A light-bulb moment for the early Universe

Cosmic dust is forged inside stars and then scattered across the cosmos when they die, most spectacularly in supernova explosions. This dust is the key building block in the formation of new stars and planets.

In the early Universe however — before the first generations of stars died out — cosmic dust was incredibly scarce. With scientists believing that the Big Bang occurred between 12 and 14 billion years ago, this is why the discovery of large quantities of stardust in a galaxy only 600 million years old, is so exciting.

Gazing back in time

The discovery was made thanks in part to the EU-funded FIRST LIGHT project, which has enabled researcher Nicolas Laporte and colleagues at University College, London, to use the Atacama Large Millimeter/submillimeter Array (ALMA) to peer even further into our cosmic past. This international astronomy facility, in which the European Southern Observatory (ESO) is a partner, is the largest astronomical project in the world and is located on a 5 000-metre plateau in Chile.

The galaxy – called A2744_YD4 – is the youngest and most remote galaxy ever identified by ALMA, and also represents the most distant detection of oxygen in the Universe. The project team has been able to estimate that the galaxy contains an amount of dust equivalent to 6 million times the mass of our sun, and found that stars were forming at a rate of 20 solar masses per year, compared to just one solar mass per year in the Milky Way. The galaxy appears to us as it was back when the Universe’s first stars and galaxies were forming.

Our cosmic dawn

So why is this significant? For a start, the detection of so much dust in such a young galaxy provides new information on when the first supernovae exploded, and hence gives us a better idea of when the first hot stars began to bathe the Universe in light. Determining the timing of this ‘cosmic dawn’ has been a key objective of astronomers for decades.

Also, the team has been able to estimate that significant star formation began approximately 200 million years before the epoch at which the galaxy is being observed. This provides researchers with an unprecedented opportunity to get closer to the point when the very first stars and galaxies appeared.

And finally, understanding when and how this first generation of stars appeared in the Universe has direct relevance to literally everything we know today. Our Sun, our home planet and even ourselves are the products — some 13 billion years later — of this cosmic dust that was created and scattered by the very first stars.

The success of the project to date suggests that the prospects for performing deeper and more extensive observations of similar galaxies are very promising. Further research could lead to the tracing of star formations even further back into the early Universe. In any case, further exciting discoveries will be expected to emanate from the FIRST LIGHT project, which is due for completion in September 2020.

For further information please visit:
CORDIS project page
UCL project page