Astronomers have worked out when the first stars began shining.
They say that this period, known as the "cosmic dawn," occurred between 250 to 350 million years after the Big Bang. Discovering when the cosmic dawn began has been the life's work of Prof Richard Ellis, from England's University College London.
He told BBC News: "The Holy Grail has been to look back far enough that you would be able to see the very first generation of stars and galaxies. And now we have the first convincing evidence of when the Universe was first bathed in starlight."
The team analysed six of the most distant galaxies. They were so far away that even with the world's most powerful telescopes they appeared as just a few pixels on the computer screen.
They are also among the earliest to have emerged in the Universe and so, by the time their images are captured by telescopes on Earth, they are seen not long after the Big Bang.
By working out their age, the team calculated the start of the cosmic dawn - when the first stars formed. Dr Nicolas Laporte, from the Kavli Institute of Astronomy in Cambridge led the analysis. "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 crucial moment in the history of the Universe occurred."
Dr Laporte said that obtaining the result was a dream come true.
"It is fantastic to think that particles of light have been travelling through space for over 13 billion years and then entered a telescope. The wonderful thing about being an astrophysicist is the ability to time travel and witness the distant past," he explained.
The Universe came into being 13.8 billion years ago in the Big Bang. After an initial flash, it 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 emerged, bringing light to the cosmos.
Critically, the new analysis also indicates that the first galaxies are bright enough and within the range where they can be seen by the James Webb Space Telescope - the successor to the venerable Hubble Space Telescope - and set to launch later this year. Astronomers may then be able to witness this crucial moment in the evolution of the Universe directly.