Black holes may be the source of mysterious dark energy. Not since Albert Einstein’s proposition of the existence of black holes in 1915, nor the first confirmation of one in 1971¹ , nor the initial proposition of the existence of dark energy in the late 1990’s² has anyone imagined this mind boggling possibility. If confirmed, it is a revolution in astronomy and would redefine what a black hole really is.

An international team of astronomers and cosmologists led by the University of Hawaii have discovered a unprecedented phenomena in studying 9 billion years of galactic evolution. The black holes keep growing when the rest of the galaxy has stopped.

The researchers studied the size of black holes from early in the universe all the way up to the present. Their focus was on the supermassive black holes that appear at the center of all large galaxies. They affect the evolution of our entire galaxy.

Small black holes orbiting in a galaxy are about 5-10 solar masses, but supermassive black holes (SMBH) are millions or billions or solar masses.

The scientists began their study with giant elliptical galaxies, a kind that were active in star formation long ago but are now full of old, quiet stars. They expected  the black holes to be growing in size in the early universe, and then stop as we get closer to the present day.

To everyone’s surprise, they found the SMBH were continuing to grow at a rapid pace, from 7 to 20 times greater in size now than billions of years ago.  Other objects in the galaxies observed did not grow.

Another surprising observation was the rate of growth was synchronized to the rate of expansion of the universe. This led to the new theory, so we need to talk about the expansion of the universe a bit.

Edwin Hubbell discovered the expansion of the universe in 1929, based on his observations of galaxies.  This was a truly revolutionary discovery, however it had been predicted by Einstein’s theory of relativity.  It’s since been confirmed by countless observations.

Forward to the 1990s, when teams of astronomers at Berkeley and Harvard were doing detailed studies of supernovae, to get more precise measurement of the rate of expansion known as the Hubble constant.  It was result that no one predicted: the rate was not a constant, and in fact the rate of expansion was accelerating considerably over time.

There was no known phenomena that could account for massively accelerating the entire known universe. So theorists came up with the term “dark energy” to explain the possible cause. Many theories were then proposed to explain how dark energy might work, including antigravity.  But there were no experiments that confirmed any of the theories. Most were refuted.

This led to a series of extremely ambitious experiments beginning around 2010, that aimed to survey all of the galaxies observable in the entire sky. This would give theorists a true big picture view of how the whole observable universe looks. Surveys with acronyms like WISE and DES are the source of data for the current study.

This is where team found the elliptical galaxies, from 9 billion years ago to today. After finding the continued growth in elliptical galaxies, they expanded their study to look at other types of galaxies. Sure enough, their black holes are growing too. And again synchronized with the rate of expansion of the universe.  

 So how are these ancient SMBH able to keep attracting so much new matter?  The astronomers suggest vacuum energy.

Vacuum energy is a concept from quantum mechanics, that has already been experimentally proven. It says that empty spacetime is actually full of incredible amounts of energy.  Under the right conditions it can spontaneously create and destroy matter and energy.

If black holes were radiating large amounts of vacuum energy it would explain both the continuing growth, and provide dark energy for expanding the universe.

A claim as bold and far reaching as this needs plenty of verification before we believe it. But it’s an incredibly exciting possibility that redefines what a black hole is, and solves the mystery of Cosmic expansion all in one concept. With actual evidence to support it.

“We’re really saying two things at once: That there’s evidence the typical black hole solutions don’t work for you on a long, long timescale, and we have the first proposed astrophysical source for dark energy,” said lead study author Duncan Farrah, from the University of Hawaii.

“Observational Evidence for Cosmological Coupling of Black Holes and Its Implications for an Astrophysical Source of Dark Energy,” Duncan Farrah et al 2023 ApJL 944 L31. doi:10.3847/2041-8213/acb704

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¹ In 1971 physicist David C. Robinson presented evidence that a strong gravitational source in a binary star system known as Cygnus X-1 was most likely a black hole.

² The idea of dark energy was first proposed in the late 1990s, based on observations of distant supernovae. In 1998, two independent teams of astrophysicists (the Supernova Cosmology Project and the High-Z Supernova Search Team) found evidence that the expansion of the universe was actually accelerating, contrary to what was expected based on the known properties of matter and gravity. They hypothesized that some mysterious force, which they called “dark energy,” was responsible for the observed acceleration. The concept of dark energy is still an active area of research in astrophysics, and its true nature and properties are still not fully understood.