Daily news

9 January 2004

Space molecules point to organic origins

The most complex molecules yet found in space have shown astronomers how such organic matter is created. The evidence points to a rare type of star as the origin for life’s building blocks.

Two hydrocarbon molecules called anthracene and pyrene occur in a nebula called the Red Rectangle, 1000 light years from Earth, according to results presented at the American Astronomical Society meeting in Atlanta, Georgia.

The core of the nebula harbours a dying and turbulent star
The core of the nebula harbours a dying and turbulent star

(Image: NASA/JPL/Raghvendra Sahai)

A team led by Adolf Witt of the University of Toledo, Ohio, used telescopes in Chile and Arizona to examine ultraviolet light emitted by the nebula, and found the spectral signatures of these molecules.


The two molecules contain 24 and 26 atoms respectively, making them about twice the size of the previous record holder, a molecular chain of 13 atoms. They are made of linked rings of carbon atoms, and belong to a class of molecules called polycyclic aromatic hydrocarbons (PAHs). “If you see a diesel truck in front of you blowing out black smoke, that is mostly PAHs” notes Witt.

Molecule factory

There is evidence that huge quantities of PAHs exist in deep space, from the infrared light they emit, and amino acids have been found in meteorites landing on Earth. Organic molecules like these must have rained down on the early Earth, and may have helped life to begin.

But the source of these complex molecules has been uncertain, but Witt is now convinced that they originated in places like the Red Rectangle.

At the core of the nebula is a star about the mass of the Sun, but far older. It is near the end of its life, going through a brief turbulent stage in which convection currents dredge up carbon-rich material from deep within the star.

Carbon and hydrogen get caught up in the stellar wind and blown out to form the nebula, and as the gas cools, atoms collide to form larger and larger molecules.

The discovery of anthracene and pyrene is strong evidence that this process is really happening. And these two molecules are almost certainly far from the biggest being built in the Red Rectangle.

“There is no limit – eventually this will form particles of a million atoms or more,” Witt told New Scientist. “We are looking into a factory for organic molecules.”