Peering billions of
light-years back to when the Universe was just 10 percent of its current age,
astronomers have spotted a colossal pile-up: 14 young, starbursting galaxies
merging into one of the most massive structures in the Universe. Using some of
the most powerful telescopes in operation today, an international research team
discovered the extremely dense concentration of hot galaxies careening towards
each other.
Eventually the megamerger
will form a cluster of galaxies, gravitationally bound by dark matter and
ultimately smooshing together into one ginormous galaxy. This stage of the
merger is called a protocluster, and it's an extraordinary find.
"Having caught a
massive galaxy cluster in throes of formation is spectacular in and of
itself," said Scott Chapman, an astrophysicist at Dalhousie University,
one of the authors on a new paper published in Nature. "But the fact that
this is happening so early in the history of the Universe poses a formidable
challenge to our present-day understanding of the way structures form in the
universe."
The protocluster, named
SPT2349-56, is 12.4 billion light-years away, populated by dusty galaxies that
are forming stars at a furious rate - up to 1,000 times faster than the Milky
Way. Yet they're crammed into a space just three times bigger than our whole
galaxy.
In itself, the protocluster
would be a rare find, but there's another twist to the story. It's one of two
such recent discoveries. Publishing in arXiv last September, and their findings
accepted into The Astrophysical Journal, a team of researchers announced they'd
found a protocluster of 10 dusty starburst galaxies in the early Universe too.
They nicknamed it the Dusty Red Core.
You can fully expect to
discover all kinds of things forming in the early Universe - stars, galaxies,
clusters of galaxies - but the size and composition of these protoclusters is a
conundrum.
"The lifetime of dusty
starbursts is thought to be relatively short, because they consume their gas at
an extraordinary rate," explained astrophysicist Iván Oteo from the University
of Edinburgh, lead author on the arXiv paper.
"At any time, in any
corner of the Universe, these galaxies are usually in the minority. So, finding
numerous dusty starbursts shining at the same time like this is very puzzling,
and something that we still need to understand."
After the Big Bang,
according to our current models of the Universe, everything was still dark for
a while. It wasn't until around 1 billion years later that the Universe became
fully ionised and transparent, and we see the first galaxies start appearing. These
clusters appear about 1.4 billion years after the Big Bang. The models of the
Universe's evolution predict that, while these clusters can exist, they ought
to have taken much longer than that to evolve.
"How this assembly of
galaxies got so big so fast is a mystery," said Tim Miller, a PhD
candidate at Yale University, and lead author on the Nature paper.
"It wasn't built up
gradually over billions of years, as astronomers might expect. This discovery
provides a great opportunity to study how massive galaxies came together to
build enormous galaxy clusters."
SPT2349-56 was first seen as
a faint smudge of light imaged by the South Pole Telescope in 2010, but it was
unusual enough to warrant further investigation with something more powerful. The
European Southern Observatory's (ESO) Atacama Large Millimetre Array (ALMA) and
the Atacama Pathfinder Experiment (APEX) telescopes were then used to image the
object in higher resolution, showing more detail.
Often objects that early in
the Universe are too faint for our telescopes to pick up, but there may be more
of these protoclusters out there, the researchers said. "These discoveries
by ALMA are only the tip of the iceberg. Additional observations with the APEX
telescope show that the real number of star-forming galaxies is likely even
three times higher," said ESO astronomer Carlos De Breuck.
"Ongoing observations
with the MUSE instrument on ESO's VLT are also identifying additional
galaxies." The SPT2349-56 paper has been published in the journal Nature,
and the Dusty Red Core paper can be read on the preprint resource arXiv.
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