Cepheus B is a molecular cloud (mainly consisting of cool molecular hydrogen) and a stellar nursery in our Milky Way, located about 2,400 light-years away from Earth. It is part of a large and active region of star formation in the constellation Cepheus.
There are hundreds of very young stars inside and around the cloud, ranging from a few million years old outside the cloud to less than a million years old in the interior.
While astronomers have long understood that stars and planets form from the collapse of a cloud of gas, the question of the main causes of this process has remained open for a long time.
One option was that the cloud cools, gravity gets the upper hand, and the cloud falls in on itself. The other possibility is that a “trigger” from some external source (like radiation from a massive star or a shock from a supernova) initiates the collapse. Some studies have noted a combination of triggering mechanisms in effect.
Researchers found that star formation in Cepheus B is mainly triggered by radiation from one bright, massive star (HD 217086) outside the molecular cloud. Radiation from this star drives a compression wave into the cloud-triggering star formation in the interior, while evaporating the cloud’s outer layers. They saw indeed a wave of star and planet formation that is rippling through the cloud.
Analysis revealed slightly older stars outside the cloud, and the youngest stars with the most protoplanetary disks in the cloud interior, exactly what is predicted from the triggered star formation scenario.
By combining the data from the Chandra X-ray Observatory and the Spitzer Space Telescope, researchers have shown that radiation from massive stars may trigger the formation of many more stars than previously thought.