Using NASA’s Hubble Space Telescope, astronomers have for the first time produced a detailed illustration of the Milky Way galaxy in its early stages of formation.

Researchers constructed the image by studying the evolution of about 400 galaxies similar to the Milky Way, and by observing their development over 11 billion years.

“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 in a news release.

Images from sister galaxies reveal the Milky Way began as a faint, blue, low-mass object containing a large amount of gas, which fuelled rapid star formation. 

“By tracing the Milky Way’s siblings, we find that our galaxy built up 90 per cent of its stars between 11 billion and 7 billion years ago, which is something that has not been measured directly before,” Van Dokkum said.

About 9 billion years ago, when the galaxy was just 4 billion years old, Milky Way-like galaxies were creating around 15 stars a year. Today, a new star emerges only once a year in the Milky Way.

Images from the Hubble Space Telescope also suggest that before growing into a spiral, the Milky Way began as a flat disk with a bulge in the middle. While Earth and the sun resided in the disk, the bulge was home to ancient stars and a supermassive black hole.

“These galaxies show us the whole Milky Way grew at the same time, unlike more massive elliptical galaxies, in which the central bulge forms first,” said study co-leader Shannon Patel of Leiden University.

In order to study the galaxies in detail, researchers used three of the largest Hubble programs:

  • The 3D HST survey
  • The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
  • The Great Observatories Origins Deep Survey

The astronomers measured the distances and sizes of the galaxies, and calculated the mass of each galaxy by looking at their colours and brightness.

“In these observations, we’re capturing most of the evolution of the Milky Way,” said researcher Joel Leja of Yale University. “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.”

The study was published in The Astrophysical Journal on Nov. 11.

NASA is set to launch the James Webb Space Telescope in 2018 in order to further explore the first galaxies that formed in the universe.