We've been calling it the Milky Way, but its true color has actually been unknown. Now, a team of scientists has determined more precisely that our galaxy is indeed white.
The Milky Way is the color of snow when viewed one or two hours after dawn, says Jeffrey Newman, professor of physics and astronomy at the University of Pittsburgh. Newman and colleagues set out to put the Milky Way in context in terms of its color.
"The Milky Way is well within range you would see as white," Newman says, adding that it is bluer than light from an incandescent bulb, but redder than sunlight at noon.
The scientists used the Sloan Digital Sky Survey, which has data on nearly a million other galaxies out there, to look at 1,000 galaxies that resemble the Milky Way in the number of stars and the rate at which new stars are being born. These are factors that relate to the overall color of the galaxy. It's easier for scientists to see the color of other galaxies than the color of our own, since they can't actually travel outside of it to view it from a distance.
It appears that every year, somewhere in the Milky Way, about two new stars on average come into being. They tend to form in clouds of gas and dust throughout the galaxy, and a single cloud can give rise to up to 1,000 stars. The Orion Nebula is an example of a place where new stars are forming, Newman said.
As a galaxy gets older, its light becomes more red. A bluer galaxy would be younger because blue stars are relatively short-lived, Newman explains. By short-lived, he means a few million years, and these massive stars are the ones likely to explode in a supernova. But for stars less than eight times the mass of the sun, a star instead sheds its outer layer and becomes a white dwarf.
Our galaxy, which about 100,000 light-years across, has stars as much as 13 billion years old. When you look up at sky, even on the clearest night in the desert you are only seeing stars as much as a couple thousand light years away. Andromeda, the closest galaxy to the Milky Way, is more red, meaning it's older and further toward its retirement. It will shut down its star formation faster than the Milky Way.
The research was presented Wednesday at the American Astronomical Society meeting in Austin, Texas.