(Sen) - The Hubble Space Telescope has revealed the first visual evidence of how our galaxy, the Milky Way, assembled itself into the spiral of stars we see today.
Using Hubble's deep-sky surveys to study the evolution of 400 galaxies similar to the Milky Way and noting their appearance at various stages of development over a time span of 11 billion years, astronomers found the Milky Way likely began as a faint, blue, low-mass object containing lots of gas. Gas is the fuel for star birth and the blue colour is an indicator of rapid star formation.
The Milky Way was also probably a flat disk with a bulge in the middle, both of which grew simultaneously into the pinwheel seen today. The Sun and Earth reside in the disk and the bulge is full of older stars and a supermassive black hole that probably grew along with the galaxy.
"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. 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."
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