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Newborn stars in the Milky Way


Brazilian researchers have identified two star clusters in a molecular cloud located in remote regions of our galaxy, a distance well beyond the typical one in which stars form. The results of this study, published in Monthly Notices of the Royal Astronomical Society, shed light on some models of star formation and show how the space around the galaxy is much less empty than you might imagine.

nube_HRK81.4-77.8

Credit: Camargo et al. 2015

Brazilians astronomers have made a remarkable discovery: they have identified two star clusters in the peripheral regions of the Milky Way. The results of this study, published in Monthly Notices of the Royal Astronomical Society, shed light on some models of star formation and show how the space around the galaxy is much less empty than you might imagine.
We know that the Milky Way has a bar structure and its branch spiral arms consist of stars, gas and dust. If it was cut view, it would appear relatively flat and you would see most of the material is distributed in the disk and in the central regions. Stars form in dense agglomerations of gas, in so-called giant molecular clouds (Giant Molecular Clouds, GMC), which are mainly located in the inner regions of the galactic disk. If there are many compressions in a single GMC, then you can have favorable conditions to generate almost all the stars, a process that ultimately leads to the formation of a star cluster.

WISE_Camargo438

Credit: D. Camargo/NASA/WISE

Analyzing the data space observatory WISE (Wide-Field Infrared Survey Explorer), the researchers, led by Denilso Camargo, Federal University of Rio Grande do Sul in Porto Alegre, Brazil, and author of the study, not only found GMC distributed thousands of light years above and below the galactic plane, but they have identified one that surprisingly contains two star clusters. It is the first time that astronomers found that there are “newborn” stars in these peripheral regions of the galaxy. Named with the name of the principal author, Camargo and Camargo 438 439, the clusters are in the giant molecular cloud HRK 81.4-77.8. It is believed that this cloud formed 2 million years ago and it extends for about 16,000 light years below the galactic disk, a distance beyond the typical one in which stars form.

Ammassi_Camargo

Credit: D. Camargo/NASA/WISE

To explain the formation of these two clusters, Denilso proposed two hypotheses. In the first, based on the so-called “chimney model”, violent events of high energy, such as supernova explosions, expel gas and dust out of the galactic disk. The material then falls into a fusion process which ultimately causes the formation of a GMC. The “fireplace model”, however, requires the explosion of hundreds of massive stars, of different generations, so that it creates a “super wind” that pushes the cloud HRK 81.4-77.8 in the position where it is now. In addition, over millions of years, the “bubble” created by the stellar explosions may have further compressed the material forming more stars and thus feeding the expulsion of other material, creating a kind of “galactic fountain” where the gas and dust fall again in the galactic disk. The other idea, however, is based on the fact that the interaction between the Milky Way and satellite galaxies, that of the Magellanic Clouds, may disrupt the gas that falls into the galaxy leading to the formation of a new GMC and then the birth of new stars.

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