Early dark energy may solve two cosmological puzzles

September 13 () –

A new study by MIT physicists proposes that a mysterious force known as early dark energy may solve two of the biggest puzzles in cosmology.

One is the “Hubble tension”, which refers to a mismatch in measurements of the expansion rate of the universe. The other involves observations of numerous bright early galaxies that existed at a time when the early universe should have been much less crowded.

Now, the MIT team (Massachusetts Institute of Technology) has found that both puzzles could be solved if the early universe had an additional, fleeting ingredient: early dark energy. Dark energy is an unknown form of energy that physicists suspect is driving the expansion of the present-day universe. Early dark energy is a similar hypothetical phenomenon that may have made only a brief appearance, influencing the expansion of the universe in its early moments before disappearing completely.

Some physicists have suspected that early dark energy could be the key to resolving the Hubble tension, as the mysterious force could accelerate the early expansion of the universe. in an amount that would resolve the measurement mismatch.

MIT researchers have now discovered that early dark energy could also explain the puzzling number of bright galaxies astronomers have observed in the early universe. In their new study, published today in Monthly Notices of the Royal Astronomical Societythe team modeled galaxy formation in the first few hundred million years of the universe. When they incorporated a dark energy component only in that earlier time frame, they found that the number of galaxies that emerged from the primordial environment and flourished to match astronomers’ observations.

“We have these two open puzzles coming up,” he says. in a statement study co-author Rohan Naidu, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research. “We’ve found that, in fact, early dark energy is a very elegant and sparse solution to two of the most pressing problems in cosmology.”

According to standard cosmological and galaxy formation models, The universe should have taken its time to form the first galaxiesIt would have taken billions of years for primordial gas to coalesce into galaxies as large and bright as the Milky Way.

But in 2023, NASA’s James Webb Space Telescope (JWST) made a surprising observation. With an ability to look further back in time than any other observatory to date, the telescope discovered a surprising number of bright galaxies as large as the modern Milky Way in the first 500 million years, when the universe was only 3 percent of its current age.

“The bright galaxies that JWST saw would be like seeing a cluster of lights around large cities, whereas theory predicts something like the light around more rural environments like Yellowstone National Park,” Shen says. “And we don’t expect that cluster of light this early.”

For physicists, the observations imply that there is either something fundamentally wrong with the physics underlying the models or a missing ingredient in the early universe that scientists have not accounted for. The MIT team explored the possibility of the latter, and whether the missing ingredient might be primitive dark energy.

Physicists have proposed that early dark energy is a kind of antigravitational force that kicks in only at very early times. This force would counteract the inward pull of gravity and accelerate the early expansion of the universe, in a way that would resolve the mismatch in measurements. Thus, Early dark energy is considered the most likely solution to the Hubble tension.

The MIT team explored whether early dark energy could also be the key to explaining the unexpected population of large, bright galaxies detected by JWST. In their new study, the physicists considered how early dark energy might affect the early structure of the universe that gave rise to the first galaxies. They focused on the formation of dark matter halos, regions of space where gravity turns out to be stronger and where matter begins to accumulate.

THE SKELETON OF THE GALAXY

“We think that dark matter halos are the invisible skeleton of the universe,” Shen explains. “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 matter halos.“.

The team developed an empirical framework for early galaxy formation, which predicts the number, luminosity, and size of galaxies that should form in the early universe, given some measurements of “cosmological parameters.” Cosmological parameters are the basic ingredients, or mathematical terms, that describe the evolution of the universe.

Physicists have determined that there are at least six main cosmological parameters, one of which is the Hubble constant, a term that describes the rate of expansion of the universe. Other parameters describe density fluctuations in the primordial soup immediately after the Big Bang, from which dark matter halos form.

The MIT team reasoned that If early dark energy affects the early expansion rate of the universe, in a way that resolves the Hubble tension, then could affect the balance of the other cosmological parametersin a way that could increase the number of bright galaxies that appear at early times. To test their theory, they incorporated an early dark energy model (the same one that resolves the Hubble tension) into an empirical galaxy formation framework to see how the first dark matter structures evolve and give rise to the first galaxies.

“What we show is that the skeletal structure of the early universe is altered in a subtle way, where the amplitude of the fluctuations increases and larger halos and brighter galaxies are obtained. than those that existed in previous times, rather than in our more conventional models,” Naidu says. “That means things were more abundant and more packed together in the early universe.”