New research using the ESA’s Planck telescope has revealed that the first stars to shine in the universe sprouted up 100 Million years later than originally thought.
Studying the universe is like piecing together a 13.8 Billion year story, from the time of the Big Bang to the present. We study objects in the local Galaxy to piece together the present state, and we look further from Earth to see back in time and visit the earlier chapters to determine the long term evolution of the universe.
When the universe was 380,000 years old, it was large enough for the total energy inside to form the first particles, and it became transparent. This led to the Cosmic Microwave Background Radiation (CMBR) image we see today, and kicked off a period known as the ‘dark ages’ where there was no light. A few hundred million years of expansion later, the universe saw the light from the first stars permeate the darkness, and eventually they formed Galaxies and filled the vast darkness with light.
The newest complete Planck map shows not only the temperature of the CMBR, but also the polarization of the light, which offers clues about the ancient universe.
Before the 380,000th birthday of the universe, protons, neutrons, and electrons regularly collided with each other and with light, meaning light couldn’t travel very far, creating a ‘foggy’ universe. As it expanded and cooled, the particles formed neutral atoms that would not interact with the light, meaning it could travel further. Eventually the universe cooled enough and the light was set free to travel nonstop to the present day, where its redshift now makes up the CMBR.
Light is polarized when it vibrates in a preferential direction, and is a result of a photon’s interaction with a particle. This means that the observed polarization of the universe by Planck is a look back to the final interactions of light with the early particles of the Universe.
But there is more to the story. When the dark ages ended and the first stars formed, the starlight could split atoms up into protons and neutrons again, beginning an epoch of the universe called ‘reionization.’ The newly ionized universe would occasionally interact with the CMBR photons, leaving another tell-tale imprint on the polarization. Once the universe grew large enough, the ionizing light from stars did not dominate the universe, and it once again became neutral, leaving the CMBR’s polarization in it’s final state.
By studying the polarization maps from Planck in detail, researchers have fine tuned measurements of when these periods occurred, and found that reionization began 100 million years later than originally thought, making the oldest stars 100 million years younger.
This is why we strive to obtain higher resolution data from the CMBR. We are looking at the information the early universe has given us, and using our knowledge of light we can crack the code and probe the conditions that led to our existence 13 Billion years later.