Astronomers discovered when the first stars began to shine.
They say this period, known as the “cosmic dawn,” occurred between 250 to 350 million years after the Big Bang.
The results of the study, published in the British monthly scientific journal Notices of the Royal Astronomical Society, indicate that the first galaxies are bright enough to be seen by NASA’s James Webb Space Telescope, which is due to launch later this year.
The goal of the work of Professor Richard Ellis, of University College London (UCL), in the United Kingdom, was to find out when the cosmic dawn began.
He told BBC News: “The Holy Grail was looking back far enough to be able to see the first generation of stars and galaxies. And now we have the first convincing evidence of when the universe was first immersed in starlight.”
The team analyzed six of the most distant galaxies. They were so far away that, even with the most powerful telescopes in the world, they could only appear by a few pixels on a computer screen.
They are also among the first to appear in the universe, and therefore, by the time their images are taken by telescopes on Earth, they are seen not long after the Big Bang.
Measuring its age, the team calculated the beginning of the cosmic dawn – when the first stars formed. The analysis was conducted by Nicholas Laporte of the Kavli Institute of Astronomy in Cambridge, UK.
“This is one of the biggest questions in modern cosmology. This is the first time we have been able to predict from observations when this pivotal moment in the history of the universe occurred.”
According to Laporte, getting the result was a dream come true.
“It’s great to think that particles of light traveled through space for over 13 billion years and then got into the telescope. The cool thing about being an astrophysicist is being able to travel through time and see the distant past,” he explains.
The universe appeared 13.8 billion years ago, in the Big Bang. After an initial flash, he went through a period known as the Cosmic Dark Ages. According to the new study, 250 to 350 million years after the Big Bang, the first stars appeared and brought light into the universe.
Crucially, the new analysis also indicates that the first galaxies are bright enough and are within the range that can be seen by the James Webb Space Telescope – the successor to the venerable Hubble Space Telescope. Astronomers may then be able to witness this pivotal moment in the evolution of the universe firsthand.
Professor Catherine Heymans, a royal astronomer from Scotland, says she is “extremely excited” about the possibility.
“It is amazing that as humans, as a small civilization on planet Earth, we can create a telescope that we can send into space and we can peek into the past of the universe, as if it was only a few hundred million years after the Big Bang!”
Many of the early stars were very different from our Sun, they were much denser and only burned hydrogen. But these objects created the next generation of stars that led to the formation of heavier elements on the periodic table.
Everything but hydrogen, helium, and lithium forms inside stars when they explode at the end of their lives.
Therefore, we are, after all, made up of stars born near the cosmic dawn.
“Because we ourselves are the product of stellar evolution, we look to our own origins,” Ellis says.
Researchers analyzed starlight from galaxies using the Hubble and Spitzer Space Telescopes. They estimated the age of galaxies by examining the proportion of hydrogen atoms in the atmospheres of their stars. The larger the stars, the greater the proportion of hydrogen atoms.
The team then calculated how far the galaxies are. Since the light from these galaxies takes time to reach us, the further away we are from them, the more astronomers will notice them.
Since the six galaxies the team studied lie within the bounds of objects that can be observed with telescopes, they are also among the oldest known.
The team required 70 hours of observation, using four of the largest ground-based telescopes to estimate their distances: ALMA (the Atacama Large Millimeter Array), the VLT (Very Large Telescope) and the Gemini Southern Telescope – all located in Chile – as well as the “Twin” Keck Telescopes in Hawaii.
These measurements allowed them to confirm that they were observing these galaxies when the universe was 550 million years old. Knowing the age and time of existence of the galaxies allowed the team to calculate when the first stars were born.
Similar estimates have been made using only individual galaxies, but this is the first significant estimate based on a representative set of them.