JWST Peers Deep Into The Universe’s Early Galaxies, Revealing Something Surprising : ScienceAlert

The first galaxies may have formed much earlier than previously thought, according to observations from the James Webb Space Telescope that are reshaping astronomers’ understanding of the early universe.

Researchers using the powerful observatory have now published papers in the journal Astrophysical Journal Letterscapturing two extremely bright, extremely distant galaxies, based on data collected during Webb’s first few days of operation in July.

Their extreme brightness suggests two intriguing possibilities, astronomers said on a NASA phone call Thursday.

The first is that these galaxies are very large, with many low-mass stars like galaxies today, and they had to start forming 100 million years after the Big Bang that happened 13.8 billion years ago.

This is 100 million years earlier than the end of the so-called cosmic dark age, when the universe contained only gas and dark matter.

A second possibility is that they are composed of “Population III” stars, which have never been observed but are thought to have consisted of only helium and hydrogen, before heavier elements were present.

Because these stars burned so brightly at extreme temperatures, the galaxies made from them would not need to be as large to account for the brightness Webb sees, and could have started forming later.

“We’re seeing galaxies so bright, so bright at this early time, that we’re really uncertain about what’s going on here,” Garth Illingworth of the University of California, Santa Cruz, told reporters.

The rapid discovery of galaxies also defied expectations that Webb would need to survey a much larger volume of space to find such galaxies.

“It’s kind of surprising that there are so many that formed so early,” added astrophysicist Jeyhan Kartaltepe of the Rochester Institute of Technology.

The most distant starlight

The two galaxies were found to have definitely existed about 450 and 350 million years after the Big Bang.

The second of these, called GLASS-z12, now represents the most distant starlight ever seen.

The more distant objects are from us, the longer it takes for their light to reach them, and so to look into the distant universe is to look into the deep past.

Because these galaxies are so far from Earth, by the time their light reaches us, it has been stretched by the expansion of the universe and shifted into the infrared region of the light spectrum.

Webb can detect infrared light at a much higher resolution than any instrument before it.

Illingworth, who co-authored the GLASS-z12 paper, told AFP that disentangling the two competing hypotheses would be a “real challenge”, although the idea of ​​Population III was more appealing to him as it would not require the overturning of existing cosmological models.

The teams hope to soon use Webb’s powerful spectrometer instruments – which analyze the light from objects to reveal their detailed properties – to confirm the galaxies’ distance and better understand their composition.

The Atacama Large Millimeter/submillimeter Array (ALMA), a ground-based telescope in northern Chile, could also help weigh the mass of the two galaxies, which would help decide between the two hypotheses.

“JWST has opened a new frontier, bringing us closer to understanding how it all began,” summarized Tommaso Treu of the University of California, Los Angeles, principal investigator on one of the Webb projects.

© Agence France-Presse

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