Snapshot of the early universe
doi:10.1038/nindia.2012.187 Published online 19 December 2012
Researchers have developed a new sensitive probe that might help catch glimpses of the early universe. The probe is capable of measuring the energy density of gravitational waves (GWs), which are thought to have left a signature in cosmic microwave background (CMB) photons polarized and scattered when the universe was over 300,000 years old.
CMB photons form the CMB radiation, the leftover radiation from the Big Bang, the fiery birth of the universe around 14 billion years ago. Since the Big Bang, the universe has undergone explosive expansion, generating GWs as ripples in the fabric of space. These GWs might have affected the polarization of photons getting scattered off the electrons which were then busy in combining with nuclei to form the first atoms, mostly hydrogen, during the recombination epoch. In recent time, super-massive black holes have added to the effect of GW background on photons.
Existing probes are sensitive to GWs emanating from pre-recombination epochs when the universe was much younger than 300,000 years old. However, no probes are available to detect GWs from the recombination and post-recombination epochs at cosmological scales.
To design a probe sensitive to GW signatures from the recombination and post-recombination epochs, the researchers devised a new technique that measured minor GW-induced perturbations in the polarized CMB photons that bathe the universe uniformly in all directions. They looked at two types of polarized photons – B mode and E mode. They found that B mode photons could measure the GW background from the recombination and post-recombination epochs.
"With this new sensitive probe, we could peer back in time glimpsing all epochs after the recombination epoch that set off the process of atom formation when the universe was older than 300,000 years," says lead researcher Tarun Souradeep from Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India.