Star formation began about 200 million years earlier than previously believed. Astronomers have found stardust in a galaxy 13.2 billion light years away. The galaxy A2744_YD4 located in the constellation Sculptor is one of the oldest and farthest galaxies ever observed. The discovery could help scientists find out how the first stars formed and died.

Stardust in A2744_YD4 galaxy
WikiImages / Pixabay

Why the discovery of stardust in a young galaxy is so surprising

Astronomers led by Nicolas Laporte of University College London spotted the ancient stardust using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile. Findings of the study were described in the journal Astrophysical Journal Letters. Researchers were surprised to find cosmic dust in such a young galaxy.

The early universe that emerged after the Big Bang 13.8 billion years ago consisted primarily of hydrogen and helium, with small traces of lithium. The heavier elements such as carbon, silicon, and aluminum were formed inside stars. Stardust is formed by dying stars that explode and scatter the heavy elements across the universe. That’s why the discovery of stardust in a galaxy that was just 600 million years old is so surprising.

Ionic oxygen also detected in the galaxy

Nicolas Laporte, the lead author of the study, said in a statement that the detection of massive amounts of cosmic dust in A2744_YD4 indicates that the galaxy was already polluted by the explosion of dying stars. Astronomers measured the star formation rate in the distant galaxy, and found that 20 solar masses of stars were born in A2744_YD4 every year. By comparison, our Milky Way galaxy produces only one solar mass per year.

Using data from ALMA, astronomers estimated that the first stars had formed and died in only 200 million years. Besides interstellar dust, ALMA also detected ionic oxygen, making it the most distant detection of oxygen in the universe. ALMA was able to detect A2744_YD4 mainly because of the gravitational effects of Pandora’s Cluster, a giant cluster of galaxies between Earth and A2744_YD4.

Gravitational lensing helped ALMA detect the galaxy

The gravity around Pandora’s Cluster magnified the light coming from A2744_YD4 in a process called gravitational lensing, enabling ALMA to detect its light. Astronomers said the galaxy contained stardust equivalent to six million times the mass of our Sun. The combined mass of all stars in A2744_YD4 was about two billion times the solar mass of our Sun.

Until now, early galaxies were studied based on the measurements of their colors and masses. ALMA has enabled astronomers to study them using chemistry. The upcoming James Webb Space Telescope could enable the discovery of even more distant galaxies, revealing further details about how the first stars and galaxies evolved.