Astronomers have analyzed Hubble's deep-sky surveys of 400 galaxies similar to the Milky Way to study their evolution and noted their appearance at various stages of development over a time span of 11 billion years, the space agency reported Thursday.
The analysis suggests the Milky Way likely began as faint, blue, low-mass object containing lots of gas, fuel for subsequent star birth, astronomers said.
A blue color is an indicator of rapid star formation, they said.
From a flat disk with a bulge in the middle, the Milky Way would have slowly evolved into the majestic spiral form see today, they said.
"For the first time, we have direct images of what the Milky Way looked like in the past," study co-leader Pieter G. van Dokkum of Yale University said. "Of course, we can't see the Milky Way itself in the past. We selected galaxies billions of light-years away that will evolve into galaxies like the Milky Way.
"By tracing the Milky Way's siblings, we find that our galaxy built up 90 percent of its stars between 11 billion and 7 billion years ago, which is something that has not been measured directly before."
At the peak of star formation, when the universe was about 4 billion years old, the Milky Way-like galaxies were pumping out about 15 stars a year. By comparison, the Milky Way today is creating only one star a year, the astronomers said.