Ancient Dust-Rich Galaxy Could Shed Light On The First Generation Of Stars In The Universe

We are all, as Carl Sagan once remarked, made of star stuff. You, the screen you are currently reading these words on, the chair you are sitting on and the planet you live on are all the end result of 13.8 billion years of cosmic evolution — a process that began with the birth and death of the first stars.

Understandably, getting a clearer picture of the formative years of the universe — the era when the first stars and galaxies “switched on” — is of vital interest to scientists. One way this can be done is by studying distant galaxies, through which we get a glimpse of what the early universe was like.

Read: Universe's Oldest Stars Discovered In An Ancient, Bright Galaxy

In a study published in the latest edition of the Astrophysical Journal Letters, a team of researchers associated with the Atacama Large Millimeter/submillimeter Array (ALMA) describe the detection of glowing stardust in a galaxy seen when the universe was just 600 million years old. This galaxy, named A2744_YD4, is not only the most remote one seen by ALMA, it is also the most distant detection of dust and oxygen so far.

The galaxy is estimated to contain an amount of dust equivalent to six million times the mass of our sun. The presence of cosmic dust shows that star formation in the universe began approximately 200 million years before the epoch at which the galaxy is being observed.

“The chemical elements in these [cosmic dust] grains are forged inside stars and are scattered across the cosmos when the stars die, most spectacularly in supernova explosions, the final fate of short-lived, massive stars,” the European Southern Observatory, which operates ALMA, said in a statement. “Today, this dust is plentiful and is a key building block in the formation of stars, planets and complex molecules; but in the early Universe — before the first generations of stars died out — it was scarce.”

The ALMA telescopes also revealed the presence of ionized oxygen in the galaxy, making it the farthest —and thus the earliest — sources of the gas in the universe. The presence of oxygen in this distant galaxy gives us a hint to when and how the first galaxies formed and what caused the cosmic “reionization.”

The universe burst into existence nearly 13.8 billion years ago in an event we now know as the Big Bang. In the beginning, the cosmos was a hot soup of ionized gas — with electrons and ions of hydrogen and helium buzzing around. Then, roughly 400,000 years after the Big Bang, the universe entered an era of “recombination,” wherein it cooled down enough to allow ions to recombine into atoms. Although this era is believed to be the first time light shone in our universe, it didn’t last long. The universe was soon plunged into the “dark ages” — the time before the birth of the first stars.

When the first generation of stars were born, they emitted strong radiation that ionized hydrogen once again, and also led to the synthesis of other heavier elements such as carbon and oxygen. Scientists believe that studying the heavy elements from this era would provide essential clues to what triggered reionization and what led to the birth of the first galaxies about 100 million years after the Big Bang.

“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,” study lead author Nicolas Laporte from the University College London said in the statement.