Scientists had hoped that the world’s most advanced space telescope would deliver the unexpected, and “the universe did not let us down,” said Tommaso Treu, principal investigator for the GLASS-JWST Early Release Science Program and a professor at the University of California at Los Angeles.

“We discovered there are many more distant galaxies than we had been expecting,” Treu said. “Somehow the universe has managed to form galaxies faster and earlier than we thought.”

The big bang, a theory embraced by many scientists, holds that our universe began as a dense, hot bundle of matter so compact that it would have resembled a single point. That bundle then expanded rapidly, giving rise to a primordial soup of tiny particles that ultimately coalesced into the universe we see today.

The new discoveries, announced by NASA at a news briefing Thursday, draw the curtain back on what the developing universe looked like a few hundred million years after its momentous beginning.

One of the two galaxies dates to about 350 million years after the big bang, making it the most distant galaxy ever discovered. The second new galaxy is estimated to have existed about 400 million years after the birth of the cosmos.

Although 350 million years seems an unimaginably long time after the big bang, it is relatively early in the life of our universe.

“The universe is 13.8 billion years old. We’re looking back through 98 percent of all time to see a galaxy like this,” said Garth Illingworth, an astronomer from the University of California at Santa Cruz who helped conceive of the idea for the Webb telescope in the 1980s.

He added, “I fully expect we will find some even more distant galaxies.”

Astronomers speak of these distant galaxies as appearing very red. That’s because they are so far away and moving so fast that the wavelengths of light are stretched by the expanding universe.

Inside the galaxies themselves, however, the view is very different.

“It’s really sort of a small blob of stars and gas. Very, very blue. Very chaotic,” Illingworth said, adding that these far-off galaxies are only a twentieth the size of our own Milky Way.

Galaxies this distant are composed mostly of hydrogen and helium, but they include smaller amounts of other elements. The lack of elements is a sign of youth. It has taken hundreds of millions of years to develop the elements that exist today.

The stars in these early galaxies also are a million times brighter than our sun.

“We’re trying to figure out if they are really young stars,” said Dan Coe, an astronomer with the Space Telescope Science Institute in Baltimore.

The Webb telescope, Treu said, “has opened up a new frontier, bringing us closer to understanding how it all began, and we’ve just started to explore it.”

A $10 billion collaboration between NASA and the European and Canadian space agencies, the James Webb Space Telescope took 30 years to construct and uses 18 hexagonal mirrors. The images and data from the telescope offer glimpses of history that could only be imagined up to now.

The early images and data from the telescope brought home “how quickly our understanding of galaxies is changing,” said Jeyhan Kartaltepe, associate professor at the Rochester Institute of Technology and co-investigator for the Cosmic Evolution Early Release Science Survey.

Coe added, “Webb has just blown us away at every step.”

Looking back to the very early universe allows humans to ask profound questions about our place in the cosmos.

“It’s part of our origin story,” Illingworth said.