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The region around the center of our Milky Way galaxy glows colorfully in this new version of an image taken by NASA's Spitzer Space Telescope. (NASA/JPL-Caltech)
Our Milky Way, and the nearest spiral galaxy, M31 or the Andromeda Galaxy, have now passed through most of their star formation, according to new research from Swinburne University of Technology in Australia.
Using modeling and comparison with a multitude of other known galaxies, astronomers determined that our galaxy is at the mid-point between being a young blue galaxy and a dying red galaxy.
According to the research paper, the Milky Way is a “green valley” galaxy, transitioning between a young blue galaxy and an old red one.
“The properties we've looked at all point to the Milky Way having global colors that we'd classify as green–they’re midway along an evolutionary track between ‘blue and star forming’ and ‘red and dead,’” said co-author Darren Croton in a university press release.
Although astronomers have been able to determine the color index of far away galaxies, it has been a hard task to measure the Milky Way from inside.
“Determining the state of our own galaxy while we’re stuck inside it is very difficult to do,” Croton said. “The phrase ‘it’s hard to see the forest for the trees’ really rings true here,” he added.
To determine our galaxy's color index, the researchers had to simulate the evolution of the star formation process of 25 million galaxies taken from the Sloan Digital Sky Survey and Galaxy Zoo. They then selected those that resembled the Milky Way regarding star formation rate and other similarities, such as the total mass of its stars and its shape.
But there are still around 1.5 billion years to go before the Milky Way becomes an aged red galaxy.
“Star formation in our galaxy will continue to decrease, but those concerned about the Milky Way’s decline needn’t worry just yet–retirement is still a long way off,” said co-author Simon Mutch in the release.
The researchers expect another episode of star formation in five billion years, when the Milky Way collides and merges with M31, deforming both galaxies in the process.The findings will be published in the Astrophysical Journal.
