The first galaxies may have formed far earlier than previously thought, according to observations from the James Webb Space Telescope that are reshaping astronomers' understanding of the early universe.
Two of the most distant galaxies seen to date are captured
in these Webb pictures of the outer regions of the giant galaxy cluster Abell
2744. (NASA, ESA, CSA, T. Treu/UCLA) |
Researchers using the powerful observatory have now
published papers in the journal Astrophysical Journal Letters, documenting twoexceptionally bright, exceptionally distant galaxies, based on data gathered
within the first few days of Webb going operational in July.
Their extreme luminosity points to two intriguing
possibilities, astronomers on a NASA press call said Thursday.
The first is that these galaxies are very massive, with lots
of low-mass stars like galaxies today, and had to start forming 100 million
years after the Big Bang which occurred 13.8 billion years ago.
That is 100 million years earlier than the currently held
end of the so-called cosmic dark age, when the universe contained only gas and
dark matter.
A second possibility is that they are made up of
"Population III" stars, which have never been observed but are
theorized to have been made of only helium and hydrogen, before heavier
elements existed.
Because these stars burned so brightly at extreme
temperatures, galaxies made of them would not need to be as massive to account
for the brightness seen by Webb and could have started forming later.
"We are seeing such bright, such luminous galaxies at
this early time, that we're really uncertain about what is happening
here," Garth Illingworth of the University of California at Santa Cruz
told reporters.
The galaxies' rapid discovery also defied expectations that
Webb would need to survey a much larger volume of space to find such galaxies.
"It's sort of a bit of a surprise that there are so
many that formed so early," added astrophysicist Jeyhan Kartaltepe of the
Rochester Institute of Technology.
Most distant starlight
The two galaxies were found to have definitely existed
approximately 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 us, and so to gaze at the distant universe is to see
into the deep past.
As these galaxies are so distant from Earth, by the time
their light reaches us, it has been stretched by the expansion of the universe
and shifted to the infrared region 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," though the Population III idea was more appealing to him, as
it would not require upending existing cosmological models.
Teams are hoping to soon 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 telescope in northern Chile, might also be able to help in weighing the
mass of the two galaxies, which would help decide between the two hypotheses.
"JWST has opened up a new frontier, bringing us closer
to understanding how it all began," summed up Tommaso Treu of the
University of California at Los Angeles, principal investigator on one of the
Webb programs.
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