Our Milky Way Galaxy Is as White as, Well, Milk

Artist’s concept of the Milky Way galaxy. Picture courtesy NASA/JPL

There’s certainly no shortage of gorgeous pictures of the Milky Way as seen from Earth, many of which show our home galaxy in shades of purple, pink, blue, and cream.

But what we see in these pictures can be colored by two big factors:

  • Many astrophotographers use filters to capture different wavelengths of light not visible to the naked eye, which are then colorized into hues our eyes can recognize.
  • Also, what we see of the Milky Way from Earth is a view looking edge-on, which means lots of light gets blocked by dense dust—embedded as we are in one of our galaxy’s spiral arms, we can see only a thousand to two thousand light-years in any direction.

To the naked eye at night, the arc of the Milky Way appears to glow white, but that’s only because our eyes aren’t sensitive enough to grasp color in low-light conditions.

(Related: “Voyager Probes Detect ‘Invisible’ Milky Way Glow.”)

So if we had an outsider’s perspective floating a few light-years away from our galaxy, what color would the Milky Way actually be?

A Hubble Space Telescope picture of the galaxy M104. Picture courtesy NASA/ESA and The Hubble Heritage Team STScI/AURA

It turns out “the Milky Way has the right name for the wrong reasons,” researcher Jeffrey Newman, an astronomer at the University of Pittsburgh, said this week during a meeting of the American Astronomical Society in Austin, Texas.

According to a new study by Newman and colleagues, the Milky Way really is milky white—or, more precisely, it’s the color of “fine-grain, new spring snow in the early morning or late evening, about an hour away from dawn or sunset.”

(Also see “Pictures: Best Astronomy Photos of 2011 Named.”)

The trick to figuring this out was to look at the color and brightness of other, known galaxies using the vast catalog collected by the Sloan Digital Sky Survey.

The researchers could then compare the Milky Way to galaxies that should be very similar, in terms of the amount of stars present and the rate of new star formation.

These factors are known to affect galaxies’ color and brightness because stars of different ages tend to fall into well-defined color groups: younger stars are bluer while older stars are redder.

Galaxies forming lots of new stars look bluer from a distance, while galaxies where star formation is tapering off will look redder.

(Also see “Mysterious Structures Balloon From Milky Way’s Core.”)

In their new study, the Pittsburgh team found a set of hundreds of galaxies with well known colors that essentially match the other stellar properties of the Milky Way.

Based on these Milky Way analogs, the scientists could infer our galaxy’s color: a snowy white that’s right on the dividing line between the redder and bluer galaxies.

But that means the Milky Way won’t be white for long, in cosmic terms.

The rate of star formation in our galaxy is slowing, and “a few billion years from now, our galaxy 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,” Newman said in a statement.

Eventually, “the Milky Way’s spiral arms will fade into obscurity when there are no more blue stars left.”

(Related: “New Milky Way Map Created; Shows Fewer Main Arms.”)

Changing Planet