When NASA’s Webb telescope first expanded our view of the early cosmos, astronomers expected to see black holes and the humble beginnings of galaxies.
Instead, they were presented with the surprising sight of seemingly fully developed, gigantic structures.
These galaxies appeared to be evolving at an extraordinary rate that exceeded theoretical predictions, leading some researchers to question the validity of the Standard Model of cosmology.
Reassessing early galaxies
A recently published study in Astronomical Journalled by a research team at the University of Texas at Austin, suggests that our initial assessment of these early galaxies may have been too generous.
It turns out that the culprits behind this cosmic illusion are none other than black holes.
According to Austin graduate student Katherine Chworowsky, who led the study, “We still see more galaxies than predicted, although none of them are massive enough to ‘destroy’ the universe.”
These cosmic giants are not as heavy as they seem at first glance.
The evidence came from Webb’s Cosmic Evolution Early Release Science (CEERS) survey, led by Steven Finkelstein, professor of astronomy at UT Austin and co-author of the study.
Cosmic trick of black holes
This Webb telescope suggests that galaxies that appear excessively large are likely to host black holes that rapidly consume gas.
This friction in the high-speed gas releases heat and light, making these galaxies appear much brighter than if their luminosity came solely from stars.
This additional glow gives the impression that these galaxies contain more stars and are therefore more massive than estimated.
After accounting for the deceptive brightness of these so-called “little red dots,” the galaxies fit the Standard Model’s predictions exactly, prompting one of the study’s co-authors to reiterate his confidence in the model.
“So the bottom line is that there is no crisis with the standard model of cosmology,” Finkelstein said. “When you have a theory that has held up for so long, you have to have overwhelming evidence to really throw it out. And that’s just not the case.”
A galactic dilemma
While this revelation about galaxies and black holes solves the main problem, researchers are still faced with a smaller puzzle: Webb’s data on the early universe still contain about twice as many massive galaxies as expected by the Standard Model.
According to one theory, stars may have formed faster in the early universe than they do today.
“Perhaps galaxies in the early universe were better at converting gas into stars,” Chworowsky said, suggesting that the early universe may have been denser and gas ejection during star formation was less likely.
Next steps in cosmic investigation
Astronomers are currently analyzing the spectra of the “little red dots” discovered by Webb.
There is evidence of fast-moving hydrogen gas, indicating black hole accretion disks.
This supports the theory that the light from these red objects comes from gas swirling around black holes, rather than from stars. Further observations are underway to solve this intriguing mystery.
Despite our growing knowledge of the cosmos, new questions continue to emerge. The standard model of cosmology appears to be intact, but it opens up new avenues for studying star formation.
Chworowsky notes: “And so this fascination remains. Not everything is fully understood. That’s what makes this kind of science so exciting, because it would be a terribly boring field if you found out everything with a single publication or there were no more questions to answer.”
Black holes: galaxies reimagined
The study’s findings not only challenge our initial ideas about the mass and size of early galaxies, but also cause astronomers to rethink how galaxies formed and evolved over cosmic time.
Traditionally, galaxies were thought to grow by a gradual accumulation of gas and the merging of smaller galaxies, with their mass steadily increasing through the formation of stars.
However, the deceptive luminosity of active black holes introduces a new factor that must be taken into account.
This finding suggests that the presence of supermassive black holes at the centre of these galaxies may have played a more influential role in their early evolution than previously thought.
The strong gravitational forces and energy emissions of black holes could significantly affect the surrounding gas, triggering accelerated star formation or, conversely, ejecting gas and thus preventing further star growth.
Because of their dual role as creators and destroyers, black holes are central to understanding the dynamics of galaxies.
The full study was published in the journal The Astrophysical Journal.
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