The astronomers studied the evolution of 400 galaxies similar to ours and noted their appearance over a course of 11 billion years. The believe our galaxy began as a faint blue mass of objects containing a lot of gas.
"For the first time, we have direct images of what the Milky Way looked like in the past," said study co-leader Pieter G. van Dokkum of Yale University. "Of course, we can't see the Milky Way itself in the past."
They found that the Milky way was a flat disk with a bulge in the center, which grew into the spiral we see nowadays. The disk contains the Earth and the Sun, while the bulge contains older stars and a huge black hole that grew along with the galaxy.
At the peak of star formation, when the universe was about 4 billion years old, the Milky Way and similar galaxies were forming 15 stars a year. By comparison the Milky Way is creating only one star a year.
"These deep surveys allow us to see the smaller galaxies. In previous observations we could only see the most luminous galaxies in the distant past, and now we can look at more normal galaxies. Hubble gives us the shapes and colors of these spirals as well as their distances from Earth. We also can measure the rates at which each part of the galaxies grew. All of this is difficult to do from the ground," said team member Joel Leja of Yale University.