This scheme shows a possible scenario for the formation of protostars (top row), based on four very young protostars (bottom row) observed by VLA (orange) and ALMA (blue).

Stars form in molecular clouds, huge clouds of gas (with a small percentage of the dust) that can contain enough mass to generate thousands, and even millions, of stars like the Sun. The embryos of future stars are hidden in the interior of these clouds, making observing the star formation process, as well as the disks from which planets are born, difficult. Now, an international team of astronomers has completed the largest sampling of newborn stars developed to date, with over three hundred protoplanetary disks discovered.

According to star formation models, the birth of stars begins with the fragmentation of the cloud. Each fragment will undergo a slow process of contraction until the stellar embryo, or protostar, forms, which grows by accumulating material through a rotating disk around it. S

At the same time, the star expels the excess material along its polar axis in the form of a powerful jet, which stabilizes its rotation and allows it to continue growing. However, these early stages of star formation still have unknowns.

This image shows the molecular clouds of Orion, the objective of the study. The yellow dots indicate the location of the protostars observed in a background image taken by Herschel. The side panels show nine young protostars photographed by ALMA (blue) and the VLA (orange).

“Thanks to today’s powerful instrumentation, such as radio telescopes ALMA (Atacama Large Millimeter / submillimeter Array) and VLA (Very Large Array), we can observe increasingly earlier stages in the process of star formation, when powerful ejections of matter still coexist with the development of disks around them, which constitute the seed of possible planetary systems ”, he comments Ana Karla Díaz-Rodríguez, researcher of the Institute of Astrophysics of Andalusia who participates in the work.

“These results, with the detection of hundreds of planetary systems in the clouds of Orion, Illustrate very well the diversity of physical conditions in which this process can occur. Orion is a region rich in young stars, where high-mass and low-mass protostars coexist, and whose formation takes place both in isolation and in groups, which is why their study is of great relevance for this field, ”he comments. Mayra Osorio, researcher of the IAA-CSIC who participates in the result.

The sample obtained has allowed, for example, to compare the mass and average size of young protoplanetary discs with discs in a more advanced evolutionary state. The researchers have found that although they all show a similar size, the young disks are much more massive, suggesting that the larger planets form at very early stages in star formation.

Peculiar protostars

Among the hundreds of images in the sample, four objects stand out, which have an irregular and “lumpy” shape and are opaque even to radio waves, which could be indications that they are in a stage prior to that of a protostar. To define themselves as a typical protostar, stars must not only have a flat disk around them, but also the bipolar jet that releases material, but at what point in the formation of the star the jet is generated is still unknown.
For example, one of the stars in the study, HOPS 404, shows a material flow moving at two kilometers per second, when the typical speed in these structures is between ten and one hundred kilometers per second.

“We are facing a large and swollen sun that is still accumulating mass, but that has just begun to expel matter to lose angular momentum and continue to grow,” he says. Nicole Karnath, researcher of the University of Toledo (Ohio, USA) headed by one of the two published articles. It is one of the smallest flows we have seen, and it presents itself as one of the first stages in the formation of a protostar. ”

ALMA and the VLA observed more than three hundred protostars and their young protoplanetary disks in Orion. This image shows a subset of stars, including some binaries. The ALMA and VLA data complement each other: ALMA sees the structure of the outer disk (in blue), and the VLA observes the inner disks and star nuclei (orange).

These four objects represent a rarity and, although researchers cannot confirm their age, they estimate that they are less than ten thousand years old. For stars like the Sun, the process of gravitational contraction is believed to end after ten million years, at which point the thermonuclear reactions that define a star itself begin. We are thus facing truly young objects.

REFERENCES

N. Karnath et al. “Detection of Irregular, Sub-mm Opaque Structures in the Orion Molecular Clouds: Protostars within 10000 years of formation?”. The Astrophysical Journal. J. J. Tobin et al. «The VLA / ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. A Statistical Characterization of Class 0 and I Protostellar Disks «. The Astrophysical Journal.

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