| Hubble space telescope
New Delhi, Sept. 17: Astronomers who peered deep into space and far back in time looking for the earliest bright galaxies in the universe have reported finding signs of the evolution of the first galaxies.
The observations by two astronomers at the University of California, Santa Cruz, provide fresh evidence for the gradual build-up of large galaxies packed with stars over long periods of time as smaller galactic bodies collided and merged.
The astronomers used the Earth-orbiting Hubble Space Telescope to hunt for the earliest bright galaxies.
In a research paper set to appear in the journal Nature, the astronomers have reported finding hundreds of bright galaxies about 900 million years after the Big Bang. But when they looked deeper about 200 million years earlier in time, there was only one galaxy large and bright enough to be visible.
“This deficient number of luminous galaxies 700 million years after the Big Bang suggests that dramatic changes were happening to galaxies at early times in the universe,” team member Rychard Bouwens told The Telegraph.
“Our finding is not entirely unexpected within existing paradigms about galaxy formation, but it does allow us to push back our observations of galaxies to even earlier epochs than before,” Bouwens said.
Previous studies had explored galaxies in the universe when it was about a billion years old.
The new observations have allowed astronomers to conduct a thorough and robust exploration of the universe when it was just 700 million years old — an era when bright and large galaxies packed with hundreds of billions of stars were very few in number.
Using data from surveys conducted by the Hubble Space Telescope in the past, the scientists searched for galaxies that had emitted light just 700 million years after the Big Bang. The search revealed only one such galaxy or — by tweaking the search criteria a bit — at the most four such galaxies.
The researchers said if galaxies that existed 700 million years after the Big Bang were the same as those that existed 900 million years after the Big Bang, they would have expected to find many more galaxies.
The large number of bright galaxies 200 million years later suggests that smaller galaxies would have been merging during the time to form bigger, visible ones. “The smaller pieces coming together were also galaxies but smaller — with less stars, less hydrogen and less mass,” said Bouwens.