Merging data from two infrared space telescopes, astronomers have spotted forming stars brightening and dimming every few weeks, providing a glimpse into the violent, tumultous conditions inside the cocoons of baby stars.

Created using data from the Herschel and Spitzer space telescopes, this composite image of Orion nebula. Hotter gas visible to Spitzer appears in blue, as do more evolved embryonic stars. Green and red represent cooler dust viewed by Herschel. Credit: NASA/ESA/JPL-Caltech/IRAM
 
Stars form out of clumps of gas which coalesce, collecting material until they gain enough mass to spark nuclear fusion.

Scientists do not know what causes the embryonic stars to flicker, but follow-up observations may yield clues whether the stars are going through hot, bright phases, or if material in the object's inner disk casts a shadow, causing it to temporarily dim in the apertures of telescopes.

The incubating bodies have not yet become full-fledged stars.

The European Space Agency's Herschel observatory and NASA's Spitzer space telescope contributed to the findings announced this week. Scientists recognized the fleeting stellar activity inside Orion nebula, a famous star-forming cloud visible visible to binoculars and backyard telescopes in northern fall and winter.

The nebula lies below the belt in the constellation Orion.

Astronomers used observations of cold dust with Herschel's far-infrared instrument over six weeks in 2011, coupled with archive data from two of Spitzer's mid-infrared sensors, which see hotter gas at shorter wavelengths.

Infrared telescopes allow researchers to see through the veil of thick dust blocking views in visible light. Such imagery is critical for understanding the birth of stars.

"Yet again, Herschel observations surprise us and provide more interesting insights in to what happens during the very earliest phases of stars and planet formation," said Goran Pilbratt, ESA's Herschel project scientist.

Herschel and Spitzer detected young stars varying in brightness by more than 20 percent over just a few weeks. The material emitting infrared light is relatively cool, so scientists believe it must be distant from the hot cores of the forming stars.

Researchers suspect cooler gas lies far away from the star's inner disk, and it should take years or centuries for it move closer to the object's glowing nucleus.

"Herschel's exquisite sensitivity opens up new possibilities for astronomers to study star formation, and we are very excited to have witnessed short-term variability in Orion protostars," said Nicolas Billot, an astronomer at IRAM, an international research institute in Grenada, Spain.

"Follow-up observations with Herschel will help us identify the physical processes responsible for the variability," Billot said.