Since 1922, astronomers have been baffled as to the precise origin and composition of the diffuse interstellar bands seen through the Milky Way's stellar medium. This new interactive map doesn't solve the mystery, but it shows us exactly where these enigmatic molecules reside.

Image: Lan, Zasowski & Menard

In the 1920s, Berkeley graduate student Mary Lea Heger photographed two weird features in the spectra of distant binary stars. Pam Graham from the CSA explains:

These features appeared as absorption lines–dark lines resulting from the absence of photons at distinct frequencies in a continuous spectrum–but they were much wider and more diffuse than the atomic spectral lines ordinarily seen in stars. They also appeared to be stationary, even though spectral lines produced by stars in a binary system should shift back and forth in wavelength due to the Doppler effect.

By 1938, astronomer Paul Merrill had confirmed the unidentified nature of these broad absorption features, called absorption bands, and established their origin in interstellar rather than circumstellar regions.


Since then, the exact nature of these molecules in the the diffuse interstellar bands (DIB) has eluded scientists. It's clear that these lines are caused by a variety of molecules, but precisely which of many thousands of possible molecules is unknown.

Now, in an effort to make sense of the relevant data, researchers from Johns Hopkins's Sloan Digital Sky Survey have created an interactive map of the molecules responsible for causing the feature. The new map required an analysis of massive amounts of data and the power of statistical analysis.


The new map combined data from two parallel studies, one that focused on the densest parts of our galaxy (using infrared observations that can pierce through the dust clouds and reach obscured stars), and one that used visible light to locate the mysterious molecules located above the plane of the galaxy (where the signatures tend to be weak and tough to measure).

"We do not have a full map yet, but we can already see a lot of interesting patterns," noted Brice MĂ©nard in a Johns Hopkins statement.

And indeed, the point of the new map is to guide researchers "toward the best observations and laboratory experiments to pin down the properties and nature of these enigmatic molecules."


The work has already revealed strange features in front of 60,000 stars in a wide range of environments.

"For the first time, we can see how these mysterious molecules are moving around the galaxy," Gail Zasowski said. "This is extremely useful and brings in new connections between these molecules and the dynamics of the Milky Way."

You can find the interactive map here.

Their work was recently presented at the 225th meeting of the American Astronomical Society in Seattle. More here.