The team determines that a nebula is much younger than previously believed

In the southern sky, about 4,300 light-years from Earth, lies RCW 120, an enormous glowing cloud of gas and dust. This cloud, known as an emission nebula, is formed from ionized gases and emits light at different wavelengths. An international team led by researchers from West Virginia University studied RCW 120 to analyze the effects of star feedback, the process by which stars bring energy back to their environment. Their observations have shown that stellar winds cause the region to expand rapidly, enabling them to limit the age of the region. These findings indicate that RCW 120 must be less than 150,000 years old, which is very young for such a nebula.

About seven light-years from the center of RCW 120 lies the boundary of the cloud, where an abundance of stars forms. How are all these stars formed? To answer the question, we must dig deep into the origin of the nebula. RCW 120 has one young, massive star at its center, which generates powerful star winds. The star winds of this star are very similar to those of our own sun in that it throws material from space into space. These stars wind shock and compress the surrounding gas clouds. The energy introduced into the nebula causes the formation of new stars in the clouds, a process known as ‘positive feedback’ because the presence of the massive central star has a positive effect on future star formation. The team, with MVDO postdoctoral researcher Matteo Luisi, used SOFIA (the Stratospheric Observatory for Infrared Astronomy) to study the interaction of massive stars with their environment.

SOFIA is an aerial observatory consisting of a 2.8 meter (2.8 meter) telescope transported by a modified Boeing 747SP aircraft. SOFIA observes in the infrared regime of the electromagnetic spectrum, which is just beyond what humans can see. For observers on the ground, water vapor in the atmosphere blocks much of the light from space that infrared astronomers want to measure. However, the crossing altitude of seven miles (13 km) places SOFIA above most of the water vapor, allowing researchers to study star-forming regions in a way that is not possible from the ground. Overnight, the observatory takes flight observation of magnetic fields, star-forming regions (such as RCW 120), comets and nebulae. Thanks to the new upGREAT receiver installed in 2015, the aerial telescope can make more accurate maps of large parts of the sky than ever before. The observations of RCW 120 are part of the SOFIA FEEDBACK survey, an international effort led by researchers Nicola Schneider at the University of Cologne and Alexander Tielens at the University of Maryland, using upGREAT around a multitude of star-forming regions where to take.

The research team chose to observe the spectroscopies [CII] line with SOFIA, which is released from diffuse ionized carbon in the star-forming region. “The [CII] line is probably the best detection of feedback on a small scale, and – unlike infrared images – it gives us velocity information, which means we can measure how the gas moves. The fact that we can now observe [CII] easily over large regions in the air with upGREAT makes SOFIA a very powerful tool for investigating star feedback in more detail than was previously possible, ‘says Matteo.

Use them [CII] comments from SOFIA, the research team found that RCW 120 expands at 33,000 mph (15 km / s), which is incredibly fast for a nebula. From this rate of expansion, the team was able to place an age limit on the cloud and find that RCW 120 is much younger than previously believed. With the age estimate, they were able to deduce the time it took before the star formation kicked in at the boundary of the nebula after the central star was formed. These findings suggest that positive feedback processes take place on very short time scales and suggest the idea that these mechanisms may be responsible for the high star formation rate that occurred during the early stages of the universe.

The team hopes to extend this kind of analysis to the study of more star-forming regions. Matteo says: ‘The other regions we look at with the FEEDBACK survey are in different stages of evolution, have different morphologies, and some have many stars with large masses, as opposed to only one in RCW 120. We can then use this information to determine which processes primarily drive activated star formation and how feedback processes differ between different types of star-forming regions. ”