(ORDO NEWS) — Observations of supermassive black holes at the centers of galaxies point to a likely source of dark energy – the “missing” 70% of the universe.
Measurements of ancient and dormant galaxies show that black holes are growing more than expected, in line with the phenomenon predicted by Einstein’s theory of gravity.
The result potentially means that nothing new needs to be added to our picture of the universe to explain dark energy: the source is black holes combined with Einstein’s gravity.
This conclusion was reached by a group of 17 researchers from 9 countries, led by the University of Hawaii and including physicists from Imperial College London and STFC RAL Space.
Study co-author Dr. Dave Clements of the Imperial Department of Physics said: “This is a truly amazing result.
We started by looking at how black holes grow over time and found the answer to one of the biggest questions in cosmology.”
Study co-author Dr Chris Pearson of STFC RAL Space said: “If the theory is correct, then it will revolutionize the whole of cosmology because we finally have a solution to the origin of dark energy that has baffled cosmologists and theoretical physicists for more than 20 years. years”.
Gravity versus dark energy
In the 1990s, it was discovered that the expansion of the universe is accelerating – everything is moving away from everything else at a faster and faster rate. It’s hard to explain – the gravitational pull between all objects in the universe should slow down the expansion.
To explain this, it has been suggested that “dark energy” is more responsible for pushing things apart than gravity.
This was due to a concept proposed by Einstein, but later rejected, of a “cosmological constant” that opposes gravity and keeps the universe from collapsing.
This concept was revived with the discovery of the accelerating expansion of the universe, the main component of which is a kind of energy embedded in space-time itself, called vacuum energy. This energy pushes the universe further apart, accelerating the expansion.
However, black holes presented a problem – their extremely strong gravity is hard to resist, especially at the centers where everything collapses into a singularity.
The new result shows that black holes gain mass in a way that contains vacuum energy, providing a source of dark energy and eliminating the need for singularities to form at the center.
Black hole growing pains
The conclusion was made as a result of studying nine billion years of the evolution of a black hole. Black holes form when massive stars approach the end of their lives.
When they are at the centers of galaxies, they are called supermassive black holes.
They contain millions or billions of times the mass of our Sun within them in a relatively small space, creating extremely strong gravity.
Black holes can grow in size by accreting matter, for example by devouring stars that come too close, or by merging with other black holes.
To find out if these effects alone could explain the growth of supermassive black holes, the team looked at nine billion years of data.
The researchers looked at giant elliptical galaxies that evolved early in the universe and then became dormant.
Dormant galaxies have finished forming stars, leaving little material for the black hole to accrete at the center, meaning any further growth cannot be explained by these normal astrophysical processes.
Comparison of observations of distant galaxies (when they were young) with local elliptical galaxies (which are old and dead) showed much more than predicted growth due to accretion or mergers: modern black holes are 7-20 times larger than they were 9 billion years back.
Cosmological interaction
Further measurements with related populations of galaxies at different points in the evolution of the Universe show a good agreement between the size of the Universe and the mass of black holes.
They show that the measured amount of dark energy in the universe can be explained by the vacuum energy of a black hole.
This is the first observational evidence that black holes actually contain vacuum energy and that they are “linked” to the expansion of the universe, increasing in mass as the universe expands a phenomenon called “cosmological coupling.”
If further observations confirm this, the cosmological connection will change our understanding of what a black hole is.
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