A stellar burst reveals the formation mechanism of massive stars

An outburst from a massive star in formation produced due to the sudden intake of material coming from its accretion disk, has been detected for the very first time.

This discovery is the most solid evidence so far that high mass stars are formed through a similar process to that which gives rise to the low mass ones.

Stars with low mass, like the Sun, are formed from big fragments of clouds of gas and dust, which condense until a central object, or proto star, is formed, growing it up by absorbing gas from a surround disk, and expelling the surplus material through a couple of jets located on both poles. However, it was not known if the most massive stars, with tens of the Sun mass, are formed through the same mechanism. The study of an outburst detected on the massive star in formation NIRS 3, and published today in Nature Physics, has provided the most solid evidence that, in effect, all stars are formed the same.


NIRS 3, with about twenty times the mass of the Sun, and with a structure consisting on a central object (the proto star), a disk and two jets on both poles, underwent a sudden increase of luminosity in the autumn of 2015 that launched an international observation campaign from ground and space telescopes (Gemini, ESO/VLT, ESO/MPG, NASA/SOFIA, CAHA).

First campaign data were obtained with PANIC, an infrared panoramic camera installed at the Calar Alto Observatory (Almería) 2.2m telescope, and co-developed by the Instituto de Astrofísica de Andalucía (IAA-CSIC), which allowed to confirm that this sudden outburst came from NIRS 3, and not from near stars. “It is one of the first results obtained with PANIC camera, and it constitutes an excellent example of the possibilities of this new instrument”, José Miguel Ibáñez (IAA-CSIC), software responsible of PANIC and co-author of the paper, points.

Later observations with PANIC, carried out since November 2015 until February 2016, allowed to detect what is known as light-echo, which showed how the sparkle shifts from its origin towards to the star’s jets, allowing estimating the date of the burst, which was in the middle of 2015.

nirs3After analyzing the data, the research team concluded that it was an accretion burst, a habitual phenomenon with the formation of stars having low mass, but never seen on massive stars, which is due to the lumpiness of the disk that feeds the formation star: in occasions, the star absorbs disk fragments that produce a sudden luminosity increase.

The detection of an accretion burst in NIRS 3 constitutes the most solid evidence we have up to date of that, in effect, high mass stars are formed through a similar process to the one which gives rise to the low mass ones. However, they are much more intense bursts, that can release as much energy as that one produced by the Sun over a hundred thousand years”, points Alessio Caratti o Garatti, researcher at the Dublin Institute of Advanced Studies, who heads the job.

In this way, the other model, which proposed that massive stars are formed with the fusion of less massive stars, would be discarded, establishing in this manner a unified stellar formation process. With some differences, as the massive stars will have much bigger disks and will exhibit a higher material absorption rate than the ones with low mass and, therefore, will end their growth process faster.

The German-Spanish Calar Alto Observatory is located at Sierra de los Filabres, north of Almería (Andalucía, Spain). It is jointly operated by the Instituto Max Planck de Astronomía in Heidelberg, Germany, and the Instituto de Astrofísica de Andalucía (CSIC) in Granada, Spain. Calar Alto has three telescopes with apertures of 1.23m, 2.2m and 3.5m. A 1.5m aperture telescope, also located at the mountain, is operated under control of the Observatorio de Madrid. 


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