NASA / EAS / STScI/J Hester and P Scowen (Arizona State University)
The Eagle Nebula, captured here by the Hubble Space Telescope, contains molecular hydrogen that can be seen only when it interacts with other molecules in space.
updated 6/15/2012 12:10:44 PM ET 2012-06-15T16:10:44

Scientists have untangled the structure of an elusive space molecule that may help astronomers better understand the vast clouds of interstellar gas across our Milky Way galaxy.

Unable to directly detect the coldest clouds of the most plentiful molecule in the universe, astronomers must rely on its interactions to find it. The search should become easier with an improved understanding of the compound H2-CO, frequently used as a tracer chemical.

After obtaining a very accurate reading of the most plentiful variety of this compound, an international team of scientists was able to map its distribution across space.

Tracking what you cannot see
H2-CO is important because it could be the key to locating molecular hydrogen in space. After the Big Bang, this crucial molecule, along with small traces of helium, dominated. Stars and galaxies formed as clouds of the material collapsed in on themselves.

Even today, molecular hydrogen makes up nearly three-quarters of the mass of the universe. Yet despite being so plentiful,  it is nearly invisible when in its coldest state. Scientists can detect it only through its interactions with other elements. [ The Universe: Big Bang to Now in 10 Easy Steps  ]

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Enter the weakly interacting complex H2-CO, which astronomers can use to locate these hidden clouds of hydrogen.

"Almost all information about the most abundant molecule in space, H2, is obtained indirectly from measurements of the spectra of CO," Piotr Jankowski of the Nicolaus Copernicus University in Poland told by email.

By targeting clouds where carbon monoxide and hydrogen interact, in combinations such as H2-CO, astronomers can learn more about the dominant molecule in the universe. Because the complex isn't a completely new molecule, but instead two pieces that fit together, unraveling the mystery of the tracer complex will allow astronomers to understand more about molecular hydrogen as well.

"This procedure has been performed successfully for the first time for a complex of this size and for so complicated a spectrum," Jankowski said.

Back to basics
When molecular hydrogen (H2) and carbon monoxide (CO) come together to form the weakly interacting complex H2-CO, both fragments maintain their separate identities, rather than creating a brand-new molecule. The complex comes in two varieties, based on how the spin of the two bound molecules' nuclei align. When the nuclear spins are aligned in the same direction, the molecule is in its "ortho" state; when these spins are anti-aligned, it is in its "para" version. Although molecules in the ortho state are more abundant, they have also been more challenging for scientists to understand.

The difficulty comes from the combination of the compound's rotational motion with the vibrations between its components. In most molecules, the vibrational effects are more energetic than their rotational motion. However, this is not the case for the H2-CO complex, which renders the light spectrum coming from it much more complicated.

"There is no simple division of vibrations and rotations," Jankowski said.

Instead, the larger size of the vibrations tends to mask the signals of the rotational motion.

Jankowski, who was part of an international team that cracked the challenging code, explained that instead of simply observing the complex, the group used advanced theoretical methods to derive the theoretical spectrum, which almost perfectly matched up with what they saw in the experiment.

But the molecule was so complex that the team found themselves going back to the basics of quantum physics.

"We had to abandon the spectroscopic models and calculate the theoretical spectrum from first principles," Jankowski said.

The research appeared in the online version of the journal Science May 31.

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Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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