavelength range from 360 nanometers to 980 nanometers, covering the optical and near-infrared spectrum critical for measuring high-redshift objects.

Survey and data collection

The main survey targets four primary classes of objects: luminous red galaxies, emission line galaxies, quasars, and the Lyman-alpha forest in quasar spectra. Target selection relies on pre-existing imaging data from projects like the Legacy Surveys conducted at the Kitt Peak National Observatory, the Cerro Tololo Inter-American Observatory, and the Wide-field Infrared Survey Explorer satellite. Data collection is automated, with the system capable of reconfiguring its fiber array for a new field of view in under two minutes. The survey has already collected spectra for millions of objects, generating petabytes of raw data processed by supercomputers at the National Energy Research Scientific Computing Center.

Key findings and cosmological impact

Early data releases have produced the largest and most detailed maps of the universe ever made, already providing stringent new constraints on the Lambda-CDM model. Key publications in journals like the Astrophysical Journal have reported precise measurements of the cosmic distance scale and the matter density of the universe. The final dataset is expected to transform our understanding of dark energy, potentially revealing whether its strength has changed over cosmic time. The legacy data will also support a wide range of ancillary science, from studies of the Milky Way to the physics of distant quasars, influencing the direction of future flagship missions like the Nancy Grace Roman Space Telescope and the Vera C. Rubin Observatory.

Category:Astronomical instruments Category:Cosmology Category:Dark energy