A team of astronomers including an Indian graduate student Nivedita Mahesh from Arizona State University have discovered for the first time signals from “cosmic dawn” the moment when the universe’s earliest stars emerged, making a significant breakthrough in our understanding of the evolution of cosmos.
When the universe was formed in the Big Bang event 13.8 billion years ago there was no sun, no stars, no light, it was a dark place. 3,70,000 years after the Big Bang first atoms, primordial hydrogen was formed. The findings by a team led by Judd Bowman, an astronomer at Arizona State University in Tempe, published in journal Nature on 28 February, tell us that the first stars were born around 13.62 billion years ago in what astronomers call as ‘cosmic dawn’ when the whole universe was awash with ultraviolet rays, and first stellar death— explosions in supernovae, formation of stellar black holes, took place around 13.55 billion years ago. For comparison, Sun and Earth formed around 4.6 billion years ago.
Cosmologist came up with an ingenious idea to find when the early stars emerged. First stars rich in hydrogen were massive, tens and thousands time massive than our Sun. Massive stars live fast and burn out fast. The intense ultraviolet light from them would ionise the gas enveloping the stars. The ionised hydrogen gas would absorb the cosmic microwave background (CMB) radiation, the afterglow of the Big Bang at a characteristic wavelength.