Radio finds unknown molecules in space

BY KULVINDER SINGH CHADHA

ASTRONOMY NOW

Posted: 16 February, 2009

A sea change in the way radio astronomy is conducted has been responsible for finding a whole swathe of unidentified molecules in space.

Astronomers of the National Radio Astronomy Observatory used the Robert C. Byrd radio telescope at Green Bank, West Virginia, to find 720 spectral lines. “About 240 of those are from unknown molecules,” says Dr Anthony Remijan. As a comparison, only 150 molecules have been identified by astronomers over the past 40 years, including sugars, alcohols, and PCAs (a group of chemicals found in burnt toast).

Remijan and his colleagues are part of the Prebiotic Interstellar Molecule Survey (PRIMOS), which is a project studying a star-forming region near the Milky Way’s centre. “We're making available to all scientists the best collection of data below 50-gigahertz ever produced for the study of interstellar chemistry,” Remijan says proudly.

Click to enlarge. The chemical cycle of stars and planets was discussed at the ‘Cosmic Cradle of Life’ symposium in Chicago. Image: Bill Saxton, NRAO/AUI/NSF.

Beforehand, astronomers would often decide what molecule(s) they would want to find, and then search a narrow band of radio wavelengths for their signature. Instead, what Remijan’s team have done is search a broad range of wavelengths and made this data available for scientists to explore and study. This brings radio astronomy spectroscopy more in line with what’s done in other wavelength regions, such as the infrared and optical. The reason that this hasn’t happened before is, as Remijan says, “We have not had a telescope with the frequency coverage and sensitivity available to conduct this type of survey. The completion of the Robert C. Byrd Telescope provided the first real opportunity to attempt this type of survey.”

So have any of the molecules been identified yet? “To date, no. We are still working on compiling the frequencies and intensities of these unknown transitions which will help with the later identification of these species.” Amusingly however, Remijan describes how certain unwanted features ‘jump out’ of the spectra, “At the low frequencies we are observing that the major features are not astronomical at all! In fact they are interference from ground based transmitters and satellites broadcasting in the same frequency band.”

Remijan goes on to say how transmissions from satellites such as XM and Sirius mask any weak spectral features from large molecules in those particular ranges, making them hard to identify. “That’s another reason why we are doing the survey though, to identify these roadblocks to our investigation.” This is of importance as large molecules are the precursors of biological activity and identifying them in large numbers should tells us where we should be looking for life.