Baryonic acoustic oscillations
After the Big Bang, the matter in the universe was almost evenly distributed, like a great sea of particles. Gravity tried to put this matter together to form galaxies. But when matter came together, it got very hot, and that heat caused matter to push outward. Thus a kind of chain of «bounces» was created: gravity attracted it, heat pushed it away, and it started again.
This tug-of-war game created something akin to sound waves traveling through the universe, like the ripples that form in water when you throw a stone. These waves expanded in the form of bubbles, dragging some of the matter with them.
About 380,000 years after the Big Bang, the Universe cooled enough for the first atoms to form. At that point, gravity won the game, and it was able to start forming galaxies and other large structures. The bubbles of matter that had formed earlier left a kind of «imprint» on the distribution of galaxies: these are the acoustic oscillations of baryons, or baryonic acoustic oscillations (BAOs).
Baryon acoustic oscillations are thus bubbles of millions of galaxies that are distributed across a spherical surface, forming a shell that encloses a very massive supercluster of galaxies at the center.
Although these structures are subtle, they are very important. By studying them, astronomers can better understand how the Universe expands and how that expansion has changed over time.
Ho’oleilana
Ho’oleilana is a Hawaiian word meaning «murmurs of awakening» and appears in a Hawaiian song of creation that evokes the origin of things.
It is considered to be a BAO since it is a bubble formed by a multitude of galaxies whose diameter coincides with what was predicted from the Big Bang theory: 500 million light years.
At the center of Ho’oleilana is the Boötes supercluster of galaxies. On the surface of this bubble we find millions of galaxies that are grouped together to form groups that in turn come together in larger structures such as the galaxy clusters and superclusters of Coma, Hercules, Leo or the Sloan Great Wall.
It is important to note that this structure is actually very subtle and that it is totally submerged in the general distribution of galaxies that forms the superstructure of the Universe. Advanced statistical means are needed to detect this object as an excess over the almost uniform distribution of galaxies that fills all space. If we consider all galaxies, the spherical structure would hardly be noticeable.
The 3D model
The first thing you notice about the model is its spherical shape: we have in our hands the representation of a bubble of galaxies that originated only 380,000 years after the Big Bang.
The spherical surface is strewn with small balls that represent groups of galaxies, which in turn belong to larger groupings: galaxy clusters and superclusters.
The gaps in the surface of the sphere are real, although some have been exaggerated to allow access to its interior.
Inside, in the center, we find a ball of balls: it is the Boötes supercluster. It has been hooked to the surface of the bubble with thin pillars that do not actually exist, but which allow the supercluster to be kept in its central position within the bubble.
On the surface of the bubble, we locate some of the most relevant galaxy clusters:
- Hercules supercluster
- Coma Cluster
- Leo supercluster
- Corona Borealis Supercluster
- Ursa Major Supercluster
- Sloan Great Wall
The model has been created by Emilio Terol, from a 3D rendering of the real data made by Daniel Pomarède and published in «Ho’oleilana: An Individual Baryon Acoustic Oscillation?» by R. Brent Tully, Cullan Howlett, and Daniel Pomarède, The Astrophysical Journal (2023).
This work has been carried out with a grant from the R&D&I ‘Proof of Concept’ 2022 (PDC2022) call for projects, financed by the European Union through the NextGenerationEU Recovery, Transformation and Resilience Plan. Project’s reference: PDC2022-133930-I00.