Ancient Stardust Offers Glimpse Into First Stars

This artist’s impression shows what the very distant young galaxy A2744_YD4 might look like. Observations using ALMA have shown that this galaxy, seen when the universe was just 4 percent of its current age, is rich in dust. Such dust was produced by an earlier generation of stars and these observations provide insights into the birth and explosive deaths of the very first stars in the universe. (Credit: ESO/M. Kornmesser)

(CN) – A dust-filled galaxy roughly 13 billion light-years from Earth may help determine the timing of the “cosmic dawn” – when hot stars first illuminated the universe.

In a study published Wednesday, an international team of astronomers present findings on A2744_YD4, the youngest and furthest galaxy ever observed using the European Southern Observatory’s Atacama Large Millimeter/submillimeter Array, or ALMA.

The galaxy appears to us as it was when the universe was only 600 million years old – providing the team a snapshot of the period in which the first stars and galaxies were forming.

“Not only is A2744_YD4 the most distant galaxy yet observed by ALMA, but the detection of so much dust indicates early supernovae must have already polluted this galaxy,” lead author Nicolas Laporte, a researcher at University College London, said.

Determining the timing of early hot-star formation is one of the primary objectives of modern astronomy. However, this period can only be indirectly explored through the study of early interstellar dust.

The team estimates the amount of dust found in A2744_YD4 was equivalent to 6 million times the mass of our sun. The galaxy’s total stellar mass – the combined mass of its stars – is 2 billion times the mass of our sun. The young galaxy produced 20 new stars a year, while the Milky Way galaxy births only one star a year.

“This rate is not unusual for such a distant galaxy, but it does shed light on how quickly the dust in A2744_YD4 formed,” co-author Richard Ellis of University College London said. “Remarkably, the required time is only about 200 million years – so we are witnessing this galaxy shortly after its formation.”

The observations of A2744_YD4 were made possible because the galaxy lies behind a massive galaxy cluster called Abell 2744. A phenomenon called gravitational lensing magnified the more distant A2744_YD4 by about 1.8 times, allowing the team to see further back into the early universe.

“Further measurements of this kind offer the exciting prospect of tracing early star formation and the creation of the heavier chemical elements even further back into the early universe,” Laporte said.


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