A giant molecular cloud in which massive stars are forming studied with the SOFIA flying telescope

The SOFIA flying telescope was used to study a giant molecular cloud that is a star-forming area cataloged as W51 in order to analyze the newly formed or still forming stars within it. The researchers combined the observations made with SOFIA with those made over time with NASA’s Spitzer and Herschel space telescopes to obtain more complete information on those stars. There was a particular interest in the massive stars and one of them seems really huge, with a mass estimated at about 100 times the Sun’s. If that estimate is confirmed by follow-up observations it’s one of the most massive stars in formation in the Milky Way.

The W51 giant molecular cloud is relatively close in astronomical terms, being almost 17,000 light years from Earth. It’s in fact one of the molecular clouds closest to the Earth, a reason why it’s been the subject of many studies over time with the use of a number of instruments suitable for detecting star formation activity that occurs inside it. The large amount of gas, especially hydrogen, that makes up W51 blocks many electromagnetic frequencies so they need to use instruments capable of detecting the ones that pass through gas and dust such as radio waves, X-rays and infrareds.

Several radio telescopes have been used to detect radio waves from the W51 molecular cloud while NASA’s Chandra X-ray observatory detected X-rays and discovered about 600 young stars. Detections of infrared emissions have been performed with NASA’s Spitzer and Herschel space telescopes and more recently with the SOFIA flying telescope. In particular, the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) made it possible to study massive newborn stars within W51.

SOFIA (Stratospheric Observatory for Infrared Astronomy) is a project of NASA and DLR, the German space agency, which uses a modified Boeing 747SP to allow the use of a 2.5 meter diameter telescope. This flying telescope specializes in infrared astronomy thanks to the fact that at the altitudes where it flies, between 12 and 14 kilometers, there’s much less water vapor to absorb that kind of light.

The purpose of this study, like that of others of the W51 molecular cloud, is to better understand the processes that lead to the birth of massive stars. They represent less than 1% of the total stars, so the known cases of young massive stars forming in the Milky Way are rare. W51 is perfect for this type of research because the large amount of hydrogen it contains favors the birth of massive stars, to the point that various star clusters inside it have just formed or are in their formation process and contain massive stars.

In the top image (NASA/SOFIA/Lim and De Buizer et al. and Sloan Digital Sky Survey) the oldest star in the W51 molecular cloud is shown at the top left, in the middle of a yellowish bubble. The most recent generations can typically be found in areas near the center of the image, near the brightest bubble just to the left of the central area. In the background there’s a star field taken from the Sloan Digital Sky Survey.

Even putting together the data collected from different telescopes the results must be analyzed carefully. For example, from the combination of those from SOFIA, Spitze and Herschel a star within the W51 molecular cloud seems to have a mass around 100 times the Sun’s. That’s not impossible because even more massive stars are known but itns an exceptional case therefore deserves further observations to understand whether it’s really a single super-giant star or there are a number of siblings so close as to seem a single object.

The electromagnetic emissions from the massive young stars in the W51 molecular cloud are very intense and can have a considerable influence on the surrounding area, for example by ionizing the gas. It’s a hostile environment where no life form similar to the Earth’s could be born and in any case those stars consume their hydrogen at very high speed so they have a life of no more than a few tens of millions of years. They’re also the stars in which most of the elements heavier than hydrogen and helium are formed, which are scattered throughout interstellar space after they explode into supernovae. This means that they’re at the same time hostile to life as we know it and yet indispensable for producing the elements needed for the formation of living organisms.

The W51 molecular cloud seen by the Chandra and Spitzer space telescopes (Image X-ray: NASA/CXC/PSU/L.Townsley et al; Infrared: NASA/JPL-Caltech)
The W51 molecular cloud seen by the Chandra and Spitzer space telescopes (Image X-ray: NASA/CXC/PSU/L.Townsley et al; Infrared: NASA/JPL-Caltech)

Leave a Reply

Your email address will not be published. Required fields are marked *