A team of astronomers led by the University of Portsmouth have found evidence of dynamical dark energy.

“We are excited to see that current observations are able to probe the dynamics of dark energy at this level and we hope that future observations will confirm what we see today,” lead author of the study Professor Gong-Bo Zhao, from the Institute of Cosmology and Gravitation (ICG) at the University of Portsmouth and the National Astronomical Observatories of China (NAOC), said in a statement.

Dark energy is represented by its Equation of State (EoS)—the ratio of pressure and energy density of dark energy.

In the traditional Lambda-Cold Dark Matter model, dark energy is essentially the cosmological constant—the vacuum energy with a constant EoS of -1. In this model dark energy has no dynamical features.

A team within the SDSS-III (BOSS) collaboration performed a successful measurement of the Baryonic Acoustic Oscillations (BAO) at multiple cosmic epochs with a high precision in 2016.

Based on this measurement—and a method developed by Zhao for dark energy studies— the researchers found evidence of dynamical dark energy at a significance level of 3.5 sigma. This suggests that the nature of dark energy may not be the vacuum energy, but some kind of dynamical field, particularly for the quintom model of dark energy whose EoS varies with time and crosses the -1 boundary during evolution.

The findings shed light on the nature of dark energy, which may not be the cosmological constant introduced by Albert Einstein more than a century ago.

“Since its discovery at the end of last century, dark energy has been a riddle wrapped in an enigma,” Co-author Professor Bob Nichol, Director of the ICG, said in a statement. “We are all desperate to gain some greater insight into its characteristics and origin.

“Such work helps us make progress in solving this 21st Century mystery.”

The next step will be to confirm the dynamics of dark energy by next-generation astronomical surveys.