An international team of researchers, including Professor of Astrophysics and Scientific Computing, Andreas Efstathiou, has found observational evidence that there is a link between black holes and dark energy.
CNA spoke with Rector of the European University Cyprus, Professor of Astrophysics and Scientific Computing, Prof. Andreas Efstathiou, on this discovery, which explains the nature of dark energy without resorting to any new theories in physics and for the first time proposes an astrophysical source for dark energy.
The international team of researchers consists of 17 scientists from nine different countries and has recently published two papers.
Professor Efstathiou said that the team found observational evidence that there is a link between black holes and dark energy when we consider that black holes exist in a Universe which is expanding. This is referred to as cosmological coupling.
These new measurements, if supported by further evidence, redefine our understanding of what a black hole is, he explained.
He told CNA that if cosmological coupling is confirmed, it would mean that black holes never entirely disconnect from our universe, that they continue to exert a major influence on the evolution of the universe into the distant future.
What are black holes and dark energy
Invited to explain the two concepts, the Professor told CNA that "black holes and dark energy are two of the most mysterious concepts in astrophysics and cosmology."
Black holes, he explained, are the end product of the evolution of massive stars. Their gravity is so strong that not even light escapes and we know of their existence mainly from the influence they exert on their surroundings.
He said that of special interest are supermassive black holes, which have millions or billions times the mass of the sun, and which are found at the centers of galaxies.
Furthermore, he recalled that the Nobel prize in Physics in 2020 was awarded to Roger Penrose for his theoretical work on black holes, and Andrea Ghez and Reinhard Genzel for their work on finding evidence for a supermassive black hole at the center of our galaxy.
As regards dark energy, he told CNA that it is the mysterious form of energy that is believed to permeate the Universe and which drives its accelerated expansion discovered in 1998.
The Nobel prize in Physics in 2011 was awarded to Saul Perlmutter, Brian P. Schmidt and Adam G. Riess for this discovery.
"So far there has not been a convincing explanation for the nature and origin of dark energy" he pointed out.
Professor Efstathiou told CNA that "our team found observational evidence that there is a link between black holes and dark energy when we consider that black holes exist in a Universe which is expanding," adding that "this is referred to as cosmological coupling."
He said that the team of researchers which consists of 17 scientists from 9 different countries has recently published two papers, one in “The Astrophysical Journal” and the other in “The Astrophysical Journal Letters”, that studied supermassive black holes at the hearts of ancient and dormant elliptical galaxies.
The first paper found that these black holes gain mass over billions of years in a way that cannot easily be explained by standard galaxy and black hole processes, such as mergers or accretion of gas.
The second paper finds that the growth in mass of these black holes matches predictions for black holes that not only cosmologically couple, but also enclose vacuum energy - material that results from squeezing matter as much as possible without breaking Einstein's equations, thus avoiding a singularity.
The paper then shows that the combined vacuum energy of black holes produced in the deaths of the universe's first stars agrees with the measured quantity of dark energy in our universe.
The significance of this discovery
"The importance of this discovery is that it explains the nature of dark energy without resorting to any new theories in physics" Professor Efstathiou told CNA.
He added that dark energy is explained by Einstein’s theory of general relativity when black holes are set in the context of an expanding Universe.
"Our study for the first time proposes an astrophysical source for dark energy", he stressed.
These new measurements, he added, if supported by further evidence, "redefine our understanding of what a black hole is".
Furthermore, he said that the study provides a framework for theoretical physicists and astronomers to further test and shed light on the idea.
The current generation of dark energy experiments such as the Dark Energy Spectroscopic Instrument and the Dark Energy Survey are expected to contribute in this effort.
"If cosmological coupling is confirmed, it would mean that black holes never entirely disconnect from our universe, that they continue to exert a major influence on the evolution of the universe into the distant future" he underlined.
European University Cyprus involvement
Asked about the involvement of the University in this study, he said that he has been collaborating with the first author of the two papers (Prof Duncan Farrah at the University of Hawaii) and other members of the team for more than two decades.
Another key collaborator, he added, is Dr David Clements at Imperial College London and Dr Chris Pearson at the Rutherford Appleton Laboratory in Oxfordshire.
"Our main interest in most of the work I have done in the past with members of this team has mainly been the study of supermassive black holes in a class of galaxies known as ultraluminous infrared galaxies or ULIRGs", he told CNA.
The Professor explained that ULIRGs are the result of the merger of two large spiral galaxies and are destined to become elliptical galaxies.
This work and expertise, he went on to say, were essential for the conclusion reached in the first paper that black holes in elliptical galaxies gain more mass in the last 10 billion years than can be explained by known processes in galaxy evolution.
"Our team also has expertise in studying the star formation history of the Universe. This expertise was essential for the calculations in the second paper that show that the amount of dark energy in the Universe today (~68% of the total) can be explained by the black holes created by the death of massive stars in the history of the Universe", he concluded.
Source: Cyprus News Agency