Astronomers this week detailed findings showing how our own galaxy, the Milky Way, may have looked when it was first forming.

The research, published recently in The Astrophysical Journal, shows that the Milky Way was likely once a blue-hued, gas-filled, low-mass object. It then gained mass and became a flat disc shape with a slight bulge in its center. Over time, the galaxy and the supermassive black hole at its center grew and formed the spiral shape that we observe today.

“You can see that these galaxies are fluffy and spread out,” said Shannon Patel, another co-author of the study and an astronomer at Leiden University. “There is no evidence of a bulge without a disk, around which the disk formed later.”

The research used the Hubble Space Telescope to perform deep-sky surveys of 400 galaxies chosen from a catalog of more than 100,000 galaxies for their similarities to the Milky Way. Astronomers were able to observe those Milky Way-like galaxies and place them each along an 11 billion year-long development path. They found evidence that our galaxy’s peak star formation period occurred when the universe was only 4 billion years old, with stars forming at a rate of around 15 per year.

“For the first time, we have direct images of what the Milky Way looked like in the past,” said Pieter van Dokkum, a co-author of the study and an Astronomer at Yale University. “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.”

(Image courtesy NASA/ESA)