the scientist

[Voice of Hope February 25, 2023](Editor: Guo Xiao) The laws of physics state that gravity causes the universe to contract, but scientists have discovered that the universe is expanding at an accelerating rate. They call the mysterious force causing the expansion of the universe “dark energy”. Nearly 70% of the energy in the universe is dark energy that drives the expansion of the universe, but scientists have never been clear about the “holy” dark energy. An international team of researchers published two papers in The Astrophysical Journal and The Astrophysical Journal Letters stating that their observations of black holes at the centers of galaxies suggest that black holes may be the source of dark energy, in line with Einstein’s The results predicted in Stein’s theory are consistent. If the latest research is confirmed, the mystery of the origin of dark energy that has puzzled scientists for more than 20 years may be solved, which will completely change the face of cosmology.

A team of researchers led by experts at the University of Hawaii at Manoa has found the first evidence of “cosmological coupling,” which is only feasible when black holes are located in an evolving universe. These findings provide insight into what might be inside a black hole. That all changed when the Laser Interferometer Gravitational-Wave Observatory (LIGO) heard the first pair of black holes merge in late 2015, notes Kevin Crocker, professor of physics and astronomy. The signal fits well with predictions, but extending those predictions to millions or billions of years? Fitting a black hole model to our expanding universe? It’s not at all clear how to do this. In the first study, the team determined how to use existing black hole measurements to find cosmological coupling.

Scientists know galaxies are key because they can have a lifespan of billions of years, and most galaxies contain a supermassive black hole. But choosing the right kind of galaxy is crucial. “We decided we could help resolve this issue by focusing only on black holes in passively evolving elliptical galaxies,” said study co-author Sara Petty, a galaxy expert at Northwestern Research Associates. By focusing only on elliptical galaxies with no recent activity, other known processes cannot easily alter the black hole mass of galaxies, the scientists claim. Scientists then used these populations to observe how the mass of its central black hole has changed over the past 9 billion years. The scientists found that the earlier they looked, the less massive the black holes were relative to their current mass.

The black hole is 7 and 20 times larger than it was 9 billion years ago, which is so important that scientists think that the cosmic coupling may be too responsible. In other words, the study found that these black holes accumulated mass over billions of years in a way that is difficult to explain with standard galaxy and black hole processes such as mergers or gas accretion. In the second study, the team investigated the possibility that cosmic coupling could explain the black hole growth observed in the first study. Crocker argues that you can think of coupled black holes as rubber bands that stretch as the universe expands. As it stretches, its energy increases. Einstein’s E=mc2 tells that mass is proportional to energy, so black hole mass will also increase.

“How much the mass increases depends on the coupling strength, a variable called k.” Since black hole mass growth due to cosmological coupling depends on the size of the universe, which was smaller in the past, the black hole mass in the first study had to decrease The correct amount is required for the cosmological coupling explanation to work. The results show that the mass expansion of these black holes is consistent with predictions for black holes that are not only cosmologically coupled, but also contain vacuum energy, which is compressed by compressing as much as possible without violating Einstein’s equations and preventing singularities. produced by matter. The researchers studied three groups of elliptical galaxies, each representing a collection of five different black hole populations, from times when the universe was about one-half and one-third its present size. They found that k was roughly positive 3 in each comparison.

In 2019 mathematics professor Joel Weiner predicted this value for a black hole with vacuum energy rather than a singularity. Crocker and Weiner have shown that if k is 3, then the total contribution of all known black holes to the dark energy density of the universe is nearly constant, as indicated by dark energy measurements. Using the latest measurements of the earliest star formation rates provided by the James Webb Space Telescope, the team found that the numbers agree. They then showed that the measured dark energy in our universe matches the vacuum energy of the black holes that formed when the universe’s first stars died when the singularity did not exist. Typical black hole solutions don’t work on very long timescales, and we now have the first proposed source of dark energy, says astrophysicist Duncan Farah.

While that’s not to say that others haven’t suggested a source of dark energy, this is the first observational paper that doesn’t add anything new to the universe as a source of dark energy: Einstein’s theory of black hole gravity in black holes is dark energy. These studies provide physicists and astronomers with a framework for further testing, and for the current generation of dark energy experiments, such as the Dark Energy Spectrograph and the Dark Energy Survey, to shed light on this idea. Farah believes that, if confirmed, this would be a remarkable result, pointing the way to the next generation of black hole solutions. This measurement explains why the expansion of the universe is accelerating.

Astrophysicist Ethan Siegel summed it up: “Extraordinary claims require extraordinary evidence.” The ability to repeatedly verify results is one of the most important qualifications for evidence to be considered reliable. In other words, the results have to be proven time and time again, using different methods. The authors therefore acknowledge and hope that repeated observations will confirm their unusual view.

Editor in charge: Li Jingrou