What Color Is The Milky Way?
January 12, 2012

What Color Is The Milky Way?

Astronomers from University of Pittsburgh seeking to find the true color of our very own Milky Way have revealed that it is so white that it would resemble a fresh blanket of snow to the naked eye.

The astronomers said the color of the galaxy is important because it reveals age, ranging from young blue galaxies with new stars still being born, to older red ones that rarely form new stars. It seems we are right in the middle of this range.

The Pittsburgh University team wanted to find out how our galaxy looked from the outside -- a difficult task given the Earth is deep inside the galaxy. By comparing star types in other galaxies, the team concluded that ours is unsurprisingly white. But not just any white: specifically, like spring snow at an hour after sunrise or before sunset.

The researchers presented their findings this week at the 219th American Astronomical Society meeting.

“For astronomers, one of the most important parameters is actually the color of the galaxy,” Jeffrey Newman of the University of Pittsburgh told BBC News. “That tells us basically how old the stars in the galaxy are, how recently it´s been forming stars - are they forming today or did its stars form billions and billions of years ago.”

“But it´s worse than that; not only are we looking at the Milky Way from the inside, but our view is blocked by dust,” Newman added. “We can only see about one or two thousand light years in any direction.”

Because of this, clouds of gas and dust obscure all but the closest regions of the Galaxy from view, preventing researchers from getting the ℠big picture.´

“The problem is similar to determining the overall color of the Earth, when you´re only able to tell what Pennsylvania looks like,” said Newman.

To work around this problem, Newman and Timothy Licquia, a PhD student in physics at Pittsburgh University, used images taken from other, more distant galaxies that can be viewed more clearly. These galaxies were observed by the Sloan Digital Sky Survey (SDSS), a project that measured detailed properties of nearly a million galaxies and has obtained color images of roughly 25 percent of the sky.

Without the large set of galaxies studied by the SDSS, Newman and Licquia´s color determination would not be possible.

“Thanks to SDSS, the large, uniform sample needed to select Milky Way analogs already existed. We just needed to think of the idea for the project, and it was possible,” Newman said in a university press release. “Although it is a relatively small telescope, only 2.5 meters (100 inches) in diameter, SDSS has been one of the most scientifically productive in history, enabling thousands of new projects like this one.”

Newman described the color of our Milky Way as being very close to the light seen when looking at spring snow in the early morning, shortly after dawn.

Michael Ramsey, Pittsburgh U´s associate professor of geology, said that new spring snow is the whitest (natural) thing on Earth.

Our galaxy has been given many different names by other culture, usually associated with milk. Human vision is not sensitive to colors seen in faint light, so the diffuse glow of the galaxy at night appears white to us. The association has proven to very appropriate, given the Milky Way is truly white.

However, while the evidence shows that our galaxy is still in the star producing phase, it is “on its way out,” according to Newman.

In a few billion years, the Milky Way “will be a much more boring place, full of middle-aged stars slowly using up their fuel and dying off, but without any new ones to take their place,” he said. “It will be less interesting for astronomers in other galaxies to look at, too: The Milky Way´s spiral arms will fade into obscurity when there are no more blue stars left.”

The Milky Way´s color is also very close to the cosmic color measured by Ivan Baldry, a professor of astrophysics at Liverpool John Moores University in England. Baldry and his colleagues in 2002 measured the average color of galaxies in the local universe.

“This close match shows that in many ways the Milky Way is a pretty typical galaxy,” said Newman. “This also agrees well with the ℠Copernican Principle´ embraced by the field of cosmology–that, just as the Earth is not in a special place in the solar system, we should not expect to live in an unusual place in the Universe.”

The new color measurement will allow researchers to better understand the development of the Milky Way Galaxy and how it relates to other objects in the galaxy.

“The Milky way is in a very interesting evolutionary state right now,” Newman concluded.


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