Images from NASA’s Spitzer Space Telescope observed a splotchy pattern of infrared light. This light, the cosmic infrared background, shows splotches which are larger than individual galaxies. Researchers suggested that the extra light came from the very first galaxies after the big bang. Others suggested that it came from stars which had been thrown clear when two galaxies collided.

The Cosmic Infrared Background Experiment (CIBER) was designed to settle the debate. The team’s findings, published in the November 7 edition of the journal Science, showed that the light came from rogue stars. Surprisingly the researchers found that the number of stars that exist outside of galaxies may represent half of all stars.

Galaxies are visible from Earth because the millions of stars that make them up combine to create enough light. The individual stars between galaxies are not bright enough to be seen, even by very powerful telescopes.

“The total light produced by these stray stars is about equal to the background light we get from counting up individual galaxies,” said Jamie Bock, Caltech Professor of Physics in a statement.

Three instruments are used in CIBER including two spectrometers to determine the brightness of Zodiacal light and cosmic infrared background. The instruments were carried into space by NASA suborbital rockets. By carrying the instruments, even briefly, above the atmosphere the researchers were able to filter out the glow of the upper atmosphere.

In analyzing the data it was also necessary to remove other sources of light pollution, including light from the instruments and light from the stars and solar systems of the milky way. Finally the team compared the CIBER results to results from Sptizer measurements. The results were a very blue color.

“CIBER tells us a couple key facts. The fluctuations seem to be too bright to be coming from the first galaxies. You have to burn a large quantity of hydrogen into helium to get that much light, then you have to hide the evidence, because we don’t see enough heavy elements made by stellar nucleosynthesis”–the process, occurring within stars, by which heavier elements are created from the fusion of lighter ones–“which means these elements would have to disappear into black holes,” said Caltech Senior Postdoctoral Fellow Michael Zemcov.

In all, CIBER flew four missions. The recently published results discuss the second and third launches from 2010 and 2012. Results from the fourth flight, a non-recovered flight that ended in the Atlantic Ocean, are still being analyzed.

The results to date do not definitively answer the question, because of unexplained fluctuations and a continuing inability to account for all of the light. “The color still isn’t quite blue enough to match the data. But even so, the brightness of the fluctuations implies this signal is important in a cosmological sense, as we are tracing a large amount of cosmic light production,” said Brock.

Future experiments should provide more information, including the location of these stray stars in relation to the galaxies they once belonged to.