Is this bubble of galaxies a “fossil” from the Big Bang?

Astronomers have discovered a bubble of galaxies 1 billion light-years across which they believe could be a “fossilised” remnant from the Big Bang.

The bubble is about 820 million light-years from Earth and sits within a web of galaxies. It is described in a paper published in the Astrophysical Journal.

The bubble was found using data from Cosmicflows-4 – the largest dataset of distances to galaxies.

Structures such as this massive bubble are predicted in the Big Bang theory of the universe. It is believed that there were tiny ripples in the hot, dense and mostly uniform matter at the beginning of time.

During the first 400,000 years of the universe, all the stuff in the cosmos was a hot, dense plasma similar to the interior of the Sun. While gravity tried to pull regions of the plasma together, radiation was pushing them apart. This interplay between gravity and radiation is what is believed to have caused these ripples in the embryonic universe.

As the universe underwent the rapid inflation known as the Big Bang, these density ripples, called Baryon Acoustic Oscillations (BAO), also grew. These ripples would expand into massive structures, influence the distribution of galaxies and also produce other cosmic configurations.

This is the first identification of a single structure associated with a BAO.

It has been dubbed “Hoʻoleilana” – a Hawaiʻian term from the creation chant Kumulipo which describes the origin of structure and relates to the celestial bodies.

The bubble itself is made up of previously known structures, thought to be some of the largest arrangements of matter in the universe. It comprises several galactic superclusters, each containing 10 clusters of galaxies and spanning 200 million light-years. At the bubble’s centre is the Bootes void – a 330 million light-year empty expanse.

How does something so large go unnoticed for so long? Funnily enough, its sheer size is actually what has made Hoʻoleilana so hard to spot.

“We were not looking for it. It is so huge that it spills to the edges of the sector of the sky that we were analyzing,” says Dr Brent Tully, an astronomer at the University of Hawai‘i’s Institute for Astronomy. “As an enhancement in the density of galaxies it is a much stronger feature than expected. The very large diameter of one billion light years is beyond theoretical expectations.”

Previously, parts of Hoʻoleilana’s shell have been spotted but not identified as part of a BAO. In 2016, the Sloan Digital Sky Survey saw part of Hoʻoleilana’s shell, but its true size remained unknown until now.