Physicist Gregory Tarlé from the University of Michigan, along with an international team of researchers, has discovered new evidence of “cosmological coupling”—a previously unobserved phenomenon from Einstein’s theory of gravity that links black holes to the expansion of the universe. Their findings, published in The Astrophysical Journal and The Astrophysical Journal Letters, suggest that black holes, particularly those at the center of ancient galaxies, could be the source of dark energy, the mysterious force that makes up 70% of the universe’s energy.

The first study explored how black holes in ancient elliptical galaxies have grown over billions of years. Normally, black holes increase in mass through processes like accreting gas or merging with other black holes. However, the research team discovered that the mass of these black holes had increased far beyond what such processes could explain. The black holes were found to be 7 to 20 times larger today than they were 9 billion years ago.

This unexpected mass growth led the researchers to suspect cosmological coupling, which occurs when black holes gain mass as the universe expands. This phenomenon, predicted by Einstein’s equations but never before observed, could explain the massive increase in black hole size over time.

The second study investigated whether this growth could be explained solely by cosmological coupling. The researchers likened the process to a rubber band stretching as the universe expands. As the rubber band stretches, its energy increases, and so does the mass of the black hole. The key to determining how much mass a black hole gains lies in a variable called “k,” which measures the coupling strength between black holes and the universe.

By analyzing five different black hole populations, the team calculated a value of k close to 3, a figure predicted by previous studies for black holes that contain vacuum energy, rather than a singularity. This finding supports the idea that black holes could contribute to dark energy, the mysterious force accelerating the universe’s expansion.

If these findings hold up under further scrutiny, they could change our understanding of black holes and dark energy. Rather than existing as isolated entities, black holes would be deeply connected to the universe’s evolution, continuing to influence its expansion.

Previous theories proposed various sources for dark energy, but this study is the first to suggest that black holes themselves could be responsible, with no need for additional exotic matter or forces. As Duncan Farrah, lead author of the studies, stated, “Black holes in Einstein’s theory of gravity are the dark energy.”

The implications of this discovery are profound. If cosmological coupling is confirmed, it would provide a framework for understanding the universe’s evolution and offer new directions for research in dark energy experiments, such as the Dark Energy Spectroscopic Instrument and the Dark Energy Survey. This finding could finally explain why 70% of the universe’s energy is composed of dark energy—and why it exists now.