Five-year quest to map Universe and unravel mysteries of 'dark energy'

Andromeda Galaxy

Astrophysicists from the University will work with an international team to capture and study the light from tens of millions of galaxies.

  • 17 May 2021
  • 5 min read

A five-year quest to map the Universe and unravel the mysteries of ‘dark energy’ officially begins today in the United States, with the help of an international team of scientists.

The team - including astrophysicists from the University of Portsmouth - will use the Dark Energy Spectroscopic Instrument (DESI) to capture and study the light from tens of millions of galaxies and other distant objects in the Universe. 

The technology allows the team to see ten times more galaxies than ever before and to look back billions of years in time.

By gathering light from some 30 million galaxies, DESI will help the scientists construct a 3D map of the Universe with unprecedented detail. The data will help them better understand the repulsive force associated with ‘dark energy’ that drives the acceleration of the expansion of the Universe across vast cosmic distances. 

Kitt Peak National Observatory

Kitt Peak National Observatory near Tucson, Arizona

Dr Becky Canning, from the University’s Institute of Cosmology and Gravitation, said: “DESI will revolutionise our understanding of how our Universe and its galaxies evolved. 

"In just the survey validation phase DESI has already taken spectra of more than a million unique objects, already comparable or surpassing all previous spectroscopic surveys, and the five-year survey has only just begun!"

"Spectroscopy of such large numbers of galaxies not only enables us to measure characteristics of our Universe and properties of its galaxies with a high precision, developing a deeper understanding of how we came to be, but it also enables us to search for exciting and incredibly rare events which might lead to the discovery of new physics."

The DESI instrument is located at the Kitt Peak National Observatory near Tucson, Arizona. It has new optics that increase the field of view of the telescope and includes 5,000 robotically controlled optical fibres to gather spectroscopic data from an equal number of objects in the telescope’s field of view. 

Project director, Berkeley Laboratory’s Michael Levi, said the DESI is different from previous sky surveys: "We will measure ten times more galaxy spectra than ever obtained before. These spectra get us a third dimension."

Instead of two-dimensional images of galaxies, quasars, and other distant objects, he explains, the instrument collects light, or spectra, from the cosmos such that it "becomes a time machine where we place those objects on a timeline that reaches as far back as 11 billion years ago."

 

Spectroscopy of such large numbers of galaxies not only enables us to measure characteristics of our Universe and properties of its galaxies with a high precision, but it also enables us to search for exciting and incredibly rare events which might lead to the discovery of new physics.

Dr Becky Canning, Senior Lecturer

The formal start of DESI’s five-year survey follows a four-month trial run of its custom instrumentation that captured four million spectra of galaxies - more than the combined output of all previous spectroscopic surveys.

Spectra collected by DESI are the components of light corresponding to the colours 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. The detailed distribution of galaxies in the map is expected to yield new insights on the influence and nature of dark energy. 

DESI is an international science collaboration managed by the Lawrence Berkeley National Laboratory (Berkeley Lab) with primary funding from the U.S. Department of Energy (DOE) Office of Science.

"Dark energy is one of the key science drivers for DESI" says project co-spokesperson Kyle Dawson, a professor of physics and astronomy at University of Utah. "The goal is not so much to find out how much there is—we know that about 70 per cent of the energy in the Universe today is dark energy—but to study its properties," he says. 

The Universe is expanding at a rate determined by its total energy contents, Dawson explains. As the DESI instrument looks out in space and time, he says, "we can literally take snapshots today, yesterday, 1 billion-years-ago, 2 billion-years-ago—as far back in time as possible. We can then figure out the energy content in these snapshots and see how it is evolving."

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