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 Lettersdocumenting two exceptionally bright, exceptionally distant galaxies, based on data collected in the first few days after Webb became operational in July.
Their extreme brightness points to two intriguing possibilities, astronomers said Thursday during a NASA press call.
The first is that these galaxies are very massive, with many low-mass stars like today’s galaxies, and they should have started forming 100 million years after the Big Bang, which happened 13.8 billion years ago.
That’s 100 million years earlier than the current 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 believed to have been made only of helium and hydrogen before heavier elements existed.
Because these stars burned so brightly at extreme temperatures, the galaxies made from them would not have to be so massive to account for the brightness observed by Webb and could form later.
“We’re seeing such bright, such bright galaxies at this early time, we’re really unsure about what’s going on here,” Garth Illingworth of the University of California at Santa Cruz told reporters.
The rapid discovery of the galaxies also defied expectations that Webb would have to explore a much larger volume of space to find such galaxies.
“It’s a bit of a surprise that so many formed so early,” added Rochester Institute of Technology astrophysicist Jeyhan Kartaltepe.
The two galaxies were found to have existed for at least about 450 and 350 million years after the Big Bang.
The second of these, called GLASS-z12, now represents the farthest starlight ever seen.
The further away objects are from us, the longer it takes for their light to reach us, and so to look at 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 other instrument.
Illingworth, who co-authored the article on GLASS-z12, told AFP that disentangling the two competing hypotheses would be a “real challenge”, although the Population III idea was more appealing to him because it would not require existing to turn cosmological models upside down.
Teams soon hope to use Webb’s powerful spectrograph 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, may also be able to help weigh the masses of the two galaxies, which could help decide between the two hypotheses.
“JWST has opened a new frontier, helping us better understand how it all started,” summarizes Tommaso Treu of the University of California at Los Angeles, principal investigator on one of the Webb programs.
© Agence France-Presse