To the list of cosmic superlatives must now be added a new item: the oldest dust.
It’s
not behind your refrigerator or underneath the bed. It’s in a galaxy
with only a number for a name in a constellation called Sculptor, and so
far away that its distance barely has any meaning. The light from
A2744_YD4, as it is known, has been on its way to us for 13.2 billion
years, since the universe was only 600 million years old.
Where
the galaxy is “now” is only a mathematical extrapolation — about 30
billion light-years from here, according to the standard cosmological
math. An international team led by Nicolas Laporte of University College
London, using the Atacama Large Millimeter/submillimeter Array, or ALMA, a radio telescope in Chile,
was able to see this galaxy only because its light had been amplified
by the gravity of a massive cluster of galaxies lying right in front of
it.
Interspersed
with radio emissions from stars, the astronomers were surprised to find
the characteristic heat emanations from some six million solar masses
of dust. The dust consisted of tiny grains of carbon, silicon and
aluminum — an austere and unevolved version of the same stuff
under your fingernails, and in the dust bunnies under your bed. The big
news is that it existed in such quantities only 600 million years after
the Big Bang.
The
primordial universe, as it emerged from the Big Bang, consisted almost
entirely of hydrogen and helium, the simplest and lightest elements,
according to astronomers, with only a slight trace of lithium. The
heavier elements, needed for planets and us among other things, were
manufactured in stars, which then blew up. As the story goes, the
exploding stars scattered their ashes across space where they could be
incorporated into new stars and repeat the cycle, gradually enriching
the chemistry of the cosmos.
The
new observations show that this relentless progression from dust to
better-and-better dust had already been jump-started by the time the
universe was just 600 million years old. The first stars had already
been born and died in less than 200 million years in a wave of supernova
explosions, according to Richard Ellis, of the European Southern
Observatory and the University College London, and one of the leaders of
a paper published in Astrophysical Journal Letters.
At
the time, in the baby boom years of the universe, the young galaxy was
feeling its oats, pumping out 20 new stars a year. By comparison the Milky Way, our own galaxy, today births only one star a year.
The
new results augur a bright future for the ALMA telescope, a $1.5
billion array of antennas tuned to record the heat emanations of stars
and dust, and NASA’s coming James Webb Space Telescope,
designed to investigate the early days of the universe. “More
observations should pinpoint the period when galaxies began to be first
polluted by heavy elements,” Dr. Ellis said in an email from London.
“Until
now, studies of early galaxies have largely been based on measures of
colors and masses,” he said. “Now, finally, we are using chemistry.”
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