Early Dark Energy May Solve Two Biggest Mysteries in Cosmology

Of all the mysteries facing astronomers and meteorologists today, the “Hubble Controversy” still persists! This term refers to the apparent inconsistency of the expansion of the Universe (aka. the Hubble Constant) when internal measurements are compared to those of the Cosmic Microwave Background (CMB). Astronomers hoped that observations of the earliest galaxies in the Universe by the James Webb Space Telescope (JWST) would solve this mystery. Unfortunately, Webb proved that the previous measurements were correct, so the “tension” endures.

Since JWST made its observations, many scientists have suggested that the existence of Early Dark Energy (EDE) could explain the Hubble Tension. In a recent study supported by NASA and the National Science Foundation (NSF), researchers from the Massachusetts Institute of Technology (MIT) suggested that EDE could solve two cosmic mysteries. In addition to the Hubble Gravity, it may explain why Webb saw as many galaxies as there were during the early Universe. According to current models of the universe, the Universe should have had very few people at that time.

The research was led by Xuejian Shen and colleagues from the Department of Physics and the Kavli Institute for Astrophysics and Space Research (MTK) at MIT. They were joined by researchers from the NSF AI Institute for Artificial Intelligence and Basic Interaction (IAIFI) at MIT, the University of Texas at Austin, and the Kavli Institute for Cosmology (KICC) and the Cavendish Laboratory at the University of Cambridge. A paper detailing their findings was recently published in the journal Monthly Notices of the Royal Astronomical Society.

To recap, Dark Energy is the theoretical form of energy that is believed to be driving the expansion of the Universe today. The theory first emerged in the 1990s to explain the study of the elderly Hubble Space Telescopewhich showed that cosmic expansion appeared to be accelerating over time. The EDE is similar but is thought to have appeared shortly after the Big Bang, which then disappeared after affecting the expansion of the early Universe. Like Dark Energy, this force would counteract the gravity of early galaxies and temporarily accelerate the expansion of the Universe.

The existence of this energy may also explain why measurements of the Hubble Constant are inconsistent. Short of General Relativity being wrong (despite being repeatedly proven for over a century), EDE is considered the most likely solution to the Hubble Tension. Similarly, Webb’s 2023 survey revealed a surprising number of bright galaxies just 500 million years after the Big Bang that were comparable in size to the modern Milky Way. These results challenge standard models of galaxy formation, which predict that galaxies take billions of years to form and grow.

For their research, the team focused on the formation of “Dark Matter Halos,” a hypothetical region that allows protogalaxies to collect gas and dust, leading to the formation and growth of stars. As stated in a recent MIT News story:

“The bright galaxies that JWST saw would be like seeing a cluster of lights near big cities, while theory predicts something like light near a more rural environment like Yellowstone National Park. And we don’t expect that light clustering so early. We believe that dark halos is the invisible skeleton of the universe. Dark matter structures form first, and then galaxies form within these structures. Therefore, we expect the number of bright galaxies to be proportional to the number of large dark halos.

The team developed an empirical framework for early galaxy formation that included the “six cosmological parameters”—basic mathematical terms that describe the evolution of the Universe. This includes the Hubble Constant, which describes the expansion of the universe, while the parameters describe the change in density immediately after the Big Bang, in which dark halos were created. The team theorized that if the EDE affected the early expansion of the universe, it could also affect other parameters that could explain the appearance of many massive galaxies shortly thereafter.

To test their theory, the team simulated the formation of galaxies within the first few hundred million years of the Universe. This model included EDE to determine how dark matter structures evolved and produced the first galaxies in the Universe. As study co-author Rohan Naidu, a post writer with MKI, explained:

“You have these two puzzles coming up. We see that indeed, early dark energy is a very elegant and rare solution to two of the most pressing problems in the universe. What we show is that the skeletal structure of the early universe is changed in a subtle way where the amplitude of the fluctuations goes up, and we get bigger halos, and brighter galaxies that are in place earlier, more so than in our more vanilla ones. examples. It means that things were more plentiful, and more concentrated in the early world.

““We demonstrated the potential of early dark energy as a unified solution to two major problems facing the universe,” added co-author Mark Vogelsberger, MIT professor of physics. In the future, we may incorporate this into larger global models to see what detailed predictions we get.

Further Reading: MIT News, MNRAS