Heavy Stars Do Not Feed On Dust Disk But on Debris (Planetary Science)

A team of astronomers led by the Netherlands has discovered that massive stars form differently than their little brothers and sisters. Where small stars often have an ordered disk of dust and matter around them, the material supply for large stars is a chaotic mess. The researchers used the telescopes of the Atacama Large Millimeter / submillimeter Array (ALMA) and recently published their findings in the Astrophysical Journal .

It is well known how young, small stars form. They extract matter from a disk of gas and dust in a relatively organized way. Astronomers have seen many of these dust discs around young, bright stars, but never around young, massive stars. The question was therefore whether large stars form in the same way as small stars.

“Our observations now provide convincing evidence that the answer is no,” says Ciriaco Goddi, affiliated with Radboud University Nijmegen and the ALMA center of expertise Allegro at Leiden University.

Goddi led a team that studied three very young massive stars in star-forming region W51 about 17,000 light-years from Earth. The researchers specifically looked for large, stable discs with outwardly moving jet streams of material perpendicular to the plane of the disc. Such discs should be visible with the high resolving power of the ALMA telescopes.

Goddi: “But instead of stable disks, we found that the feeding zone of young massive stars looks like a chaotic mess.”

Text continue after image.

ALMA image of the chaotic mess surrounding the young massive star W51e2e. 
Gray is dust close to the star. 
Red and blue is material that moves rapidly away from the star in jet streams. 
The red material is moving away from us. The blue material is moving towards us. 
(c) Goddi, Ginsburg, et al., Sophia Dagnello, NRAO / AUI / NSF.

The observations showed wisps of gas coming towards the young, massive stars from all directions. In addition, the researchers saw so-called jets that indicate that there may be small disks invisible to the telescope. It also appears that one of the three stars studied has turned a disk about a hundred years ago. In short: chaos.

The researchers conclude that these massive young stars, at least in their younger years, are formed with material from multiple directions and at irregular speed. That is different from small stars where there is a stable influx of material. The astronomers further suspect that this multiple supply of material is probably the reason why large, stable discs cannot form.

“Such a disordered raid model has been proposed on the basis of computer simulations. Now we have the first observational evidence to support the model,” said Goddi.

Featured image: Artistic representation of the 4 steps at which a dust disk can become a heavy star a mess. (c) Bill Saxton, NRAO / AUI / NSF

About ALMA

ALMA consists of 66 satellite dishes spread over distances of up to 16 kilometers on the Chajnantor plateau in the Chilean Andes. It is a partnership of Europe, the United States, Canada, Japan, Taiwan, Korea and Chile. The Netherlands has built three types of receivers for the telescopes: Band 5 , Band 9 and Band 2 (under development). The image sharpness of ALMA is up to ten times that of the Hubble Space Telescope.

ALMA satellite dishes with which the observations were made. (c) ALMA / W. Garnier

Scientific article
Multidirectional Mass Accretion and Collimated Outflows on Scales of 100–2000 au in Early Stages of High-mass Protostars. By: C. Goddi, A. Ginsburg, LT Maud, Q. Zhang & Luis A. Zapata. The Astrophysical Journal, Volume 905, December 9, 2020. ( original | free preprint )

Provided by NOVA

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