Posted in | Quantum Physics

Proof for Existence of Dynamical Dark Energy Established

A team of International Scientists, which also included University of Portsmouth Astronomers, has unearthed the proof for the existence of dynamical dark energy.

The cosmological “constant” (illustrated by the straight yellow line) is introduced to explain the accelerated expansion of the Universe (shown as the expanding blue cone) due to the presence of dark energy. The study instead suggests that the contribution of dark energy to this expansion is time-dependent (grey curve). The uncertainty of this time dependency is also shown (blue shaded area). Credit: University of Portsmouth

The findings have been reported in the Nature Astronomy journal and indicate that the nature of dark energy might not be the cosmological constant established by Albert Einstein more than a century ago, which is paramount in the investigation of dark energy.

According to 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), who was the Lead Author of the study, “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.”

Since its discovery at the end of last century, dark energy has been a riddle wrapped in an enigma. 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.

Professor Bob Nichol, Co-author of the study and Director, the ICG

Unearthing the characteristics of dark energy is an important aim of modern sciences. The physical characteristics of dark energy are delineated by its Equation of State (EoS), that is, the ratio between pressure and energy density of dark energy.

In the conventional Lambda-Cold Dark Matter (LCDM) model, dark energy is typically the cosmological constant, or the vacuum energy, that has a constant EoS of -1. According to this model, there are no dynamical characteristics for dark energy.

In the year 2016, a group of Researchers, forming part of the SDSS-III (BOSS) collaboration, headed by Professor Zhao successfully and more accurately measured the Baryonic Acoustic Oscillations (BAO) at a number of cosmic epochs.

The research team adopted this measurement and a technique formulated by Professor Zhao for analyzing dark energy to find out proof for the existence of dynamical dark energy at a significance level of 3.5 sigma. The NAOC reports that this indicates that the characteristic of dark energy might not be that of vacuum energy and may be a specific type of dynamical field, particularly in the case of quintom model of dark energy wherein the EoS changes with time and surpasses the -1 boundary as part of evolution.

Next-generation astronomical surveys have to be adopted to ascertain the dynamics of dark energy. The Researchers signal the forthcoming Dark Energy Spectroscopic Instrument (DESI) survey, the goal of which is to start developing a 3D cosmic map in the year 2018.

By the next half or full decade, surveys of the world largest galaxy will offer observables that might be significant in unearthing the secrets behind dark energy.

The National Natural Science Foundation of China (NSFC), Chinese Academy of Sciences and a Royal Society Newton Advanced Fellowship supported this research.

ICG members Florian Beutler, Rob Crittenden, Kazuya Koyama Bob Nichol, Will Percival, and Levon Pogosian were also involved in this research.

This work is the culmination of many years of work in collaboration between scientists in China and the UK. Gong-Bo is one of our brightest stars holding a joint position between NAOC and here at the ICG.

Professor Bob Nichol, Co-author of the study and Director, the ICG

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