Webb observations point to a shorter cosmic dark age

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

Researchers using the powerful observatory have now published articles in the Astrophysical Journal Letters documenting two exceptionally bright, exceptionally distant galaxies, based on data collected in the first few days after Webb went live in July.

Its extreme luminosity points to two intriguing possibilities, astronomers said at a NASA press briefing.

The first is that these galaxies are very massive, with many low-mass stars like today’s galaxies, and began forming 100 million years after the Big Bang 13.8 billion years ago.

This is 100 million years earlier than the currently expected 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 were theoretically composed of only helium and hydrogen before heavier elements existed.

Because these stars burned so brightly at extreme temperatures, galaxies made from them would not have to be as massive to explain the brightness seen by Webb and could have formed later.

“We’re seeing galaxies so bright, so luminous, at this early stage that we’re really not sure what’s happening here,” Garth Illingworth of the University of California, Santa Cruz told reporters.

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

“It’s a bit surprising that so many arose so early,” added astrophysicist Jeyhan Kartaltepe of the Rochester Institute of Technology.

The two galaxies were found to definitely exist approximately 450 and 350 million years after the Big Bang.

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

The further away objects are from us, the longer it takes for their light to reach us, and so looking into the distant universe means looking into the deep past.

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

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

Illingworth, who co-authored the paper on GLASS-z12, told AFP disentangling the two competing hypotheses would be a “real challenge,” although he finds the Population III idea more attractive because they don’t require changing existing cosmological models would.

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

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

“JWST opened a new frontier and brought us closer to understanding how it all began,” said Tommaso Treu of the University of California, Los Angeles, principal investigator on one of the Webb programs.

© 2022 AFP

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