The Hubble telescope revealed images of the Milky Way's earliest days.
Researchers took a survey of 400 galaxies similar to the Milky Way in various stages of development, a Hubble news release reported.
"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. "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."
The research allowed researchers to determine how our galaxy evolved.
"A scale model of the Milky Way can be imagined by envisioning a fried egg. The egg white is the disk, where the Sun and Earth reside. The [yolk] represents the central bulge of older stars, home to a supermassive black hole that must have also grown along with the galaxy," the news release reported.
The image compiled by Hubble suggest the Milky Way's large "yolk" and flat disk grew in tandem, eventually becoming what our galaxy is today.
"You can see that these galaxies are fluffy and spread out," study co-leader Shannon Patel, of Leiden University, the Netherlands, said. "There is no evidence of a bulge without a disk, around which the disk formed later."
This evidence shows the entire Milky Way grew together, unlike some galaxies in which the bulge grows first.
Billions of years ago the Milky Way was believed to be a faint-blue hue and had a low mass. In the peak of star creation in the universe four billion years ago galaxies were creating stars at a rate of about 15 a year; now that number has dropped to one.
"These observations show that there are at least two galaxy-formation tracks," van Dokkum said. "Massive ellipticals form a very dense core early in the universe, including a black hole, presumably, and the rest of the galaxy slowly accretes around it, fueled by mergers with other galaxies. But from our survey we find that galaxies like our Milky Way show a different, more uniform path of growing into the majestic spirals we see today."
