Friday, 9 January 2015

Milky Way's Mystery Molecules --"Created by Something Existing in Interstellar Space"


By analyzing the light of hundreds of thousands of celestial objects, Johns Hopkins astronomers from the Sloan Digital Sky Survey (SDSS) have created a unique map of enigmatic molecules in our galaxy that are responsible for puzzling features in the light from stars. "Seeing where these mysterious molecules are located is fascinating," said Brice Ménard, a professor in the Department of Physics & Astronomy at The Johns Hopkins University.

"For the first time, we can see how these mysterious molecules are moving around the galaxy," said Gail Zasowski, a Johns Hopkins astronomer. "This is extremely useful and brings in new connections between these molecules and the dynamics of the Milky Way. All the recent findings concerning these mysterious features paint a picture of tough little molecules that can exist in a variety of environments, all over the galaxy."

These puzzling features in the light from stars, which astronomers call "Diffuse Interstellar Bands" (DIBs), have been a mystery ever since they were discovered by astronomer Mary Lea Heger of Lick Observatory in 1922. While analyzing the light from stars, she found unexpected lines that were created by something existing in the interstellar space between the stars and the Earth.

"Almost a hundred years after their discovery, the exact nature of these molecules still remains a mystery, but we are getting one step closer to understanding what they are made of," Ménard said. "The era of Big Data in astronomy allows us to look at the universe in new ways.

Further research showed that these mysterious lines were due to a variety of molecules. But exactly which of many thousands of possible molecules are responsible for these features has remained a mystery for almost a century.

This new map, based on SDSS data that reveals the location of these enigmatic molecules, was compiled from two parallel studies.


Zasowski, a postdoctoral fellow, led one team that focused on the densest parts of our galaxy, using infrared observations that can cut through the dust clouds and reach previously obscured stars. Johns Hopkins graduate student Ting-Wen Lan led the other study, which used visible light to detect the mysterious molecules located above the plane of the galaxy, where their signatures are very weak and harder to measure.

"We do not have a full map yet, but we can already see a lot of interesting patterns," said Ménard, who worked on both teams.

Lan's team analyzed the light from more than half a million stars, galaxies, and quasars to detect the molecules' features in the regions well above and beyond the Milky Way's disk. In addition, the team was able to see the types of environments in which these molecules are more likely to be found. Some molecules like dense regions of gas and dust, and others prefer the lonelier spots far away from stars.

"These results will guide researchers toward the best observations and laboratory experiments to pin down the properties and nature of these enigmatic molecules," Lan said.

To look toward the galactic plane, hidden behind thick clouds of cosmic dust, Zasowski's team used data from the SDSS's APOGEE survey. APOGEE observations, which make use of infrared light, can easily see through interstellar dust and measure the properties of stars all over the galaxy.

The team members detected some of the mysterious features in front of about 60,000 stars in a wide range of environments and were even able to measure the motion of these molecules.

Earlier in 2012, astronomers discovered methoxy molecules containing carbon, hydrogen and oxygen in the Perseus molecular cloud, around 600 light years from Earth. But researchers were unable to reproduce this molecule in the lab by allowing reactants to condense on dust grains, leaving a mystery as to how it could have formed.

The answer was found in quantum weirdness that can generate a molecule in space that shouldn't exist by the classic rules of chemistry. In short, interstellar space is a kind of quantum chemistry lab, that may create a host of other organic molecules astronomers have discovered in space.

The image at the top of the page shows clouds of gas and dust drifting across the southern boundary of the constellation Perseus. The collaborative skyscape begins with bluish stars of Perseus at the left, but the eye is drawn to the striking, red NGC 1499. Also known as the California Nebula, its characteristic glow of atomic hydrogen gas is powered by ultraviolet light from luminous blue star Xi Persei immediately to the nebula's right.

Farther along, intriguing young star cluster IC 348 and neighboring Flying Ghost Nebula are right of center. Connected by dark and dusty tendrils on the outskirts of a giant molecular cloud, another active star forming region, NGC 1333, lies near the upper right edge of the of the wide field of view. Shining faintly, dust clouds strewn throughout the scene are hovering hundreds of light-years above the galactic plane and reflect starlight from the Milky Way.

The map, which can be viewed at, was unveiled Jan. 8 at the 225th meeting of the American Astronomical Society in Seattle.

The researchers used data from the Sloan Digital Sky Survey. The work was supported by National Science Foundation Grant AST-1109665 and NSF postdoctoral fellowship AST-1203017.

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