Dark Energy Spectroscopic Instrument (DESI)

April 10, 2024

In May 2021, the Dark Energy Spectroscopic Instrument (DESI) began its five-year survey to map the universe and study dark energy. Recent findings from the first year of DESI observations, which included light from 6 million galaxies up to 11 billion years old, hint at potential changes in dark energy density, challenging current theoretical models.

About DESI

In October 2019, the Dark Energy Spectroscopic Instrument (DESI) was installed on the 4-meter Mayall Telescope at Kitt Peak National Observatory in Arizona, USA. The instrument underwent commissioning and testing, and in May 2021, it began its five-year survey to map the universe and study dark energy.

DESI is a state-of-the-art instrument designed to create the largest and most detailed 3D map of the universe ever made. By measuring the redshifts of millions of galaxies and quasars, DESI aims to shed light on the mysterious force known as dark energy, which is thought to be responsible for the accelerating expansion of the universe.

Instrument Design

DESI consists of a focal plane with 5,000 robotically controlled optical fibres, each capable of precisely positioning itself to collect light from a specific galaxy or quasar. The light collected by these fibres is then split into specific wavelengths using spectrographs, allowing scientists to measure the redshift and distance of the objects.

Survey Goals and Progress

Over the course of its five-year survey, DESI aims to measure the redshifts of over 35 million galaxies and quasars, covering a cosmological volume of 14 billion light-years. As of 2023, DESI has been observing galaxies for three years, with plans to continue for at least two more years.

Dark Energy and Cosmic Expansion

Dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. While the existence of dark energy is supported by observations of distant supernovae and the cosmic microwave background, its precise nature remains one of the greatest mysteries in modern cosmology.

DESI Findings and Implications

Data from the first year of DESI observations were used to create a comprehensive 3D evolutionary map of the universe. The precise distance measurements allowed scientists to calculate the universe’s expansion rate at different points in history. The DESI collaboration calculated that the universe’s expansion speed increases by 68.5 km per second every 3.26 million light-years.

Interestingly, DESI results hint at potential changes in dark energy density, with increases and decreases observed. If confirmed, these findings could lead to a complete reevaluation of our understanding of the universe and potentially new physics. Scientists speculate that dark energy could be a new invisible field or a new particle, but more data is needed to confirm the DESI findings with a higher confidence level.

Collaboration and Future Work

DESI is a collaboration of nearly 500 researchers from around the world, including scientists from the United States, United Kingdom, France, Spain, and other countries. As DESI continues its observations, the data collected will be made publicly available, allowing researchers worldwide to study and analyze the data to further our understanding of the universe and its evolution. The potential variability in dark energy density, as hinted at by DESI’s first-year results, will be a key focus of future research and could lead to groundbreaking discoveries in cosmology and fundamental physics.

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