The earliest known galaxies, detected by the Webb telescope, are beacons of the cosmic dawn

The earliest known galaxies, detected by the Webb telescope, are beacons of the cosmic dawn

NASA’s James Webb Space Telescope has spotted the earliest known galaxies, galaxies that are incredibly bright and massive considering they formed during the early stages of the universe – just 2% of its current age.

Webb, who by peering into the vast cosmic distance looks into the past, observed the galaxy as it existed about 290 million years after the Big Bang event that started the universe about 13.8 billion years ago, the researchers said. The period spanning the first few hundred million years of the universe is called the cosmic dawn.

The telescope, also called JWST, has revolutionized the understanding of the early universe since it began operating 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 rapidly forms new stars, about 20 each year.

Before Webb’s observations, scientists didn’t know galaxies could exist this early, and certainly not galaxies this luminous.

“The early universe had surprise after surprise for us,” said astrophysicist Kevin Hainline of the Steward Observatory at the University of Arizona, one of the leaders of the study published online, opening a new tab this week ahead of formal peer review.

“I think everyone’s jaws dropped,” added astrophysicist and study co-author Francesco D’Eugenio of the Kavli Institute for Cosmology at the University of Cambridge. “Webb shows that galaxies in the early universe were much more luminous than we expected.”

To date, the earliest known galaxies date back to about 320 million years after the Big Bang, as announced by the JADES team last year.

“It makes sense to call it a massive galaxy, because it is much larger than any other galaxy the JADES team has measured at this distance, and it would be challenging to understand how something this large could form in just a few hundred million years,” said Hainline.

“The fact that it is so bright is also interesting, given that galaxies tend to grow larger as the universe expands, implying that it has the potential to become significantly brighter in the next few hundred million years,” Hainline said.

Although it is relatively large for such an early galaxy, it is dwarfed by some present-day galaxies. Our Milky Way is about 100,000 light years across, with a mass equal to about 10 billion sun-sized stars.

The JADES team in the same study revealed the discovery of the second oldest known galaxy, from 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, is about 1,000 light-years across and forms about two new stars every year.

“These galaxies formed in a much more dense and gas-rich environment than today. Moreover, the chemical composition of the gas was very different, closer to the original composition inherited from the Big Bang – hydrogen, helium and traces of lithium,” said D’Eugenio.

Star formation in the early universe was much more violent than it is today, with massive, hot stars forming and dying quickly, and releasing vast amounts 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 it to a supermassive black hole in this galaxy that is consuming matter. That appears to have been ruled out by the new findings as the observed light is spread over a wider area than expected from the black hole’s vorticity.

It remains to be seen whether the other hypothesis — that the galaxy is populated by more stars than expected or by brighter stars than are around today — will hold up, D’Eugenio said.

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