Using Spitzer, scientists have detected organic molecules in galaxies viewed as they were when our universe was one-fourth of its current age of about 14 billion years. These large molecules, known as polycyclic aromatic hydrocarbons (PAHs), are comprised of carbon and hydrogen. These molecules are among the most stable hydrocarbons.
PAH molecules are very common on Earth. They form any time carbon-based materials are not burned completely. They can be found in sooty exhaust from cars and airplanes, and in charcoal broiled hamburgers and burnt toast. PAHs are one of the major forms of carbon in the space between the stars, widely observed by astronomers within our own galaxy.
The Spitzer Space Telescope is an infrared observatory in a solar (heliocentric) orbit parallel to the Earth's orbit. It takes advantage of its location in space to look at portions of the infrared spectrum that are blocked by the Earth's atmosphere. It also operates at a very low temperature, reducing background noise to achieve exceptionally high sensitivity. For more information on Spitzer see <http://www.spitzer.caltech.edu>.
Spitzer is the first telescope to detect these PAH molecules at very large distances. "This is 10 billion years further back in time than we've seen them before," said Dr. Lin Yan of the Spitzer Science Center at the California Institute of Technology in Pasadena, Calif. Yan is lead author of a study to be published in the August 10 issue of the Astrophysical Journal. Spitzer's high sensitivity enables direct detection of organics so far away.
Since Earth is approximately four-and-a-half billion years old, these organic materials existed in the universe well before our planet and solar system were formed. Spitzer found PAHs in galaxies where intense star formation had taken place over a short period of time. These "flash in the pan" starburst galaxies are nearly invisible in optical images because they are very far away and contain large quantities of light-absorbing dust. But the same dust glows brightly in infrared light and is easily spotted by Spitzer.
"These complex compounds tell us that by the time we see these galaxies, several generations of stars have already been formed," said Dr. George Helou of the Spitzer Science Center, a co-author of the study. "Planets and life had very early opportunities to emerge in the universe."