The Big Bang was the birth of the universe, but the cosmic dawn of the first stars didn't happen right away.
The first stars of the young universe didn't form until 250 million to 350 million years after the Big Bang, according to a recent study published in the journal Monthly Notices of the Royal Astronomical Society.
And this discovery exhausted the capabilities of the Spitzer and Hubble Space Telescopes, leaving it to the forthcoming James Webb Space Telescope to push empirical frontiers even closer to the Big Bang itself.
Peering into the age of the first stars
The research team analyzed six galaxies so distant that their life has taken most of the lifespan of the universe to traverse the distance to Earth. The UK-led team discovered that the galaxies under study are from a time more than 13 billion years ago, when the cosmos was just 550 million years old. The researchers evaluated images from the Spitzer and Hubble Space Telescopes, and calculated the age of these unconscionably distant galaxies at between 200 and 300 million years, which opened the theoretical gates to know when their first stars formed. "Theorists speculate that the universe was a dark place for the first few hundred million years, before the first stars and galaxies formed," said lead study author Nicholas Laporte of the University of Cambridge, in an embargoed release shared with IE.
"Witnessing the moment when the universe was first bathed in starlight is a major quest in astronomy," added Laporte. "Our observations indicate that cosmic dawn occurred between 250 and 350 million years after the beginning of the universe, and, at the time of their formation, galaxies such as the ones we studied would have been sufficiently luminous to be seen with the James Webb Space Telescope." The scientists then studied the starlight from these galaxies, as captured by Spitzer and Hubble, honing in on a marker in the energy distribution that points to the presence of atomic hydrogen in the star's atmospheres. This is how they learned the age of these very first stars.
Pushing back the frontier of astronomy toward the Big Bang
Hydrogen signatures grow stronger as stellar populations age, but grow fainter once the galaxy has surpassed its billionth year. This age-hydrogen correlation is the result of massive stars that comprise the signal burn through their nuclear fuel very rapidly, and thus die before other, smaller stars. "This age indicator is used to date stars in our own neighborhood in the Milky Way but it can also be used to date extremely remote galaxies, seen at a very early period of the universe," said Romain Meyer at UCL Physics & Astronomy and the Max Planck Institute for Astronomy in Heidelberg, Germany, who was also co-author of the study. "Using this indicator we infer that, even at these early times, our galaxies are between 200 and 300 million years old."
"Over the last decade, astronomers have pushed back the frontiers of what we can observe to a time when the universe was only 4% of its present age," said Professor Richard Ellis at UCL Physics & Astronomy, who was also a co-author of the study. "However, due to limited transparency of Earth's atmosphere and the capabilities of the Hubble and Spitzer Space Telescopes, we have reached our limit. We now eagerly await the launch of the James Webb Space Telescope, which we believe has the capability to directly witness cosmic down." It seems fitting that active telescopes like Hubble and Spitzer have reached their limit by discovering the time in the very young universe when the first stars formed. But with the Webb telescope slated for launch later this year, we might push back the frontiers of the observable universe even further, and approach the beginning of space and time during the Big Bang.