Wednesday, March 08, 2017

Our Universe’s Very Dusty Early, Early Beginnings


Photo

An artist’s impression of what the very distant young galaxy A2744_YD4 might look like. Credit M. Kornmesser/European Southern Observatory

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.”
NYT

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