Radiation stimulates star formation

A new study by two NASA observatories provides new knowledge about star formation, along with a very beautiful picture of a star-forming region in our galaxy. Research shows that radiation from large stars can stimulate the formation of many other stars.

While astronomers have long understood that stars and planets form from the collapse of a gas cloud, the question of the main cause of this process remains open.

One possible cause is the cold gas cloud, the dominant gravity and the cloud itself collapsing under its weight. Another possibility is a 'stimulus' from some external source - for example, radiation from a large star or from a supernova. Some previous studies have mentioned the combination of stimulation mechanisms.

By combining observations of Cepheus B from Chandra X-ray Observatory and Spitzer Space Telescope, researchers have made an important step forward. Cepheus B is a cloud containing most of the cool hydrogen molecules located 2400 years from Earth. There are hundreds of very young stars inside and around this cloud - from stars ages a few million years outside to less than 1 million years inside - making it an important star-forming experimental site. .

Konstantin Getman of Penn University, the lead author of the study, said: 'Looking at them, astronomers believe that the planet and stars formed from the stimulation of the radiation of big stars are quite a phenomenon rare. Our results show that this concept is wrong '.

The aforementioned form of star formation was observed in small star clusters, with a few dozen stars; But the latest results show that this phenomenon occurs in areas up to several hundred stars.

Although far from the famous Orion star-forming region, Cepheus B is in a more favorable direction for observing the stimulation process. The observation of Chandra observatory allows astronomers to choose young stars inside and around Cepheus B. Young stars often have a disturbing inner part that creates a very strong magnetic field and thereby creates credits. strong and recognizable X-ray effect.

This image, combining data from Chandra X-ray Observatory and Spitzer Space Telescope shows that the molecular cloud Cepheus B, located in our galaxy is 2,400 light-years from Earth.The molecular cloud is the remaining interstellar cold gas and dust zone from galaxy formation, and is composed primarily of hydrogen molecules.Spitzer data in red, green, and blue shows molecular clouds (in the lower part of the picture) and young stars inside and around Cepheus B;Chandra observatory data shows young stars.(Photo: NASA / CXC / PSU / K. Getman et al.; IRL NASA / JPL-Caltech / CfA / J. Wang et al.)

Spitzer data reveal whether these young stars have disk material (protoplanetary disk) around them. Because these discs exist only in young star systems where the planet is still forming, the presence of pre-planetary plates is a sign of the age of the star system.

The new study shows that star formation in Cepheus B is mostly stimulated by radiation from a large and bright star outside this molecular cloud. According to theoretical models, radiation from this star can create a wave of compression into the cloud, stimulating star formation in the inner area, and vaporizing the outer layers of the cloud. Chandra-Spitzer's analysis shows that slightly older stars are outside, while the youngest and most planetary stars are concentrated in the area within the cloud - these are exactly What is predicted from the star-forming situation due to stimulation.

Co-author Eric Feigelson, of Penn State, said: 'We have observed a wave of star and planet formation running through this cloud. Outside the cloud, stars have newborn planets while inside the cloud, planets are still in embryonic form. '

Previous observations of Cepheus B showed a band of ionized gas around the molecular cloud and facing the big star. However, a star-forming wave - an important feature in recognizing the source of star formation - has not been observed. Getman said: 'We can even determine the movement speed of this wave - about 2000 miles per hour'. The star is thought to be the source of star formation in Cepheus B, which is 20 times the mass of the sun, and at least 5 times more than any other star in Cepheus B.

Spitzer and Chandra data also show that many star and planetary formation took place in Cepheus B for millions of years, and most materials in the cloud have evaporated or transformed into stars.

Feigelson said: 'It seems that this molecular cloud has formed most of its stars, and its' reproductive' ability will soon weaken. Obviously we can understand a lot by combining data from two of NASA's great observatories. '

An article describing these results was published on July 10 in the Astrophysical Journal. Astronomers working with Getman and Feigelson include Kevin Luhman and Gordon Garmire from Penn State, Aurora Sicilia-Aguilar of Max-Planck-Institut fur Astronomie, and Junfeng Wang of the Harvard-Smithsonian Center for Astrophysics