But… what happens in those globules?

It is not the first time we talk about Orion, nor about the molecular cloud pierced by the winds of its most massive star… but this is about molecular globules. In this constant process of destruction, something is being created.

Gallery of globules detected at the edge of the expanding Orion bubble

Those who have ever read me (poor) will say that we always talk about the same areas of space. Legendary is the series about IRC+10216 (a star and its envelope, better known as CW Leonis) published on this platform, as well as studies related to the chemistry of Orion. This is because both are magnificent “laboratories” that we can observe with relative ease (translation: these places are “close” and bright enough to observe with our telescopes). The study of these areas is aided by new and increasingly precise instruments.

On this occasion, the combination of the IRAM 30 meters telescope (in Pico Veleta, Granada) and the SOFIA stratospheric telescope (which is mounted on an airplane), helped us to discover the presence of an extremely interesting phenomenon.

But let’s take perspective…  In the Orion Nebula there is a good mess. There are massive stars (of about 8 solar masses or more) being born and emitting winds and ultraviolet radiation, which, in turn, destroys the large molecular cloud in which they were born (the one that has provided them with the material and the necessary conditions to condense). In that scuffle, an international research team has detected the presence of small molecular globules.

Expanding gas bubbles – the result of the destruction of the parent cloud – form around young massive stars because wind and radiation violently “sweep” huge amounts of the material. Ultraviolet radiation is responsible for dissociating (destroying) the gas molecules. Similar shapes had previously been found around massive stars in the Milky Way, dozens of bubbles that were detected using infrared images (let’s not forget that those environments have lots of dust and that infrared makes it easy for us to “go through” the opaque outer layers and see what happens inside). The result of this whole process is that the rate of star birth slows down, as the amount of fuel available for the formation of new stars (the molecular gas) is limited.

But there is another consequence: the presence of small globules of molecular gas on the edge of these large expanding bubbles whose existence has been a surprise: “We did not expect this discovery: one does not expect the presence of molecular gas in this kind of environment so turbulent and “sterilized” by ultraviolet radiation, but we have detected a dozen globules of thick molecular gas that have survived these harsh conditions. Most of these globules can be transiting objects that eventually fade or evaporate. But we didn’t expect this script twist.”

This is said by one of the two researchers who has led this work, Javier R. Goicoechea, from the Astromol Group at the IFF-CSIC, who goes on to describe how they are: “The globules are not massive at all, their size is approximately 200 times smaller than the Orion Nebula itself and their typical mass is around a third of the mass of the Sun. That’s why we were surprised to find out what they were hiding.”

And what has been discovered inside those globules that seemed to be just lumps? Well, scientists have discovered that one of these globules is evolving to form a very young, low-mass star. Let’s say it would be the “daughter” of the one who is riding this whole mess (the young, “angry” star, the most massive in the Trapezium cluster, Orionis C, located at the center of the Orion Nebula).

The importance of the movement

To understand what was happening within the great Orion bubble there are several important parameters that until now had been difficult to obtain: knowing how it moves, what forces drive its expansion and what its chemical composition is. Thanks to the combination of the data obtained with these two facilities, the team has obtained the first images that solve the speed of the gas and show the properties of this bubble of 10 light years in size that is suffering the wrath of Orionis C, since the bubble expands at almost 50,000 km / h, providing its peculiar appearance to the iconic region that we know as “the sword of Orion”.

This information has been obtained thanks to the analysis of the emission of gases produced by molecules of carbon monoxide (CO) as well as positively charged carbon atoms (ionized carbon or C+, analyzed in the work led by Cornelia Pabst, of the University of Leiden, The Netherlands).

As the authors of these works state, “It is not yet clear whether these small objects can be a source of very low-mass stars, brown dwarfs, or planetary-mass objects. We have captured the first glimpses of the star-forming processes that are taking place within one of these small globules.”

The team hopes to be able to carry out more observations of the emission of other molecules (more sensitive to the presence of more dense gas inside the globules) to clarify their future and fate. Will they evaporate in the long run or, conversely, will they evolve into a nursery of newly formed stars?

Technical information:

This work is part of an international collaboration that leads two major complementary observation programs. One uses the 30-meter IRAM telescope in Pico Veleta, Spain (Dynamic and Radiative Feedback of Massive Stars, PI: J. R. Goicoechea) to map the emission of 12CO, 13CO and C18O (J=2-1) at a resolution of 11 arcseconds; the other uses NASA/DLR’s SOFIA airborne observatory (C+ Square-degree map of Orion, PI: Prof. A. G. G.M. Tielens) which has produced the largest map of the [CII]158 μm line (usually the brightest line in the neutral interstellar medium) at a resolution of 16 arcseconds. These Orion C+ images are also relevant as a local model in the extragalactic context as the ALMA and IRAM-NOEMA radiointerferometers can detect the emission of [CII] 158 μm from galaxies with very distant star formation (with high redshift).

The consortium consists of the following institutions: CSIC, University of Leiden, University of Cologne, IRAP-CNRS, IRAM, Max-Planck Institute for Radio Astronomy, ESAC, NASA Ames and University of Maryland.

The scientific articles related to this work are:

J. R. Goicoechea, C. H. M. Pabst, S. Kabanovic, M. G. Santa-Maria, N. Marcelino, A. G. G. M. Tielens, A. Hacar, O. Berné, C. Buchbender, S. Cuadrado, R. Higgins, C. Kramer, J. Stutzki, S. Suri, D. Teyssier, and M. Wolfire. Molecular globules in Orion’s Veil bubble. IRAM 30 m 12CO, 13CO, and C18O (2-1) expanded maps of Orion A. Accepted for publication in Astronomy & Astrophysics (2020).

– C. H. M. Pabst, J.R. Goicoechea, D. Teyssier, O. Berné, R.D. Higgins, E. T. Chambers, S. Kabanovic, R. Güsten, J. Stutzki, and A.G.G.M. Tielens: Expanding bubbles in Orion A: [CII]158μm observations of M42, M43, and NGC 1977. Accepted for publication in Astronomy & Astrophysics (2020).


Images of the Orion Nebula (M42). The left panel shows the emission of positively charged carbon atoms, observed with SOFIA, revealing a huge bubble pushed by the winds of the most massive star in the Trapezium cluster. The 12CO and 13CO images, taken with the 30-meter IRAM telescope, show the molecular gas in the cloud in which stars are forming, behind the bubble. The # numbers show the position of some of the detected globules at the edge of the bubble. Credits: Goicoechea et al. (2020).

Gallery of globules detected at the edge of the expanding Orion bubble. The reddish colors represent the emission of carbon monoxide molecules detected with the 30-meter IRAM telescope. The bluish color is an infrared image obtained by the Spitzer Space Telescope. The #1 globule coincides with the position of a very young, low-mass star. The white circle represents the angular resolution of the IRAM telescope 30-meters, approximately several times the size of the Solar System. Credits: Goicoechea et al. (2020).

Originally published in Spanish on the Naukas website: “Pero… ¿qué pasa en esos glóbulos?” (2020/07/02).

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