Massive galaxy mergers sparked bursts of star formation when Universe was 6 bln yrs old

London, Jan 3 (ANI): A survey, using data obtained from the Hubble Space Telescope, has determined that nearly all massive galaxies have undergone at least one major merger since the Universe was 6 billion years old, resulting in bursts of star formation.

According to a report in Nature News, the survey used data from the Hubble Space Telescope to study 21,902 massive galaxies as they would have appeared when the Universe - now roughly 13.7 billion years old - was between 5.2 billion and 11.2 billion years old.

Mergers tend to leave galaxies with an asymmetric, clumpy appearance, and, based on a computer analysis of these characteristics, astrophysicist Christopher Conselice at the University of Nottingham, UK, and his colleagues found evidence for at least 2,000 mergers during that epoch.

They also found a close match between the timing of the mergers and the starburst episodes.

Conselice added that a significant decline in mergers, when the Universe was about 7 billion years old, coincides with the time of a previously identified decrease in star formation.

Because each of the galaxies was imaged at just one moment in their evolution, the team extrapolated its findings to conclude that almost all of the galaxies will have undergone a merger by the present day.

Reconstructing how galaxies have merged is a vital part of understanding their evolution.

But, the survey could also help to settle a decades-long debate over whether intense episodes of star formation, known as starbursts, are triggered by large-scale galactic mergers or by processes within individual galaxies.

In today's Universe, such massive mergers are rare.

But in the past, according to Conselice, these mergers have created starburst conditions that spawned stars at a rate of about 200 solar masses per year - 100 times our own Milky Way Galaxy's current star-formation rate.

"Mergers fundamentally transform these galaxies' structure and how they evolve," said Conselice. "Two gas-rich galaxies smash together and gas clouds collide, forming stars," he added. (ANI)