Baryonic acoustic oscillations, or BAO, are three-dimensional sound waves that measure cosmic distances. These waves provide insight into the history of time and space because they indicate the expansion and cooling of the universe since its inception. A group of astronomers from the University of Hawaii recently discovered a huge BAO shell associated with several galaxies, which led to revelatory findings about how fast the universe is expanding.
Scientists can detect and identify a BAO in space because it forms a ripple-like pattern with a unique density. The origin of such patterns aligns with the birth of the universe.
In its early stages, the universe comprised evenly spaced matter. However, gravity exerted sufficient force to warp matter into galaxies, which unavoidably led to heat generation. Heat countered the effects of gravity, pushing matter farther apart.
This oppositional dynamic changed when the universe expanded, cooling and allowing gravity to pull matter closer together again. The alternating forces of gravity and heat resulted in distinct wave formations. After the Big Bang and the creation of atoms, these waves traveled through matter over the course of 380 million years. Millions of years later, the universe significantly expanded and cooled, locking the waves in place. These frozen cosmic fossils became known as BAOs.
Astronomy teams first recognized BAOs in Mexico and Australia in 2005. This discovery served as conclusive evidence of the Big Bang. Measuring the size of BAOs helped scientists map the history of the universe more precisely.
The 2005 study used statistics to estimate the size and density of around 1 million galaxies. In doing so, the researchers were able to measure cosmic distances, locate galaxies, and gain a better picture of the early universe. They found that BAOs contributed to the way galaxies clustered after the Big Bang.
For instance, the most common distance between one galaxy and another is about 500 million light years because the ripple effect of BAOs facilitated galaxy formation along the waves. Today, scientists are more likely to locate galaxies within that distance of each other.
In 2023, astronomer Brent Tully and his University of Hawaii research team discovered a BAO bubble around 820 million light years away from Earth. The bubble, named Ho’oleilana, after a Hawaiian chant, comprises an extensive shell of previously studied galactic structures.
Additionally, Ho’oleilana contains an empty sphere called the Boötes Void. While all these structures have already been identified and located by other astronomers, the BAO shell encompassing them had not been noted until Tully’s work.
With an immense diameter of 1 billion light years, Ho’oleilana’s size is bigger than expected. However, with rigorous statistical methods in use and their low margin of error, the researchers have confirmed that the universe’s expansion is happening faster than anticipated. Astronomers usually describe the expansion rate using the Hubble constant of 43.3 miles per second per megaparsec, but recent research challenges the value of the Hubble constant. These new findings illustrate that the rate is closer to 47.8, corresponding to other measurements in existing research.
