Dark energy search gives insight into expanding universe

The first results from the Dark Energy Spectroscopic Instrument (DESI) have been released. The findings will help build a picture of how the universe has evolved over 11 billion years.

DESI’s components, based on a mountain peak in Arizona, include a focal plane containing 5,000 robots which position fibres within the instrument to produce spectrographs. Its primary aim is to uncover the mysterious hypothetical “dark energy” which is believed to be the driver behind the accelerating expansion of the universe.

DESI has created the largest 3D map of the cosmos ever. The map is based on the most precise measurements to date. For the first time, cosmologists have measured the expansion history of the young universe with more than 99% accuracy.

The first year of data collected by DESI is reported in multiple papers published today, as well as preprints on arXiv, and in talks at the American Physical Society meetings in the US and Italy.

“So far, we’re seeing basic agreement with our best model of the universe, but we’re also seeing some potentially interesting differences that could indicate that dark energy is evolving with time,” says DESI director Michael Levi, a scientist at the US Department of Energy’s Lawrence Berkeley National Laboratory. “Those may or may not go away with more data, so we’re excited to start analysing our 3-year dataset soon.”

The Standard Model of Cosmology, called the Lambda-CDM model, is the simplest and best answer physicists have to the mysteries of the universe.

Lambda-CDM suggests that the matter that we can see and interact with makes up only about 5% of the “stuff” in the universe. Hypothetical dark matter and dark energy make up the rest. And they shape the expansion of the universe in opposite ways.

Dark matter, which doesn’t perceptibly interact with ordinary matter or light, accounts for about 25% of the universe. It is believed that the gravitational pull of dark matter is vital for the formation of galaxies.

Dark energy on the other hand, is speeding up the expansion of the universe. This elusive phenomenon should make up about 70% of the mass of the cosmos according to Lambda-CDM.

DESI has set a record for precision in mapping the young universe. For the epoch covering 8–11 billion years ago, it is accurate down to 0.82%. This period began less than 3 billion years after the Big Bang. It was in this epoch, about 9 billion years ago, that the first solar systems began to form in the young galaxies.

Artist’s rendering shows light from quasars passing through intergalactic clouds of hydrogen gas to desi
Artist’s rendering shows light from quasars passing through intergalactic clouds of hydrogen gas. Credit: NOIRLab/NSF/AURA/P. Marenfeld and DESI collaboration.

The map is constructed using quasars – the intensely bright light given off by dust and gas orbiting supermassive black holes.

“We use quasars as a backlight to basically see the shadow of the intervening gas between the quasars and us,” says Andreu Font-Ribera, a scientist at the Institute for High Energy Physics in Spain.

DESI will gather more data during its 5-year survey, and over time the results will become more precise. It will either confirm our best current theories of the universe, or provide clues as to how they need to be updated.

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