Astronomers have discovered (ref.) an immense bubble of galaxies that could be a “fossil” remnant of the Big Bang. The cosmic bubble, approximately 820 million light-years from Earth, is one billion light-years wide. It is located within a network of galaxies called Ho’oleilana. The term is taken from the Hawaiian creation chant Kumulipo.
These massive structures like Ho’oleilana arise in the universe as a result of small ripples in the hot, dense, and uniform material present at the beginning of the cosmos. These density ripples, called baryon acoustic oscillations (BAO), grew as the universe passed through the moments of the Big Bang. Thanks to these ripples, significant cosmic structures were born and influenced the distribution of galaxies. However, this is the first identification of a single structure associated with a BAO.
Ho’oleilana
The bubble itself is composed of previously identified structures. We are talking about some of the largest arrangements of matter in the universe. This includes several superclusters, or groups of galaxy clusters, each containing 10 clusters and extending up to 200 million light-years. At the heart of Ho’oleilana lies the Boötes supercluster and the Boötes void, a 330 million light-year-wide empty space.
“We weren’t looking for it. It’s so enormous that it extends to the edges of the sky sector we were analyzing” said Brent Tully, leader of the study and astronomer at the University of Hawaii. “The density of galaxies is a much larger feature than expected. The one-billion-light-year diameter goes well beyond theoretical expectations”.
Tully added that the characteristics of the Ho’oleilana bubble of galaxies are in agreement with the Big Bang theory. So, the BAO that originated it must be closer to Earth than expected and could have implications for the rate at which the universe expanded. The bubble was found using data sets collected by Cosmicflows-4, published in 2022, and marks the largest collection of precise galaxy distances.
Formation of the Superbubble
About 380,000 years after the birth of the cosmos, space was a sea of electrons and protons. This substance is known as plasma, which, when it cooled, allowed the formation of atoms and the birth of matter. Overly dense regions collapsed under their own gravity. This process was countered by the radiation from the Big Bang, which pushed matter apart. The cosmic tug-of-war between gravity and radiation caused ripples in the plasma.
The size of the largest of these ripples was determined by the speed at which a sound wave could travel through the plasma. This size turned out to be about 500 million light-years, and once the plasma cooled, it left behind extensive 3D ripple imprints. As the universe further aged, galaxies began to form at density peaks with tremendously large bubble-shaped cocoons.
In 2014, the same team identified the Laniakea Supercluster, which hosts the Milky Way and about 100,000 other galaxies. But it is only 500 million light-years wide, which is half the width of Ho’oleilana. The Laniakea Supercluster extends to the edge of this larger bubble.
A 3D Map
Traces of Ho’oleilana have already been discovered in the past. In 2016, the Sloan Digital Sky Survey identified part of its shell structure. However, the true extent of its size has remained hidden until now. Even previous work had failed to connect the cosmic bubble with BAO.
“I am the group’s cartographer, and mapping Ho’oleilana in three dimensions helps us understand its content and relationship with the surrounding environment” said Daniel Pomarede, a researcher at the University CEA Paris-Saclay. “It has been an extraordinary process to build this map and see how Ho’oleilana’s gigantic shell structure is composed of elements”.