Since beginning operations last year, the James Webb Space Telescope has provided an astonishing glimpse of the early history of our universe, spotting a collection of galaxies dating to the enigmatic epoch called cosmic dawn. Image for Representation.
| Photo Credit: ESA/Webb, NASA & CSA, A. Martel

Since beginning operations last year, the James Webb Space Telescope has provided an astonishing glimpse of the early history of our universe, spotting a collection of galaxies dating to the enigmatic epoch called cosmic dawn.

But the existence of what appear to be massive and mature galaxies during the universe’s infancy defied expectations – too big and too soon. That left scientists scrambling for an explanation while questioning the basic tenets of cosmology, the science of the origin and development of the universe. A new study may resolve the mystery without ripping up the textbooks.

The researchers used sophisticated computer simulations to model how the earliest galaxies evolved. These indicated that star formation unfolded differently in these galaxies in the first few hundred million years after the Big Bang event 13.8 billion years ago that initiated the universe than it does in large galaxies like our Milky Way populating the cosmos today.

Star formation in the early galaxies occurred in occasional big bursts, they found, rather than at a steady pace. That is important because scientists typically use a galaxy’s brightness to gauge how big it is – the collective mass of its millions or billions of stars.

Also Read | Billion-light-year-wide ‘bubble of galaxies’ discovered

So, according to the study, these galaxies may have been relatively small, as expected, but might glow just as brightly as genuinely massive galaxies do – giving a deceptive impression of great mass – because of brilliant bursts of star formation.

“Astronomers can securely measure how bright those early galaxies are because photons (particles of light) are directly detectable and countable, whereas it is much more difficult to tell whether those galaxies are really big or massive. They appear to be big because they are observed to be bright,” said Guochao Sun, a postdoctoral fellow in astronomy at Northwestern University in Illinois and lead author of the study published this week in the Astrophysical Journal Letters.

Webb, which was launched in 2021 and became operational in 2022, detected about 10 times more very bright galaxies from cosmic dawn than anticipated based on most theoretical models.

“According to the standard model of cosmology, there should not be many very massive galaxies during cosmic dawn because it takes time for galaxies to grow after the Big Bang. Immediately after the Big Bang, the universe was filled with a very hot, nearly uniform plasma – a fireball – and there were no stars or galaxies,” Northwestern University astrophysicist and study senior author Claude-André Faucher-Giguère said.

Also Read | Space telescope uncovers massive galaxies near cosmic dawn

“In our new paper, we show quantitatively using our simulations that the bursts of star formation produce flashes of light that can explain the very bright galaxies observed by Webb. And the reason this is so significant is that we explain these very bright galaxies without having to break the standard cosmological model,” Faucher-Giguère added.

The simulations in the study were conducted as part of the Feedback of Relativistic Environments (FIRE) research project.

The findings centered upon a phenomenon called “bursty star formation.”

“In contrast to forming stars at a nearly constant rate, the star formation activity in those early galaxies went on-and-off, on-and-off, with some large fluctuations over time. This, in turn, drives large variations in their brightness because the light seen by telescopes like JWST was emitted by the young stars formed in those galaxies,” Sun said.

The researchers have an idea of why this phenomenon occurs in smaller galaxies. In these, a batch of very large stars may form in a sudden burst, then explode as supernovas after just a few million years due to their great size. They blast gas into space that becomes ingredients for another burst of star formation. But the stronger gravitational effects in larger galaxies prevent these bursts, favoring steady star formation.

Sun expects Webb to continue to challenge our understanding of the universe and provide fresh insight, regardless of whether it meets scientific expectations.

“This is exactly how science is done and progressed,” Sun said.

This handout photograph released by the CEA on September 7, 2023, shows a 3D representation of the galaxy “Bubble”, coloured in brown. The image shows the position of the Milky Way, with a small white dot located outside the bubble on the right, in a white cloud. The blue wisps represent the “cosmic web”, the filaments of galaxies that make up other large structures in the Universe, such as Laniakea.
| Photo Credit: AFP

Astronomers have discovered the first “bubble of galaxies,” an almost unimaginably huge cosmic structure thought to be a fossilised remnant from just after the Big Bang sitting in our galactic backyard.

The bubble spans a billion light years, making it 10,000 times wider than the Milky Way galaxy.

Yet this giant bubble, which cannot be seen by the naked eye, is a relatively close 820 million light years away from our home galaxy, in what astronomers call the nearby universe.

The bubble can be thought of as “a spherical shell with a heart,” Daniel Pomarede, an astrophysicist at France’s Atomic Energy Commission, told AFP.

Inside that heart is the Bootes supercluster of galaxies, which is surrounded by a vast void sometimes called “the Great Nothing”.

The shell contains several other galaxy superclusters already known to science, including the massive structure known as the Sloan Great Wall.

Pomarede said the discovery of the bubble, which is described in research he co-authored that was published in The Astrophysical Journal this week, was “part of a very long scientific process”.

It confirms a phenomenon first described in 1970 by US cosmologist — and future physics Nobel winner — Jim Peebles.

He theorised that in the primordial universe — then a stew of hot plasma — the churning of gravity and radiation created sound waves called baryon acoustic oscillations (BAOs).

As the sound waves rippled through the plasma, they created bubbles.

Around 380,000 years after the Big Bang the process stopped as the universe cooled down, freezing the shape of the bubbles.

Also Read | Cartesian coordinates: a way to find your way 

The bubbles then grew larger as the universe expanded, similar to other fossilised remnants from the time after the Big Bang.

Astronomers previously detected signals of BAOs in 2005 when looking at data from nearby galaxies.

But the newly discovered bubble is the first known single baryon acoustic oscillation, according to the researchers.

‘Unexpected’

The astronomers called their bubble Ho’oleilana — “sent murmurs of awakening” — taking the name from a Hawaiian creation chant.

The name came from the study’s lead author Brent Tully, an astronomer at the University of Hawaii.

The bubble was discovered by chance, as part of Tully’s work searching through new catalogues of galaxies.

“It was something unexpected,” Pomarede said.

Also Read | Sahara space rock 4.5 billion years old upends assumptions about the early Solar System 

Tully said in a statement that the bubble is “so huge that it spills to the edges of the sector of the sky that we were analysing”.

The pair enlisted the help of Australian cosmologist and BAO expert Cullan Howlett, who “mathematically determined the spherical structure which best corresponded to the data provided,” Pomarede said.

This allowed the trio to visualise the three-dimensional shape of Ho’oleilana — and the position of the archipelagos of galaxies inside it.

It may be the first, but more bubbles could soon be spotted across the universe.

Europe’s Euclid space telescope, which launched into July, takes in a wide view of the universe, potentially enabling it to snare some more bubbles.

Massive radio telescopes called the Square Kilometre Array, being built in South Africa and Australia, could also offer a new image of galaxies from the viewpoint of the Southern Hemisphere, Pomarede said.