The discovery of a huge bubble of galaxies, named Hawaii

The red region (left) shows the crust surrounded by the Acoustic Baryon Oscillation, with individual galaxies depicted as small bright spots. The blue threads show the larger cosmic web, highlighting previously known features such as Laniākea. Image source: Frédéric Dorion, Animea Studio; Daniel Pomared, IRFU, CEA Paris-Saclay University

The University of Hawaii-led discovery of an enormous bubble 820 million light-years from Earth is thought to be a fossil-like relic from the birth of the universe. Astronomer Brent Tully of the University of Houston’s Institute for Astronomy and his team unexpectedly discovered the bubble within a network of galaxies. The entity was named Hoʻoleilana, a term derived from komolipu, a Hawaiian creation chant evoking the structure’s origin.

New results published in Astrophysical JournalRecall that these massive structures were predicted by the Big Bang theory, the result of three-dimensional ripples found in the matter of the early universe, known as baryon acoustic oscillations (BAO).

“We weren’t looking for it,” Tully explained. “It’s so massive that it extends to the edges of the sector of sky that we’ve been analyzing.” “As an enhancement in the density of galaxies, it is a much stronger feature than expected. The very large diameter of a billion light-years exceeds theoretical expectations. If its formation and evolution are consistent with theory, this BAO is closer than expected, which means a high value for the expansion rate of the universe.” ”

Astronomers located the bubble using data from Cosmicflows-4, which is to date the largest compilation of microdistances for galaxies. Tully co-published the extraordinary catalog in the fall of 2022. His team of researchers believes this may be the first time astronomers have identified an individual structure associated with BAO. This discovery could help advance scientists’ knowledge of the effects of galaxy evolution.

The new findings indicate that these massive structures, predicted by the Big Bang theory, are the result of three-dimensional ripples found in the matter of the early universe, known as baryon acoustic oscillations (BAO). Image source: Frédéric Dorion, Animea Studio; Daniel Pomared, IRFU, CEA Paris-Saclay University

Huge bubbles of matter

In the well-established Big Bang theory, for the first 400,000 years, the universe was a cauldron of hot plasma similar to the core of the Sun. Within the plasma, the electrons are separated from the nuclei of the atom. During this period, regions of slightly higher density began to collapse under the influence of gravity, even as the intense radiation bath tried to push the material away. This struggle between gravity and radiation made the plasma oscillate, or ripple, and spread outward.

The largest ripples in the early universe depended on the distance a sound wave could travel. This distance was determined by the speed of sound in the plasma, which is roughly 500 million light-years away, and was fixed when the universe cooled and ceased to be plasma, leaving wide three-dimensional ripples. Over the ages, galaxies have formed at density peaks, in massive bubble-like structures. The patterns of galaxy distribution, if properly characterized, can reveal the characteristics of these ancient messengers.

“I am the group’s cartographer, and mapping Hauleilana in three dimensions helps us understand its content and its relationship with its surroundings,” said researcher Daniel Pomaridy of CEA Paris-Saclay University in France. “It was an amazing process to build this map and see how the structure of Holliana’s giant crust is composed of elements identified in the past as some of the largest structures in the universe.”

The same team of researchers also identified the Laniākea Supercluster in 2014. This structure, which includes the Milky Way, is small by comparison. Laniakea, about 500 million light-years in diameter, extends to the near edge of this much larger bubble.

Detection of a single BAO

Tully’s team discovered that Hoʻoleilana was noted in a 2016 paper as the most prominent of several shell-like structures seen in the Sloan Digital Sky Survey. However, previous work did not reveal the full extent of the structure, and this team did not conclude that they had found BAO.

Using the Cosmicflows-4 catalog, the researchers were able to view the entire globular envelope of galaxies, pinpoint its center, and show that there is a statistical enhancement in galaxy density in all directions from that center. Hoʻoleilana includes many well-known structures previously discovered by astronomers, such as the Harvard/Smithsonian Great Wall of China containing the Coma Cluster, the Hercules Cluster and the Great Wall of Sloan. Boötes Supercluster is at its center. The Boötes Void Historic District, a huge empty sphere, is located within Hoʻoleilana.

Implications for Ho’oleilana

Simulation tests showed that the shell structure identified as Hoʻoleilana has a less than 1% chance of being a statistical accident. Hoʻoleilana has the theoretically expected BV properties, including the prominence of a rich supercluster at its centre. However, it turns out stronger than expected.

In detail, Holliana is slightly larger than would be expected from the Standard Model theory of cosmology, and what has been found from previous even-numbered statistical studies of galaxy separations. The size is consistent with observations of the local expansion rate of the universe and of galactic flows on large scales which also point to subtle problems in the Standard Model.

more information:
R. Brent Tully et al., Holliana: a single baryon acoustic oscillation? Astrophysical Journal (2023). doi: 10.3847/1538-4357/aceaf3

R. Brent Tully et al., Cosmicflows-4, Astrophysical Journal (2023). doi: 10.3847/1538-4357/ac94d8

Provided by the University of Hawaii at Manoa

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