By Will Dunham
WASHINGTON (Reuters) – NASA’s James Webb Space Telescope has discovered the earliest known galaxy, one that is surprisingly bright and large considering it formed during the universe’s infancy – just 2% of its current age.
Webb, who sees far back in time by gazing across vast cosmic distances, observed the galaxy as it existed about 290 million years after the Big Bang that launched the universe about 13.8 billion years ago, the researchers said. This period covering the first few hundred million years of the universe is called cosmic dawn.
The telescope, also called JWST, has revolutionized the understanding of the early universe since it became operational in 2022. The new discovery was made by the JWST Advanced Deep Extragalactic Survey (JADES) research team.
This galaxy, called JADES-GS-z14-0, is about 1,700 light-years across. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). It has a mass equivalent to 500 million stars the size of our Sun and was rapidly forming new stars, about twenty per year.
Before Webb’s observations, scientists did not know that galaxies could have existed so early, especially such luminous galaxies.
“The early universe has surprise after surprise for us,” says astrophysicist Kevin Hainline of Steward Observatory at the University of Arizona, one of the leaders of the study published online this week ahead of formal peer review.
“I think everyone’s jaw dropped,” added astrophysicist and co-author of the study Francesco D’Eugenio of the Kavli Institute of Cosmology at the University of Cambridge. ‘Webb shows that galaxies in the early universe were much brighter than we expected.’
Until now, the earliest known galaxy dated about 320 million years after the Big Bang, as announced last year by the JADES team.
‘It makes sense to call the galaxy large, because it is significantly larger than other galaxies that the JADES team has measured at these distances, and it will be challenging to understand how something so large expanded in just a few hundred million years. could form. ‘, Hainline said.
“The fact that it is so bright is also fascinating, as galaxies tend to get bigger as the universe evolves, implying that it could potentially become significantly brighter over the next hundred million years,” Hainline said.
Although it is quite large for such an early galaxy, it is dwarfed by some modern-day galaxies. Our Milky Way is about 100,000 light-years across and has a mass equivalent to about 10 billion stars the size of the Sun.
In the same study, the JADES team revealed the discovery of the second-oldest known galaxy, about 303 million years after the Big Bang. That one, JADES-GS-z14-1, is smaller – with a mass equivalent to about 100 million Sun-sized stars, spanning roughly 1,000 light-years across and forming about two new stars per year.
‘These galaxies formed in an environment that was much denser and more gas-rich than today. Moreover, the chemical composition of the gas was very different, much closer to the original composition inherited from the Big Bang: hydrogen, helium and trace amounts of gas. lithium,” D’Eugenio said.
Star formation in the early universe was much more violent than today, with massive hot stars forming and dying rapidly, releasing a huge amount of energy through ultraviolet light, stellar winds and supernova explosions, D’Eugenio said.
Three main hypotheses have been put forward to explain the brightness of early galaxies. The first attributed this to supermassive black holes in these galaxies that were gobbling up material. That seems to be ruled out by the new findings, because the observed light spreads over a larger area than would be expected from the gluttonous black holes.
It remains to be seen whether the other hypotheses — that these galaxies are populated by more stars than expected or by stars that are brighter than current galaxies — will hold up, D’Eugenio said.
(Reporting by Will Dunham; Editing by Daniel Wallis)
