Astronomers have been leapfrogging each other into the past lately. Last month, a group using the Hubble Space Telescope announced they had discovered what could be the most distant and earliest star ever seen, nicknamed Earendel, which twinkled 12.9 billion years ago, only 900 million years after the Big Bang.
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Now another
international group of astronomers, pushing the limits of the biggest
telescopes on Earth, say they have discovered what appears to be the earliest
and most distant collection of starlight ever seen: a reddish blob usefully
named HD1, which was pouring out prodigious amounts of energy only 330 million
years after the Big Bang. That realm of time is so far unexplored. Another
blob, HD2 appears almost as far away.
Astronomers can
only guess what these blobs are — galaxies or quasars or maybe something else
entirely — while they wait for the chance to observe them with the new James
Webb Space Telescope. But whatever they are, astronomers say, they could shed
light on a crucial phase in the cosmos as it evolved from pristine primordial
fire into planets, life and us.
“I am excited as
a kid who spots the very first firework in a magnificent and highly anticipated
show,” said Fabio Pacucci of the Harvard-Smithsonian Center for Astrophysics.
“This could well be one of the first glimmers of light to illuminate the cosmos
in a show that ultimately created every star, planet and even flower that we
see around us today — more than 13 billion years later.”
Pacucci was part
of a team led by Yuichi Harikane of the University of Tokyo that spent 1,200
hours using various ground-based telescopes to search for very early galaxies.
Their findings were released in The Astrophysical Journal and the Monthly
Notices of the Royal Astronomical Society. Their work was also reported in Sky
& Telescope magazine this year.
In the expanding
universe, the farther an object is from us, the faster it is moving away from
us. Just as the sound of a receding ambulance siren shifts to a lower tone,
that motion causes an object’s light to shift to longer redder wavelengths. In
search of the most distant galaxies the astronomers sifted through some 70,000
objects, and HD1 was the reddest one they could find.
“HD1’s red color
matched the expected characteristics of a galaxy 13.5 billion light years away
surprisingly well, giving me a little bit of goose bumps when I found it,”
Harikane said in a statement released by the Center of Astrophysics.
The gold standard
of cosmic distances however is the redshift, derived by obtaining a spectrum of
the object and measuring how much the wavelengths emitted by characteristic
elements have increased or shifted to the red. Using the Atacama Large
Millimeter/submillimeter Array, or ALMA — a collection of radio telescopes in
Chile — Harikane and his team got a tentative redshift for HD1 of 13, meaning
that the wavelength of the light emitted by an oxygen atom had stretched to 14
times its wavelength at rest. The other blob’s redshift has not been
determined.
That dated the
presumed galaxy to only 330 million years after time began, smack in the
hunting ground of the Webb telescope, which will also be able to confirm the
redshift measurement.
“If the redshift
from ALMA can be confirmed, then this would indeed be a spectacular object,”
said Marcia Rieke of the University of Arizona, who is a principal investigator
for the Webb telescope.
According to the
story astronomers tell, the road to the universe as we know it started about
100 million years after the Big Bang, when hydrogen and helium created in the
primordial explosion began to condense into the first stars, known as
Population 3 stars (Populations 1 and 2, which have large amounts of heavier
elements, are present in galaxies today). Such stars, composed of only hydrogen
and helium, have never been observed, and they would have been much bigger and
brighter than the ones in the universe today. They would have burned hot and
died fast in supernova explosions that then jump-started the chemical evolution
polluting a pristine universe with elements like oxygen and iron, the stuff of
us.
Pacucci said they
first thought that HD1 and HD2 were what are called starburst galaxies, which
billow with new stars. But after further research, they discovered that HD1
seemed to be producing stars more than 10 times faster than such galaxies
usually do.
Another
possibility, Pacucci said, is that this galaxy was birthing those very first
ultra luminous Population 3 stars. Yet another explanation is that all this
radiance comes from material splashing into a supermassive black hole 100
million times the mass of the sun. But astronomers have trouble explaining how
a black hole could have grown so big so early in cosmic time.
Was it born that
way — in the chaos of the Big Bang — or was it just stupendously hungry?
“HD1 would represent a
giant baby in the delivery room of the early universe,” Avi Loeb, a co-author
on Pacucci’s paper, said.
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