The molecular building blocks of life had already formed by the time the universe was only a quarter of its present age, new observations by NASA's Spitzer Space Telescope reveal. The research bolsters the case for extraterrestrial life and may shed light on the nature of galaxies in the early universe.
Lin Yan, an astronomer at the Spitzer Science Center in Pasadena, California, US, and colleagues used the telescope to observe eight galaxies at an average distance of about 10 billion light years away. The images show the galaxies as they were just 3.5 billion years after the big bang.
"In the optical, these galaxies look like little smudges - their light is obscured by dust," says Yan. But Spitzer detects the mid-infrared glow from this dust and is 100 times more sensitive than previous infrared missions.
Its spectrometer was able to pick out the signature of complex molecules in two of the galaxies. These molecules, called polycyclic aromatic hydrocarbons (PAHs), each contain about 100 carbon and hydrogen atoms and are the building blocks of even more complex organic molecules.
"Detecting these complex molecules such a long time ago really suggests it's not crazy to think about life in another solar system or galaxy," Yan told New Scientist. "There have been 10 billion years for things to form and evolve, and there are so many galaxies."
The observations also reveal information about the galaxies in which the PAHs were discovered. In galaxies nearer Earth, the molecules have been found in extremely bright "starburst" galaxies that are undergoing intense star formation. There, the molecules exist on the border of dense clouds of molecular gas and dust and regions of gas ionised by massive young stars.
But PAHs are not found in galaxies whose radiation is dominated by the violent accretion of matter around a central black hole. "These molecules are quite fragile - if the temperature is too high or the radiation field is too strong, they can get destroyed," says Yan.
She is analysing Spitzer data on about 50 other galaxies at about the same distance to see which contain PAHs. She hopes to estimate the fraction of galaxies dominated by stars compared with the fraction dominated by active black holes in the early universe.
"We're still trying to understand what the distribution of galaxies is," she says. "Once we know that, the next step is trying to understand why some galaxies formed one way and some another."
Journal reference: Astrophysical Journal (vol 628, p 604)