Milky Way came into present state as Earth and Sun formed

Disc galaxies like our own Milky Way were believed to have been formed billions of years ago, however, now scientists have found they settled into the present state as the Sun and solar system were being formed.

"Astronomers thought disk galaxies in the nearby universe had settled into their present form by about 8 billion years ago, with little additional development since," Susan Kassin, an astronomer at Goddard Space Flight Center in Greenbelt.

"The trend we've observed instead shows the opposite, that galaxies were steadily changing over this time period," Kassin said in a statement.

NASA has studied hundreds of galaxies and found that they have continued to evolve contrary to the belief that they reached their current state billions of years before the planets.

Scientists studied 544 galaxies from the W M Keck Observatory in Hawaii and found that billions of years ago, galaxies were chaotic and random but over time, rotated into disc-shaped systems.

The larger the galaxy, the more settled its mass became and over time, there were fewer mergers, they said.

The study, called the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey, examined galaxies between two billion and eight billion light-years from Earth.

Scientists focused on galaxies with emission lines bright enough to give information about its internal workings.

It is now believed that the Milky Way was still evolving around the time the Sun formed, although the physical processes behind this are still to be determined.

Researchers say the distant blue galaxies they studied are gradually transforming into rotating disk galaxies like our own Milky Way.

"Previous studies removed galaxies that did not look like the well-ordered rotating disks now common in the universe today," said co-author Benjamin Weiner, an astronomer at the University of Arizona in Tucson.

"By neglecting them, these studies examined only those rare galaxies in the distant universe that are well-behaved and concluded that galaxies didn't change," Weiner said.