NASA Hubble Space Telescope Reveals Formative Years of Milky Way Galaxy

NASA's Hubble Space Telescope has shown astronomers a bit more about the history of the Milky Way galaxy. Scientists used Hubble's deep-sky surveys of 400 similar galaxies in order to better understand our own galaxy's formative years.

"For the first time, we have direct images of what the Milky Way looked like in the past," said Pieter G. van Dokkum, one of the researchers, in a news release. "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."

By examining images of these far-flung galaxies, the astronomers found that the Milky Way likely began life as a faint, blue, low-mass object containing lots of gas. Gas in particular is important for a developing galaxy since it's the fuel for star birth. The blue color is an indicator of rapid star formation. During the course of its growth, the Milky Way probably was a flat disk with a bulge in the middle, both of which grew simultaneously into the majestic spiral that we see today.

"You can see that these galaxies are fluffy and spread out," said Shannon Patel, one of the researchers, in a news release. "There is no evidence of a bulge without a disk, around which the disk formed later." In other words, the findings reveal that the whole Milky Way grew at the same time, unlike more massive elliptical galaxies, in which the central bulge comes first.

"In these observations, we're capturing most of the evolution of the Milky Way," said Joel Leja, one of the researchers, in a news release. "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."

The findings are published in The Astrophysical Journal.