NASA`s Hubble Space Telescope has shown how Milky Way looked in it`s formative years.
Astronomers used Hubble`s deep-sky surveys to study the evolution of 400 galaxies similar to the Milky Way and noted their appearance at various stages of development over a time span of 11 billion years.
Judging from images of these far-flung galaxies, they found the Milky Way likely began as faint, blue, low-mass object containing lots of gas. Gas is the fuel for star birth and the blue color is an indicator of rapid star formation.
They also found the Milky Way probably was a flat disk with a bulge in the middle, both of which grew simultaneously into the majestic spiral seen today.
The sun and Earth reside in the disk and the bulge is both full of older stars and home to a supermassive black hole that probably grew along with the galaxy.
Co-leader Pieter G. van Dokkum of Yale University in New Haven, Connecticut, said that for the first time, we have direct images of what the Milky Way looked like in the past.
He said that the team selected galaxies billions of light-years away that will evolve into galaxies like the Milky Way.
Van Dokkum said that by tracing the Milky Way`s siblings, they found that their 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.
To identify the far-flung galaxies and study them in detail, the research team used three of the largest Hubble programs, the 3D-HST survey, the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and the Great Observatories Origins Deep Survey.
These surveys combined spectroscopy with visible and near-infrared imaging by Hubble`s Wide Field Camera 3 and Advanced Camera for Surveys.
The team`s results have been published in The Astrophysical Journal Letters.